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YEAR 2 - Principles of Pathology > 33. Bacteriology > Flashcards

33. Bacteriology Flashcards

1
Q

Describe the features that distinguish prokaryotes from eukaryotes.

A
  • Generally smaller and simpler
  • No membrane-bound organelles
  • Have haploid cells (while eukaryotes have either haploid or diploid)
  • Have single nucleus
  • Have peptidoglycan in cell walls
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2
Q

Do prokaryotes have a cytoskeleton?

A

Yes, but it is not as well defined as in eukaryotes.

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3
Q

What are the main shapes of bacteria?

A
  • Bacillus -> Rod
  • Coccus -> Sphere
  • Spirillum -> Spiral
  • Spirochaete -> Corkscrew
  • Vibrio -> Comma
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4
Q

What is a typical size for prokaryotic cells? [IMPORTANT]

A

Around 1µm (much smaller thatn eukaryotic cells)

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5
Q

What are the different cell arrangements for cell bacteria and what causes these?

A

These depend on which direction the cells divide in (i.e. in how many planes the division occurs).

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6
Q

In bacteria, what is there instead of a nucleus?

A

Nucleoid (a condensation of the DNA)

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7
Q

Compare human and bacterial DNA in terms of how long and gene-dense they are.

A
  • Human DNA is longer (around 3GB compared to just 1-6MB of bacterial DNA)
  • But bacterial DNA is much more gene-dense (i.e. more genes per unit length)
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8
Q

What are the cytoskeleton components in a bacterium? [EXTRA]

A
  • MreB -> Actin homologue
  • FtsZ -> Tubulin homologue
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9
Q

Give some examples of the historical importance of bacteria in research and medicine. [EXTRA]

A
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10
Q

What is the clinical importance of bacterial ribosomes?

A

If we understand the difference between bacterial and eukaryotic ribosome structure, we can design antibiotics that selectively target just the bacterial ribosomes.

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11
Q

What are the two main mechanisms for mutation in bacteria?

A
  • Vertical transmission of mutation -> Occur during DNA replication (just like in humans)
  • Horizontal gene transfer -> When DNA material is transferred between bacteria (does not occur in humans)
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12
Q

Give an example of a bacterium in which horizontal gene transfer is important. [EXTRA]

A
  • Enterohaemorrhagic E. coli
  • This bacterium evolved from comensual E. coli bacteria by horizontal gene transfer
  • The extra DNA enables:
    • Adhesion -> Mediated by Locus of enterocyte effacement (LEE)
    • Haemolytic uraemic syndrome -> Enabled by production of Shiga toxins
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13
Q

Compare the replication time and mutation frequency of bacteria and humans.

A
  • Humans have a much longer generation
  • Bacteria have much higher mutation frequency (due to poorer proof-reading mechanisms)
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14
Q

What is host tropism and what enables it?

A
  • Host tropism is the infection specificity of certain pathogens to particular hosts and host tissues.
  • This type of tropism explains why most pathogens are only capable of infecting a limited range of host organisms.
  • Tropism occurs do to:
    • Invasion
    • Motility
    • Attachment/Adhesions
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15
Q

Summarise host-microbe interactions in an infection, including the functions of the bacterium and host.

A

Bacterium:

  • Tropism -> Invasion, Motility, Attachment
  • Immune evasion
  • Inflict damage

Host:

  • Recognition of the pathogen and signalling
  • Innate and adaptive immune response
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16
Q

What important functions do bacterial surface molecules have during infection?

A
  • Contribute to motility, adhesion, invasion, resistance
  • Harbour molecular patterns that trigger immune responses
  • Targets for components of the complement system/immune system
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17
Q

Where is peptidoglycan found?

A

Only in bacterial cell walls.

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18
Q

What is the function of peptidoglycan?

A

Provides rigid support and helps maintain bacterial cell shape.

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19
Q

Describe the structure of peptidoglycan.

A

A polymer mesh-like structure that contains:

  • Chains of alternating monosaccharides (N-acetylmuramic acid and N-acetylglucosamine), with β-(1,4) linkages
  • Oligopeptides of up to 5 amino acids are linked to the N-acetylmuramic acid.

The oligopeptides can be cross-linked between chains, giving the mesh-like structure.

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20
Q

What are the linkages in the glycan part of peptidoglycan?

A
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21
Q

What are the monosaccharides found in peptidoglycan and which are linked to oligopeptides?

A
  • N-acetylmuramic acid -> Linked to oligopeptides
  • N-acetylglucosamine
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22
Q

Describe the differences between Gram-positive and Gram-negative peptidoglycan. What is the significance of this?

A
  • In Gram-positive bacteria, the oligopeptides contain L-lysine
  • In Gram-negative bacteria, the oligopeptides contain mesoDAP

This plays a role in differential recognition of the bacterium by the host.

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23
Q

How is peptidoglycan recognised by the host?

A
  • Nod1 receptors recognise the mesoDAP in Gram-negative bacteria
  • Nod2 receptors recognise peptidoglycan in both types of bacteria

Signalling through the Nod receptors leads to transcriptional changes that are pro-inflammatory and lead to recruitment of cells.

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24
Q

What is some clinical relevance of Nod receptors? [EXTRA]

A

Nod2 receptor (involved in recognition of peptidoglycan in all bacteria) polymorphisms are associated with Crohn’s disease.

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25
Q

Where are teichoic acids found?

A

In the peptidoglycan of Gram-positive bacteria.

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26
Q

What are the two types of teichoic acids?

A
  • Wall teichoic acid -> Reaches out from the peptidoglycan layer
  • Lipoteichoic acid -> Reaches down from the peptidoglycan layer to the lipid layer of the cell membrane
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27
Q

What are teichoic acids and what is their function?

A
  • Highly variable anionic polymers in the peptidoglycan layer of Gram-positive bacteria
  • They play a role in:
    • Cell shape, growth and division
    • Resistance to antimicrobial peptides
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28
Q

In what bacteria is the outer membrane found?

A

Gram-negative

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29
Q

What is the outer membrane of Gram-negative bacteria made of?

A

It is a lipid bilayer:

  • Inner layer -> Mostly phospholipids
  • Outer layer -> Mostly lipopolysaccharides (LPS)
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30
Q

What is the function of the outer membrane of Gram-negative bacteria?

A
  • Forms a selective barrier against bile and antimicrobial agents
  • Allows for formation of outer membrane vesicles (OMVs), which can have immunomodulatory effects
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31
Q

How is the outer membrane of Gram-negative bacteria important in the immune response?

A

It is the target site for the insertion of the membrane attack complex (MAC) and bacterial lysis by complement.

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32
Q

What is the role of lipopolysaccharides (LPS) in an infection?

A
  • Elicits inflammatory responses in humans
  • Elicit complement activation via the alternative pathway
  • Are involved in virulence and pathogenesis, by for example:
    • Allowing attachment and invasion
    • Acting via molecular mimicry to appear like host cells
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33
Q

Describe the structure of a lipopolysaccharide (LPS).

A
  • Lipid A (endotoxin)
  • Polysaccharide part:
    • Core polysaccharide -> Usually conserved within a species
    • O antigen -> Repeating polysaccharide of variable length
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34
Q

Give some examples of molecular mimicry enabled by the O-antigens of the LPS of Gram-negative bacteria. [EXTRA]

A
  • H. pylori -> Mimic Lewis blood group
  • Campylobacter -> Mimic GM1 ganglioside
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35
Q

What is an endotoxin and what is its role?

A
  • It is the Lipid A part of a lipopolysaccharide (LPS)
  • It leads to systemic inflammatory response syndrome (SIRS):
    • Fever
    • Hypotension
    • Disseminated intravascular coagulation (coagulation of blood throughout the body)
    • Activation of complement and macrophages

In other words, it is responsible for many of the roles of LPS in Gram-negative bacteria.

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36
Q

What are the two ways in which host cells can recognise endotoxins? How are endotoxins targeted?

A

Endotoxins can bind to:

  • TLR4 on the surface of host cells -> Leads to inflammatory cytokine production
  • Caspase-4 receptors on the inside of cells -> Leads to cell apoptosis

Endotoxins are targeted by antimicrobial peptides (AMPs).

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37
Q

Why is it important to know if a bacterium is Gram-positive or Gram-negative?

A
  • Helps with identification of bacterium
  • Susceptibility to complement, drugs and antibiotics
  • Impacts on immune activation and evasion
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38
Q

What are PAMPs and MAMPs? What do they interact with?

A
  • Pathogen-associated molecular patterns / Microbe-associated molecular patterns
  • These are small molecules that are conserved in all microbes, and activate innate immune responses, protecting the host from infection
  • They bind to recognition receptors on host cells, including:
    • TLRs
    • NLRs
    • Lectins
    • RIG‐I
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39
Q

What are some important MAMPs in different types of bacteria?

A
  • Peptidoglycan -> For both types of Gram bacteria
  • Lipopolysaccharides (LPS) -> For Gram-negative bacteria
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40
Q

What are TLRs?

A
  • Toll-like receptors
  • They are receptors on host cells that play a role in the innate immune system -> They bind PAMPs/MAMPs, which are highly-conserved sequences in microbes that mark them out as foreign
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41
Q

Name 5 important bacterial surface structures.

A
  1. Capsule
  2. Flagella
  3. Pilli
  4. Secretion systems
  5. Toxins
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42
Q

What are bacterial capsules and what is their role?

A
  • High molecular weight polymers on the surface of bacteria
  • They are structurally diverse and can be structural mimics of host molecules
  • They are important in resistance to the host’s immune response
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43
Q

What is the clinical importance of bacterial capsules?

A

They can be targeted by conjugate vaccines.

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44
Q

Where does the bacteria capsule lie relative to the cell wall?

A

It lies outside of the cell wall.

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45
Q

Give an example of a bacterial capsule providing resistance to the host’s immune response. [EXTRA]

A
  • In Streptococcus pneumoniae (Gram positive), the capsule provides some resistance to phagocytosis.
  • In Neisseria meningitidis (Gram negative), the capsule provides some resistance to complement lysis (since the complement pathway results in assembly of the MAC complex on the outer membrane of Gram negative bacteria)
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46
Q

What is the bacterial capsule composed of?

