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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
Q

After washing out the initial stain in Gram negative bacterial, how can you then stain them red?

A

Counter-stain with safranin

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26
Q

What does Strep. pneumoniae cause?

A

Primary lobar pneumonia
Otitis media and sinusitis
Meningitis

27
Q

What does Strep. pyogenes cause?

A 
Non-pyogenic complications:
-Streptococcal toxic shock
-Scarlet fever
-rheumatic fever 
-glomerulonephritis
Pyogenic complications:
-Abscesses
-Otitis media
-Sinusitis
-Cellulitis 
-Impetigo
28
Q

What are symptoms of pharyngitis?

A

Fever, sore throat, headache, redness in posterior pharynx and enlarged tonsils

29
Q

What is rheumatic fever?

A

inflammation in a number of tissues in the manner of an autoimmune disease

30
Q

Where in the body is Staph. aureus a commensal bacterium?

A

Nasal cavity, skin, GI and oral cavity

31
Q

Why is MRSA thought to be resistant to beta lactams?

A

Due to the mecA gene - changes binding proteins on the cell surface

32
Q

What is EHEC?

A

Enteroharmorrhagic E coli

33
Q

Effects and mechanisms of EHEC

A

Bloody diarrhoea with little or no fever

Does this by producing shiga toxin

34
Q

What is EPEC?

A

Enteropathogenic E coli

35
Q

Effects and mechanism of EPEC?

A

Associated with infantile darrhoea (watery or bloody)

36
Q

Describe effects of using thiosulfate to distinguish salmonella and shigella

A

Salmonella produces a black precipitate as it produces H2S; shigella does not produce H2S. and appears green

37
Q

What do E.coli, Shigella spp and Salmonella spp all cause?

A

Travellers’ diarrhoea, dysentery, enteric fevers, food poisoning

38
Q

What is the cell wall of mycobbacteria composed of?

A

Mycolyl-arabinogalactan-peptidoglycan (mAGP) complex

39
Q

Describe the mAGP complex

A

Mycobacterial peptidoglycan forms the basal layer
then arabinogalactan layer
mycolic acids attach to arabinogalactan layer

40
Q

What is an example of an acid fast stain?

A

Ziehl-Neelsen stain

41
Q

What is the initial stage of mTB infection?

A
  • 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
Q

What is a grauloma?

A

A compact aggregation of immune cells that form in response to persistant stimuli of an infection or non-infectious nature

43
Q

Describe the host response to mTB infection

A
  • 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
Q

What may the macrophages in the granuloma differentiate to become?

A
  • multinucleated giant cells
  • foam cells
  • epithelioid cells
45
Q

What is the centre of the granuloma called? Describe it

A

The caseum

Generally necrotic

46
Q

What happens to the granuloma in individuals with a healthy immune system?

A

The granuloma undergoes fibrosis + calcification, forming a tubercle, successfully controlling the infection
this occurs due to recruitment of fibroblasts

47
Q

What may happen in immunocompromised individuals if mTB resides as a latent infection?

A
  • can be reactivated

- may penetrate the airways and bloodstream

48
Q

Describe treatment for mTB

A 
Long-term antibacterial cocktail
First-line → 4 drug cocktail consisting of RIPE 
Rifampicin
Isoniazid 
Pyrazinamide
Ethambutol
49
Q

How may Mtb evade macrophage function?

A
  • Inhibition of phagosome-lysosome fusion
  • Inhibition of vacuolar acidification
  • Inhibition of apoptosis within Mtb infected macrophages
50
Q

What does Staph. aureus cause?

A

Abcesses
Surgical wound and burn infections
Food poisoning

51
Q

What are the two species of Clostridia that I need to know?

A

Clostridium tetani and Clostridium difficile

52
Q

What is expression of virulence determinants regulated by in S. pyogenes?

A

CO2

53
Q

What does C. difficile cause?

A

Watery diarrhoea and pseudomembranous colitis

54
Q

Why is the risk of female infection with gonorrhoea much greater than the risk of male infection?

A

Partly due to the fact that gonococcus can bind to human sperm

55
Q

How does the capsule aid immune evasion of meningococcus?

A

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
Q

How many meningococci evade complement-mediated killing?

A
  • 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
Q

Does N. gonorrhoea have a capsule?

A

No

58
Q

Give examples of immune evasion strategies of S.aureus

A
  • 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
Q

What three important toxins does S.aureus secrete?

A

y-haemolysin
Leucocidin
TSST

60
Q

What does gamma-haemolysin do?

A

S.aureus toxin

→ insert into the membrane of erythrocytes to form beta-barrel pores, causing cell lysis

61
Q

What does leucocidin do and which organism produces it?

A

S. aureus

Destroys WBCs and causes production of pus

62
Q

What does TSST cause and what organism produces it?Describe its mechanism

A

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
Q

What colour do Gram positive bacteria stain?

A

Purple

64
Q

What colour do Gram negative bacteria stain?

A

Red or pink

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