Exercise 23 Selective and Differential Media

Question 1

fn of all purpose media

Answer 1

support the growth of a wide range of genera including normal body flora, pathogens and soil microbia

Question 2

eg of all purpose mediam

Answer 2

nutrient agar, tryptic soy agar, blood agar and others

Question 3

selective media incorporates

Answer 3

chemical substances at levels just high enough to inhibit growth of some bacteria but not others

Question 4

selective media chemicals include

Answer 4

dyes, antibiotics, NaCl, dextrose, quaternary ammonium compounds, sodium azide

Question 5

what is enrichment media

Answer 5

another form of selective. contains chemicals to enhance growth of desired bacteria, other bacteria will grow but not as much

Question 6

Columbia CNA agar selective aspect

Answer 6

selective containing blood to isolate gram =ive cocci including streptococci and staphylococci

Question 7

how does Columbia CNA work to be selective

Answer 7

medium contains Colistin and Nalidixic Acid, acts to disrupt gram -ive cell membrane and block DNA replication

Question 8

can gram +ive bacilli grow on Columbia CNA

Answer 8

some may grow and others not

Question 9

what kind of media is simmons citrate agar

Answer 9

selective

Question 10

why isolated colonies on selective media not pure culture

Answer 10

inhibitors slows growth but does not kill supressed bacteria. colony of interest can touch contaminating organism

Question 11

differential media incorporates

Answer 11

chemical compounds that after inoculation and incubation produce change in appearance of bacterial growth and/or the medium surrounding the colonies

Question 12

what is blood agar

Answer 12

rich nutrient solution with 5 to 10% animal blood. supports fastidious microbes. growth of some bacteria has effect on rbi in zones surrounding colonies, called hemolysis

Question 13

alpha hemolysis

Answer 13

drab greenish/brownish halo surrounding the bacterial colony, not actual hemolysis but discolouration of medium due to cells changing colour

Question 14

beta hemolysis

Answer 14

clear zone, hemolysis due to secretion of hemolysins

Question 15

gamma hemolysis

Answer 15

no visible change or alterations of rbc in medium

Question 16

Levine Eosin-Methylene Blue EMB agar what kind of media

Answer 16

is both selective and differential

Question 17

EMB contains what to make it selective

Answer 17

dyes eosin Y and methylene blue partially inhibit growth of gram positive bacteria.

Question 18

EMB contains what to make it differential

Answer 18

dyes to differentiate between gram -ive

Question 19

what does the lactose in Levine EMB do

Answer 19

lactose fermentation yields acid, reacts with dye. lactose fermenter like E.coli form black colonies with metallic sheen