Exam 2 Flashcards
What sugar is fermented by all members of the family Enterobacteriaceae?
glucose
What arrangement of flagella is characteristic of motile members of this family?
peritrichous
What letter represents the cell wall (somatic) antigen?
O
What antigen letter is always present?
O
What letter represents the flagellar antigen?
H
What letters represent the capsular antigen?
K or Vi
What antigen will mask the cell wall (somatic) antigen in the serological typing of Salmonella?
The capsular antigen, K or Vi, will mask the cell wall (somatic) antigen, O
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 with black center
What media can produce a positive result with just growth on the medium, not requiring color change?
citrate, KCN, malonate
What is the end product in the test for the enzyme phenylalanine deaminase?
phenylpyruvic acid
Which test utilizes Kovac’s reagent to test for the enzyme tryptophanase?
indole
What are the color changes observed in a positive decarboxylase test?
purple to yellow to purple
pH indicator is used to detect what type of reaction by enteric organisms?
acid production from a carbohydrate
What does A/A mean on TSI?
glucose fermentation in the butt and lactose and/or sucrose in the slant
What does K/A mean on TSI?
ferments glucose in the butt only
What does K/K mean on TSI?
nonfermentor
What is the principle of the nitrate test?
reduction of nitrates leads to the formation of nitrites and may progress to liberation of nitrogen gas
What does the development of a pink color after the addition of zinc dust indicate?
does not reduce nitrates
What biochemical test is especially useful for the detection of a late lactose fermenting organism?
ONPG
What endpoint is produced in a positive urease test that produces the alkaline reaction of the indicator?
ammonia is liberated raising the pH causing the phenol red indicator to turn the medium fuchsia
What sugar is fermented by all coliforms that is not fermented by most enteric pathogens?
lactose
What organisms is indole positive, citrate negative, and dry pink on MacConkey?
E. coli
What organisms is the most common cause of an UTI?
E. coli
What is the principle of the VP test?
some bacteria have the ability to produce acetylmethyl carbinol (acetoin) from glucose
What is the best single test to use to differentiate Enterobacter and Klebsiella?
motility, Klebsiella is nonmotile
How can certain strains of Hafnia alvei be differentiated from Enterobacter aerogenes?
sugar fermenations
What single test is best to use to differentiate Klebsiella oxytoca from Klebsiella pneumoniae?
indole, pneumoniae is negative
What is the causative agent of bronchial pneumonia?
Klebsiella pneumoniae
What is Klebsiella pneumoniae’s typical colonial morphology?
large, mucoid, pink, stringy colonies on Mac
Other than motility, what test can be used to differentiate Klebsiella from Enterobacter?
Urea
Which test is useful in distinguishing Citrobacter and Proteus from Salmonella?
Lysine decarboxylase
How can Citrobacter freundii be differentiated from Citrobacter diversus?
Indole (diversus is positive) and H2S (diversus is negative)
Which species is chromogenic, resistant to antibiotics, associated with UTI, nosocomial infections, and wound infections?
Serratia marcesens
Which genus is characterized by “swarming” motility that is best observed on chocolate and sheep blood agar?
Proteus
How can Proteus mirabilis and Proteus vulgaris be differentiated?
Indole (vulgaris is positive) and ornithine (vulgaris is negative)
How do members of the genera Proteus and Providencia appear on LIA?
red slant
Which three genera among the Enterobacteriaceae are phenylalanine positive?
Morganella, Providencia, and Proteus
How can Morganella morganii be differentiated from Proteus species?
Morganella margin does not produce H2S or swarm
What are the distinguishing characteristics of Yersinea pestis?
It is coccobacillary, encapsulated, and shows bipolar staining
What species of Enterobacteriaceae is non-motile at 37C but motile at 25C?
Yersinia enterocolitica
Which genera give the following reactions on TSI: K/A and H2S positive?
Salmonella (significant pathogen), Edwarsiella , and Proteus
What is the Kauffman-White schema?
Describes the almost 2,000 serotypes of the genera Salmonellae
What are the typical biochemical reactions of Salmonella typhi?
TSI: K/A H2S (weakly positive)
What are the reactions of Shigella on TSI?
K/A no gas and no H2S
Which species of Salmonella is most frequently recovered from the septicemic type of Salmonella infection?
Salmonella cholerae-suis
What organisms will be missed if a stool sample is left to sit too long?
Shigella
Which serological group of Shigella is most frequently isolated in the US?
Group D Shigella sonnei
Which of the rapid ID methods for the Enterobacteriaceae has the advantage of being the easiest to set up and produces reliable results in 4 hours?
Micro-ID
What age group shows the most cases of gastroenteritis due E. coli?
Infants and toddlers, children under 10
What food is a frequent source of contamination with Salmonella?
chicken
Which body fluid should be tested in cases of carriers of Salmonella typhi?
Bile
Why do severe cases of Shigella dysenteriae produce mental confusion?
it produces a neurotoxin
What is the vector for the transmission of plague?
rat flea
What type of plague is the most contagious?
Pneumonic plague
What test is used in the lab to differentiate E. coli 0157:H7 from normal strains of E. coli?
Selective Mac agar containing 1% D-sorbitol instead of lactose, which should grow clear
In the classification of the Enterobacteriaceae, what is a tribe?
Group of biochemically similar genera
What are the IMViC tests?
Indole Motility VP Citrate
What would the results of IMViC for E. coli
+ + = =
What is the ‘nickname’ for Klebsiella pneumoniae?
Friedlander’s Bacillus
What non-pathogenic organism is so similar to Shigella biochemically that it is included in the serological typing of Shigella isolates?
Alkalescens dispar
What is true food poisoning?
Staphylococcus produces true food poisoning due to an exotoxin in 1-4 hours
What is a food infection?
Salmonella produces; have to ingest large amounts of viable organisms and takes longer
