Experiment 9: Selective, Differential, and Enriched Media

chemically defined media?

known chemical constituents

complex media?

complex materials, unknown

used for cultivation of nutrinally fastidious organisms (plant digests, animal tissue extract, blood serum)

all-purpose, general media?

nutrient agar, supports growth of many organisms

what is selective media?

has chemicals that dont sffect growth of organism u wanna isolate, discourage growth of any other organisms

what does adding sodium azide of a specific conc into culture media do?

selects for lactic acid bacteria, i.e. Streptococcus

they dont have cytochrome sustem and are unaffected by sodium azide which binds to porphyrin ring of cytochrome.

so they prevent growth of microbes w a cytochrome system

what are some selective agents and what do they do?

dyes like crystal violet, high concs of NaCl (isolate halophiles), bile salts, antibiotics, specific sugars

what are differential media?

has dyes or chemicals whcih allow us to see the diff types of colonies after incubation

example of differential media?

EMB - Eosin Methylene Blue agar

used to isolate and detect enterobacericiae (enterics) and coliform rods like E. coli

what type of colonies do E. coli produce on EMB?

small colonies with dark (almost black) centers w greenish metallic sheen

what type of colonies do Enterobacter species make on EMB?

large pink mucoid colonie w dark centeres NO metallic sheen

EMB Is what type of media?

selective and differential bc it has lactose as energy source so it grows organisms that made Beta-galactosidase (Z) enzymes which break down glucose and galactose

those who dont make beta z dont grow on EMB

emb has meth blue and eosin Y dye so it supresses growth of Gram + bact

what doesnt grow on EMB media?

those who cant make beta galactosidase

those that are Gram +

what is enriched media?

nutrient-rich growth medium, supports growth of fastidious organisms

Exp. 9 learning objectives

1. understand diffs between selective, differential, and enriched media

2. analyze growth results in ea medium

Exp. 5 Materials (in pairs)

1. Ecoli (24hr)

2. Pseudomonas aeruginosa (24hr)

3. Staphylococcus aureus (24hr) lvl 2

4. Enterococcus faecalis (24hr) lvl 2

5. Tryptic soy agar (TSA)

6. EMB agar

7. KF Streptococcal agar

8. sterile cotton swabs

Exp. 5 Method

mark each agar plate into quadrants and aseptically swab each bacterium onto each plate (1 swab per bact)

incubate at 37 deg for 48 hrs

Results - TSA Plate (enriched)

Results - EMB Plate (diff, selective)

Results - KF Streptococcal Plate (diff, selective)