Enterobacteriaceae

Question 1

Define fermentation

Answer 1

use glucose under anaerobic cond.

Question 2

Fermentative vs oxidatiive

Answer 2

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

Question 3

Overt pathogens of enterobacteriaceae

Answer 3

• salmonella
• SHigella
• YErsina

Question 4

2 non-motile enterobacteriaceae genera

Answer 4

• Klebsiella

- Shigella

Question 5

major antigens

Answer 5

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

Question 6

Diarrhoea producing strains of E.coli

Answer 6

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

Question 7

Features of E.coli

Answer 7

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

Question 8

Features of Klebsiella sp

Answer 8

• 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

Question 9

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

Answer 9

• *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

Question 10

features of Enterobacter sp.

Answer 10

• motile
• Indole Neg
• GNB
• Pale pink on MAC

Question 11

Differentiate Proteus vulgaris, P. mirabilis, P. penneri

Answer 11

1. Indole positive: P. vulgaris

2. Maltose positive: P vulgaris & P. penneri

Question 12

Differentiate Serratia marcescens, S. rubidaea, S. plymuthica

Answer 12

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

Question 13

Difference b/w endo & exotoxins:

• Gram _ bacteria
• Toxicity
• Heat Stability
• Fever producing
• antigenicity (create Aby)

Answer 13

ENDO |  EXO
GNeg  |  GPos & GNeg
Low     |  High
Stable |  Unstable
Yes      |  No
Weak  |  Strong

Question 14

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

Answer 14

• 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

Question 15

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

Answer 15

UTI

Question 16

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?

Answer 16

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

Question 17

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

Answer 17

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

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

Question 18

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

Answer 18

Letters: the antigen
numbers: the location

Question 19

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.

Answer 19

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

Question 20

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

Answer 20

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

Question 21

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

Answer 21

• Indole test detects tryptophanase

- Uses kovac’s reagent

Question 22

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

Answer 22

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

Question 23

a) How does the urea test work?

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

Answer 23

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

Question 24

distinctive features of Proteus, Providencia and Morganella sp.

Answer 24

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

Question 25

distinctive features of Serratia sp

Answer 25

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

Question 26

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

Answer 26

- C. freundii: indole v, Lac v, | - C. koseri: Indole Pos, Lac v