Enterobacteriaceae & Related Clinical Microbiology – Biochemical Identification

Vocabulary flashcards covering biochemical test interpretations, key Enterobacteriaceae profiles, stool culture patterns, and classic streptococcal identifiers.

TSIA K/K

Red slant/red butt; no carbohydrate fermentation (non-fermenter).

TSIA K/A

Red slant/yellow butt; glucose fermentation only.

TSIA A/A

Yellow slant/yellow butt; lactose and/or sucrose (or all three sugars) fermented.

LIA K/K

Purple slant/purple butt; lysine decarboxylation positive.

LIA K/A

Purple slant/yellow butt; lysine decarboxylation negative.

LIA A/A

Yellow slant/yellow butt; lysine deamination positive.

LIA R/A

Red wine slant/yellow butt; lysine deamination positive (classically Proteus).

Citrate Positive

Medium turns Prussian blue; organism utilizes citrate as sole carbon source.

Citrate Negative

Medium remains green; citrate not utilized.

Urea Positive

Medium turns bright pink; urease enzyme present.

Urea Negative

Medium remains yellow or peach; no urease activity.

Motility Positive

Growth appears hazy or murky throughout medium; organism is motile.

Motility Negative

Growth confined to stab line; organism is non-motile.

Indole Positive

Kovac’s reagent produces pink layer; organism splits tryptophan to indole.

Indole Negative

No color change after Kovac’s; indole not produced.

Methyl Red (MR) Positive

Broth turns cherry red; stable mixed-acid fermentation present.

Methyl Red (MR) Negative

Broth remains yellow; mixed-acid fermentation absent.

Voges-Proskauer (VP) Positive

Rose-pink color in surface layer; acetoin produced via butylene glycol pathway.

Voges-Proskauer (VP) Negative

No pink color; acetoin not produced.

LYS/ARG/ORN Decarboxylase Positive

Tube turns pink; specific amino-acid decarboxylation present.

LYS/ARG/ORN Decarboxylase Negative

Tube remains yellow; decarboxylation absent.

Malonate Positive

Medium turns blue; organism can utilize malonate.

Malonate Negative

Medium remains green; malonate not utilized.

Adonitol / Inositol / Sorbitol Positive

Bright pink color; specific sugar fermented.

Adonitol / Inositol / Sorbitol Negative

Medium remains clear; sugar not fermented.

Escherichia coli (biochemical profile)

Indole +, MR +, VP –, Citrate –, motile; classic lactose fermenter.

Klebsiella pneumoniae (biochemical profile)

Indole –, MR –, VP +, Citrate +; non-motile encapsulated rod.

Klebsiella oxytoca (biochemical profile)

Indole +, MR +, VP +, Citrate +; non-motile Klebsiella species.

Serratia marcescens

DNase + opportunist often producing red pigment; motile.

Proteus mirabilis (key features)

Indole –, Ornithine +, Urea super +, strong swarming motility on agar.

Proteus vulgaris (key features)

Indole +, Ornithine –, Urea super +, swarms but less than P. mirabilis.

Citrobacter freundii

Lys/Arg/Orn all –, TSIA A/A + H₂S, motile; opportunistic pathogen.

Enterobacter cloacae

Citrate +, VP +, Malonate +, motile; common nosocomial isolate.

Salmonella typhi (biochemical profile)

TSIA K/A + H₂S, Citrate +, MR +, motile; agent of typhoid fever.

Shigella sonnei (biochemical profile)

TSIA K/A, MR +, Ornithine +, non-motile; most common U.S. Shigella.

Stool culture pattern: Salmonella

TSIA K/A + H₂S, LIA K/K + H₂S, Urea −; suspect pathogen.

Stool culture pattern: Shigella

TSIA K/A, LIA K/A, Urea −; suspect pathogen.

Stool culture pattern: Yersinia enterocolitica

TSIA A/A, LIA K/A (or A/A), Urea +, Citrate −; cold-tolerant enteropathogen.

Streptococcus pneumoniae (ID features)

Gram-positive diplococci, alpha hemolysis, catalase –, bile-soluble (deoxy +), optochin sensitive.

Streptococcus pyogenes (ID features)

Gram-positive cocci, beta hemolysis, catalase –, PYR +, bacitracin sensitive (group A strep).