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MCD Year 1 > Microbiology > Flashcards

Microbiology Flashcards

1
Q

What are three shapes of bacteria?

A 
Cocci = round or ovoid
Bacilli = rod shaped
Spirilla = twisted shape
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2
Q

What is a gram stain?

A

A stain developed in the late 1800’s that distinguishes between bacterial cell walls.

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3
Q

How are bacteria gram stained?

A

They are stained with a violet dye and iodine, rinsed in alcohol and then stained with a red dye.

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4
Q

What are properties of Gram+ bacterial cell wall?

A

They have one plasma membrane and an outer cell wall made of peptidoglycan (thick) which retains the dye and appears deep violet.

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5
Q

What are the properties of Gram- bacterial cell wall?

A

They have an outer membrane and a plasma membrane with a thin periplasm made of peptidoglycan. So they appear pink with the dye.

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6
Q

Give examples of Gram+ and Gram- bacteria.

A 
Gram+ = E.coli, Salmonella, Shigella
Gram- = Staphylococcus aureus, Streptococcus pneumoniae, streptococcus pyogenes.
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7
Q

Give examples of intracellular and extracellular pathogen.

A 
Extracellular = Staphylococcus, Streptococcus, Yersinia, Neisseria.
Intracellular = Listeria, Shigella, Salmonella, Mycobacteria, Chlamydia.
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8
Q

What is the function of flagellum?

A

The flagellum is used by the bacteria to enable intracellular movement.

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9
Q

What is an injectisome?

A

A needle like protein appendage found mostly in Gram- bacteria. It helps bacteria detect eukaryotic cells and inserts proteins into the cytoplasm to enable invasion of the cell.

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10
Q

How does an injectisome help salmonella invade cells?

A

Salmonella inserts a protein into the cell using the injectisome. This protein causes actin polymerisation on the plasma membrane, causing membrane ruffling which allows the bacteria to enter via endocytosis.

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11
Q

How does Listeria manipulate actin to invade eukaryotic cells?

A

Once Listeria enters a cell via phagocytosis, it breaks out of the phagosome and using actin polymerisation, forms a tail to allow it to move through the cell and also enter other nearby cells.

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12
Q

What is the typical genomic repertoire of bacteria?

A

It encodes between 500 - 4500 proteins.

40% of it is core genes and the rest are accessory genes which vary a lot between strains.

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13
Q

How does bacteria replicate?

A

Bacteria replicate via budding. The chromosome duplicates and then the cells divides.

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14
Q

What are the three mechanisms of Horizontal Gene Transfer?

A

Transformation, conjugation, transduction.

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15
Q

What is transformation (HGT)?

A

Transformation happens when certain bacteria enter a competence state due to high density or low nutrition. Exogenous genetic material is taken in by the bacteria and incorporated into its genes.

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16
Q

What is transduction (HGT)?

A

This is the transfer of genes via a viral vector. A bacteriophage infects a bacteria and cuts the DNA into small pieces. Some of that might be packaged into the virus when it replicated. The phage then inserts that DNA into other bacteria which sometimes incorporates the DNA into its own genome.

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17
Q

What is conjugation (HGT)?

A

This is the bacterial equivalent of mating. Two bacteria form of mating bridge using a pilus and then the donor transfers a single DNA strand to the recipient which makes double stranded DNA from that strand.

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18
Q

What are pathogenicity islands?

A

They are distinct genomic islands transferred between bacteria through HGT. This is the major source of evolution in bacteria.

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19
Q

What are the two sources of bacterial infection?

A

Intrinsic - bacteria in the body travelling to a different part to cause infection.
Extrinsic - bacteria from the outside entering the body to cause infection.

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20
Q

What are the intrinsic source of infection?

A

These are the non-sterile parts of the body: nasal cavity, upper respiratory tract, stomach, mouth, small and large intestines, skin and lower genital tract.

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21
Q

What are the extrinsic routes of infection?

A

Upper respiratory tract, urogenital tract, broken skin and gastrointestinal tract.

