Enterobacteriaceae Flashcards
Define fermentation
use glucose under anaerobic cond.
Fermentative vs oxidatiive
F: breakdown of glucose anaerobically & aerobically
O: breakdown of glucose aerobically via Krebs cycle
Overt pathogens of enterobacteriaceae
- salmonella
- SHigella
- YErsina
2 non-motile enterobacteriaceae genera
- Klebsiella
- Shigella
major antigens
H: flagellar protein
K: capsular polysaccaride
O somatic: cell wall LPS
F: fimbrae> adherance
Diarrhoea producing strains of E.coli
EHEC: Enterohaemorrhagic E.coli **most virulent EPEC: ...pathogenic ETEC: ...toxigenic EIEC: ...invasive EAEC: ...aggregative
Features of E.coli
- Magenta pink on MAC
- Bright yellow on CLED
- motile
- indole pos.
- sensitive to everything
- GNB
Features of Klebsiella sp
- 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
What primary test results would you expect for a member of the family enterobacteriaceae?
- *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
features of Enterobacter sp.
- motile
- Indole Neg
- GNB
- Pale pink on MAC
Differentiate Proteus vulgaris, P. mirabilis, P. penneri
- Indole positive: P. vulgaris
2. Maltose positive: P vulgaris & P. penneri
Differentiate Serratia marcescens, S. rubidaea, S. plymuthica
Ominthine decarboxylase (ODC on API) pos: S. marcescens
Difference b/w endo & exotoxins:
- Gram _ bacteria
- Toxicity
- Heat Stability
- Fever producing
- antigenicity (create Aby)
ENDO | EXO GNeg | GPos & GNeg Low | High Stable | Unstable Yes | No Weak | Strong
Describe the key phenotypic features which would allow differentiation between the genera Escherichia, Klebsiella, Enterobacter in a clinical laboratory?
- 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
In what clinical isolate is E.coli most commonly found as a pathogen?
UTI
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?
- LF = Bright rxn on MAC & CLED
- Indole Pos
- Sensitive to everything
- (Motile)
How could you differentiate between the three swarming strains of Proteus? What would the results be?
- Indole test => Pr. vulgaris (Indole Pos), others Neg
2. Maltose => Pr. penneri (Pos), Pr mirabilis (Neg)
If a strain of E.coli was referred to as E.coli O114:H21, what do the letters and numbers signify?
Letters: the antigen
numbers: the location
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.
Hanging drop motlility test = E.coli motile, K.oxytoca non-motile
What is the slime test/string test used for and how is it performed? (uses 3% KOH).
Slime test is used to distinguish GNeg bact. from GPos.
- place 1 drop of 3% KOH on slide
- emulsify a few colonies of test bact in drop
- stir for 60 sec and gently pull away
- 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
In a routine laboratory, how can the production of the enzyme tryptophanase (by an unknown bacteria) be determined? What reagent is used?
- Indole test detects tryptophanase
- Uses kovac’s reagent
How does motility medium work? How long does it take to get a result?
- Semi-soft agar not too runny or firm allow bacteria to swarm
- Medium turns red if there’s growth
- incubated overnight
a) How does the urea test work?
b) What does visible growth in the tube mean with no colour change?
a) If bacteria produces urease -> hydrolyses urea => NH3 = pH rise (basic) = colour change (bright pink)
b) doesn’t produce ureas
distinctive features of Proteus, Providencia and Morganella sp.
- GNB
- Oxidase neg
- non-lactose F
- Motile
- Most Urea Pos
- TDA Pos
distinctive features of Serratia sp
- Red pigment (*S.marcescens, ^S.plymuthica, ^S. rubidea = ^soil bact)
- ODC Pos on API (Ornithine decarboxylase)
distinguish b/w the 2 important Citrobacter sp w/ their distinctive features: C. freundii & C. koseri
- C. freundii: indole v, Lac v,
- C. koseri: Indole Pos, Lac v