A

Polysaccharides

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47
Q

What are flagella and what is their function?

A
  • Long, thin filaments involved in bacterial motility (swimming/swarming)
  • Enable bacterial movement through rotation of the filament
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48
Q

What are the 3 components of a flagellum?

A
  • Basal body -> Embedded in the inner and outer membrane of a Gram-negative bacterium. It can spin to allow movement.
  • Hook
  • Filament
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49
Q

Draw the structure of a flagellum.

A
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50
Q

What are flagella powered by?

A

The proton motor force (chemiosmosis).

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51
Q

How quickly can the flagellum of E. coli spin and thus how fast can they move? [EXTRA]

A
  • Spin up to 15,000rpm
  • Move up to 60 body lengths/sec
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52
Q

What makes up the filaments in the flagellum of bacteria?

A

Flagellin:

  • A globular protein that arranges itself in a hollow cylinder to form the filament in a bacterial flagellum.
  • It is the principal component of bacterial flagellum, and is present in large amounts on nearly all flagellated bacteria.
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53
Q

What is the clinical importance of flagellin?

A
  • It is a MAMP, since it is a TLR5 ligand
  • Therefore, it can be used as an adjuvant (agent that improves the immune response of a vaccine) in vaccines, since it stimulates local inflammation and immune response
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54
Q

What are pili and what is their role?

A
  • Filament-containing structures on the surface of bacteria that are projections of the cell membrane
  • They have important roles in adhesion
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55
Q

What are pili made of?

A

Repeating units of pillin

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56
Q

What is the difference between pili and fimbriae?

A
  • They are essentially the same
  • Short pili are also known as fimbriae and are higher in number than long pili
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57
Q

On what bacteria are pili and fimbriae typically found?

A

Gram negative

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58
Q

What is found on the ends of pili/fimbriae?

A

Adhesive tip structures having a shape corresponding to that of specific glycoprotein or glycolipid receptors on a host cell -> e.g. they might have a lectin domain.

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59
Q

What are two examples of pili involved in UPEC (uropathogenic E. coli) infections? What is the role of each? [EXTRA?]

A
  • Pap pilus -> Upper UTI (kidneys)
  • Type I pilus -> Lower UTI (urethra, prostate, bladder)
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60
Q

Describe the role of the type I pilus of UPEC in UTIs. [IMPORTANT]

A

Type I pilus causes lower UTIs:

  • The lectin domain of the FimH tip adhesin of the type I pilus of UPEC (uropathogenic E. coli) binds to mannosylated uroplakins (found on plaques) in the bladder.
  • This allows the UPEC to bind to the bladder, causing the UTI.
  • Understanding this structure allows the design of anti-infectives.
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61
Q

What are secretion systems in bacteria?

A

Multi-protein systems that allow a wide range of substrates to be secreted from the cytosol into the extracellular space.

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62
Q

How many different secretion systems in bacteria do we know about?

A

9

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63
Q

What are secretion systems designed to allow substrate transport across?

A

The cell membrane(s) of bacteria. In Gram-negative bacteria, there is the inner and outer cell membrane, so there is an extra challenge.

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64
Q

Give some examples of the roles of bacterial secretion systems.

A
  • Cell entry [IMPORTANT]
  • Attachment
  • Replication
  • Anti-phagocytic
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65
Q

Describe the type 3 secretion systems in bacteria.

A
  • Found in many different Gram-negative bacteria
  • Type 3 secretion systems transport substrates across 3 cell membranes -> The inner cell membrane, outer cell membrane and the cell membrane of the host
  • They have a basal body (like flagella do), needle and translocon
  • Essentially they can be viewed as syringes that pump toxins directly into the host cell
  • The exact function of the secretion system varies between bacterial species, depending on what substrates are secreted
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66
Q

What are bacterial toxins?

A

Factors which poison or intoxicate host cells, killing them or altering their function.

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67
Q

What are the two types of toxin?

A
  • Exotoxins -> Secreted protein toxins
  • Endotoxins -> Lipopolysaccharides (LPS) from the outer membrane of Gram-negative bacteria (cell-associated)
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68
Q

Can bacterial toxins be entirely responsible for pathogenesis?

A
  • In some cases, yes.
  • In these cases, the disease can be replicated by simply injecting the toxin, and the bacteria causes disease only by release of the toxin.
  • For example, diphtheria toxin can cause the same changes to the tonsils as diphtheria bacteria.
  • In other cases, there are many factors involved in the disease.
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69
Q

What are some different subtypes of extracellular toxins in bacterial infections?

A

*Make sure to add more notes on this!*

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70
Q

What roles do surface structures have in colonisation and disease?

A
  • Capsules -> Bacterial resistance to phagocytosis and complement
  • Flagella -> Motility and activate inflammatory responses
  • Pili -> Adhesion to host receptors
  • Type 3 secretion systems -> Cell entry/avoidance of phagocytosis
  • Toxins -> May be sufficient to mediate disease
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71
Q

Is Gram staining suitable for identifying all bacteria?

A

No, some cannot be Gram stained. For example:

  • Mycoplasma -> Has no cell wall
  • Chlamydia -> Intracellular pathogen
  • Spirochetes -> Too thin to be visualised
  • Mycobacterium tuberculosis -> ‘Acid fast’, so Gram stain does not get through outer membrane
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72
Q

Describe the process of Gram staining.

A
  1. Primary staining with crystal violet -> Penetrates the cell wall of bacteria, regardless of their structure
  2. Staining with Gram’s solution -> This is a mixture of potassium iodide and iodine, which reacts with the crystal violet stain, forming large complexes
  3. Decolourisation using alcohol -> This leads to the break down of the outer membrane in Gram-negative bacteria, so the stain can leak out. In Gram-positive bacteria, the peptidoglycan layer is thicker, so the stain is retained more.
  4. Counter staining -> A red/pink saffranin or carbol fuschin stain is added, allowing Gram-negative bacteria to be seen.

Result:

  • Gram-positive bacteria stain purple
  • Gram-negative bacteria stain red/pink
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73
Q

Define a commensal.

A

A harmless member of the flora.

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74
Q

Define a symbiont.

A

A commensual in a mutually beneficial relationship.

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75
Q

Define a pathogen.

A

An organism that is able to cause disease.

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76
Q

What are the two main types of pathogen based on when they cause disease?

A
  • Primary pathogens -> Cause disease as a result of their presence or activity within the normal, healthy host, and their intrinsic virulence is a necessary consequence of their need to reproduce and spread
  • Opportunistic pathogens -> Normally commensal and do not harm the host, but can cause disease when the host’s resistance is low.
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77
Q

What is virulence?

A

The degree of damage inflicted by a pathogen.

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78
Q

Define avirulent.

A

Lacking virulence.

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79
Q

Define infective dose.

A

The number of micro-organisms required to cause disease.

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80
Q

Give an example of a bacterium that can cause 3 different outcomes in different patients. [EXTRA]

A

Staphylococcus aureus can act as:

  • Commensal -> In the airways of about 20% of the population
  • Opportunistic -> It can cause line infection (when germs enter the body through a tube placed in a vein to deliver nutrients and medicine)
  • Primary pathogen -> It can cause septic arthirits in some patients
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81
Q

Name some factors that determine whether a bacterium is a primary pathogen, opportunistic pathogen or commensal in a patient.

A

The outcome depends on:

  • Bacterium
  • Host
  • Route of infection
  • Dose
  • Co-infection

Note how the outcome of an infection is dependent on both pathogen factors and host factors (such as host innate immunity).

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82
Q

What are pathobionts?

A

Bacteria that can be pathogens or commensals, depending on conditions.

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83
Q

How does the diversity of commensal bacteria compare to the overall diversity of bacteria?

A

Commensal bacteria are highly specialised and exist in a highly competitive community, so they are not very genetically diverse, while bacteria in general are very diverse.

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84
Q

What sort of bacteria dominate the human microbiome?

A
  • Gram-positive anaerobic bacteria that do not cause disease.
  • The bacteria are diverse, but are SPECIFIC in the characteristics (i.e. many different types, but all similar)
  • The few pathogens that are found there are highly specialised, with additional attributes encoded by extra DNA that non-pathogens do not have
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85
Q

What is an important role of most bacteria in the human microbiome?

A

Protection against pathogens

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86
Q

What are the attributes of a pathogen necessary for virulence?

A
  • Tropism
  • Replication
  • Evasion of immune killing
  • Toxicity
  • Transmission (between hosts)
  • Aquisition of nutrients
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87
Q

What is tropism?

A

The ability of a bacterium to find and establish a niche (intracellularly or extracellularly).

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88
Q

What are Koch’s postulates, as a concept? [IMPORTANT]

A

Four criteria that were designed to establish a causative relationship between a microbe and a disease.

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89
Q

State all of Koch’s postulates.

A

In order for a microbe to be confirmed as the cause of a disease:

  • The microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms.
  • The microorganism must be isolated from a diseased organism and grown in pure culture.
  • The cultured microorganism should cause disease when introduced into a healthy organism.
  • The microorganism must be reisolated from the diseased experimental host and identified as being identical to the original specific causative agent.

In other words, it’s checking at lots of different stages that a pathogen is the one causing the disease.

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90
Q

What are molecular Koch’s postulates? [IMPORTANT]

A

A set of criteria that must be satisfied to show that a gene found in a pathogenic microorganism codes for a product that is the cause of a given disease.

(It differs from Koch’s postulates in that Koch’s postulates seek to find the microbe causing disease, while molecular Koch’s postulates seek to find the exact genes causing disease)

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91
Q

Who established molecular Koch’s postulates?

A

Stanley Falkow

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92
Q

Genes that satisfy molecular Koch’s postulates are often refer to as…

A

Virulence factors

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93
Q

State all of molecular Koch’s postulates.

A

In order to prove that a gene is the virulence gene that causes a disease, it must be shown that:

  • The virulence factor is expressed by the pathogen
  • Deletion of the gene causes attenuation of the virulence
  • Complementation with the gene should restore virulence
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94
Q

What are some potential routes and sources of infection?

