microbio lab- week 3

MSA (mannitol salt agar) plate

selective for salt tolerant organisms, colonies will grow if

differential for mannitol fermentation, indicated by pH- phenol red

since fermentation results in organic acids, pH will be lowered- acidic, turns yellow when it is positive

EMB plate (eosin methylene blue)

selective for gram negative bacteria

TSA plate

control, not selective or differential for anything, all colonies should grow

serial dilution

phenol red carbohydrate broth

tests for fermentation of glucose

red, negative for fermentation= neutral pH

yellow= fermentation and gas production, acidic pH

Kilgler’s Slant

tests for: H2S and cysteine desulfurase activity

sulfide (H2S) + Fe in media = black precipitate

motility tube

cells stabbed in the center, motile cells will move from the center, non motile will stay

pink color to indicate activity (TTC)

VP Test (voges-proskauer)

used barritt’s reagent wich reacts with acetoin- red colored product

indole production test (tryptone broth)

adding kovac’s reagent, reacts with indole forming reddish product at the top

negative indole production results in yellow solution in the tube from the reagant

phenylalanine deaminase

adding ferric chloride, reacts with phenylpyruvic acid to form a dark green color on the slant