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(3002) Clinical Micro > Enterobacteriaceae > Flashcards

Enterobacteriaceae Flashcards

1
Q

Define fermentation

A

use glucose under anaerobic cond.

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2
Q

Fermentative vs oxidatiive

A

F: breakdown of glucose anaerobically & aerobically
O: breakdown of glucose aerobically via Krebs cycle

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3
Q

Overt pathogens of enterobacteriaceae

A
  • salmonella
  • SHigella
  • YErsina
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4
Q

2 non-motile enterobacteriaceae genera

A
  • Klebsiella

- Shigella

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5
Q

major antigens

A

H: flagellar protein
K: capsular polysaccaride
O somatic: cell wall LPS
F: fimbrae> adherance

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6
Q

Diarrhoea producing strains of E.coli

A 
EHEC: Enterohaemorrhagic E.coli **most virulent
EPEC: ...pathogenic
ETEC: ...toxigenic
EIEC: ...invasive
EAEC: ...aggregative
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7
Q

Features of E.coli

A
  • Magenta pink on MAC
  • Bright yellow on CLED
  • motile
  • indole pos.
  • sensitive to everything
  • GNB
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8
Q

Features of Klebsiella sp

A
  • pale pink on MAC
  • pale yellow on CLED
  • non-motile
  • Mucoid capsules = stringy like cheese
  • Idole +ve = K. oxytoca
  • Indole -ve= K. pneumonia
  • GNB
  • catalase pos.
  • lactose fermenter
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9
Q

What primary test results would you expect for a member of the family enterobacteriaceae?

A
  • *Oxidase test: neg
  • *Catalase test: +ve
  • *O-F test: fermentative
  • Shape: 5mm, grey colonies on BA w/ opaque centers (fried egg)
  • Glucose acid: +ve
  • *non-haemolytic
  • *motility: peritrichous flagella
  • facultative anaerobes: Grow w/ or w/out O2
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10
Q

features of Enterobacter sp.

A
  • motile
  • Indole Neg
  • GNB
  • Pale pink on MAC
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11
Q

Differentiate Proteus vulgaris, P. mirabilis, P. penneri

A
  1. Indole positive: P. vulgaris

2. Maltose positive: P vulgaris & P. penneri

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12
Q

Differentiate Serratia marcescens, S. rubidaea, S. plymuthica

A

Ominthine decarboxylase (ODC on API) pos: S. marcescens

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13
Q

Difference b/w endo & exotoxins:

  • Gram _ bacteria
  • Toxicity
  • Heat Stability
  • Fever producing
  • antigenicity (create Aby)
A 
ENDO |  EXO
GNeg  |  GPos & GNeg
Low     |  High
Stable |  Unstable
Yes      |  No
Weak  |  Strong
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14
Q

Describe the key phenotypic features which would allow differentiation between the genera Escherichia, Klebsiella, Enterobacter in a clinical laboratory?

A
  • Escherichia: *LF (Bright on MAC & CLED), *motile, Indole Pos, Hi Biochem activity
  • Klebsiella: *LF (pale/less intense), *non-motile, variable Indole
  • Enterobacter: Variable LF (pale/less intense), Motile, Indole neg
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15
Q

In what clinical isolate is E.coli most commonly found as a pathogen?

A

UTI

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16
Q

How could you presumptively identify E.coli in a culture (agar plate) from a clinical specimen? i.e. what set of features would
give you enough confidence to report the organism as being E.coli without setting up an API or testing on MALDI-TOF?

A
  • LF = Bright rxn on MAC & CLED
  • Indole Pos
  • Sensitive to everything
  • (Motile)
17
Q

How could you differentiate between the three swarming strains of Proteus? What would the results be?

A
  1. Indole test => Pr. vulgaris (Indole Pos), others Neg

2. Maltose => Pr. penneri (Pos), Pr mirabilis (Neg)

18
Q

If a strain of E.coli was referred to as E.coli O114:H21, what do the letters and numbers signify?

A

Letters: the antigen
numbers: the location

19
Q

By what method could you easily differentiate between a mucoid strain of E.coli and a mucoid strain of K.oxytoca? List the result for each.

A

Hanging drop motlility test = E.coli motile, K.oxytoca non-motile

20
Q

What is the slime test/string test used for and how is it performed? (uses 3% KOH).

A

Slime test is used to distinguish GNeg bact. from GPos.

  1. place 1 drop of 3% KOH on slide
  2. emulsify a few colonies of test bact in drop
  3. stir for 60 sec and gently pull away
  4. Observe for slime/string as you pull away
    * GNeg Bact pos bc KOH break down of thin cell wall (peptidoglycan) = releases contents like DNA = thick consistency
21
Q

In a routine laboratory, how can the production of the enzyme tryptophanase (by an unknown bacteria) be determined? What reagent is used?

A
  • Indole test detects tryptophanase

- Uses kovac’s reagent

22
Q

How does motility medium work? How long does it take to get a result?

A
  • Semi-soft agar not too runny or firm allow bacteria to swarm
  • Medium turns red if there’s growth
  • incubated overnight
23
Q

a) How does the urea test work?

b) What does visible growth in the tube mean with no colour change?

A

a) If bacteria produces urease -> hydrolyses urea => NH3 = pH rise (basic) = colour change (bright pink)
b) doesn’t produce ureas

24
Q

distinctive features of Proteus, Providencia and Morganella sp.

A
  • GNB
  • Oxidase neg
  • non-lactose F
  • Motile
  • Most Urea Pos
  • TDA Pos
25
Q

distinctive features of Serratia sp

A
  • Red pigment (*S.marcescens, ^S.plymuthica, ^S. rubidea = ^soil bact)
  • ODC Pos on API (Ornithine decarboxylase)
26
Q

distinguish b/w the 2 important Citrobacter sp w/ their distinctive features: C. freundii & C. koseri

A
  • C. freundii: indole v, Lac v,

- C. koseri: Indole Pos, Lac v

(3002) Clinical Micro (19 decks)

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