A
  • Respiratory
  • Faecal-oral
  • Direct contact
  • Vector borne
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95
Q

Name two examples of bacteria that can cause diarrhoea.

A
  • Vibrio cholera
  • Clostridium difficile
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96
Q

What type of bacterium is Vibrio cholera?

A

Gram negative curved bacterium (O-antigen possessing)

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97
Q

What are the symptoms and treatment of diarrhoea cause by Vibrio cholera? [EXTRA]

A

Symptoms:

  • Sudden onset of fast, watery diarrhoea
  • No blood or mucous -> Loss of electrolytes (Described as rice water stool)
  • May cause death

Treatment:

  • Fluid replacement
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98
Q

Describe the exotoxins released by Vibrio cholera and how they act. [EXTRA]

A

Cholera toxin is a type of AB toxin:

  • It is an A1B5 toxin, so for every 1 A subunit there are 5 B subunits
  • A subunit is the active component
  • B subunit allows binding to host cells (remember: B for binding) -> Binds to GM1 ganglioside
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99
Q

Describe how Vibrio cholera causes diarrhoea. [EXTRA]

A
  • It releases AB toxins (exotoxins)
  • The B subunits bind to GM1 gangliosides so the toxin enters the host cell
  • The A subunit ribosylates G proteins, which maintains them in their active state
  • Therefore, adenylate cyclase activity is high and cAMP is increased
  • This opens ion channels in the membrane, leading to loss of chloride ions
  • Water follows, resulting in diarrhoea
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100
Q

What are AB toxins?

A
  • Toxins that are secreted by certain bacteria, including:
    • Cholera
    • Diphtheria
    • Pertussis toxin (associated with whooping cough)
    • E. coli
  • They consist of B subunits, for attachment to the host cell, and A subunits for toxicity within the cell
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101
Q

What type of bacterium is Clostridium difficile?

A

Gram positive rod, spore-forming

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102
Q

What are the symptoms and treatment of diarrhoea cause by Clostridium difficile?

A

Symptoms:

  • Diarrhoea
  • Inflammation of colon
  • May cause death

Treatment:

  • Stool transplant
  • Antibiotics
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103
Q

What is a large risk factor for Clostridium difficile infection?

A

It often follows a course of antibiotics.

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104
Q

Describe the exotoxins released by Clostridium difficile and how they act. [EXTRA]

A

Toxin A:

  • Enterotoxin
  • Enters host cell via apical surface

Toxin B:

  • Cytotoxin
  • Enters host cell via basolateral surface

In each toxin, there is an enzymatic domain, translocation domain and binding domain.

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105
Q

Describe how Clostridium difficile causes diarrhoea.

A
  • The bacterium releases two types of exotoxin -> Toxin A and toxin B
  • Both bind to host cell receptors via binding domain -> This leads to endocytosis into an endosome
  • The endosome is acidified inside the cell
  • This leads to cleavage of the toxin, so that the translocation domain is free to insert itself into the membrane of the endosome
  • This releases the enzymatic domain of the toxin out of the endosome
  • The enzymatic domain glycosylates G proteins (rho GTPases), which inactivates them
  • Somehow this leads to diarrhoea and inflammation
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106
Q

Give some experimental evidence for Clostridium difficile.

A

The host receptors that C. diff binds to were discovered by genome-wide CRISPR–Cas9-mediated screens.

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107
Q

Name two examples of bacteria that can cause systemic infection.

A
  • Staphylococcus aureas
  • Neisseria meningitidis
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108
Q

What are the two important types of protein in Staphylococcus aureas responsible for its virulence?

A
  • Surface proteins -> Tropism + Immune evasion
  • Secreted proteins -> Toxicity + Immune evasion
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109
Q

What type of bacterium is Staphylococcus aureus?

A

Gram positive

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110
Q

What are some examples of surface proteins on Staphylococcus aureus and what are their functions? [IMPORTANT?]

A

For tropism:

  • MSCRAMS (microbial surface components recognizing adhesive matrix molecules) -> Collection of proteins that bind to ECM proteins (such as elastin, colagen, fibronectin)

For immune evasion:

  • Protein A -> Binds to Fc subunit of IgG, rendering the antibody useless
  • Coagulase -> Bind fibrinogen and prothrombin (and activate prothrombin), leading to clot formation around the bacteria. This allows it to reside there and protect it from the immune system.
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111
Q

How are surface proteins attached in Gram positive bacteria?

A

They are covalently linked to peptidoglycan.

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112
Q

How are surface proteins in Staphylococcus aureas (Gram positive) attached to the peptidoglycan?

A

Sortase enzyme attaches the proteins via peptide bonds:

  • The sortase recognises specific sequences at the C-terminus of the membrane proteins -> This is an LPXTG motif
  • It uses this motif to cleave the protein and then attach it to the peptidoglycan by a peptide bond

The identification of the LPXTG motif by Olaf Schneewind allowed for the genome to be searched for other potential surface proteins, and therefore search for new vaccine candidates.

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113
Q

How do MSCRAMS (in Staphylococcus) interact with matrix proteins?

A
  • Repeating units of the bacterial receptor bind to repeating units of the matrix proteins -> Although the interaction is weak, the cumulative avinity is strong
  • Altering the structure of matrix proteins (such as fibrinogen) -> This is recognised by integrins, which then mediate uptake of bacteria into cells
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114
Q

How does Staphylococcus aureus evade complement?

A
  • The bacterium secretes inhibitors of complement -> These act by preventing activation of C5
  • There are surface-expressed proteins that target other parts of complement -> e.g. Levels of immunoglobulins + Inhibitors of C3 conversion
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115
Q

What is an enterotoxin?

A

A toxin that targets the small intestine (i.e. the enterocytes)

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116
Q

What are some exotoxins secreted by Staphylococcus aureus?

A
  • Enterotoxins -> Leads to gastroenteritis (food poisoning)
  • TSST-1 -> Leads to toxic shock syndrome (TSS)
  • Exfoliation toxin -> Leads to Staphylococcus scalded skin syndrome
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117
Q

What are superantigens? [IMPORTANT]

A
  • A type of bacterial toxin that act by inappropriately activating T-cells.
  • They do this by forming cross-bridges between MHC molecules on antigen-presenting cells and the T-cell receptor (between conserved regions).
  • This leads to non-specific activation, leading to mass release of cytokines and upregulation of T-cell activity
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118
Q

What type of bacterium is Neisseria meningitidis and where does it infect?

A

Non-O-antigen possessing Gram negative coccus, typically residing in the upper airway

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119
Q

Does Neisseria meningitidis cause disease?

A
  • It is found in about 10% of the population and it does not cause disease in most
  • In some individuals, it causes severe systemic disease that may involve bacterial meningitis.
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120
Q

What causes Neisseria meningitidis to be pathogenic in some individuals?

A

There are two features:

  • The bacterium reaches very high concentrations in the systemic circulation (up to 1013 bacteria/individual)
  • The bacterium blebs (sheds membrane vesicles) as it grows within the body -> This frees up endotoxin lipid A (part of LPS) from the Gram-negative outer membrane
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121
Q

What is the immune response to Neisseria meningitidis? What is the evidence for this?

A
  • The immune response is mainly via the complement pathway
  • We know this because of high rates of meninogcoccal disease in individuals with complement pathway defects
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122
Q

How does positive feedback occur in the complement system?

A
  • The alternative pathway of activation acts as an amplification loop
  • It is kept in check by negative regulators, such as factor H
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123
Q

How are pathogenic strains of Neisseria meningitidis able to reach such high concentrations in the blood and therefore cause disease?

A
  • Due to the capsule, of which there are 13 serogroups:
    • In serogroup B, the bacterial capsule has alpha 2‐8 linked polysialic acid -> This is the same molecule that is on neural cell adhesion molecule 1 in infancy, meaning that the immune system does not respond to it -> Molecular mimicry
    • This also means that vaccines against serogroup B strains are not feasible
  • The bacteria can also bind complement factor H (via factor H binding protein) -> This factor is responsible for downregulating complement, so the bacteria are less susceptible to complement.
  • The bacteria is regulated by temperature via RNA thermocensors -> These are sequences in the untranslated region of mRNA that fold into a hairpin loop if the temperature is low, so that no translation can happen. If the temperature rises, the RNA is translated.
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124
Q

How do RNA thermosensors work?

A
  • These are sequences in the untranslated region of mRNA that fold into a hairpin loop if the temperature is low, so that no translation can happen.
  • If the temperature rises, the RNA is translated.
  • Therefore, the immune defence mechanisms are only switched on when the temperature is high (like in the systemic circulation).
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125
Q

What is a trigger entry mechanism for bacteria entering a host cell?

A

Where injection of effectors by the bacterium in the host cell cytoplasm triggers large-scale cytoskeletal rearrangements and ruffles formation allowing the bacterium to be engulfed and internalized. For example, Shigella bacterium does this.

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126
Q

Give some examples of intracellular pathogens (which are adapted to survive within host cells).

A
  • Listeria
  • Shigella
  • Salmonella
  • Mycobacteria
  • Coxiella
  • Legionella
  • Mycobacterium
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127
Q

What are the main ways in which intracellular pathogens can survive within host cells? Which bacteria use each strategy?

A

Once taken up by a phagocyte, the bacterium is within an endosome, which the phagocyte plans to fuse a lysosome with. The bacteria can avoid this by:

  • Escaping the endosome -> Shigella, Listeria
  • Prevent fusion with the lysosome -> Salmonella, Mycobacteria
  • Being able to survive in the phagolysosome -> Coxiella, Legionella, Mycobacterium
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128
Q

How can Mycobacterium tuberculosis survive inside host cells? [IMPORTANT]

A
  • Has a cell wall containing mycolic acids
  • This prevents fusion of the lysosome with the phagosome that the bacterium is in, so it can survive
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129
Q

Describe the concept of the inflammasome. [EXTRA]

A
  • The inflammasome is a complex within host cells that acts to detect and respond to intracellular pathogens
  • The foreign stimulus binds to a sensor protein, which acts via an adaptor to set off an effector
  • The effector leads to cleavage of inactive proteins within the cell that they lead to an inflammatory response -> Cytokines become active
  • Gasdermin D is also activated -> This leads to cell lysis (in essence this is tactical suicide of the cell)
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130
Q

What is gasdermin D? How does it work? [IMPORTANT]

A
  • It is a pro-molecule in host cells, in the inactivated state at rest since it is folded over on itself
  • It is activated by cleavage by inflammatory caspases in response to intracellular pathogens
  • One domain polymerises to form pores in the cell membrane that lead to cell lysis -> This is a form of cell suicide in order to protect the cell when it is infected, which also releases inflammatory cytokines
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131
Q

What is pyroptosis?

