MICRO Enterics

Question 1

Common genera of Enterobacteriaceae that are pathogenic

Answer 1

• Klebsiella
• Shigella
• Salmonella
• Escherichia
• Proteus
• Citrobacter
• Serratia
• Yersinia
• Enterobacter
• Providencia
• Morganella

Question 2

Normal flora in the gastrointestinal tract

Answer 2

• Enterobacteriaceae
• CNS
• Anaerobes
• Diphtheroids
• Enterococcus sp.
• Candida sp.

Question 3

Obligate pathogens in the GI

Answer 3

• Salmonella enterica
• STEC; E.coli O157:H7
• Yersinia enterocolitica
• Shigella sp.
• Campylobacter jejuni
• Vibrio cholerae

Question 4

Which pathogens are implicated in food poisoning/ food toxemias (5)?

Answer 4

• S. aureus
• B. cereus
• Clostridioides difficile
• C. perfringens
• C. botulinum

Question 5

Which bacteria is associated with gastric, peptic and duodenal ulcers ?

Answer 5

Helicobacter pylori

Question 6

Salmonella on MAC and HEK

Answer 6

MAC: wh
HEK: translucent blue-green +/- black center

Question 7

Shigella on MAC and HEK

Answer 7

MAC: wh
HEK: translucent green

Question 8

Yersinia on MAC and HEK

Answer 8

MAC: wh
HEK: pink/yellow

Question 9

Yersinia on CIN

Answer 9

Cefsulodin Irgasan Novobiocin:
- “bulls-eye;” translucent with red center

Question 10

E. coli O157:H7 on SORB/SMac and CHROMagar Stec

Answer 10

colorless

Question 11

Campylobacter on CBF

Answer 11

Campylobacter Blood Free:
- gy, moist, fltspr, or raised

Question 12

Describe Principle of Tube Indole

Answer 12

• bacteria capable of hydrolyzing tryptophan (in peptone water) to form indole ?
• detected by colour rxn with dimethylamino benzaldehyde (Kovac’s)
• tube test could also check for motility before adding Kovac’s by performing a wet mount
• differentiates lactose fermenters:
  a). E. coli = POS
  b). Klebsiella oxytoca (POS) vs K. pneumoniae (NEG)

red = POS

Question 13

What is the general rule for order of inoculation of media plates and biochemicals ?

Answer 13

• liquid to solid
• least selective to most selective

Question 14

What is the purpose for CNA ?

Answer 14

Colistin Naladixic Acid:
- selects for gram POS bacteria
- inhibits gram neg, normal flora
- enhances beta hemolysis

Question 15

What is the purpose of PEA when incubated anaerobically ?

Answer 15

• isolates strict anaerobes
• facultative gram neg anaerobes (ie. Enterobacteriaceae) DO NOT GROW
• gram pos will grow (S. aureus)

Question 16

Which planting media is used for a spot indole ?

Answer 16

BAP or CHOC; tryptophan is present

Question 17

Describe Principle of Spot Indole

Answer 17

• more sensitive than tube indole
• can’t check for motility first
• useful for organisms that won’t grow in peptone water (anaerobes)
• colony transferred to filter paper; saturated w/ spot indole reagent (p-dimethylaminocinnanaldehyde);
• blue/green = POS
• pink = neg

Question 18

List 2 conditions that must be met for decarboxylation to occur. Why is a control tube needed ?

Answer 18

1. Acidic (due to decarboxylation of amino acids)
2. Anaerobic (mineral oil)
   - control tube ensures that color change = decarboxylation

Question 19

Describe CHROMagar STEC media. Why do Shiga-Toxin-producing organisms need to be identified ?

Answer 19

CHROMagar STEC:
- selective and differential
- qualitative, direct differentiation of Shiga-like toxin producing E. coli
- toxic shock syndrome is fatal

Question 20

3 sugars (%) in TSI

Answer 20

Sucrose (1.0%) - slant
Lactose (1.0%) - slant

Glucose (0.1%) - butt

Question 21

Which organism is a sick A/A on TSI ?

Answer 21

Yersinia enterocolitica

Question 22

Tube indole reagent

Answer 22

(Kovac’s) Dimethyl benzaldehyde

Question 23

What is Cary-Blair media for ?

Answer 23

• transport of rectal and fecal specimens
• preserves enteric pathogens

Question 24

T or F: toxins of C. perfringen causes fever and vomiting

Answer 24

FALSE; C. perfringen DOES NOT cause fever and vomiting

Question 25

Oxidase Prinicple

Answer 25

- oxidation of colourless TMPD = dark PURPLE indophenol - result depends on the presence of cytochrome C (bacteria whose ETC has cytochrome c oxidase)

Question 26

This media may inhibit oxidase activity and thus should not be used when doing an oxidase test

Answer 26

MAC

Question 27

A differential medium, used as a screen test for enteric pathogens on the basis of carbohydrate fermentation, HS production, and gas production

Answer 27

Triple Sugar Iron (TSI)

Question 28

Triple Sugar Iron (TSI)

Answer 28

A differential medium, used as a screen test for enteric pathogens on the basis of carbohydrate fermentation, HS production, and gas production Sucrose/ lactose = slant Glucose = butt Fermentation = yellow (A) No fermentation = red (K)

Question 29

Citrate utilization

Answer 29

- organism uses citrate as their sole source of carbon - pos = growth (blue due to alkaline end products produced) - useful for differentiation of lactose fermenters (Kleb and Enterobacter utilize citrate but E. coli does not)

Question 30

Medium method for motility is not useful for these organisms

Answer 30

STRICT AEROBES like Pseudomonas will not grow in the depth of medium (use microscopic examination)