MLA Week 3

Question 1

selective media

Answer 1

inhibits growth of one type while facilitating the growth of another type of bacteria

Question 2

differential media

Answer 2

does not inhibit any growth but rather designed so different bacteria produce different characteristics in the media so you can tell apart

Question 3

Sheep blood agar plate

Answer 3

differential media for bacteria able to produce hemolysins which produce difference in hemolytic technique of bacteria…beta alpha gamma

Question 4

Sabouraud dextrose agar

Answer 4

used to cultivate fungi, is selective based on pH of 5.6 and higher concentration of dextrose than bacteria prefer

Question 5

Mannitol salt agar

Answer 5

selective because 7.5% salt is inhibitory to most bacteria except staphylococcus species…differential mong staphylococci based on ability to ferment mannitol and turn phenol red pH indicator yellow if positive

Question 6

MacConkey Agar

Answer 6

selective for gram negative because crystal violet and bile salts inhibit gram positive, then differential for lactose fermenters…deep pink and non-lactose…pale pink or violet

Question 7

TSI agar

Answer 7

contains sugars glucose, sucrose, and lactose in ratio of 1:10:10

Question 8

Entire Yellow TSI agar (yellow slant and butt)

Answer 8

means bacteria able to ferment all sugars of glucose sucrose and lactose, therefore changing pH phenol indicator to yellow throughout the tube

example is eschericia

Question 9

Alkaline (red) slant, yellow butt TSI

Answer 9

bacteria only ferments the glucose

example is salmonella

Question 10

Alkaline slant (red) alkaline butt (red) TSI

Answer 10

bacteria does not ferment any of the sugars

Question 11

sodium thiosulfate in TSI agar

Answer 11

contained in the agar, and some species will reduce which makes hydrogen sulfide of H2S…leading to a black precipitate

Example is salmonella

Question 12

MIO test (motility indole Prnithine Decarboxylase

Answer 12

used to identify different members of the Enterobacteriaceae

Question 13

Motility in MIO testing

Answer 13

stab straight down, non motile will only grow along stab while motile will grow away from stab

Question 14

Indole in MIO testing

Answer 14

indole is made by some enterobacteriaceae in breakdown of tryptophan…detected by adding kovac’s reagent which extracts the indole and turns in red

Question 15

Ornithine decarboxylase in MIO testing

Answer 15

used to see if organism can decraboxylate ornithine and will show as a light purple color at bottom of tube, if purple at top please ignore

Question 16

citrate utilization

Answer 16

tests for organisms using sodium citrate as sole source of carbon, these organisms make an alkaline reaction on Simmons citrate slant making the indicator blue, if negative then will remain green

Question 17

urease test

Answer 17

tests for ability to hydrolyze urea into ammonia Co2 and H2O

Proteus is positive fast urea hydrolysis (pink)
Klebsiella is positive slow hydrolysis (pink)
Escherichia and other non urea hydrolysis organisms are negative and show up as agar remaining yellow or peach