A
  • A form of programmed cell death that occurs when a cell is invaded by intracellular pathogens
  • It leads to increased inflammatory response due to release of cytokines
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132
Q

What is the advantage of intracellular life for intracellular pathogens?

A

It is a way for the pathogen to avoid immune responses.

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133
Q

What type of bacterium are Shigella and Salmonella?

A

O-antigen-possessing Gram-negative intracellular bacteria

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134
Q

Where do Shigella and Salmonella infect?

A
  • Shigella -> Colon
  • Salmonella -> Small intestine
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135
Q

How do Shigella and Salmonella enter cells (from the GI tract)?

A
  • Cross the epithelial barrier via M-cells (sentinel antigen-presenting cell that present antigens to macrophages underlying them)
  • These M-cells are phagocytic by nature
  • After this, the bacteria are then taken up by macrophages, in which pyroptotic cell death happens (in the case of Shigella)
  • Sa**lmonella tend to prefer to stay in the macrophages and replicate there, while Shigella prefer to escape
  • After this, the bacteria invade epithelial cells through the basolateral membrane using the type 3 secretion system
  • Finally, the cell undergo cell-to-cell spread to adjacent cells
136
Q

What are the symptoms of Shigella and Salmonella? Why?

A
  • They can lead to inflammatory diarrhoea
  • This is because they cause pyroptotic cell death (of phagocytes), which leads to release of cytokines that attract neutrophils
  • This leads to the breakdown of the integrity of the epithelial barrier
137
Q

How can Shigella move within and between cells?

A

It has the ability to polymerise actin, forming foci behind it. This polymerisation of actin drives the movement of the bacterium.

138
Q

What is the type 3 secretion system used for in Shigella and Salmonella?

A
  • Shigella -> Cell entry
  • Salmonella -> Cell entry / Replication
139
Q

How is the type 3 secretion system encoded in Shigella?

A

It is encoded in a plasmid, by a 30kb entry region.

140
Q

How did Shigella evolve?

A
  • It evolved from E. coli 4 separate times, so there are now 4 strains.
  • Each time this involved the uptake of a plasmid.
141
Q

Give some experimental relevance of Shigella.

A

Shigella was the bacteria in which LPS activating caspase 4 (and thus causing pyroptosis) was detected. (Shi, 2014)

142
Q

Give a summary of the detection of different PAMPs intracellularly and what the effects of this are.

A
  • LPS -> Binds to caspase 4 -> Pyroptosis
  • Peptidglycan -> Binds to Nods -> Inflammasome activation -> Pyroptosis + Cytokine release
143
Q

Describe the type 3 secretion systems in Salmonella.

A

There are two type 3 secretion systems:

  • For entry -> SPI-1
  • For intracellular replication -> SPI-2
144
Q

Give some experimental relevance of Salmonella.

A
  • The importance of the SPI-2 type 3 secretion system can be deomonstrated by viewing wild-type Salmonella and SPI-2 mutant Salmonella with green fluorescent protein to demonstrate growth.
  • The wild-type replicates much faster inside a macrophage, showing the role of SPI-2 in Salmonella replication.
145
Q

Give an example of a Gram-positive intracellular pathogen.

A

Listeria -> Causes food poisoning and more serious diseases in the immunocompromised, elderly and pregnant women

146
Q

How does Listeria enter host cells and what happens after this? [EXTRA]

A

Enter by a zipper mechanism:

  • Bacteria just adhere to the host cell and then sink into the cell and enter.
  • This is mediated by internalin A and internalin B

After this, the bacteria escape the phagosome (via pores they form) and undergo motility due to actin-mediated motility (manipulation of host cytoskeleton).

147
Q

Give some experimental evidence related to variation in bacteria.

A

(Welch, 2002) Extensive mosaic structure revealed by the complete genome sequence of uropathogenic E. coli:

  • The paper took 3 isolates of E. coli:
    • Standard lab strain
    • K12 strain (used for cloning in the lab)
    • Uropathogenic strain
  • They found that only 40% of genes were core genes, common to all of the strains
  • The rest were accessory genes that make each strain unique
  • Therefore, there is a LOT of variation within a species
148
Q

What is the pangenome?

A
  • The pangenome is the entire gene set of all strains of a species.
  • It includes genes present in all strains (core genome) and genes present only in some strains of a species (variable or accessory genome).
149
Q

What are the 3 main mechanisms for horizontal gene transfer in bacteria?

A
  • Transformation
  • Transduction
  • Conjugation
150
Q

Describe horizontal gene transfer by conjugation.

A
  • Cell-to-cell contact between two different strains of bacteria
  • DNA is transferred via a plasmid
  • The DNA coding for a mating bridge is on a plasmid
  • The conjugation machinery recognises an OriT (origin of transfer) on the plasmid
  • The plasmid is made into a single strand of DNA, before being transferred across
  • In the recipient, the DNA is made to be double-stranded, so that both the recipient and donor have the plasmid
151
Q

In what bacteria is horizontal gene transfer by conjugation common?

A

Many Gram-positive and Gram-negative bacteria, particularly enteric bacteria.

152
Q

Describe horizontal gene transfer by transformation.

A
  • Transformation is when bacterial cells take up DNA from the environment
  • Double-stranded DNA in the surroundings are broken down into single-stranded DNA
  • This single-stranded DNA is then taken up by specific uptake mechanisms
153
Q

In what bacteria is horizontal gene transfer by transformation common?

A
  • Neisseria
  • Streptococcus
154
Q

Describe horizontal gene transfer by transduction.

A
  • Genes from the bacterium are incorporated into the genome of a bacterial virus (bacteriophage)
  • The genes are then carried to another host cell when the bacteriophage initiates another cycle of infection
155
Q

In what bacteria is horizontal gene transfer by transduction common?

A

Many Gram-positive and Gram-negative

156
Q

How do bacteria respond to horizontal gene transfer by phages (transduction)?

A

They have an innate immune system to combat it.

157
Q

How does a bacterium’s innate immunity work?

A
  • It uses a range of restriction enzymes
  • The restriction enzymes cut up DNA which is transduced into the bacterium by phages
  • It recognises foreign DNA because it is not methylated (most bacterial DNA is methylated by methylases), so the bacterium’s DNA is not cut up
158
Q

How does a bacterium’s adaptive immunity work?

A

CRISPR/Cas:

  • When a cell is infected by a phage, the sequences of the phage are cut up by the Cas endonuclease and integrated into the CRISPR repeats
  • The spaces between the repeat sequences form the sequence specificity of the recognition of repeat invasion
  • This means that the spacing pattern acts as an identifier of any infection in the future

[CHECK THIS AND ADD MORE]

159
Q

What does CRISPR stand for?

A

Clustered regularly interspaced short palindromic repeat

160
Q

Describe the source of DNA for most horizontal gene transfer.

A
  • The source of DNA for lots of horizontal gene transfer is unknown
  • In our gut, it is believed to be our own flora that contributes a large amount of DNA, particularly for antibiotic resistance, etc.
161
Q

What is the effect of horizontal gene transfer on bacterial phenotypes and virulence?

A

It can confer properties such as antibiotic resistance, and lots of virulence is due to that.

162
Q

Compare the ideas of intergenomic and intragenomic variation.

A
  • Intergenomic variation is where DNA is introduced into a bacterium from an external source
  • Intragenomic variation is where DNA mutates or is altered within the bacterium itself
163
Q

Name the different types of intragenomic variation.

A
  • Point mutation
  • Phase variation
  • Antigenic variation
164
Q

What is phase variation (in bacteria)? [IMPORTANT]

A
  • It is the on/off switching of genes, without changing the sequence.
  • It is heritable, but it can be reversed!
165
Q

Name two ways in which phase variation can occur in bacteria.

A
  • Inverter elements
  • Homopolymeric tracts
166
Q

How does phase variation occur by invertable elements? Explain using an example.

A
  • Example: The expression of Type 1 fimbriae in E. coli​, a fim switch is used to control whether the fimbriae are expressed
  • If the fim element is inverted, then the promoter elements in the fim do not line up with the fimbriae gene, so it is not expressed
  • FimB encodes an invertase that switches between the inverted and non-inverted alignment
167
Q

How does phase variation occur by homopolymeric tracts? Explain using an example.

A
  • Example: In Neisseria meningitidis, expression of PorA (an outer membrane protein) is controlled by homopolymeric tracts
  • Homopolymeric tracts are lengths of repeated nucleotid, either in the promoter or in the open reading frame (ORF)
  • DNA polymerase has relatively low affinity over repeating sequences, so the length of the tract can increase or decrease during replication
  • This causes the gene to shift in or out of frame
  • This can be reversed in subsequent rounds of replication
  • Aside from this, PorA can be interrupted by insertion of mobile DNA within the bacterium, which enters the ORF and stops translation
168
Q

What is antigenic variation (in bacteria)?

A

The mechanism by which a bacterium alters the proteins or carbohydrates on its surface and thus avoids a host immune response.

169
Q

How does antigenic variation occur?

A

The sequence of a gene coding for a protein can change by:

  • Point mutation
  • Uptake of DNA by horizontal gene transfer
170
Q

Which bacterial proteins are most commonly affected by intragenomic variation?

A
  • Mostly surface structures
  • But also restriction/modification systems -> This means that certain bacteria would be more prone to uptake DNA by horizontal gene transfer thatn others
171
Q

Can bacteria change their genes in response to changes in the environment?

