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Bacteriology - Specific pathogens Flashcards

1
Q

What are the Gram positive bacteria I need to know?

A 
Streptococcus pneumoniae
Streptococcus pyogenes
Staphylococcus aureus 
MRSA
Clostridum spp
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2
Q

What are the enteric O-antigen-possessing Gram negative bacteria?

A

E. coli
Shigella spp
Salmonella spp
EHEC and EPEC

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3
Q

What are the mycobacteria I need to know?

A

Mycobacterium tuberculosis

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4
Q

What are the non-O-antigen.-possessing Gram negative bacteria that I need to know?

A

Neisseria gonorrhoeae

Neisseria meningitides

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5
Q

What does the catalase test distinguish between?

A

Staphylococcus and streptococcus

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6
Q

What bacteria give a positive catalase test?

A

Staphylococcus

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7
Q

What does the coagulase test distinguish?

A

Staph aureus or staph epidermidis

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8
Q

What bacteria give a positive coagulase test?

A

Staph Aureus

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9
Q

What test allows differentiation between different forms of streptococcus?

A

Haemolysis

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10
Q

What type of streptococcus is optichin sensitive?

A

Streptococcus pneumonia

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11
Q

What type of streptococcus is not optichin sensitive?

A

Streptococcus viridans

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12
Q

What can you do following beta haemolysis?

A

Lancefield typing to confirm Group D streptococci

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13
Q

What test would you use to identify a Gram negative coccus?

A

Oxidase

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14
Q

What does a positive oxidase test on a Gram negative coccus mean?

A

Neisseria

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15
Q

What test would you use to test Gram negative rods?

A

MacConkey agar

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16
Q

What does growing on MacConkey agar allow differentiation of bacteria based on?

A

lactose fermentation

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17
Q

Which two Gram negative bacteria ferment lactose?

A

E.coli and Klebsiella

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18
Q

How do you differentiate between E.coli and Klebsiella?

A

Indole test

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19
Q

Which organism gives you a positive indole test?

A

E.coli

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20
Q

What do you use to identify proteus?

A

Urease test

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21
Q

What do you use to identify shigella and salmonella?

A

Negative urease test, then use H2S → Salmonella gives positive H2S

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22
Q

What are the initial reagents of Gram staining?

A

Crystal violet and Gram’s iodine

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23
Q

What do the initial reagents of Gram staining react with to produce a purple colour?

A

Bacterial ribonucleotides

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24
Q

In Gram negative bacteria, what is the initial purple colour washed away by?

