Biochemical Tests for Identification
of Enterobacteriaceaecontinued
Clinical Microbiology Review 179
TEST PRINCIPLE INTERPRETATION OTHER
Methyl red (MR)
Voges-Proskauer (VP)
Citrate
Urease
Phenylalanine
deaminase (PD)
Little acid produced by this pathway.
Organisms that are VP pos are usually
methyl red neg & vice versa.False neg if cap not loose. Klebsiella&
Enterobacterare pos.Proteus& Morganellaare rapid urease
producers.Proteus, Providencia, Morganellaare pos.Acid products formed when glucose
is metabolized by mixed acid
fermentation pathway. Color
change in pH indicator.Acetoin is produced from alternate
pathway for glucose metabolism.If organism can use citrate as sole
source of carbon, pH ↑, pH indica-
tor changes color.Urease breaks down urea. Ammonia
released, pH ↑, pH indicator
changes color.Phenylalanine deaminase
deaminates phenylalanine to
phenylpyruvic acid, which reacts
with ferric chloride to produce
green color.Pos = red color after addition
of methyl red (pH indicator)Pos = red color when alpha-
naphthol & KOH addedPos = green to blue, or growthPos = yellow to pinkPos = green color after
addition of ferric chloridecontinued...