A

They can’t change the genes on purpose, but the bacteria can sense the environment and change gene expression in response.

172
Q

Give an example of a bacterium sensing its environment and making changes to gene expression in response.

A

A fall in intra‐cellular iron levels triggers de‐repression of diphtheria toxin gene.

173
Q

What is quorum sensing? [IMPORTANT]

A

Bacteria’s ability to detect and to respond to cell population density by gene regulation.

174
Q

Give an example of quorum sensing.

A

Once the bacteria reach a high population density and the stationary phase, the bacteria show bioluminescence.

175
Q

Give some examples of quorum sensing in various bacteria.

176
Q

What molecules are involved in quorum sensing in Gram-positive and Gram-negative bacteria?

A
  • Gram positives: Peptides
  • Gram negatives: Secondary metabolites
177
Q

What is the relevance of quorum sensing in the human gut microbiome?

A
  • There is evidence that bacteria in the gut can produce decoy molecules that can throw-off the quorum sensing of pathogens, which eliminates them.
  • This study looked at Bacillus as the probiotic (Piewngam, 2018)
178
Q

What are two component systems and how do they work?

A
  • Two component systems are very simple systems used in basic stimulus-response coupling mechanism to allow organisms to sense and respond to changes in many different environmental conditions.
  • How it works:
    • Sensor kinase in the membrane detects change in environment
    • The kinase domain phosphorylates a response regulator, which leads to a response
179
Q

Define antimicrobial.

A

Interferes with growth and reproduction of a ‘microbe’.

180
Q

Define antibiotic.

A

Reduces or eliminates harmful bacteria.

181
Q

How are antimicrobials related to antibiotics?

A

Antibiotics are a type of antimicrobial.

182
Q

Define bactericidal.

A

Kills bacteria.

183
Q

Define bacteriostatic.

A

Halts bacterial growth.

184
Q

Draw a graph to show the difference between the terms bactericidal and bacteriostatic.

185
Q

What is the idea of selective toxicity in antibiotic use?

A

The idea that an antibiotic must be effective against the bacterium but not against the host.

186
Q

What are some concepts that allow for selective toxicity of antibiotics?

A
  • Target not present in the host
  • System/structure is different from the host
  • Differential access of target (i.e. easier to access target in bacterium)
187
Q

Why are companies pulling out of antibiotic development?

[EXTRA]

A
  • Because it is not profitable.
  • The drugs that make the most money are those which are used by patients for their whole lives, such as srugs to manage arthiritis.
  • Antibiotics are curative, meaning that they are used only for a week or two, until the infection is cleared, so they do not make as much money.
188
Q

Describe the history of antibiotic research. [EXTRA]

A
  • First there was the golden age of antibiotic discovery
  • This was followed by the void, where companies began to withdrawn from antibiotic research, since it was viewed as there already being enough and it not being profitable
189
Q

Which bacteria are considered more of a threat in terms of antibiotic resistance: Gram positive or Gram negative?

A

Gram-negative

190
Q

Describe the list of bacteria at high risk of developing antibiotic resistance. [EXTRA]

A
  • In 2016, the WHO produced a list of bacterial species that were most of a threat in terms of developing antibiotic resistance.
  • Those in the highest category are all Gram-negative.
191
Q

What are the ESKAPE pathogens? [EXTRA?]

A

It is an acronym for the 6 common bacteria that are known to have developed a high degree of antibiotic resistance, so they posed a threat to humans, especailly those immunocompromised.

192
Q

Give an example of governmental efforts to slow antibiotic resistance developing.

A
  • The UK Government has produced a 5 year plan (2019-2024) called “Tackling antimicrobial resistance”
  • The plan calls for more optimal use of antibiotics in animals and agriculture, as well as improved surveillance of AMR
193
Q

Compare the amount of antibiotic use in humans and animals.

A

About 10 time more antibiotics are used in agriculture than medicine.

194
Q

Can antimicrobial resistance jump from bacterial species in animals to humans? [EXTRA] [INTERESTING]

A
  • It is widely believed that antibiotic resistance in animals can contribute significantly to antibiotic resistance in humans
  • This was contested by (Mather, 2013), when they compared Salmonella in humans and in local animals. They found that there was no evidence of transmission of anitbiotic resistance.
  • Therefore, this paper has been used a lot to support use of antibiotics by large farming companies, especially in lobbying.
  • However, it has been criticised a lot as a paper, since most of our food does not come from local animals, so it is not ideal to just compare humans to local animals.
195
Q

State the main types of antibiotic and their mechanism of action. [IMPORTANT]

A
  • Beta-lactams -> Inhibition of cell wall synthesis
  • Macrolides, Aminoglycosides + Chloramphenicol -> Inhibition of protein synthesis
  • Sulphonamides -> Anti-metabolites
  • Quinolones -> Inhibitors of nucleic acid synthesis by binding to DNA gyrase
  • Isoniazid -> Blocks long-chain mycolic acids
  • Rifamycins -> Inhibition of transcription
  • 2,4-diaminopyridines -> Inhibition of folate metabolism (and hence of DNA synthesis)
196
Q

How do beta-lactam antibiotics work? Are they bactericidal or bacteriostatic? Name some examples.

A

Inhibition of cell wall synthesis:

  • They are structural analogues of the peptide cross-bridges in peptidoglycan
  • Therefore, they can preferentially bind to the transpeptidase enzymes (one of the penicillin binding proteins PBPs)
  • This stops transpeptidation, so the peptidoglycan cannot form
  • They are BACTERICIDAL

Examples:

  • Penicillins:
    • Penicillin
    • Amoxicillin
    • Benzylpenicillin
    • Flucloxacillin
197
Q

Draw the structure of beta-lactam antibiotics.

A

They all have this beta-lactam ring.

198
Q

What are some different examples of beta-lactam antibiotics? [IMPORTANT]

A
  • Penicillins:
    • Penicillin
    • Amoxicillin
    • Benzylpenicillin
    • Flucloxacillin
  • Cephalosporins [EXTRA - Discovered by Abraham in the Dunn school)
  • Monobactams [EXTRA?]
  • Carbapenems [EXTRA?]
199
Q

Are beta-lactams more effective at treating Gram-positive or Gram-negative infections?

A

Gram-positive

200
Q

Give an example of a glycopeptide antibiotic and explain how it works. Is it bactericidal or bacteristatic? [EXTRA?]

A
  • Vancomycin
  • This works by targetting peptidoglycan directly (as opposed to its synthesis, like with beta-lactams)
  • It binds to D-alanine D-alanine cross-bridges
  • It is BACTERISTATIC and specific to Gram-positive bacteria
201
Q

Give some clinical relevance of vancomycin. [EXTRA]

A
  • It is an antibiotic that targets the D-alanine D-alanine cross-bridges in peptidoglycan.
  • Antibiotic resistance has developed by including D-lactate instead of alanine.
202
Q

Compare the structure of eukaryotic and prokaryotic ribosomes that enables the selective targetting of bacterial ribosomes.

203
Q

Give some examples of antibiotics that work by inhibition of protein synthesis.

A
  • Aminoglycosides -> Gentamicin, Tetracyclin, Streptomycin
  • Macrolides -> Erythromycin
  • Chloramphenicol
204
Q

How do aminoglycoside antibiotics work? Are they bactericidal or bacteriostatic? Name the main examples.

A
  • Inhibition of protein synthesis by binding to ribosomes
  • They are BACTERICIDAL
  • Examples:
    • Streptomycin
    • Tetracyclin
    • Gentamicin
205
Q

How do macrolide antibiotics work? Are they bactericidal or bacteriostatic? Name the main examples.

A
  • Inhibition of protein synthesis by binding to ribosomes
  • They are BACTERICIDAL/BACTERIOSTATIC
  • Examples:
    • Erythromycin
206
Q

How does chloramphenicol antibiotics work? Are they bactericidal or bacteriostatic?

A
  • Inhibition of protein synthesis by inhibiting peptidyl transferase enzyme in ribosomes.
  • They are BACTERICIDAL/BACTERIOSTATIC
207
Q

How do 2,4-diaminopyridine antibiotics work? Are they bactericidal or bacteriostatic? Name the main examples.

A
  • They inhibit folate synthesis and therefore DNA synthesis
  • They are BACTERIOSTATIC (but bactericidal when combined with sulfonamides)
  • Examples:
    • Trimethoprim
208
Q

How do sulphonamide antibiotics work? Are they bactericidal or bacteriostatic?

A
  • They inhibit folate synthesis and therefore DNA synthesis
  • They are BACTERIOSTATIC (but may be bacteriocidal when combined with trimethoprim)
209
Q

State the two types of antibiotic that block processes in the synthesis of folate.

A
  • Sulphonides
  • Trimethoprim

These are often used together.

210
Q

What enzymes do sulphonamide and trimethoprim act on?

A
  • Sulphonamide -> Dihydropteroic acid synthase (DAS)
  • Trimethoprim -> Dihydrofolate reductase (DHFR)
211
Q

Is sulphonamide still commmonly used?

A
  • No, it is rarely used because of resistance.
  • However, it may be combined with trimethoprim, since they both act to reduce DNA synthesis (by blocking production of folate)
212
Q

How do rifamycin antibiotics work? Are they bactericidal or bacteriostatic? Name some examples.

A
  • They inhibit transcription
  • They are BACTERICIDAL or BACTERIOSTATIC
  • Examples:
    • Rifampicin
213
Q

What may rifampicin be used for?

A

Treatment of tuberculosis.

214
Q

How do quinolone antibiotics work? Are they bactericidal or bacteriostatic? Name some examples.

A
  • They inhibit DNA synthesis by inhibiting DNA gyrase
  • They are BACTERICIDAL or BACTERIOSTATIC
  • Examples:
    • Ciprofloxacin
215
Q

What can quinolones be used for?

A

Treatment of UTIs.

216
Q

What is metronidazole? [EXTRA?]

