Enterobacteriaceae Flashcards
Which are VP positive?
Klebsiella oxytoca Klebsiella pneumoniae Enterobacter cloacae Enterobacter aerogenes Serratia marcescens Hafnia alvei
Which are PAD positive?
Proteus mirabilis Proteus vulgaris Providencia rettgeri Providencia stuarti Providencia alcalifaciens Morganella morganii
Which are VP negative, PAD negative, and citrate positive?
Most Salmonella
Citrobacter freundii
Citrobacter koseri
Which are VP negative, PAD negative, and citrate negative?
Escherichia coli Shigella ABC Shigella sonnei Salmonella typhi Salmonella paratyphi A Yersinia enterocolitica Yersinia pestis Yersinia pseudotuberculosis Edwardsiella tarda
VP positive, lactose positive
Klebsiella oxytoca
Klebsiella pneumoniae
Enterobacter cloacae
Enterobacter aerogenes
VP positive, lactose negative
Serratia marcescens
Hafnia alvei
Distinguish Serratia marcescens from Hafnia alvei
Citrate, DNAse, sucrose or D-sorbitol fermentation, or gelatin hydrolysis. Positive is Serratia marcescens, negative is Halfnia alvei
L-arabinose, L-rhamnose, or D-xylose fermentation. Positive is Halfnia alvei, negative is Serratia marcescens.
Distinguish Klebsiella from Enterobacter.
Ornithine decarboxylase or motility test. Negative is Klebsiella, positive is Enterobacter.
Distinguish Klebsiella pneumoniae from Klebsiella oxytoca
Indole test. Positive is Klebsiella oxytoca, negative is Klebsiella pneumoniae.
Distinguish Enterobacter cloacae from Enterobacter aerogenes.
Lysine decarboxylase test. Positive means Enterobacter aerogenes, negate Enterobacter cloacae.
VP negative, PAD negative, citrate positive. Distinguish most salmonella species from citrobacter.
Lysine decarboxylase. Positive is Salmonella ( not typhi or paratyphi), negative is Citrobacter.
Distinguish Citrobacter freundii from Citrobacter koseri
H2S test or adonitol fermentation. Positive is Citrobacter freundii, negative is Citrobacter koseri.
Indole test. Positive is Citrobacter koseri, negative is Citrobacter freundii.
PAD positive. distinguish Proteus from Morganella and Providencia
H2S on TSI. Proteus is positive, Morganella and Providencia are negative
Distinguish Proteus mirabilis from Proteus vulgaris
Indole test. Proteus vulgaris is positive, Proteus mirabilis is negative
Distinguish Morganella from Providencia
Citrate test. Morganella is negative, Providencia is positive
Distinguish between Providencia stuartii, Providencia rettgeri, and Providencia alcalifaciens
Best way: Providenicia alcalifaciens is negative in urea hydrolysis and Providencia stuartii cannot ferment aldonitol.
Others:
Providencia alcalifaciens produces most gas when fermenting glucose
Providencia rettgeri can ferment mannitol.
Of the VP negative, PAD negative, Citrate negative species, which are motile?
Salmonella typhi
Salmonella paratyphi A
Escherichia coli
Edwardsiella tarda
Distinguish Salmonella typhi from Salmonella paratyphi
Gassy glucose fermentation. Salmonella paratyphi is positive, Salmonella typhi is negative.
What VP negative, PAD negative, Citrate negative, motile species are gassy glucose positive
Salmonella paratyphi
Escherichia coli
Edwardsiella tarda
What distinguishes Escherichia coli, especially from Edwardsiella tarda?
Lactose fermentation. E coli is positive, Edwardsiella is negative
Distinguish Salmonella paratyphi A from Edwardsiella tarda
Indole test or Lysine decarboxylation. Edwardsiella tarda is positive, Salmonella paratyphi A is negative
Of the VP negative, PAD negative, Citrate negative species, which are non motile?
Shigella and Yersinia
Of Shigella spp and Yersinia spp, which are ornithine decarboxylase positive?
Shigella sonnei and Yersinia enterocolitica
Of Shigella spp and Yersinia spp, which are ornithine decarboxylase negative?
