LECT | entero biochemical tests Flashcards
- has crystal violet to inhibit Gram negative along with bile salt
- Carbohydrate : lactose
MacConkey
f lactose is fermented by the bacteria in the McConkey, the indicator neutral red will turn
red or pink.
Use for detection of enteric pathogens from fecal specimen or selective enrichment broth
Hektoen Enteric Media
Enhances the recovery of enteric pathogens from fecal specimen
Gram Negative Broth
Contains bile salts as its gram positive bacteriostatic agent; selective for Salmonella species & some strains of Shigella specially from stool specimen
Salmonella shigella
Selective media use to isolate Salmonella and Shigella species from stool and other species containing mix flora
Xylose-lysine deoxycholate
More or less use for differentiation of Vibrio instead of Enterobacteriaceae; Vibrio species are differentiated whether they ferment sucrose and not lactose
TSBS (Thiosulfate citrate bile salts sucrose)
Principle: Cytochrome oxidase participates in electron transport and in nitrate metabolism
Reagent: 1% tetramethyl-p-phenylenediamine dihydrochloride
Positive: dark blue
Caution: Do not use iron containing wire, do
not interpret results after 10 seconds
Enterobacteriaceae = Oxidase negative
OXIDASE TEST
Also called Kovac’s method
OXIDASE TEST
PRINCIPLE: The organisms produce nitrate reductase, which converts the nitrate (NO3) to nitrite (NO2).
Nitrite + SULFANILIC ACID = diazonium salt diazonium salt + alphanaphthylamine = red, water-soluble azo dye (+)
NITRATE REDUCTION
NITRATE REDUCTION
No color change + zinc = red
result is?
NEGATIVE RESULT
NITRATE REDUCTION
No color change + zinc = no color change
result is?
POSITIVE RESULT
Determine whether a gram negative rod utilizes glucose, and lactose or sucrose fermentatively and forms hydrogen sulfide
TRIPLE SUGAR IRON AGAR TEST
TRIPLE SUGAR IRON AGAR TEST
- indicator of Hydrogen sulfide
Ferric ammonium citrate
TRIPLE SUGAR IRON AGAR TEST
-Incubation period
18-24 hours
Reaction in TSI should not be red more than 24 hours of incubation, because?
aerobic oxidation of the fermentation products from lactose and/or sucrose proceeds, and the slant eventually reverts to the alkaline state.
production of H2 S (sodium thiosulfate reduced to H2 S) requires what type of an environment
acidic environment
Principle: tryptophanase
Reagent:
1% paradimethyaminocinnamaldehyde
Positivebluewithin20seconds
Caution: Inoculum should not be selected
from MacConkey agar
INDOLE
used to determine the presence of the enzyme tryptophanase and is a rapid method that can be used in lieu of the tube test
Spot Indole Test
. Bacteria with tryptophanase are capable of hydrolyzing tryptophan to
pyruvate, ammonia, and indole
- same chemicals as the Kovac preparation, + absolute ethyl alcohol
- more sensitive for detecting small amounts of indole.
- also be used to differentiate organisms under anaerobic conditions.
- Positive: Pink- to wine-colored sing after addition of appropriate reagent
Ehrlich’s reagent