A
  • An antibiotic used for treating anaerobic infections.
  • Intracellularly, it is converted into a toxic form after being converted by a bacterial enzyme.
217
Q

How does isoniazid antibiotic work? Is it bactericidal or bacteriostatic? [IMPORTANT]

A
  • Blocks long-chain mycolic acids (unique to Mycobacteria)
  • Bactericidal to growing organisms, otherwise bacteriostatic
218
Q

Summarise the different ways in which antibiotics work and which antibiotic classes fall into each category.

219
Q

How do the properties of antibiotic derivatives differ from the original antibiotic?

A

The derivatives can have a different spectra of activity, bioavailability, and adverse effects.

220
Q

What are some reasons why antibiotics may be used in combination?

A
  • Empiric therapy when pathogen is unknown
  • Synergistic action (cell wall/protein synthesis)
  • Combining ‐cidal with ‐static in general
  • Reduce emergence of resistance
221
Q

Give some experimental evidence for combination antibiotic therapy. [EXTRA]

A
  • Combination antibiotic therapy is believed to be effective in critical patients, since there is a greater likelihood that the pathogen is susceptible to at least one of the antibiotics, although there is some disagreement about whether the combination of drugs significantly increases their effect due to synergistic actions and whether the combination directly decreases the likelihood of resistance developing as a consequence of cumulative action.
  • Therefore, it is argued that once a bacterium has been isolated and the degree of drug-resistance experimentally deduced, there is rarely substantial advantage to use of more than one drug that the bacterium is susceptible to. (Tamma, 2012)
  • This can prevent development of resistance.
222
Q

How does the choice of antibiotic change before and after a pathogen is identified?

A
  • Before the identity of the pathogen is known, many antibiotics are used. They are likely to be broad-spectrum antibiotics.
  • After the pathogen is identified, just one specific antibiotic is used, to prevent the development of resistance.
223
Q

What is the minimum inhibitory concentration?

A

The minimum concentration of an antibiotic that must be maintained throughout treatment, in order to ensure that the drug is effective.

224
Q

What are two examples of the consequences of the indiscriminate use of antibiotics?

A
  • Drug resistance
  • Elimination of normal microbiota
225
Q

What is synergism in antibiotic use?

A

When multiple applied antibiotics work together to produce an effect more potent than if each antibiotic were applied singly.

226
Q

What is antagonism in antibiotic use?

A

When one antibiotic inhibits the use of another, so that they should not be used in combination.

227
Q

Name the different ways in which resistance to antibiotics can be achieved.

A
  • Decreased uptake
  • Efflux
  • Drug inactivation
  • Target modification
  • Target amplification
228
Q

How can decreased uptake of antibiotics occur in bacteria? Give an example.

A
  • The cell wall can become more impermeable by changes to the structure and transporters
  • Mutations in porins in Gram-negative bacteria
229
Q

How can efflux of antibiotics occur in bacteria? Give an example.

A
  • There can be membrane pumps
  • e.g. Tetracycline can be exported by membrane pumps
230
Q

What are multi-drug efflux systems?

A

Systems made of active transporters that export a wide a variety of substrates from cells and consequently are capable of conferring resistance to a wide range of chemotherapeutic agents.

231
Q

How can inactivation of antibiotics occur in bacterial cells? Give an example.

A
  • There can be production of enzymes to break down the antibiotic
  • Examples:
    • Beta-lactamases in penicillin resistance
    • Phosphotransferases in aminoglycoside resistance
232
Q

How can antibiotic target inactivation occur in a bacterial cells? Give an example.

A
  • It can occur due to mutations in the targets for the antibiotic
  • Examples:
    • DNA gyrase mutations -> Prevent quinolones binding
    • Penicillin binding proteins (transpeptidases) mutations -> Prevent beta-lactam binding (but can still bind to peptidoglycan)
233
Q

What mechanism underlies MRSA’s resistance to penicillins?

A
  • The Mec genetic element encodes a different PBP (penicillin binding protein)
  • This means that the target for penicillins is altered in structure
234
Q

How can antibiotic target amplification occur in a bacterial cells? Give an example.

A
  • The bacteria can express lots of copies of the target for the antibiotic, so that the competitive inhibition of the antibiotic is overcome
  • e.g. Sulphonamide resistance can be caused by production of lots of the enzyme that sulphonamides inhibit
235
Q

What are integrons?

A

A mobile DNA element in a bacterium that can capture and carry genes, particularly those responsible for antibiotic resistance.

236
Q

How do integrons work? What is their structure?

A

Integrons have:

  • An integrase that enables the addition of new DNA to the integron
  • A promoter that enables expression of the DNA
  • A recombination site (and a recombination site on the new incoming casette), so that the new DNA can be added to the integron

This means that a plasmid can contain multiple resistance genes that the bacterium ‘collects’. These can collectively be passed on using the plasmid.

237
Q

Are bacteria the problem or plasmids the problem in antibiotic resistance?

A

It is really the plasmids, because they are where the antibiotic resistance genes tend to be found.

238
Q

What are plasmids?

A
  • Circular, extrachromosomal DNA found in bacteria
  • Transferable between strains
  • There are many copies
  • Move by transformation or conjugation
239
Q

Give an example of a mechanism of antibiotic resistance that can occur in non-resistant bacteria.

A
  • Groups of bacteria can form large colonies
  • These can produce biofilm, which can protect the bacteria from antibiotics
240
Q

How are biofilms important in human infections?

A
  • Dental biofilms
  • Pneumonia in CF patients
  • Endocarditis, osteomyelitis
  • Artificial surfaces:
    • Catheter‐related infections
    • Contact lens infections
    • Prosthetic joints

They are difficult to eradicate due to antibiotic resistance and resistance to phagocytosis.

241
Q

What are some approaches to combatting the development of antimicrobial resistance?

242
Q

What are some approaches in a CLINICAL SETTING to combatting the development of antibiotic resistance?

A
  • Avoid unnecessary antibiotics
  • Know local sensitivities
  • Narrow spectrum vs. broad spectrum rapid diagnostics -> So that the change from broad spectrum to narrow spectrum drugs is done at the right time and ASAP
  • Directly observed therapy (DOTS)
  • Drug combinations
  • Antibiotic policies
  • Develop new drugs
243
Q

What are all of the different important bacterial pathogens listed in the spec?

[IMPORTANT]

A

Gram positive:

  • Streptococcus pneumoniae
  • Streptococcus pyogenes
  • Staphylococcus aureus (including MRSA)
  • Clostridium difficile
  • Clostridium tetani

Gram negative (O-antigen possessing):

  • Escherichia coli
  • Shigella
  • Salmonella

Gram negative (Non-O-antigen possessing):

  • Neisseria gonorrhoeae
  • Neisseria meningitides

Mycobacteria:

  • Mycobacterium tuberculosis
244
Q

For Streptococcus pneumoniae, state:

  • Gram type
  • Diseases it causes
  • Features mentioned in the spec
A
  • Gram positive
  • Causes: Primary lobular pneumonia
245
Q

For Streptococcus pyogenes, state:

  • Gram type
  • Diseases it causes
  • Features mentioned in the spec
A
  • Gram positive
  • Causes:
    • Pharyngitis (sore throat)
    • Cellulitis (skin infection)
    • Rheumatic fever
    • Glomerulonephritis (glomerulus injury)
  • Features:
    • CO2 may regulate the expression of virulence determinants
246
Q

For Staphylococcus aureus, state:

  • Gram type
  • Diseases it causes
  • Features mentioned in the spec
A
  • Gram positive
  • Causes:
    • Abcesses (a form of skin infection)
    • Surgical wound and burn infections
    • Food poisoning
  • Features:
    • Examples of adhesins, aggressins (e.g. toxins) and antibiotic resistance genes carried by mobile genetic elements (in Staphs & Streps).
247
Q

What Streptococcus species makes up most of Streptococcus group A?

A

Streptococcus pyogenes

248
Q

What is MRSA resistant to?

A

Penicillins, such as methicillin.

249
Q

For Clostridium difficile and Clostridium tetani, state:

  • Gram type
  • Diseases it causes
  • Features mentioned in the spec
A
  • Gram positive
  • Causes:
    • Clostridium difficile -> Watery diarrhea
    • Clostridium tetani -> Tetanus
  • Features:
    • Anaerobic
    • Spore forming
250
Q

For Escherichia coli, state:

  • Gram type
  • Diseases it causes
  • Features mentioned in the spec
A
  • Gram negative (O-antigen-possessing)
  • Causes:
    • Travellers’ diarrhoea
    • Dysentery (intestinal inflammation and cramps)
    • Food poisoning
    • Fever
251
Q

For Shigella species, state:

  • Gram type
  • Diseases it causes
  • Features mentioned in the spec
A
  • Gram negative (O-antigen-possessing)
  • Causes:
    • Travellers’ diarrhoea
    • Dysentery (intestinal inflammation and cramps)
    • Food poisoning
    • Fever
252
Q

For Salmonella species, state:

  • Gram type
  • Diseases it causes
  • Features mentioned in the spec
A
  • Gram negative (O-antigen-possessing)
  • Causes:
    • Travellers’ diarrhoea
    • Dysentery (intestinal inflammation and cramps)
    • Food poisoning
    • Typhoid fever
253
Q

For Neisseria gonorrhoeae, state:

  • Gram type
  • Diseases it causes
  • Features mentioned in the spec
A
  • Gram negative (Non-O-antigen-possessing)
  • Causes:
    • Gonorrhoea
  • Features:
    • There are differences between men and women in terms of asymptomatic carriage
    • Main steps of infection and transmission cycle, key interactions, importance of sialylation and capsule for evasion (ADD FLASHCARDS)
254
Q

For Neisseria meningitides, state:

  • Gram type
  • Diseases it causes
  • Features mentioned in the spec
A
  • Gram negative (Non-O-antigen-possessing)
  • Causes:
    • Meningitis
  • Features:
    • Main steps of infection and transmission cycle, key interactions, importance of sialylation and capsule for evasion (ADD FLASHCARDS)
255
Q

Compare how frequently Neisseria gonorrhoeae infections are asymptomatic in men and women.

[IMPORTANT]

A

Women are much more likely to carry asymptomatic infection.