Shigella ABC
Yersinia pseudotuberculosis
Yersinia pestis
Distinguish Shigella sonnei and Yersinia enterocolitica
Sucrose fermentation. Yersinia enterocolitica is positive, Shigella sonei is negative
Distinguish Yersinia pseudotuberculosis, Yersinia pestis, and the ABC serotypes of Shigella
Yersinia pseudotuberculosis is urea hydrolysis positive, and Shigella ABC are Xylose fermentation negative.
What are the three layers of LPS?
O antigen, core and lipid A
What three types of antigen are used for serotyping?
Capsule antigens (eg K) Cell wall antigens( eg O) Flagella antigens (eg H)
What happens to the O antigen when boiled
Nothing, the O antigen is heat stable
What is the most exposed antigen?
If the bacteria have a capsule, the antigens there, called K antigens, are most exposed.
How to expose O antigens?
Boil the sample for 30 minutes or more to degrade the capsule
Are flagella antigens heat stable
no.
When are H antigens monophasic?
When they consist of all the same antigen.
When are flagela antigens diphasic?
When they consist of two different antigens
How are Salmonella species characterized?
By their O and H antigens into more than 46 serotypes
What is the Shigella A serotype called?
Shigella dysenteriae
What is the Shigella B serotype called
Shigella flexneri
What is the Shigella C serotype called?
Shigella boydii
Where is Shigella sonnei most common?
USA
Where is Shigella flexneri most common
outside the USA
What is the capsular antigen for Salmonella also called?
the virulence or “vi” antigen
How is the O157 serotype of E coli identified?
antiserum O157, and no growth on a sorbitol medium. Or use a chromogenic medium.
Why is O157 E coli a concern?
It produces a shiga-like toxin causing hemorrhagic colitis or hemolytic uremia
An enterobacteria grows on sorbitol media. Patient’s symptoms suggest shiga toxins. What can it be?
Shigella A, or an shiga toxin producing E. coli that is not O157.
How to detec shiga toxins in non-o157 strains of E.coli?
immunoassay or genetic test.
Patient presents with diarrhea and fever. Which enterobacteria should be considered?
Salmonella Shigella enteropathic E. coli (O157 or others) Edwardsiella Yersinia enterocolitica
Patient presents with pneumonia. Which enterobacteria should be considered
Klebsiella pneumoniae
Newborn shows signs of meningitis. Which enterobacteria should be considered?
Escherichia coli
Citrobacter
Which enterobacteria causes the plague?
Yersinia pestis
Patient has a UTI. WHat enterobacteria should be considered?
E. coli!
also:
Klebsiella, Proteus miabilis, Enterobacter (all much rarer)
Which enterobacteria are Lactose positive?
E. coli, Klebsiella, Enterobacter
Citrobacter may be positive or negative
Which enterobacteria are H2S positive?
Salmonella, except paratyphii A usually
Citrobacter freundii
Proteus
Edwardsiella
Which enterobacteria are non motile?
Yersinia, Klebsiella, Shigella
Common characteristics of enterobacteria
Gram negative rods Short, fat, bipolar (safetypins) Oxidase negative Glucose fermenting (most produce gas) Nitrate reducing
What does a positive glucose fermentation test look like? What does it mean?
media contains glucose and phenol red indicator. fermentation produces acid, medium turns yellow. need a growth control to prove bacteria are growing
What does a positive oxidase test look like? What does it mean?
Touching the bacteria to a paper containing phenylene diamine turns the paper blue. The bacteria produce cytochrome oxidase.
What does a positive Nitrate to nitrite test look like? What does it mean?
bacteria are suspended in KNO3 broth. add sulfanilic acid and naphthylamine.
If no color change is seen, add zinc.
positive is red before zinc or no color after zinc
negative is no color before zinc or red after zinc.
if no color change, either nitrate remains or it was reduced beyond nitrite to ammonia or nitrogen gas
What does a positive Indole test look like?
touch the bacteria to a paper with tryptophan, add an aldehyde
positive = color change
uzing benzaldehyde, it’s red
using cinnamaldehyde, it’s blue
How are the VP and MR tests related?
start with feeding the bacteria some glucose. then test whether the products were acids (MR) or alcohols (VP)
What does a positive Methyl Red test look like?
when methylred is added to incubated glucose broth, it turns red.