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22
Q

Give examples of pathogens targeting the URT.

A

Viruses: Influenza, Rhinovirus, Measles, Varicella
Bacteria: MRSA, Streptococcus (pneumoniae and pyogenes), Neisseria Meningitidis.

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23
Q

Give examples of infections acquired via the URT

A

URT: Tonsillitis, sinusitis, pharyngitis.
LRT: Bronchitis, Pneumonia, Empyema.
Adjacent tissues: Meningitis, brain abscess, middle ear infection.
Bloodstream: bacteraemia.

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24
Q

Give examples of pathogens targeting the UT.

A

Intrinsic (large intestine): E. coli, Candida, Streptococcus group B.
Extrinsic (via catheters): E. coli, Klebsiella.

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25
Q

Give examples of pathogens targeting the genital tract.

A

Intrinsic (large intestine): Streptococcus group B, candida.

Extrinsic (STD): Neisseria Gonorrhoeae, Chlamydia trachomatis, HIV.

26
Q

Give examples of infections acquired via the urogenital tract.

A

UTI: Cystitis, Pyelonephritis.
GTI: Gonococcal urethritis, pelvic inflammatory disease, tubo-ovarian disease.
Bloodstream: Bacteraemia.
Pregnancy: Neonatal group B strep, Neonatal gonococcal conjunctivitis.

27
Q

Give examples of bacteria that target broken skin.

A

Streptococcus pyogenes, MRSA, bowel flora (surgery), pasteurella multocida (dog bites), Aeromonas hydrophila (medicinal leeches).

28
Q

What are the consequence of infection via broken skin?

A

Superficial infection, cellulitis, abscess, myositis, gangrene, bacteremia.

29
Q

Give examples of pathogens that enter via the faecal oral route.

A

Bacteria: E. coli, Vibrio cholerae, Salmonella, Listeria, Clostridium difficile.
Viruses: Hep A and E, Norovirus.

30
Q

What are the consequences of infection acquired via the GI tract?

A

Diarrhoea, vomiting, dysentery, typhoid, septic arthritis.

31
Q

Define pathogenicity.

A

It is the ability to cause disease.

32
Q

What are the factors affecting pathogenicity?

A

Infectivity: ability to establish an infection.
Virulence: the severity or harmfulness of the disease.

33
Q

Define infectious dose.

A

The number of bacteria required to initiate an infection.

34
Q

What are the factors affecting infectious dose?

A

Route of transmission (stomach acid increases dose required); Ability to colonise host; tropism (finding a niche); motility; replication speed; immune evasion.

35
Q

What are the features that enhance virulence?

A

Toxin production; degradation of host molecules; interference with host cell function; immune evasion.

36
Q

What is an antibiotic?

A

It is an antimicrobial agent produced by a microorganism that kills other microorganisms.

37
Q

How does antibiotic resistance develop?

A

A population of bacteria have variation. Some may have antibiotic resistance. Antibiotics in that population acts a selection pressure. So the ones with resistance outcompetes the rest and become the dominant strain in the population.

38
Q

Why does antibiotic resistance lead to increased mortality, morbidity and cost?

A

More time for effective therapy; more approaches (e.g. surgery) required; more expensive drugs required; more toxic drugs used; less effective second choices used.

39
Q

Give examples of multi-drug resistant pathogens.

A

Gram+ : MRSA, Streptococcus pneumoniae, clostridium difficile, enterococcus spp, Mycobacterium tuberculosis.
Gram- : E. coli, Salmonella spp, Pseudomona aeruginosa, Neisseria gonorrhoeae.

40
Q

What is the function of aminoglycosides?

A

They are bactericidal antibiotics (e.g. streptomicin) that target 30S ribosomal subunit and RNA proofreading, affecting protein synthesis.
Limited use previously due to toxicity but now increasing due to resistance to other antibiotics.

41
Q

What is the function of Rifampicin?

A

It is a bactericidal antibiotic that targets subunits in RNA polymerase.
Spontaneous resistance frequent and it makes secretion orange/red which lowers compliance.

