Enteric Key Biochemical Reaction Review Biochemical reactions ...

Enteric Key Biochemical Reaction Review
Biochemical reactions when Motility is not available (multi‐test systems)
The purpose of this document is to focus your studying on the organisms that you are to identify by
phenotypic and biochemical reactions. The identification schemes in this document do not contain the
complete list of common biochemical reactions for these organisms; these are abbreviated ways to narrow
down your choices and chose the most probable organism. Please reference your Enterobacteriaceae lecture
notes for a complete listing of biochemical reactions.
Enterobacteriaceae (Gram negative rods)
How is this defined? What is true about these organisms?
Gram‐negative rod
Growth on MacConkey
Oxidase Negative (in most cases)
Glucose fermenter
Nitrate positive
Lactose‐Fermenting, Gram‐Negative Rods (Pink growth on MacConkey Agar)
KIA reaction: A/A or yellow/yellow with or without H2S
Common choices:
Escherichia coli, Klebsiella species, Enterobacter species, Citrobacter freundii
What is the first reaction to look at when identifying a Lactose Fermenting GNR (Pink on the MAC)?
Citrate/VP negative
Citrate negative/VP negative: Escherichia coli or Citrobacter freundii
Next reaction: Indole
Indole positive: Escherichia coli
Indole negative: Citrobacter freundii
Usually H2S positive
Citrate positive: Klebsiella species, Enterobacter species or Citrobacter freundii
Next reaction (if motility result is not available): ODC (ornithine decarboxylase)
ODC positive : Enterobacter species or Citrobacter freundii
Next reaction: LDC
LDC negative:
Enterobacter cloacae: VP positive
Citrobacter freundii : VP negative
LDC positive:
Enterobacter aerogenes
ODC negative: Klebsiella species or Citrobacter freundii
Next reaction: LDC
LDC positive:
Klebsiella pneumoniae: Indole negative (non‐motile)
Klebsiella oxytoca: Indole positive (non‐motile)
LDC negative:
Citrobacter freundii (usually H2S positive)
Non‐lactose fermenting, Gram‐Negative Rods (Clear growth on the MacConkey Agar)
KIA reaction: K/A or red/yellow with or without H2S
Most common choices:
Proteus species, Morganella morganii, Providencia species, Salmonella species, Shigella species,
Serratia species, Citrobacter species

What is the first reaction to look at when identifying a Non‐Lactose Fermenting GNR?
LDA/TDA reaction (deaminates lysine or amino acid tryptophan)
LDA/TDA positive
Proteus mirabilis
Proteus vulgaris
Morganella morganii
Providencia species
Next reaction: H2S
H2S positive
Proteus mirabilis: Strongly urease positive, indole negative, ODC positive
Proteus vulgaris: Strongly urease positive, indole positive, ODC negative
H2S negative
Morganella morganii: urease positive, indole positive, ODC positive
Providencia species
LDA/TDA negative
Salmonella species
Shigella species
Shigella sonnei
Serratia species
Citrobacter freundii
Citrobacter koseri
Next reaction: H2S
H2S positive
Salmonella species: LDC positive (ONPG negative)
Citrobacter freundii: LDC negative (ONPG positive)
H2S negative
Shigella species
Shigella sonnei
Serratia species
Citrobacter species
Next reaction: ODC
ODC negative
Shigella species: ONPG and LDC negative (non‐motile)
Citrobacter freundii: ONPG positive and LDC negative
ODC positive
Shigella sonnei: ONPG positive, LDC negative (non‐motile)
Serratia species: ONPG positive, LDC positive
Citrobacter freundii: ONPG positive, LDC negative, indole negative