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Medicine Phase 2a > Microbiology > Flashcards

Microbiology Flashcards

1
Q

Define Pathogen

A

Organism that causes or is capable of causing disease

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2
Q

Define Commensal

A

Organism which colonises the host but causes no disease in normal circumstances

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3
Q

Define Opportunist pathogen

A

Microbe that only causes disease if host defences are compromised

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4
Q

Define Pathogenicity (aka Virulence)

A

The degree to which a given organism is pathogenic

/any strategy to achieve this

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5
Q

Define Asymptomatic carriage

A

When a pathogen is carried harmlessly at a tissue site where it causes no disease

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6
Q

What % of bacteria are pathogenic

A

2-5%

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7
Q

True or False:

There are more bacteria in the colon that there are cells in the body

A

True

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8
Q

What does Gram Stain test for?

A

Gram positive (single membrane) or Gram negative (double membrane) bacteria

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9
Q

Describe the process of Gram staining

A

Apply a primary stain such as crystal violet (purple) to heat fixed bacteria
Add iodine which binds to crystal violet and helps fix it to the cell wall
Decolourise with ethanol or acetone
Counterstain with safranin (pink)

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10
Q

What colour is gram stained Gram-Negative bacteria

A

Pink

Remember piNk - Negative

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11
Q

What colour is gram stained Gram-Positive bacteria

A

Purple

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12
Q

Why do you get the pink colour in gram negative bacteria

A

The decolouriser interacts with the lipids and cells lose their outer lipopolysaccharide membrane and the crystal violet-iodide (CV-I) complexes, thus they appear pink with counterstain

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13
Q

Why do you get the purple colour in gram positive bacteria

A

the decoloriser dehydrates the cell wall and the CV-I (crystal violet-iodine) gets trapped in the multi-layered peptidoglycan resulting in a purple appearance with counterstain

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14
Q

While gram staining can differentiate most bacteria, what stain can be used for those that can’t be gram stained

A

Ziehl-Neelsen Stain

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15
Q

Give example of bacteria that can be identified by Ziehl-Neelsen Stain, but not gram stain

A

Mycobacteria e.g. TB are acid-fast bacilli do NOT take up the gram stain

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16
Q

What does Ziehl-Neelsen stain differentiate between

A

Acid-fast and Non acid-fast bacilli

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17
Q

What colour are acid-fast bacilli under Ziehl-Neelsen Stain and give example

A

Red

e.g. mycobacterium

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18
Q

What colour are non acid-fast bacilli under Ziehl-Neelsen Stain and give example

A

Blue

e.g. E.coli

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19
Q

Describe the catalase test

A

Add H2O2 to bacteria and see for bubbling reaction (positive reaction)

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20
Q

What is Catalase test used to differentiate between

A

Staphylococci (catalase POSITIVE)

Streptococci (catalase NEGATIVE)

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21
Q

What is result from catalase test for many gram-negative bacteria e.g. E.coli and fungi

A

Catalase POSITIVE

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22
Q

What is Coagulase test and what can is be used for?

A

Test on Staphylococcus bacteria
Staphylococcus aureus is coagulase positive (clumping seen)
Other Staphylococci are coagulase NEGATIVE (no clumping)

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23
Q

What is coagulase and what bacteria produces it?

A

Enzyme produced by Staphylococcus. aureus that converts (soluble) fibrinogen in plasma to (insoluble) fibrin

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24
Q

What is haemolysis in regard to bacteria

A

Ability of bacteria to break down red blood cells in blood agar

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25
Q

Expression of what is required for haemolysis by bacteria

A

Expression of haemolysin

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26
Q

Describe Alpha haemolysis in haemolysis test

A

An indistinct zone of partial destruction of RBCs appears around the colony - often accompanied by a greenish to brownish opaque discolouration of medium

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27
Q

What bacteria are alpha haemolytic

A 
Streptococcus Pneumoniae (cause lobar pneumonia and meningitis)
Oral streptococci
Viridans Streptococci (can cause infective endocarditis)
S.intermedius
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28
Q

What test can be used to distinguish between Viridans streptococci and Streptococcus pneumoniae

A

Optochin Test

pneumoniae are sensitive, viridans resistant

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29
Q

Describe Beta Haemolysis in Haemolysis test

A

A clear, colourless zone appears around the colonies, in which RBCs have undergone complete lysis

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30
Q

Name bacteria that are Beta haemolytic

A 
Streptococci pyogenes
Streptococci agalactiae
(many other streptococci)
Staphylococcus aureus
Listeria monocyotgenes
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31
Q

How can differentiate Staphylococcus aureus from other beta haemolytic bacteria

A

Appearance on blood agar - creamy yellow

Positive Coagulase Test also

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32
Q

How can you future differentiate between Beta haemolytic bacteria

A

Lancefield grouping (detecting surface antigens)

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33
Q

Give the groups in Lancefield classification

A

A, C, G - tonsillitis and skin infection
B - neonatal sepsis and meningitis
D - urinary tract infection (=enterococci)

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34
Q

What is meant by Gamma haemolysis

A

Implies NO haemolysis

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35
Q

What colour is seen in Alpha Haemolysis test result

A

Green or Brown

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36
Q

What bacteria are alpha haemolytic

A

strep pneumonia

strep viridans

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37
Q

What colour is seen in beta haemolysis test result

A

No colour

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38
Q

What bacteria are beta haemolytic

A

Strep pyogenes

Staph aureus

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39
Q

What is optochin test used to differentiate between?

