MICRO Enterics Flashcards
Common genera of Enterobacteriaceae that are pathogenic
- Klebsiella
- Shigella
- Salmonella
- Escherichia
- Proteus
- Citrobacter
- Serratia
- Yersinia
- Enterobacter
- Providencia
- Morganella
Normal flora in the gastrointestinal tract
- Enterobacteriaceae
- CNS
- Anaerobes
- Diphtheroids
- Enterococcus sp.
- Candida sp.
Obligate pathogens in the GI
- Salmonella enterica
- STEC; E.coli O157:H7
- Yersinia enterocolitica
- Shigella sp.
- Campylobacter jejuni
- Vibrio cholerae
Which pathogens are implicated in food poisoning/ food toxemias (5)?
- S. aureus
- B. cereus
- Clostridioides difficile
- C. perfringens
- C. botulinum
Which bacteria is associated with gastric, peptic and duodenal ulcers ?
Helicobacter pylori
Salmonella on MAC and HEK
MAC: wh
HEK: translucent blue-green +/- black center
Shigella on MAC and HEK
MAC: wh
HEK: translucent green
Yersinia on MAC and HEK
MAC: wh
HEK: pink/yellow
Yersinia on CIN
Cefsulodin Irgasan Novobiocin:
- “bulls-eye;” translucent with red center
E. coli O157:H7 on SORB/SMac and CHROMagar Stec
colorless
Campylobacter on CBF
Campylobacter Blood Free:
- gy, moist, fltspr, or raised
Describe Principle of Tube Indole
- 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
What is the general rule for order of inoculation of media plates and biochemicals ?
- liquid to solid
- least selective to most selective
What is the purpose for CNA ?
Colistin Naladixic Acid:
- selects for gram POS bacteria
- inhibits gram neg, normal flora
- enhances beta hemolysis
What is the purpose of PEA when incubated anaerobically ?
- isolates strict anaerobes
- facultative gram neg anaerobes (ie. Enterobacteriaceae) DO NOT GROW
- gram pos will grow (S. aureus)
Which planting media is used for a spot indole ?
BAP or CHOC; tryptophan is present
Describe Principle of Spot Indole
- 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
List 2 conditions that must be met for decarboxylation to occur. Why is a control tube needed ?
- Acidic (due to decarboxylation of amino acids)
-
Anaerobic (mineral oil)
- control tube ensures that color change = decarboxylation
Describe CHROMagar STEC media. Why do Shiga-Toxin-producing organisms need to be identified ?
CHROMagar STEC:
- selective and differential
- qualitative, direct differentiation of Shiga-like toxin producing E. coli
- toxic shock syndrome is fatal
3 sugars (%) in TSI
Sucrose (1.0%) - slant
Lactose (1.0%) - slant
Glucose (0.1%) - butt
Which organism is a sick A/A on TSI ?
Yersinia enterocolitica
Tube indole reagent
(Kovac’s) Dimethyl benzaldehyde
What is Cary-Blair media for ?
- transport of rectal and fecal specimens
- preserves enteric pathogens
T or F: toxins of C. perfringen causes fever and vomiting
FALSE; C. perfringen DOES NOT cause fever and vomiting
Oxidase Prinicple
- oxidation of colourless TMPD = dark PURPLE indophenol
- result depends on the presence of cytochrome C (bacteria whose ETC has cytochrome c oxidase)
This media may inhibit oxidase activity and thus should not be used when doing an oxidase test
MAC
A differential medium, used as a screen test for enteric pathogens on the basis of carbohydrate fermentation, HS production, and gas production
Triple Sugar Iron (TSI)
Triple Sugar Iron (TSI)
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)
Citrate utilization
- 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)
Medium method for motility is not useful for these organisms
STRICT AEROBES like Pseudomonas will not grow in the depth of medium (use microscopic examination)
