Lab Diagnosis of Bacteria causing gastroenteritis/diarrhea

Staphylococcus aureus• Gram positive cocci in

grape like clusters taken from blood

• Golden yellow colonies in blood agar

Clostridium perfringens

-Nagler’s test on medium containing egg yolk-Opacity around the line of growth ( positive)

-Double zone hemolysisBeta-lysis and Alpha lysis

-Gram positive , spore forming rods

Campylobacter jejuni

• Gram negative bacilli taken from stool specimens

• Skirrow’s medium with antibiotics, reduced oxygen at 42 degree celcius .

Vibrio cholerae

• Gram negative, comma shaped bacilli

• Yellow colony (sucrose fermenting) on TCBS (thiosulphate-citrate-bile-sucrose) agar

Escherichia coli

• Gram negative rods

• Coliform(lactose fermenters)

• Pink colony on MacConkey agar

Bacillus cereus

• Gram positive rods with central and oval spores

• Schaeffer-Fulton stain showing green mature spores

Salmonella enterica

• Gram negative rods

• Salmonella-Shigella agar showing pale colonies with black center

• Salmonella enterica on XLD agar( xylose-lysine-deoxycolate)

• Black colony, agar turned blue on Hektoen agar.