State test results

A

Sensitive to optochin (clear zone around disc) - Streptococcus pneumoniae

Resistant to optochin (no clear zone/will be growth around disc) - Viridans streptococci and other alpha haemolytic streptococci

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40
Q

What is seen by Streptococcus pneumoniae in Optochin test?

A

Clear zone around disc

Susceptible to optochin

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41
Q

What bacteria could be present if no clear zone seen around disc in optochin test

A

Resistant to optochin
Viridans streptococci
(and other alpha haemolytic streptococci)

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42
Q

What is Viridans streptococci also known as

A

Infective endocarditis

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43
Q

What does Oxidase test test?

A

Tests if micro-organism contains a cytochrome oxidase - an enzyme of the bacterial electron transport chain

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44
Q

What bacteria are Oxidase positive (oxidase test)

A

Aerobic bacteria

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45
Q

What bacteria are oxidase negative (oxidase test)

A

May be aerobic or anaerobic

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46
Q

Give examples of oxidase positive bacteria

A

P. aeruginosa
V. cholerae
Campylobacter e.g. C. jejuni
Helicobacter

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47
Q

What would you seen in positive oxidase test

A

Blue

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48
Q

What would you see in a negative oxidase test

A

No colour change

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49
Q

What are only bacteria that can grow in MacConkey Agar

A

Gram Negative Bacilli

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50
Q

What can MacConkey agar be used to differentiate between?

A

Lactose-fermenting and non-lactose fermenting gram-negative bacilli
e.g. Enterobacteria (gut coliforms)

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51
Q

Why can only gram negative bacteria grow on MacConkey agar

A

Bile salts present on agar inhibit gram-positive bacteria and inhibit the swarming of a gram-negative bacterium Proteus spp.

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52
Q

What colour do bacteria that ferment lactose appear on MacConkey agar and why do they appear this colour

A

Pink/Red

pH indicator in agar - bacteria that ferment lactose produce lactic acid

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53
Q

Give examples of bacteria that test positive on MacConkey agar

A

E.coli
Klebsiella Pneumoniae (typical organism that causes biliary infection)
Enterobacter spp.

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54
Q

What colour do non-lactose fermenting bacteria appear on MacConkey agar

A

White/transparent

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55
Q

Give example of non-lactose fermenting bacteria

A

Salmonella spp

Shigella spp.

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56
Q

What is XLD agar used to differentiate between?

A

Salmonella and Shigella

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57
Q

How does salmonella appear on XLD agar

A

Red/pink colonies some with black spots

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58
Q

How does shigella appear on XLD agar

A

Pink/red colonies

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59
Q

What is meant by cocci

A

Round and Spherically shaped bacteria

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60
Q

Name 3 Gram Positive Cocci

A

Staphylococci
Streptococci
Enterococci

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61
Q

What is meant by bacilli

A

Rod shaped bacteria and straight

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62
Q

Name 2 Gram Negative Cocci

A

Neisseria

Moraxella

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63
Q

Name 5 Gram Positive Bacilli

A 
Bacillus e.g. B. anthrancis
Clostridia (Anaerobic bacilli) 
Corynebacteria e.g. C. diptheriae
Listeria monocytogenes
Propionibacteria
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64
Q

Name 6 Gram negative bacilli

A 
E coli
Compylobacter
Pseudomonas
Salmonella
Shigella
Proteus
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65
Q

What makes up the capsule of bacteria cell

A

A polymer of sugar that protects bacteria from host immune system
Can inhibit parts of the innate immune system

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66
Q

Give an example of a bacteria with a capsule

A

Pneumonia

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67
Q

What makes up the cell wall of a bacteria

A

Phospholipid membrane

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68
Q

Why are bacteria considered prokaryotes

A

Do not have a nuclear membrane

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69
Q

How is genetic material in bacteria found

A

One circular chromosome

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70
Q

Where is bacterial RNA polymerase found

A

Bacterial cytoplasm

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71
Q

Describe specific features cell envelope of Gram Positive bacteria

A

Single cytoplasmic membrane
Large amount of peptidoglycan on outer surface
Do not have endotoxin (lipopolysaccharide)

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72
Q

Describe cell envelope of gram negative bacteria

A

Have 2 membranes (inner and outer)
Have a smaller amount of peptidoglycan
Outer membrane has lipopolysaccharide (endotoxin) which the immune system can react to -> endotoxic shock

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73
Q

Describe Gram positive bacteria cell envelope from outer to inner

A

Capsule
Large petidoglycan
Cytoplasmic membrane

*lipoteichoic acid hold cytoplasmic membrane to peptidoglycan

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74
Q

Describe Gram negative bacteria cell envelope from outer to inner

A 
Capsule
Terminal sugars
O antigen
Lipid A
Outer membrane
Lipoprotein (and periplasmic space)
Peptidoglycan
Inner membrane
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75
Q

What parts of gram negative bacteria cell envelope from LPS (endotoxin)

A

Terminal sugars
O antigen
Lipid A

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76
Q

Name mucosal surfaces open to bacterial colonisation

A 
Nasal cavity
Larynx
Stomach
Colon
Need to keep the lungs, gall-bladder, kidneys and eyes STERILE
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77
Q

What is a chain of 2 cocci called?