256
Q

What are the different tests for identifying bacterial species that you need to know?

[IMPORTANT]

A
  • Gram staining
  • Cellular morphology and colony morphology
  • Catalase
  • Coagulase
  • Oxidase
  • Streptococcal carbohydrate antigen grouping (Lancefield typing)
257
Q

What is bile salt testing useful for?

A

Media containing bile acids are helpful for identifying bacteria that survive in the small intestine, a feature of many Enterobacteriaceae.

258
Q

What is MacConkey agar and what is it useful for?

[IMPORTANT]

A
  • A medium used to differentiate between Gram-negative bacteria based on their ability to digest lactose.
  • It contains a pH indicator and lactose.
  • If the bacteria can digest carbohydrates, acid is produced and the result is pink colonies.
  • If the bacteria cannot digest carbohydrates, acid is not produced and the result is colourless colonies.
259
Q

What does a pink MacConkey agar indicate?

A

The bacteria can digest carbohydrates, so acid is produced and the result is pink colonies.

260
Q

What does a colourless MacConkey agar indicate?

A

The bacteria cannot digest carbohydrates, acid is not produced and the result is colourless colonies.

261
Q

What is often added to MacConkey agar and why?

A
  • Bile salts
  • This is because MacConkey is useful for distinguishing between Gram-negative bacteria that can grow in the intestine, so bile salts are used to kill any Gram-positive bacteria and those not adapted to living in the intestines
262
Q

What is the catalase test and what is it used for?

[IMPORTANT]

A
  • A test for the presence of a bacterial enzyme that breaks down hydrogen peroxide.
  • A drop of hydrogen peroxide is applied to a bacterial colony using a glass capillary tube. A positive result is the appearance of bubbles on the surface of the colony.
  • The ability of bacteria to degrade hydrogen peroxide can directly impact where they can live and the types of infection they cause.
263
Q

What is the haemolysis test and what are the different results?

[EXTRA?]

A

It is where a blood agar is used to test the haemolytic properties of an unknown bacterium.

264
Q

What is Lancefield typing and what is it used for?

[IMPORTANT]

A
  • It is a.k.a. Streptococcal carbohydrate antigen grouping
  • It is used to differentiate between the different Streptococcus species, which each show different carbohydrate antigens.
  • It is an agglutination assay. The latex particles coated with specific antibodies will only agglutinate in the presence of the homologous antigen, and will remain in suspension otherwise.
  • The results as stated as Group A, Group B, etc.
265
Q

What is the oxidase test and what is it used for?

[IMPORTANT]

A

A test that detects cytochrome oxidase, a transmembrane protein complex of the respiratory electron transport chain, which is present in aerobic organisms that can use oxygen as a terminal electron acceptor.

266
Q

What is the urease test and what is it used for?

[EXTRA?]

A
  • It is a test for the urease enzyme
  • It is used to test for bacteria such as H. pylori
  • Urease can split urea to generate ammonia and CO2, leading to a rise in pH. The test includes a pH indicator, typically phenol red, which turns red when the pH rises above 8.
267
Q

What is the coagulase test and what is it used for?

[IMPORTANT]

A
  • It is a test for the coagulase enzyme
  • It is used to differentiate between Staphylococcus aureus and a coagulase-negative Staphylococcus
  • A positive Coagulase test is detected by aggregation/clumping of the latex particles.
268
Q

What is XLD agar and what is it used for?

A
  • Xylose, Lysine, Deoxycholate
  • It is used to differentiate between Salmonella and Shigella.
  • XLD plates contain deoxycholate which is a bile salt, making them selective for Gram-negative bacteria that can grow in the intestine.
  • XLD also contains a pH indicator (phenol red). Acidification results in yellow colouration, while alkalisation results in pink to red coloration.
  • Xylose, sucrose and lactose in XLD help differentiate Salmonella and Shigella. As Shigella cannot ferment these carbohydrates, its colonies are red on XLD.
  • Salmonella can ferment xylose which would result in yellow colonies through acidification. However, Salmonella also metabolises lysine (due to its lysine decarboxylase) which produces cadaverine, raising the pH so Salmonella and Shigella colonies are both red on XLD.
  • Therefore, the media also contains sodium thiosulphate and ferric ammonium citrate. Salmonella can convert sodium thiosulphate to H2S. This reduces the ferric ammonium citrate to iron sulphide which has a black colour. Hence, Salmonella form red colonies with black centres.
269
Q

Some bacterial species apart from Salmonella produce H2S. Why do these not produce black colonies on XLD agar?

A

They do not produce lysine decarboxylase, which the Salmonella use to produce an adequately alkaline environment for H2S production.

270
Q

Draw the flowchart of diagnostic tests for identifying unknown bacteria.

271
Q

Summarise the different lab tests required to test for various Streptococcus species.

A
  • Gram-positive
  • Coccus
  • Negative catalase
  • Alpha haemolysis + Optochin sensitive -> Streptococcus pneumoniae
  • Beta haemolysis + Lancefield type A -> Streptococcus pyogenes
272
Q

Summarise the different lab tests required to test for Staphylococcus aureus.

A
  • Gram-positive
  • Coccus
  • Positive catalase
  • Positive coagulase
273
Q

Summarise the different lab tests required to test for Clostridia species.

A
  • Gram-positive
  • Bacillus
274
Q

Summarise the different lab tests required to test for Escherichia coli.

A
  • Gram-negative
  • Bacillus
  • Growth in bile salts
  • Positive lactose fermentation (MacConkey)
  • Positive indole test
275
Q

Summarise the different lab tests required to test for Shigella species.

A
  • Gram-negative
  • Bacillus
  • Growth in bile salts
  • No lactose fermentation (MacConkey)
  • Negative oxidase test
  • Negative urease test
  • No H2S production
276
Q

Summarise the different lab tests required to test for Salmonella species.

A
  • Gram-negative
  • Bacillus
  • Growth in bile salts
  • No lactose fermentation (MacConkey)
  • Negative oxidase test
  • Negative urease test
  • Positive H2S production
277
Q

Summarise the different lab tests required to test for Neisseria species.

A
  • Gram-negative
  • Coccus
  • Positive oxidase test
278
Q

What other pathogen does tuberculosis interact with?

[EXTRA]

A

HIV -> There is an increased incidence in HIV patients.

279
Q

What is a concern with treatment of tuberculosis?

[EXTRA]

A

Extensively drug-resistant TB (XDR TB) is a rare type of multidrug-resistant tuberculosis that is a potential danger.

280
Q

Describe the current situation with tuberculosis globally.

[EXTRA]

A
  • The total global incidence is decreasing
  • But co-infection with HIV is increasing and the proportion of cases of XDR TB (Extensively drug-resistant TB) are increasing
  • This is partly due to collapsing medical systems in the Soviet bloc contributing to the development of XDR TB
281
Q

What is the route of transmission of tuberculosis?

A

Respiratory droplets

282
Q

Describe the tissue tropism of tuberculosis.

A
  • Infection starts in lungs
  • May also spread to anywhere in body (15% cases):
    • Central nervous system
    • Lymphatic system
    • Genitourinary systems
    • Bones and joints
    • Disseminated (miliary TB)
283
Q

What are the symptoms of tuberculosis infection?

A
  • General symptoms -> Fever, weight loss, weakness, cachexia
  • Symtoms of lung infection -> Cough, chest pain
  • Symtoms of extra-pulmonary infection -> Affecting CNS, lymphatic system, genitourinary system, bones and joints
284
Q

Draw a graph to show the different stages of TB infection.

A
  • In all cases, there is a primary infection before adaptive immunity kicks in.
  • After immunity develops, in most cases the bacterial load drops and there is a chronic infection. In around 5% of cases, the adaptive immunity is not sufficient, so there is primary disease.
  • Of those with chronic infection, there are few symptoms, but there is the possibility of reactivation, which leads to post-primary disease.
285
Q

When can tuberculosis be transmitted between hosts?

A
  • During primary disease
  • During post-primary disease
286
Q

What parts of the lung does tuberculosis infect in the primary infection and what does it form?

[IMPORTANT]

A
  • The mid-zone of the lung.
  • It forms a small area of granulomatous inflammation, known as a Ghon focus.
  • It can then spread to a regional lymph node.
287
Q

What is a primary complex (in relation to tuberculosis infection)?

A

It is the Ghon focus together with the infected regional lymph node, which are infected in a primary infection of tuberculosis.

288
Q

What is this?

A

It is a Ghon complex seen in tuberculosis primary infection, made up of:

  1. Ghon focus
  2. Infected regional lymph node
289
Q

What causes primary infection of tuberculosis to develop into primary disease?

A
  • If the infection is not kept in check, the bacterium can spread from the Ghon focus, or via the bloodstream and through the lungs.
  • The pleural space, entire airways, retina, CNS and other organs may be affected.
290
Q

Describe what you can see in this X-ray.

A
  • It is a tuberculosis infection, shown by the infected lymph node.
  • There is fluid in the pleural cavity, showing that there has been progression to primary disease.
291
Q

How does tuberculosis affect the retina?

A

It can lead to deposits on the retina.

292
Q

How does tuberculosis affect the CNS and CSF?

A
  • In the CNS, it can lead to meningitis, which is inflammation of the meninges
  • It can also lead to hydrocephalus

This is dangerous because the CSF is a sterile environment usually.

293
Q

What are the symptoms of post-primary disease (reactivation) in tuberculosis infection?

A

Cavitary lung disease, mostly in the upper lobes of the lungs.

294
Q

What are some risk factors for reactivation of tuberculosis, leading to post-primary disease?

A
  • Age
  • Malnutrition
  • HIV
  • α‐TNF
  • Steroid therapy
295
Q

Summarise the disease progression of tuberculosis infection.

296
Q

For Mycobacterium tuberculosis, state:

  • Gram type
  • Diseases it causes
  • Features mentioned in the spec
A
  • Cannot be gram stained (sometimes considered Gram positive though)
  • Causes tuberculosis
  • Features:
    • Slow growth
    • Mycolic acid cell wall
    • Few surface targets
    • Resistance to phagolysosomal killing
    • Macrophage subversion
    • Primary infection: Ghon focus formation, granuloma formation
    • Reactivation
    • Role of T cells in control of replication of tubercle bacillus
297
Q

What is the morphology of Mycobacterium tuberculosis?