Wha does a positive Voge Proskauer test look like?
When KOH and alpha Napthol are added to incubated glucose broth, it turns red at the top.
what does a positive citrate test look like?
with onl citrate for carbon and ammonium phosphate for nitrogen, the metablites are alkaline. The media’s bromthymol blue indicator turns blue.
What does a positive Phenylalanine decaminase test look like?
the addition of iron chloride to incubated bacteria in a media with phenylalanine turns the top of the media green when positive
What results are possible in triple sugar iron agar?
Stab bacteria into media. Possible results are
yellow slant and butt uses lac or suc
red slant yellow butt can’t use lac or suc
red slant and butt cant use sugar, used peptones instead ( wont happen with enterics)
black obscuring a presumed acid. Means it is h2s positive in addition to sugar use
Gas bubbles or space at bottom means gassy glucose positive
What is a lysine iron agar good for detecting?
Salmonella except paratyphi a
How does a LIA test work?
Lysine Iron Agar starts purple
Stab the loop into the agar. The small amount of glucose is fermented, so the agar turns yellow at first.
If it is lysine decarboxylase positive, the alkaline products with turn it back to purple all over
If it is lysine deaminase positive, the slant will turn red ( only PRoteus and providencia)
If it is unable to use lysine, the butt stats acid and the slant goes purple.
Ornithine or lysine decarboxylation test.
Agar has bromcresol purple and the amino acid. Stab the agar, add oil on top.
Purple is positive, no color is negative
Onpg test
Onpg tests for lactose fermentation. Some bacteria are lactose positive in other media, but others are only onpg positive.
Positive means it turns yellow
Onpg positive enterobacteria
The lactose positive ones: klebsiella, E. coli, Enterobacter and Citrobacter freundii.
The lactose negative ones: Shigella sonnei Citrobacter koseri Hafnia alvei Serratia marcescens Yersinia, particularly enterocolitica
What is a positive urea hydrolyse test?
Urea plus Phenol red indicator, hydrolysis is alkaline, so agar turns pink.
What media are supportive?
Blood
Chocolate
What media are lactose differential?
MacConkey and EMB
What does a strong lactose fermenter look like on MacConkey?
Red or pink
What does a non lactose fermenter look like on MacConkey?
Clear
What does a strong lactose fermenter look like on EMB?
Green or black and metallic
What does a lactose fermenter look like on EMB After 24-48 hours?
Purple
What does a non lactose fermenter look like on EMB?
Clear
What does hektoen enteric agar contain?
Bile salts, lactose, sucrose, indicator, sodium thiosulfate and ferric ammonium chloride
What does hektoen enteric detect?
Lactose or sucrose fermentation. Turns yellow
H2s turns black dots.
How is hek used?
Salmonella and shigella turn the medium blue. Others turn it yellow. If its yellow we mostly don’t care
Salmonella (except paratyphi ) is h2s positive so it will precipitate the iron. Shigella grows green, salmonella black.
What is is SS agar?
Lots of bile salts to inhibit most everything but salmonella and shigella (also Proteus)
Lactose, neutral red indicator, ferric citrate.
How does SS agar differentiate species?
Red media means lactose fermentation. Not shigella or salmonella.
Colorless colonies with black center are salmonella
Colorless colonies with no black center are probably shigella, but may be proteus.
What is in XLD agar?
Low amount if bile salts
Lactose, sucrose, xylose,
Phenol red, h2s substrates
How does XLD agar distinguish species?
If it turns yellow, it can use sugars, so not shigella
Salmonella with turn yellow at first, but them red from lysine, and colonies will have black from. H2S.
CIN agar differentiates what?
Yersinia enterolitica will look like red bullseyes on media incubated at room temp.
What does E. coli O157 look like on chromogenic agars?
On rainbow agar it looks black or grey.
On chrom o157 it looks mauve
What broths are good for enhancing recovery of shigella or salmonella?
GN broth for both, Selenite F broth for just salmonella