A

diplococcus

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78
Q

Give example of a curved rod

A

Vibrio

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79
Q

Give example of spiral rod

A

Spirochaete

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80
Q

At what temperatures can bacteria survive?

A

Between -80°C and 80°C (120°C for spores)

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81
Q

What needs to happen to destroy bacteria stored in spores

A

Need to be autocleaved

only certain bacteria types can make spores

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82
Q

Between what pH can bacteria survive

A

4-9

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83
Q

How long can bacteria survive in water/desiccation

A

2 hours to 3 months

50 years for spores

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84
Q

How do you measure bacteria growth

A

By shining light on bacteria and measuring absorption

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85
Q

By what method do bacteria divide

A

Binary fusion

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86
Q

In growth rate graph of bacteria, why is there Lag phase at the start?

A

Due to bacteria taking in nutrients needed to divide and grow

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87
Q

In growth rate graph of bacteria, what causes the exponential phase to end and go into stationary phase

A

Due to nutrients running out

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88
Q

What can happen after stationary phase of bacteria growth?

A

Plateaus at total

Bacteria become ‘Viable’ to death phase

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89
Q

What are phases of bacteria growth

A

Lag
Exponential (log) growth (in colony forming units)
Stationary
Total or Viable

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90
Q

Endotoxin is mostly produced by what bacteria

A

Gram Negative bacteria

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91
Q

Can endotoxin be produced by viruses?

A

No, only bacteria

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92
Q

Where is endotoxin in gram negative bacteria and what is name of molecule

A

Component of outer membrane

LIPOPOLYSACCHARIDE

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93
Q

What happens in body if host immune system recognises endotoxin

A

Consequently have a huge response known as endotoxic shock

Action is non-specific

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94
Q

What is effect of heat on endotoxin

A

Endotoxin stable on exposure to heat

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95
Q

Can endotoxin be converted to a toxoid?

A

No

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96
Q

Which bacteria secrete exotoxin

A

Gram positive and gram negative bacteria

MOSTLY gram POSITIVE bacteria

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97
Q

Describe action (and possible actions) of exotoxin

A

Action is specific:

  • Can inhibit NS - botulism
  • Can stimulate the NS - tetanus
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98
Q

What disease results from exotoxins inhibiting the nervous system

A

Botulism

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99
Q

What disease results from exotoxins stimulating the nervous system

A

Tetanus

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100
Q

What is effect of heat on exotoxin?

A

Unstable on exposure to heat

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101
Q

What is a toxoid

A

A non-active toxin

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102
Q

Can exotoxin be converted to a toxoid?

A

Yes

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103
Q

Describe bacterial transcription

A

RNA polymerase acts on bacterial chromosome to form mRNA

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104
Q

One what ribosomes does translation on bacteria occur?

A

Occurs at 30s/50s ribosome to produce proteins

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105
Q

What types of mutations can occur on bacterial chromosome?

A

Base substitution
Deletion
Insertion

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106
Q

What could be result of bacterial mutation on effectiveness of antibiotic?

A

Mutations can cause antibiotics to be ineffective on the bacteria since protein coded for is altered by mutation meaning it is no longer susceptible to the antibiotic

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107
Q

What is plasmid (R factor)

A

Small circular piece of DNA

(Initially known as R factor (resistance factor) due to the role they play in antibiotic resistance)

Many bacteria have plasmids and many plasmids carry antibiotic resistance genes

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108
Q

Bacterial gene transfer: Define transformation

A

The genetic alteration of a bacterial cell via the uptake of a exogenous substance e.g. via plasmid

109
Q

Bacterial gene transfer: Define Transduction

A

Process by which foreign DNA is introduced into a bacteria

via vector or virus e.g. via a bacteriophage (virus)

110
Q

Bacterial gene transfer: Define Conjugation

A

The transfer of genetic material between bacterial cells by direct cell-cell contact e.g. via sex pilus

111
Q

What is the normal habitat of Staphylococcus

A

On nose and skin

112
Q

Is Staphylococcus coagulase positive or negative

A

Can be either

S. aureus is coagulase positive

113
Q

What is function of coagulase?

A

Converts fibrinogen to fibrin i.e. clot

Some bacteria use it to protect against white blood cells e.g. staph. aureus

114
Q

What is the common clinical presentation of Staphylococcus aureus?

A
  • Pain in shoulder
  • Elevated temperature
  • MRI scan - disc injection and OTSEOMYELITIS (bone infection) C6 and C7
  • Blood cultures show Staphylococcus aureus
  • Treat with flucloxacillin (antibiotic) for 3 months
  • Staph. aureus is responsible for around 90% of osteomyelitis
115
Q

How is Staphylococcus aureus spread

A

Aerosol and Touch e.g. coughing and breathing

116
Q

What is Methicillin Resistant Staphylococcus Aureus resistant to?

