Microbiology Lab Tests Summary

Microbiology Lab Tests Summary USTMED ’07 Sec C AsM ([email protected] [email protected]) TEST

HOW

TSI

MEDIUM

Fermentation of sugar

LIA

Decarboxylation of amino acid

PRESENT

TSIA (3 sugars, Fe, agar)

LIA (lysine, Fe, agar)

Glucose, lactose, sucrose

Lysine (ornithine, arginine)

PH INDICATOR

OBSERVE

Phenol red

Sugar fermentation

Bromcresol purple

H2S production Gas production Deamination (slant)

RESULTS

Lys decarboxylation (butt) MIO

Citrate utilization test Urease test

Diffuse growth, indole production, decarboxylation of amino acid

MIO media

Ornithine, indole (if tryptophanase is present

Bromcresol purple, kovac’s reagent (HCl, dimethyl aminobenzaldehyde)

Use citrate as an inorganic carbon source

Simmon’s citrate agar (SCA)

Sodium citrate

Bromthymol blue

Hydrolyze urea

(Stuart) urea broth or Christensen’s agar

urea

Phenol red

motility Indole production Ornithine decarboxylation (butt) citrate→ammonia, change in color of medium (sign of citrate utilization) Production of NH4 and CO2 (H2O)

Alkaline butt/slant – red (-) Acid butt/slant – yellow (+) Black butt Crack, bubbles, displacement Alkaline - purple Acid/red - red Alkaline – purple (+) Acid – yellow (-) Diffuse growth vs. growth along stabline (+) red ring w/ Kovac’s Alkaline – purple (+) Acid – yellow (-) Blue slant – (+) Green slant – (-) Fuschia pink (+) Salmon pink (-)

NOTES

Due to a.a. decarboxylation

Streak slant Stab butt Portal of entry is also portal of exit; stab up to the bottom Don’t shake (semisolid) Read motility and decarboxylation before Kovac’s Bacteria are called autotrophs Soil bacteria don’t have this ability Media becomes alkaline

Agar TYPE

PURPOSE

CONTENTS

INDICATOR

MacConkey Agar

g (-), LFO

Bile salts & lactose

Neutral red, crystal violet

Salmonella Shigella agar

Inhibits normal flora coliforms, differentiation of stool pathogens

Bile salts, brilliant green agar, lactose, ferric ammonium citrate

Neutral red, sodium thiosulfate

Xylose, Lysine, Deoxycholate (XLD) Agar

Inhibits gram (+), selective for E.coli (?), inhibits proteus swarming

Xylose, lysine, ferric ammonium citrate

Hektoen Enteric Agar

Inhibits normal flora of lower GI tract

Bile salts, lactose, sucrose, starch & salicin, ferric ammonium citrate

Eosin Methylene Blue Agar (EMB)

G(-), LFO

Phenol red, sodium thiosulfate

OBSERVE

Acid – pink colonies(+) LFO Alkaline – colorless colonies (-) NLFO

H2S production

FeS (+) black centered color Normal flora – pink (salmonellashigella) Pathogens - colorless Acid- yellow (+) Alkaline – red (-) Lysine Decarboxylase Black centered colonies

fermentation Lysine decarboxylase H2S production

Lactose, Eosin & Methylene blue

Bromthymol blue, sodium thiosulfate

Eosin & methylene blue

REACTION

Fermentation (produces acid) bile salts precipitation fermentation

Acid – pink/red colonies(+) LFO Alkaline – colorless colonies (-) NLFO

fermentation

Green (-) NLFO alkaline Orange/yellow (+) LFO acid

H2S production

Black centered colonies

fermentation

Purple – LFO Green metallic sheen – E.coli (Rapid) Colorless colonies - NLFO

NOTES

Brown pH 6.8-8.0 Red pH < 6.8 Bile salts also inhibits g(+) Bile salts Inhibits gram (+) bacteria; brilliant green inhibits gram (-) coliform; ferric ammonium citrate + sodium thiosulfate produces H2S Fermentation is the first reaction Red colonies Enterobacteriaceae are xylose (+) except shigella pH > 7.6 blue pH ranges 6.0-7.6 green pH < 6.0 yellow Enterobacteriaceae are xylose (+) except shigella Purple color is precipitated eosin & methylene blue absorbed when lactose fermented