A

Alcohol and acetone

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25
After washing out the initial stain in Gram negative bacterial, how can you then stain them red?
Counter-stain with safranin
26
What does Strep. pneumoniae cause?
Primary lobar pneumonia Otitis media and sinusitis Meningitis
27
What does Strep. pyogenes cause?
``` Non-pyogenic complications: -Streptococcal toxic shock -Scarlet fever -rheumatic fever -glomerulonephritis Pyogenic complications: -Abscesses -Otitis media -Sinusitis -Cellulitis -Impetigo ```
28
What are symptoms of pharyngitis?
Fever, sore throat, headache, redness in posterior pharynx and enlarged tonsils
29
What is rheumatic fever?
inflammation in a number of tissues in the manner of an autoimmune disease
30
Where in the body is Staph. aureus a commensal bacterium?
Nasal cavity, skin, GI and oral cavity
31
Why is MRSA thought to be resistant to beta lactams?
Due to the mecA gene - changes binding proteins on the cell surface
32
What is EHEC?
Enteroharmorrhagic E coli
33
Effects and mechanisms of EHEC
Bloody diarrhoea with little or no fever | Does this by producing shiga toxin
34
What is EPEC?
Enteropathogenic E coli
35
Effects and mechanism of EPEC?
Associated with infantile darrhoea (watery or bloody)
36
Describe effects of using thiosulfate to distinguish salmonella and shigella
Salmonella produces a black precipitate as it produces H2S; shigella does not produce H2S. and appears green
37
What do E.coli, Shigella spp and Salmonella spp all cause?
Travellers' diarrhoea, dysentery, enteric fevers, food poisoning
38
What is the cell wall of mycobbacteria composed of?
Mycolyl-arabinogalactan-peptidoglycan (mAGP) complex
39
Describe the mAGP complex
Mycobacterial peptidoglycan forms the basal layer then arabinogalactan layer mycolic acids attach to arabinogalactan layer
40
What is an example of an acid fast stain?
Ziehl-Neelsen stain
41
What is the initial stage of mTB infection?
- transmission via droplet infection - receptor-mediated phagocytosis by alveolar macrophages to internalise the bacteria - then reside in phagosomes by arresting phagosome maturation and preventing fusion with the lysosome
42
What is a grauloma?
A compact aggregation of immune cells that form in response to persistant stimuli of an infection or non-infectious nature
43
Describe the host response to mTB infection
- infected macrophages release TNF-a which causes inflammation and IFN-gamma which is responsible for the recruitment of further macrophages to the site of infection - Granuloma forms with infected cells at the centre as more immune cells are recruited
44
What may the macrophages in the granuloma differentiate to become?
- multinucleated giant cells - foam cells - epithelioid cells
45
What is the centre of the granuloma called? Describe it
The caseum | Generally necrotic
46
What happens to the granuloma in individuals with a healthy immune system?
The granuloma undergoes fibrosis + calcification, forming a tubercle, successfully controlling the infection this occurs due to recruitment of fibroblasts
47
What may happen in immunocompromised individuals if mTB resides as a latent infection?
- can be reactivated | - may penetrate the airways and bloodstream
48
Describe treatment for mTB
``` Long-term antibacterial cocktail First-line → 4 drug cocktail consisting of RIPE Rifampicin Isoniazid Pyrazinamide Ethambutol ```
49
How may Mtb evade macrophage function?
- Inhibition of phagosome-lysosome fusion - Inhibition of vacuolar acidification - Inhibition of apoptosis within Mtb infected macrophages
50
What does Staph. aureus cause?
Abcesses Surgical wound and burn infections Food poisoning
51
What are the two species of Clostridia that I need to know?
Clostridium tetani and Clostridium difficile
52
What is expression of virulence determinants regulated by in S. pyogenes?
CO2
53
What does C. difficile cause?
Watery diarrhoea and pseudomembranous colitis
54
Why is the risk of female infection with gonorrhoea much greater than the risk of male infection?
Partly due to the fact that gonococcus can bind to human sperm
55
How does the capsule aid immune evasion of meningococcus?
All capsule serogroups expect A contain sialic acid in their capsule, which allows the meningococcus to become less visible to the host immune system via molecular mimicry
56
How many meningococci evade complement-mediated killing?
- By expression of the lipoprotein, factor H binding protein →mimic the host by recruiting factor H which is an inhibitor of the alternative pathway - Expression of Neiserria surface protein A which also binds to human factor H - Binding of PorA to C4b-binding protein
57
Does N. gonorrhoea have a capsule?
No
58
Give examples of immune evasion strategies of S.aureus
- SpA → released following hydrolysis, binds the Fc part of IgG, reducing activation of complement - Adenosine synthase A → anti-inflammatory (converts extracellular AMP to adenosine, an anti-inflammatory) - Sbi (staphylococcal binder of immunoglobuin) → binds with C3 and factor H
59
What three important toxins does S.aureus secrete?
y-haemolysin Leucocidin TSST
60
What does gamma-haemolysin do?
S.aureus toxin | → insert into the membrane of erythrocytes to form beta-barrel pores, causing cell lysis
61
What does leucocidin do and which organism produces it?
S. aureus | Destroys WBCs and causes production of pus
62
What does TSST cause and what organism produces it?Describe its mechanism
S. aureus - Superantigen that binds to MHCII, which leads to activation of Th cells without any need to undergo intracellular processes This may lead to a cytokine storm and symptoms of toxic shock → high fever, rash, vomiting, diarrhoea, hypotension, death
63
What colour do Gram positive bacteria stain?
Purple
64
What colour do Gram negative bacteria stain?
Red or pink

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