A

B-lactams antibiotics
Gentamicin
Erythromycin
Tetracycline

117
Q

What are virulence/pathogenic factors associated with Staphylococcus aureus

A
  • Pore-forming toxins (some produce these)
  • Proteases
  • Toxic shock syndrome toxin (TSST) which stimulates cytokine release
  • Protein A which is a surface protein which binds immunoglobulins in wrong orientation
118
Q

Give examples of Pore-forming toxins

A
  • PVL toxin which is produced by many MRSA strains and causes haemorrhage pneumonia
  • Alpha-haemolysin which can induce apoptosis (at low levels) or cause widespread necrosis (at high levels)
119
Q

Give example of protease pathogenic factor

A

Exfoliatin

causes salted skin syndrome

120
Q

What conditions are associated with Staphylococcus aureus

A 
Wound infections (staph.aureus very good at colonising these)
Abscesses
Osteomyelitis
Scalded skin syndrome
Toxic shock syndrome
Food poisoning
121
Q

Give examples of coagulase negative staphylococci

A

Staph. epidermis

Staph. saprophyticus

122
Q

What is main virulence factor of Staph.epidermis

A

Ability to form persistent biofilms

123
Q

Where do opportunistic infections by staph epidermis generally occur

A

Prosthetic limbs

Catheters

124
Q

What is associated with Staphylococcus saprophyticus

A

Acute cystitis

125
Q

What are 3 ways of classifying Streptococci

A

Haemolysis
Lancefield typing
Biochemical properties

126
Q

In haemolysis to differentiate streptococci, give example of alpha haemolytic strep and colour seen in test

A

Strep. intermedius

Green/Brown

127
Q

In haemolysis to differentiate streptococci, give example of beta haemolytic strep and colour seen in test

A

Strep. pyogenes

Clear/colourless

128
Q

In haemolysis to differentiate streptococci, give example of gamma haemolytic strep and colour seen in test

A

Strep. mutans

No lysis

129
Q

How can further differentiate beta haemolytic streptococci

A

Lancefield typing

130
Q

Describe process of Lancefield typing

A

A method of grouping CATALASE NEGATIVE and COAGULASE NEGATIVE bacteria based on the bacterial carbohydrate cell surface antigens

131
Q

Give example of group A lance field typed strep

A

Strep. pyogenes

132
Q

Give example of group B lance field typed strep

A

Strep. agalactiae

neonatal infections

133
Q

What infections can be caused by Streptococci pyogenes

A

Wound infections such as cellulitis
Tonsillitis and pharyngitis (most common)
Otitis media
Scarlet fever

134
Q

What causes scarlet fever

A

Erythrogenic toxin

135
Q

What is Otitis media

A

group of inflammatory diseases of the middle ear

136
Q

Give examples of complications caused by Streptococci pyogenes

A

Rheumatic fever
Glomerulonephritis
Scarlet fever (erythrogenic toxin)
Immunologically mediated complications (so prompt treatment)

137
Q

What is meant by erythrogenic toxin being a super antigen

A

it gives rise to an exaggerated immunological response and increased circulating cytokine levels

(causes Scarlet fever)

138
Q

How can assess risk of complications caused by Strep, pyogenes

A

assessment of risk can be estimated from the Anti-Streptolysin O titre

139
Q

Streptococci pyogenes: Give examples of of secreted virulence factors

A 
Hyaluronidase
Streptokinase
C5a peptidase
Streptolysins O and S toxin
Erythrogenic toxin (exaggerated response)
140
Q

What is function of Hyaluronidase (Streptococci pyogenes secreted virulence factor)

A

Spreading (of bacteria)

141
Q

What is function of Streptokinase (Streptococci pyogenes virulence factor)

A

Breaks down clots

142
Q

What is function of C5a peptidase (Streptococci pyogenes virulence factor)

A

Reduces chemotaxis

143
Q

What is function of Streptolysins O and S toxin (Streptococci pyogenes virulence factor)

A

Binds cholesterol

144
Q

Streptococci pyogenes: Give examples of of surface virulence factors

A

Hyaluronic acid capsule

M protein

145
Q

What is function of Hyaluronic acid capsule (Streptococci pyogenes surface virulence factor)

A

Protection

146
Q

What is function of M protein (Streptococci pyogenes surface virulence factor)

A

Surface protein that encourages complement degradation

147
Q

What is the common clinical presentation of Streptococci pneumoniae

A

Heavy smoker with nasal congestion and fever
2 days later gets cough and severe chest pain
Rust-coloured sputum
Chest X-ray shows consolidation
Blood and sputum culture show Strep. pneumoniae (draughtsman colonies)

148
Q

What is meant by consolidation on chest X ray

A

Lung filled with liquid

149
Q

In what % of population do you find a normal commensal in oro-pharynx

A

30%

150
Q

What infections are caused by Strep. pneumoniae

A

Pneumonia
Otitis media
Sinusitis
Meningitis

151
Q

What are pre-disposing factors of Strep. pneumoniae

A 
Impaired mucus trapping (e.g. viral infection)
Hypogammaglobulinemia
Asplenia (no spleen)
Diabetes
Renal disease
Sickle cell disease
Very young (<2)
152
Q

Define Hypogammaglobulinemia

A

low levels of serum immunoglobulins which are required for efficient phagocytosis

