Lab exam

Question 1

what is the main purpose of staining?

Answer 1

to increase contrast between the specimen and the backround

Question 2

Gram stains differentiate based on _____ Properties

Answer 2

cell wall

Question 3

what are the 4 steps to gram staining?

Answer 3

1. crystal violet 1 min
2. grams iodine 1 min
3. decoulorize until rinse runs clear
4. safranin 1 min

Question 4

gram positive bacteria are ____ while gram negative bacteria are _____

Answer 4

purple, pink

Question 5

what is the main goal of streak plating?

Answer 5

isolate a single colony from mixed populations

Question 6

what is the purpose of serial dilutions?

Answer 6

used to get sample down to a countable number

Question 7

colony count is countable between?

Answer 7

30 and 300

Question 8

what is msa used for?

Answer 8

for plasma coagulating staphlococci

Question 9

what type of bacteria grows on msa?

Answer 9

halotolerant bacteria

Question 10

what is the indicator used in msa?

Answer 10

phenol red

Question 11

when will phenol red change the from red to yellow ?

Answer 11

below a ph of 6

Question 12

mannitol fermentation is positive when?

Answer 12

colour change from red to yellow

Question 13

what is differentiated in EMB?

Answer 13

gram negative enteric bacteria

Question 14

what is the sugar used for fermentation in EMB?

Answer 14

lactose

Question 15

HE is used to?

Answer 15

differentiate gram negative bacteria

Question 16

when is a black precipitate present in HE?

Answer 16

when H2S2 reacts with ferric ammonium

Question 17

what colour do lactose fermenters turn in HE?

Answer 17

pink

Question 18

what colour do lactose fermenting organisms turn in MAC?

Answer 18

pink, red

Question 19

what is colliform bacteria?

Answer 19

rod shaped, gram -, non spore forming, ferments lactose with acid and gas when incubated at 35-37

Question 20

what is TSI used for?

Answer 20

differentiates between enterobacteriaceae

Question 21

how is a black percipitate formed in TSI?

Answer 21

H2S reacts with ferrous sulfate

Question 22

what is oxidation fermentation?

Answer 22

determines whether an organism utilizes glucose by fermentation or oxidation

Question 23

what is deamination?

Answer 23

presence of deaminase enzyme (break down amino acids) whether ferric chloride reacts with phenylpyruvic acid

Question 24

what colour is positive and negative for urease?

Answer 24

+ pink, - yellow

Question 25

what is the lipase test?

Answer 25

ability to break down triglycerides into glycerol and fatty acids

Question 26

what is positive and negative for lipase?

Answer 26

+ halo - no halo