A

Branched rods

298
Q

How long does it take to culture Mycobacterium tuberculosis?

A

4-6 weeks (it is slow-growing)

299
Q

What makes understanding the pathogenesis of tuberculosis difficult?

A
  • Human specific -> So it is difficult to study in animal models
  • Slow growing
  • Difficult to perform molecular genetics
  • Chronic infection -> Difficult to study
300
Q

Can Mycobacterium tuberculosis be Gram stained?

A

No, because the mycolic acid in the cell wall does not allow absorption of the stain.

301
Q

How is Mycobacterium tuberculosis stained for?

A

Ziehl-Neelsen stain:

  • Stain with carbol fuchsin (pink)
  • Attempt to destain with acid and alcohol mixture -> Mycobacteria are acid-fast and alcohol-fast, so they should not destain
  • Counterstain using methylene blue
302
Q

Describe the structure and important features of the Mycobacterium tuberculosis cell wall.

A
  • Lipoarabinommannan -> Two sugars attached to a lipid
  • Mycolic acids -> Negatively-charged
  • Glycolipids -> Associate with the mycolic acids
303
Q

What is a hypothesis for why Mycobacterium tuberculosis grows so slowly?

A
  • Mycobacteria have chromosomal toxin-antitoxin systems (TA) systems that produce a toxin that is harmful to the bacterium, as well as an antitoxin that protects against the toxin
  • These TA systems are usually found on plasmids, so that when the bacterium loses its plasmid, the toxin out-survives the antitoxin and causes the cell to die -> Used for plasma maintenance
  • However, mycobacteria have a TA system on their chromosomes, which may contribute to their slow growth (even if both the toxin and antitoxin are present)
304
Q

What is some clinical relevance of TA systmes in Mycobacterium tuberculosis?

A

The antitoxins in the bacterium can be targeted, so that the toxins are uncontrolled and lead to bacterial cell suicide.

305
Q

What is formed at the site of tuberculosis infection in the lungs?

A

Granuloma (a.k.a. Ghon focus)

306
Q

Describe the formation of granulomas in tuberculosis primary infection. Include signalling factors.

A
  • Macrophages in the lungs (attempt to) phagocytose the Mycobacterium tuberculosis (Mtb) -> TLR2 recognition of Mtb leads to Myd-88 controlled secretion of TNF-α
  • This leads to recruitment of circulating monocytes, which differentiate into tissue macrophages
  • There is then increased vascularity to the area due to VEGF (vascular endothelial growth factor)
  • (Foamy) Macrophages and helper T cells surround the bacterial cells -> Helper T cells secrete IFN-γ
  • A fibrous cuff also forms around the bacterial cells, reducing vascularisation of the bacterial cells -> This leads to hypoxia that causes the bacteria to become dormant
  • Langhans multinucleated giant cells appear -> Due to the joining of macrophages
  • Eventually, in the centre of the granuloma, caesum appears, which is necrotic material
307
Q

Summarise the main cells involved in granuloma formation.

A
  • Macrophages
  • Monocytes (which differentiate into tissue macrophages)
  • Helper T cells
  • Langhans multinucleated giant cells appear
308
Q

What triggers the formation of a granuloma in Mycobacterium tuberculosis infection?

A
  • Macrophages in the lungs (attempt to) phagocytose the Mycobacterium tuberculosis (Mtb)
  • TLR2 recognition of Mtb leads to Myd-88 controlled secretion of TNF-α
  • This leads to recruitment of circulating monocytes, which differentiate into tissue macrophages and begin granuloma formation
309
Q

What causes a Mycobacterium infection to become latent?

A

The bacterium are trapped in a granuloma, with reduced vascularisation. This means the area is hypoxic, which reduces bacterial replication and causes the bacteria to become dormant.

310
Q

What type of cell is this and when is it seen?

A
  • Langhans giant cell (Note the spelling)
  • It is seen in tuberculosis infections -> Due to the fusion of macrophages, driven by IFN-γ
311
Q

What is the function of Langhans giant cells?

A
  • They do not have a phagocytic role, so they appear to reduce killing of bacteria
  • Couldn’t find any function online [CHECK]
312
Q

What are foamy macrophages (a.k.a. foam cells) and how are they related to tuberculosis?

A
  • They are macrophages that contain lipid bodies
  • These are formed when Mycobacterium tuberculosis prevents the cell from pumping out LDL cholesterol
  • The bacteria make use of this LDL cholesterol
313
Q

How is caseous material in granulomas formed?

A

It is derived from LDL and most likely released from foamy macrophages.

314
Q

What cell type do Mycobacterium tuberculosis enter primarily?

A

Macrophages

315
Q

How does Mycobacterium tuberculosis enter cells?

A

There are many phagocytic receptors that allow the bacterium to be taken up in phagocytes by phagocytosis.

316
Q

Which PRR is activated by Mycobacterium tuberculosis?

A
  • TLR2 -> This is activated by lipoproteins and glycolipids
  • There is lots of redundancy in the co-receptors, including TLR1
317
Q

How does Mycobacterium tuberculosis survive in macrophages

[IMPORTANT]

A
  • Prevents acidification of the phagosome at an early stage:
    • The mechanism for how it does this is poorly understood.
    • Lipoarabinomannan (LAM) is thought to play a part in this, but dead Mycobacterium tuberculosis cannot fully inhibit phagosome maturation, so there must also be something about the live bacterium.
  • Can resist antimicrobial stresses:
    • Enters cell via CR3, which avoids stimulating the oxidative burst
    • Detoxifies reactive oxygen species by producing superoxide dismutase and catalase
    • Has heat shock proteins Hsp70 and Hsp60 to refold damaged proteins and uses the proteasome to degrade damaged proteins.
    • Has DNA repair systems.
318
Q

Give some experimental evidence relating to how Mycobacterium tuberculosis survives phagocytosis.

[EXTRA]

A
  • Latex beads coated with lipoarabinomannam (LAM) are phagocytosed but the phagosome does not mature.
  • Thus, LAM is likely to play a large role in preventing phagocytosis by preventing phagosome maturation.
319
Q

What are some enzymes that Mycobacterium tuberculosis produces to detoxify reactive oxygen species produced by phagocytes?

A
  • Superoxide dismutase
  • Catalase
320
Q

Where in the macrophage does Mycobacterium tuberculosis exist?

A
  • Mostly in a partially acidified, immature phagosome
  • But there is also some evidence that it might enter the cytosol using an Esat-6 secretion system (type 7 secretion system)
321
Q

Summarise when latent Mycobacterium tuberculosis infection may be reactivated (leading to post-primary disease). What does this tell us?

A

It happens when the immune system is compromised:

  • Age
  • Malnutrition
  • HIV
  • Steroid therapy

This tells us about the importance of CD4+ T cells, TNF signalling and macrophage function in containing the disease. (since if they are removed, the disease increases).

322
Q

Which cells are particularly important in control of replication of Mycobacterium tuberculosis?

[IMPORTANT]

A
  • CD4+ T cells
  • This explains why HIV patients are at an increased risk of reactivation of latent tuberculosis
323
Q

What explains the tissue damage seen in Mycobacterium tuberculosis reactivation (post-primary disease)?

A

Tissue damage is due to increased inflammatory signalling

324
Q

Describe the vaccine for tuberculosis.

A
  • Bacille Calmette-Guerin (BCG) -> Live attenuated bovine tuberculosis bacterium (Mycobacterium bovis)
  • This bacterium lost its virulence towards human hosts by growth in special culture medium, Middlebrook 7H9
  • Efficiency of vaccination is variable (0-80%).
  • Very efficient against tuberculous meningitis in children, but not so efficient against pulmonary tuberculosis. Not effective in adults.
325
Q

Describe treatment of tuberculosis.

A
  • Treatment is long (over 6 months) due to chronic infection
  • Multiple drugs are used (4 drugs initially) to combat the emergence of drug resistance
326
Q

What are transposons?

A
  • A transposable element is a DNA sequence that can change its position within a genome, sometimes creating or reversing mutations and altering the cell’s genetic identity and genome size.
  • Transposition often results in duplication of the same genetic material.
327
Q

What are some examples of disinfection and sterilisation that you need to know?

A
  • Pasteurization
  • Autoclaving
  • Hypochlorite
  • Halogenated phenols
  • Gamma-irradiation
328
Q

What is debridement?

A
  • Debridement is a procedure for treating a wound in the skin. It involves thoroughly cleaning the wound and removing all hyperkeratotic (thickened skin or callus), infected, and nonviable (necrotic or dead) tissue, foreign debris, and residual material from dressings.
  • It may be used in e.g. necrotizing fasciitis
329
Q

What are septicaemia and bacteraemia?

A

Septicemia is a clinically significant form of bacteremia complicated by toxemia, fever, malaise, and often shock.

330
Q

How do clostridial toxins work?

A
  • The toxin acts by modifying host cell GTPase proteins by glucosylation, leading to changes in cellular activities.
  • This involves actin condensation and cell rounding, which is followed by death of the cell
331
Q

What are two important types of E. coli you need to know about?

A
  • EHEC -> Enterohemorrhagic E. coli
  • EPEC -> Enteropathogenic E. coli
332
Q

Describe EHEC.

A
  • Enterohemorrhagic E. coli (EHEC) causes severe intestinal infection and bloody/non-bloody diarrhoea.
  • It’s different from other E. coli because it produces a potent toxin called Shiga toxin.
  • This toxin damages the lining of the intestinal wall, causing bloody diarrhea.
  • The Shiga toxin acts to block protein synthesis in the host cell.
333
Q

Describe EPEC.

A

Enteropathogenic E. coli (EPEC) is the causative agent of watery diarrhoea.

334
Q

How Neisseria species perform immune evasion?

A

Sialylation and the capsule are important.

YEAR 2 - Principles of Pathology (18 decks)

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