153
Q

Why can asplenia increase infection risk

A

since spleen produces protein called tuftsin which acts to enhance phagocytosis so with no spleen then no tuftsin and this impaired phagocytosis and thus risk of infection

154
Q

Why does being less than 2 years old increase risk of Strep. pneumoniae

A

since immune response to polysaccharide antigens is very poor

155
Q

Name 4 virulence factors about Strep. pneumoniae

A

Polysaccharide capsule (84 types) is antiphagocytic. (There is a polyvalent vaccine available for those under 2 but this only protects against 23/84 types.)
TEICHOIC ACID binds to choline receptors
PEPTIDOGLYCAN helps protect bacteria
PNEUMOLYSIN CYTOTOXIN is a pore-forming toxin

156
Q

Name a pore-forming toxin

A

Pneumolysin cytotoxin

C Dif for virus

157
Q

What is another name for oral streptococci?

A

Viridans streptococci

some cause dental caries or abscesses

158
Q

What is haemolysis result from Viridans streptococci?

A

Alpha or non-haemolytic

159
Q

Which Viridans strep are important in infective endocarditis?

A

S.sanguinis

S.oralis

160
Q

What is the group of the most pathogenic Viridans strep called?

A

Milleri group

161
Q

Which bacteria are included in Milleri group

A

S.intermedius
S.anginosis
S.constellatus

162
Q

Which organs are affected by Milleri group

A

Cause deep organ abscesses in Brain and Liver

163
Q

Describe the clinical presentation of Corynebacterium diphtheriae

A 
Child with severe sore throat
Fever and malaise for 2 days
Lymphadenopathy (swollen) in neck
Rapid breathing
Thick greyish membrane on tonsils
Swab shows Gram - Positive Bacilli (Rods)
164
Q

What is common presentation of Corynebacterium diphtheriae treated with

A

Anti-toxin (pre-formed antibody to toxin) and Erythromycin (antibiotic helps remove symptoms and stop carriage and spread but does not destroy pathogen)

165
Q

How does Corynebacterium diphtheriae spread?

A

Droplet spread

166
Q

What causes Corynebacterium diphtheriae symptoms?

A

Production of a toxin that inhibits protein synthesis:

Inactivates elongation factor-2 in host cells by adding ADP-ribosyl group to aa dipthamide

167
Q

How can we prevent Corynebacterium diphtheriae

A

Vaccination with toxoid (inactivated toxin)

168
Q

How can we select for/isolate Corynebacterium diphtheriae from throats of patients?

A

Can grow in the presence of POTASSIUM TELLURITE

169
Q

Name something present in cell wall of gram negative bacteria but not gram positive

A

Lipopolysaccharide

endotoxin that forms outer outer leaflet of outer membrane of gram-negative bacteria

170
Q

What comprises Lipopolysaccharide

A

Lipid A
Core (R) antigen
Somatic (O) antigen

171
Q

What is Lipid A (LPS)

A

The toxic portion of LPS that is anchored in the outer leaflet of the outer membrane

172
Q

What is Core (R) antigen (LPS)

A

Short chain of sugars, some are unique to LPS

173
Q

What is Somatic (O) antigen (LPS)

A

A highly antigenic repeating chain of oligosaccharides

174
Q

Why is it more difficult for Gram-Negative bacteria to secrete a toxin than Gram-Positive?

A

Since the toxin/effector protein needs to travel past two membrane instead of one

175
Q

Name the cell surface antigens of gram-negative bacteria

A 
K antigen (EPS capsule)
H antigen (flagellum- tails around bacteria)
O (somatic) antigen (LPS)
176
Q

How is Shigella different to Salmonella on cell surface antigens

A

Shigella has NO H antigen
since it does not have flagellum

Salmonella does have a H antigen since it does have flagellum

177
Q

What shape are Enterobacteria (coliforms)

A

Rods/Bacilli

178
Q

Which of these is true:

  • Most are motile i.e. have flagella
  • Some are intestinal parasites
  • Are able to grow in anaerobic conditions
A

All of them

179
Q

What can be used to differentiate between lactose and non-lactose fermenting enterobacteria

A

MacConkey agar

180
Q

Give examples of enterobacteria

A

Salmonella
Shigella
Escherichia coli (E.coli)
Klebsiella pneumoniae (opportunistic)

181
Q

Describe features of Escherichia coli

A

Have flagella
Pathogenic or
Commensals - most abundant facultative anaerobe (is able to respire anaerobically - doesn’t mean can’t respire aerobically)
Many strains/serotypes, but all share a common ‘core’ genome

182
Q

What is meant by many pathogenic E.coli having acquired pathogenicity

A

Acquired pathogenicity from other bacteria by ‘mating’ and acquiring pathogenic blocks of genes

183
Q

Name virulence factors for E.coli causing travellers diarrhoea

A

Has pilli which enable it to adhere to tissue of the small intestine.
When it binds to the tissue it releases a labile toxin that alters the role of the Gs protein on the GI cell surface meaning it can no longer stimulate adenyl cyclase resulting in more Cl- being released into the GI lumen.
Results in diarrhoea as water follows Cl-

184
Q

What is name of strain of E.coli that causes travellers diarrhoea

A

Enterotoxigenic E.coli (ETEC)

185
Q

Name 4 species of Shigella (very closely related to E.coli)

