Lab exam Flashcards
what is the main purpose of staining?
to increase contrast between the specimen and the backround
Gram stains differentiate based on _____ Properties
cell wall
what are the 4 steps to gram staining?
- crystal violet 1 min
- grams iodine 1 min
- decoulorize until rinse runs clear
- safranin 1 min
gram positive bacteria are ____ while gram negative bacteria are _____
purple, pink
what is the main goal of streak plating?
isolate a single colony from mixed populations
what is the purpose of serial dilutions?
used to get sample down to a countable number
colony count is countable between?
30 and 300
what is msa used for?
for plasma coagulating staphlococci
what type of bacteria grows on msa?
halotolerant bacteria
what is the indicator used in msa?
phenol red
when will phenol red change the from red to yellow ?
below a ph of 6
mannitol fermentation is positive when?
colour change from red to yellow
what is differentiated in EMB?
gram negative enteric bacteria
what is the sugar used for fermentation in EMB?
lactose
HE is used to?
differentiate gram negative bacteria
when is a black precipitate present in HE?
when H2S2 reacts with ferric ammonium
what colour do lactose fermenters turn in HE?
pink
what colour do lactose fermenting organisms turn in MAC?
pink, red
what is colliform bacteria?
rod shaped, gram -, non spore forming, ferments lactose with acid and gas when incubated at 35-37
what is TSI used for?
differentiates between enterobacteriaceae
how is a black percipitate formed in TSI?
H2S reacts with ferrous sulfate
what is oxidation fermentation?
determines whether an organism utilizes glucose by fermentation or oxidation
what is deamination?
presence of deaminase enzyme (break down amino acids) whether ferric chloride reacts with phenylpyruvic acid
what colour is positive and negative for urease?
+ pink, - yellow
what is the lipase test?
ability to break down triglycerides into glycerol and fatty acids
what is positive and negative for lipase?
+ halo - no halo