42
Q

What is the function of Vancomycin?

A

It is a bactericidal that targets cell wall biosynthesis and wall crosslinking.
Previously limited use due to toxicity but now used for MRSA.

43
Q

What is the function of Linezolid?

A

It is a bacteriostatic that binds to 50S rRNA subunits to inhibit initiation of protein synthesis.
Gram+ spectrum of activity.

44
Q

What is the function of Daptomycin?

A

It is a bactericidal that targets bacterial cell membrane.

It has a Gram+ spectrum of activity but has limited use and dose due to toxicity.

45
Q

What are the targets for antibiotic therapy?

A

Cell wall synthesis, protein synthesis, nucleic acid replication, plasma membrane and synthesis of metabolites.

46
Q

What are the mechanisms of antibiotic resistance?

A

Altered target site through mutations; inactivation of antibiotics by degradation; altered metabolism (switching metabolic pathway or outcompeting the antibiotic in inhibition); decreasing drug accumulation (preventing drug entry or increasing eflux or drug).

47
Q

What is the function of Macrolides?

A

They are antibiotics (e.g. erythromycin) that work against Gram+ and Gram- infections by targeting 50S ribosomal subunits to prevent aminoacyl transfer and truncate polypeptides.

48
Q

What is the function of quinolones?

A

It is a broad spectrum synthetic bactericidal. It targets topoisomerase IV in Gram+ and DNA gyrase in Gram-.

49
Q

What are the reasons for high rate of Hospital Acquired Infections?

A

High number of ill people with weakened immune systems; more pathogens present; staff act as vectors; open wounds; inserted medical devices; patients receiving high doses of increasing selection pressure.

50
Q

What are some of the approaches used to prevent the emergence of drug-resistant bacteria?

A

Better prescribing strategies such as tighter control; reduced use of broad-spectrum antibiotics; combination therapy; quicker identification of infections caused by resistant strains; knowledge of local strains.

51
Q

What are viruses?

A

Viruses are infectious obligate intracellular parasites. They are about 10^-7 metres in diameter.

52
Q

Define obligate parasites.

A

It is a parasitic organism that can’t complete its life cycle without using another organism.

53
Q

What are the properties of RNA viral genomes?

A

They are smaller and more unstable than DNA virus genomes. So viruses use complex coding strategies to make more proteins from them. They also use reverse transcriptases to replicate. The lack of proofreading mechanism in this leads to high mutation rate.

54
Q

What are the properties of DNA virus genomes?

A

They are larger than RNA viruses which means they have more accessory genes to avoid immune responses in hosts.

55
Q

What is the function of segmented genomes?

A

Segmenting the genomes allows the virus to easily recombine it, in a process called reassortment, to form many variations but this means its is more difficult to package it.

56
Q

What are the different ways viral genomes are encapsulated?

A

Capsid: a protein shell.
Enveloped: a lipid covering derived from host membrane.
Some are non-enveloped.

57
Q

What are the different ways viruses can be classified?

A

They can be classified based on morphology or their genome.

58
Q

Describe a generic virus replication cycle.

A

The virus enters the cell and it uses the host proteins and ribosomes to make mRNA and then regulatory proteins. It also uses the host to replicate its DNA. Then the virus makes structural proteins which are assembled to form new virus. These burst out of the cell to infect new cells.

59
Q

How are viruses detected?

A

Viral genome: PCR
Viral antigen: IFA (Indirect fluorescent antibodies), ELISA (Enzyme-linked Immunosorbent Assay)
Virus particles: EM
Antibodies to viruses: serology.

60
Q

How are viruses cultivated in a lab?

A

Viruses are provided with continuous lines of permissive transformed cell cultures to grow in. Some viruses (e.g. norovirus, Hep C) have no permissive cell lines.

61
Q

How are viruses manipulated in labs?

A

Viruses are introduced to permissive cells in specific environments. The viruses direct synthesis of all their compartments de novo for that environment which means mutations can be reverse engineered in viruses.

MCD Year 1 (8 decks)

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