A

S.dysenteriae
S.flexneri
S.boydii
S.sonnei (commonest cause)

186
Q

What is result of shigella damage to intestinal mucosa

A

Acute infection of the large intestine

Painful diarrhoea often with blood and mucus in the stools

187
Q

Describe the pathogenesis of Shigella infection

A

Bacteria are acid-tolerant so can survive and pass through the stomach.
Infective dose is just 100 bacteria so v easy to be infected.
Shigella target microfold (M) cells and induce their own uptake by M-cells.
They then cross the epithelial cell layer where they are engulfed by macrophages.
However once engulfed they induce apoptosis of macrophages resulting in the release of damaging free radicals, resulting in an inflammatory response and cell damage.
Eventually bacteria will be destroyed by neutrophils.
Some shigella also release a Shiga Toxin with disrupts protein synthesis resulting in necrosis

188
Q

What is infective dose of Shigella required to be infected

A

100 bacteria

thus extremely easy

189
Q

How can Shigella spread

A

Person-to-peron or via contaminated water or food

190
Q

Where are microfold cells found

A

Gut-associated lymphoid tissue (GALT) of Peyer’s Patches and in the Mucosa-Associated Lymphoid Tissue (MALT).

191
Q

What is function of microfold cells

A

Initiate mucosal immunity responses and allow for the transport of microbes across the epithelial cell layer from the gut lumen where interactions with immune cells can take place.

192
Q

What can result from release of Shiga Toxin in body

A

Disrupts protein synthesis resulting in necrosis:
-Toxin targets the kidney resulting in haemolytic uraemia syndrome which can lead to death
(-Shiga toxin is also produced by some E.coli e.g. EHEC)

193
Q

Name 2 species of Salmonella

A

S.enterica

S.bongori (rare, results from reptile contact)

194
Q

What Salmonella bacteria is responsible for Salmonellosis

A

S.enterica

195
Q

What infections can be caused by salmonella

A

Gastroenteritis (frequent cause of food poisoning from milk and poultry)
Enteric fever - typhoid (systemic disease)
Bacteraemia

196
Q

What is bacteraemia

A

Presence of bacteria in blood - uncommon

197
Q

What can cause Enteric fever - typhoid

A

Salmonella typhi

Salmonella paratyphi

198
Q

What can result from Enteric fever - typhoid

A 
Fever
Headache
Dry cough
Splenomegaly (enlarged spleen)
Hepatomegaly (abnormal enlargement of liver)
Diarrhoea (may develop)
199
Q

How long does Gastroenteritis take to resolve

A

Resolves in a week
6-36 hour incubation
Localised infection

200
Q

Describe the pathogenesis of salmonellosis

A

Ingestion of contaminated food/water.
Has a high infective dose - need to ingest a significant amount for infection.
Salmonella mediates its endocytosis across the gut lumen.
Gastroenteritis or Enteric fever

201
Q

Describe pathogenesis of salmonellosis to Gastroenteritis

after salmonella mediates its endocytosis across gut lumen

A

Bacteria presence results in chemokine release and neutrophil recruitment.
This results in neutrophil-induced tissue injury due to the inflammatory response.
There is fluid and electrolyte loss due to cell damage resulting in diarrhoea.
Eventual inflammation/necrosis of gut mucosa.

202
Q

Describe pathogenesis of salmonellosis to enteric fever (S.typhi and S.paratyphi)
(after salmonella mediates its endocytosis across gut lumen)

A

Migrates to basolateral membrane of cells in the intestinal lumen (Peyers patch) where it results in inflammation and ulceration -> diarrhoea.
However, initially there is little damage to gut mucosa.
Bacterias then engulfed and SURVIVES then spreads systemically via the lymph nodes.
Then enters bloodstream via thoracic duct and then multiplies in the macrophages of the liver, spleen and bone marrow resulting in septicaemia which results in massive fever.
Then spreads to gall bladder from liver where person can be carrier state from 1 year to rest of life.

203
Q

Where can Salmonellae typhi and S.paratyphi spread to once engulfed in enteric fever

A 
Survives after being engulfed
Spreads systemically via lymph nodes
Enters bloodstream via thoracic duct
Multiplies in macrophages of liver, spleen and bone marrow
Septicaemia => massive fever
204
Q

What is meant by nosocomial infection

A

Hospital acquired infection

205
Q

What different nosocomial infections are caused by Klebsiella pneumoniae

A

Pneumonia
Blood stream infections
Wound or surgical site infections
Meningitis

206
Q

How would you describe Klebsiella pneumoniae

A

Opportunistic pathogenic enterobacteria

207
Q

Describe features of Vibrio cholerae (Gram Negative)

A

Facultative anaerobe
Curved rods/bacilli with single polar flagellum
Results in cholera - the most severe diarrhoeal disease
No fever or blood seen
Voluminous watery stools

208
Q

How is vibrio cholerae spread

A

Faecal-oral route - faecal contaminated water and uncooked shellfish

209
Q

Why is a high dose of vibrio cholerae required for infection

A

Sensitive to acid

e.g. requires many to get past stomach acid

210
Q

How long would incubation be for someone with vibrio cholerae

A

5 hours (multiplies in small intestine)

211
Q

Describe stools of someone with vibrio cholerae

A 
Voluminous watery (rice-water) stools
i.e. secretory diarrhoea
212
Q

How many litres can be lost per day in person with vibrio cholerae infection and what is the result of his

A

Can lose 20 litre/day plus electrolytes, results in:

  • Dehydration and subsequent death
  • 60% mortality
213
Q

Why is there no blood or fever in vibrio cholerae infection?

