exam 2 Flashcards
what sugar is fermented by ALL of the family enterobacteriaceae?
glucose
what arrangement of flagella is characteristic of motile members of this family?
peritrichous
what letter is used to represent the cell wall (somatic) antigen?
O
The flagellar antigen?
H
The capsular antigen?
K or Vi
which of the above antigens may mask the cell wall antigen in the serological typing of salmonella?
K or Vi
how would an organism that ferments lactose and produces H2S appear on XLD?
yellow with black center
how would an organism that ferments lactose and produces H2S appear on HE?
orange colonies with black center
name several media in which a positive result can be growth in the medium even if there is no accompanying color change?
citrate
KCM
malenate
what is the end product in the test for the enzyme phenylalanine deaminase?
phenyl pyruivc acid phenylalanine deaminase (enzyme)
which test utilizes Kovac’s reagent to test for the enzyme tryptophanase?
indol
what are the color changes observed in a positive decarboxylase test, starting with the initial uninoculated color?
starts purple because all ferment glucose so they turn yellow but if glucose runs out they utilize amino acids it turns back to purple
positive test - purple - yellow - purple
negative test - purple to yellow
a pH indicator is generally used to detect what type of reaction by enteric organisms?
carbohydrate fermentation that produces acid
interpret the following reactions observed on TSI : A/A K/A AND K/K
A/A: lactose &or sucrose fermenters / glucose fermenter
K/A: nonlactose &or nonsucrose fermenter/ glucose fermenter
K/K : nonfermenter
*if it cannot ferment lactose or sucrose it will utilize peptones to change the top the different colors
what is the principle of the nitrate test?
the reduction of nitrates (NO3) to nitrites (NO2) and may progress to liberation of NO2
test 1 examines for nitrites
if none test 2 is performed looking for residual nitrates
then if still none you add zinc dust
stays clear +
what does the development of a pink color only after the addition of Zn dust indicate?
negative test result
what biochemical test is especially useful for the detection of a late lactose fermenting organism?
ONPG
what endpoint is produced in a positive urea test that produces the alkaline retain of the indicator?
ammonia
what sugar is fermented by the coliforms (normal intestinal flora like E. Coli or Enterobacter) that is NOT fermented by most enteric pathogens (like salmonella and shigella)
lactose
what organism is indole positive, citrate negative, dry pink on MacConkey, and produces a green, metallic sheen on EMB?
E. Coli
what organism is most common cause of a UTI
E. Coli
what is the principle of the VP test?
inoculate .2 ml MR-VP broth with no more than one colony incubate for 4-6 hours add 3 drops alpha-naphthol then 2 drops KOH then wait five minutes for color change
what is the best single test to use to differentiate enterobacter and klebsiella?
motility
how can certain strains of Hafnia alvei be differentiated from enterobacter aerogenes?
sugar fermentation