A

No invasion or damage to mucosa

214
Q

What is most common treatment for Vibrio cholerae infection

A

Oral rehydration

how 80% are treated

215
Q

Name virulence determinants of Vibrio cholerae

A

Pilli

Cholera toxin

216
Q

Vibrio cholerae: what are pills for

A

Colonisation

217
Q

Vibrio cholerae: what are results of Cholera toxin

A

Results in uncontrolled cyclic AMP production
Therefore activates protein kinases
Causes modification of ion transporter activity causing loss of Cl- and Na+
Results in massive H2O loss
(acts in same way as E.coli labile toxin)

218
Q

Describe features of Pseudomonas aeruginosa

A

Motile-single polar flagellum
Opportunistic (serious cause of nosocomial infections)
Multiple antibiotic resistance

219
Q

Give examples of localised effects of acute infections by Pseudomonas aeruginosa

A

Burn/surgical wounds
UTIs (catheters)
Keratitis (inflammation of cornea)

220
Q

Give examples of systemic (bacteraemic) effects of acute infections by Pseudomonas aeruginosa

A

Bacteraemic effect:
Neutropenic patients (low on neutrophils)
e.g. leukaemia, in chemotherapy, AIDS

221
Q

Give examples of opportunistic bacteria

A 
Pseudomonas aeruginosa (gram negative)
Klebsiella pneumoniae (Enterobacteria gram negative)
222
Q

True or False: Pseudomonas aeruginosa is the leading cause of nosocomial pneumonia in ICU patients

A

True

223
Q

Why are cystic fibrosis patients more likely to have chronic infection by Pseudomonas aeruginosa?

A

Have poor functioning Cl- transporters meaning they have dehydrated lung mucus , which is perfect environment for bacteria to grow.
Virtually impossible to remove pseudomonas in cystic fibrosis patient since antibiotic resistant

224
Q

In what demographic would you mostly see infections by Haemophilus influenzae

A

Young children and adult smokers

225
Q

What infections can be caused by Haemophilus influenzae

A 
Important cause of Meningitis (when it crosses blood-brain barrier, aged <5) and bronchopneumonia
Epiglottitis
Sinusitis
Otitis media (ear infection)
Bacteraemia
Cystic fibrosis and COPD lung infections
226
Q

Give features of Haemophilus influenzae

A

Non-motile
Fastidious (specific requirement for survival)
Exclusively human parasite

227
Q

Does Haemophilus influenzae grow on blood agar or chocolate agar and why

A

Will NOT grow on BLOOD agar which supports growth of many other fastidious bacteria, as can not access harm in this form

Will ONLY grow on chocolate agar
Chocolate agar = blood agar heated to 8- degrees to allow release of haem by RBCs

228
Q

Name 3 virulence determinants of Haemophilus influenzae

A

Pilli - adherence to epithelial cells and mucin
Capsule
Lipopolysaccharide endotoxin - results in inflammation

229
Q

What strains of bacteria are capsulate and which are non-capsulate

A

Commensals and respiratory tract pathogens are non-capsulate

Invasive strains are capsulate (can penetrate the nasopharyngeal epithelium)

230
Q

In what % of population can you get nasopharyngeal carriage of Haemophilus influenzae

A

25-80%

231
Q

Name two types of Beta-Proteobacteria

A

Bordetella pertussis

Neisseria

232
Q

What is (B) pertussis

A 
Whooping cough
(short rods/bacilli)
233
Q

Describe transmission of Bordetella pertussis

A

Aerosol transmission
Adheres to ciliated epithelia of upper respiratory tract/trachea
(Highly contagious with a low infect dose)

234
Q

Describe symptoms of Bordetella pertussis

A

Non-specific flu-like symptoms
Followed by Paroxysmal coughing
(cough followed by inhalation resulting in whooping sound)
Can lead to sub-conjunctival haemorrhage

235
Q

Give two species of Neisseria (Beta-Proteobacteria)

A

N.meningitidis

N.gonorrhoeae

236
Q

Describe appearance of Neisseria (Beta-Proteobacteria)

A

Non-flagellated diplococci (go around in pairs)

237
Q

Where is Neisseria (Beta-Proteobacteria) found during an infection

A

Present in polymorphonuclear lymphocytes of CAF or urethral discharge during infection.

238
Q

In what % of the population would you find N.meningitis that is asymptomatic in nasopharynx

A

5-10%

239
Q

Describe transmission of N.meningitis

A

Person-person aerosol transmission

240
Q

Describe the pathogenesis of N.meningitis

A

Crosses the nasopharyngeal epithelium and enters the bloodstream in a small proportion of colonised individuals:

  • Asymptomatic bacteraemia (if low numbers of bacteria) or Septicaemia if high
  • Meningitis - colonisation in subarachnoid space after crossing the blood-brain barrier
  • High risk of mortality in the septicaemic form
241
Q

Give virulence determinants of N.meningitis

A 
CAPSULE
-non-capsulaed only found in nasopharynx
-capsule is anti-phagocytic
PILLI
promote colonisations and cell invasion
LPS (Lipopolysaccharide)
Results in cytokine cascade and inflammatory response which can lead to sepsis
242
Q

Can N.gonorrhoea be asymptomatic?

A

Not a commnesal but can be asymptomatic (30% of infected females)

243
Q

Describe transmission of N.gonorrhoea

A

Person to person only

244
Q

Is N.gonorrhoea capsulated?

A

Non-capsulated

Unlike N.meningitis

245
Q

N.gonorrhoea is an STD which results in:

A

Urethritis (with additional infection of female genitalia)

Infection of Fallopian tubes if infection ascends

246
Q

Give examples of 2 e-Proteobacteria

A

Campylobacter

Helicobacter pylori

247
Q

Give 2 examples of Campolybacter (e-Proteobacteria)

A

C.jejuni

C.coli

248
Q

Describe Campylocater shape

A

Spiral bacilli (rods)

249
Q

True or False:

Campylobacter is the most common cause of food poisoning in UK and US

A

True and from:

  • Undercooked poultry e.g. BBQ
  • Unpasteurised milk
250
Q

Describe infective dose, key symptom and duration of campylobacter

A

Low infective dose.
Results in mild-sever diarrhoea often with blood - usually self-limiting within a week.
Shed in faeces for around 3 weeks.

251
Q

**Describe 2 virulence factors of Campylobacter

A

INVASINS - invades ileal and colonic epithelial cells, resulting in local acute inflammatory response i.e. tissue damage

Cytolethal Distending Toxin (CDT) - arrests the cell cycle meaning target cells swell and lyse

252
Q

Describe features of Helicobacter pylori

A 
Require CO2 (micro-aerophilic)
Spiral shaped
Present in 50% of global population but only a fraction will develop disease
253
Q

What diseases can be caused by Helicobacter pylori

A

Major role in gastritis and peptic ulcer disease

Implicated in gastric adenocarcinoma

254
Q

**Describe a virulence factor of Helicobacter pylori

A

Urease - hydrolyses urea to generate ammonia to act as a buffer to gastric acid

255
Q

Describe features of Chlamydia bacteria

A

Very small

Non-motile

256
Q

Describe the 2 developmental stages in growth cycle of Chlamydia

A

Elementary bodies (EBs) - dormant:

  • Infectious
  • Enter cell through endocytosis
  • Prevent phagosome fusion

Reticulate bodies (RBs) - metabolically active and fragile:

  • Replicative
  • Non - infectious
257
Q

What is most common STD

A

Chlamydia trachomatis

usually Asymptomatic

258
Q

What diseases can result from Chlamydia trachomatis?

A

Usually asymptomatic but:
Can spread to uterus and ovaries resulting in pelvic inflammatory disease
Can cause Conjunctivitis (STD)
Can cause trachoma - blindness tat is spread via flies

259
Q

What are most common sites/modes of infection caused by Gram-Negative pathogens?

A 
Respiratory tract
Urinary tract
GI tract
Meningitis
STIs
Wound infections
260
Q

What are most common Gram Negative bacteria that infect Respiratory tract?

A

Bordetella pertussis

Haemophilus influenzae

261
Q

What are most common Gram Negative bacteria that infect Urinary tract?

A

Some E.coli strains

Klebsiella pneumoniae

262
Q

What are most common Gram Negative bacteria that infect GI tract?

A 
Vibrio Cholera
Shigella dysenteriae
some E.coli strains
Campylobacter jejuni
Helicobacter pylori
263
Q

What gram negative bacteria can cause meningitis

A

Neisseria meningitidis

Haemophilus influenzae

264
Q

What gram-negative bacteria can cause STIs

A

Klebsiella pneumoniae

Chlamydia trachomatis

265
Q

What gram-negative bacteria can cause wound infections

A

Pseudomonas aeruginosa

some E.coli strains

266
Q

Chains of purple cocci are seen on a gram film. They show alpha haemolysis when grown on blood agar. They don’t grow near the optochin disc. These are probably:

a) Streptococcus pneumoniae
b) Staphylococcus epidermidis
c) Viridans Streptococci
d) Group A streptococci (S. pyogenes)
e) Neisseria meningitidis

A

Streptococcus pneumoniae

Chains of purple cocci on gram film
Alpha hameolysis on blood agar
No optochin disc growth

267
Q

Which of these is a gram negative bacillus that ferments lactose?

a) Shigella sonnei
b) Listeria monocytogenes
c) Neisseria meningitidis
d) Eschericia coli
e) Streptococcus pyogenes

A

d) Eschericia coli

268
Q

Which is incorrect? Haemophilus influenzae is an important cause of:

a) meningitis in pre-school children
b) Otitis media
c) Pharyngitis
d) Gastroenteritis
e) Exacerbations of Chronic Obstructive Pulmonary Disease (COPD)

A

d) Gastroenteritis

269
Q

Which is a normally sterile site?

a) Pharynx
b) Urethra
c) Cerebrospinal Fluid
d) Lung
e) Skin

A

Cerebrospinal fluid

Medicine Phase 2a (22 decks)

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