Diff mediasv

differential media

1. • Labs #6 (whitewhite) and #7 (green)
• Overall scheme: Lab #6 (whitewhite) , last page
Biochemical Tests and
Diagnostic Media

2. SIM medium: Motility test
POSITIVE:
Organism moves
away from stab
NEGATIVE:
Organism does NOT
move away from
stab

3. SIM medium: Sulfur test
H
2
S-POSITIVE:
black precipitate
formed
H
2
S-NEGATIVE:
no black
precipitate
formed

4. Simmon’s citrate agar slant
positive
negative

5. Diagnostic Media
•Mannitol salt agar
•Eosin methylene blue (EMB) agar
•Brilliant green agar

6. Selective medium
Selects for the GROWTH of some
organisms and inhibits the growth of
other organisms.
i.e. Some organisms grow on a selective medium
whereas others do not grow (or do not grow well) on that
same medium.

7. Differential medium
Differentiates between one type of
organism and another type of organism.
Different types of organism look different from each
other when grown on differential media.

8. Mannitol salt agar
Selective medium
High salt (NaCl) concentration in medium favors organisms
that tolerate high salt concentration, e.g. Staphylococcus.
Staphylococcus
aureus
grows
Serratia
marcescens
does not grow

9. Mannitol salt agar
Differential medium
Differentiates among staphylococci

10. Mannitol salt agar
Differential medium
Differentiates among staphylococci

11. Mannitol salt agar
Differential medium
Differentiates among staphylococci:
• pathogenic Staphylococcus species ferment mannitol to

produce acid (yellow medium)(yellow medium)
Staphylococcus
ferments
mannitol
(yellow)(yellow)

12. Mannitol salt agar
Differential medium
Differentiates among staphylococci:
• pathogenic Staphylococcus species ferment mannitol to

produce acid (yellow medium)(yellow medium)
• less pathogenic Micrococcus (a staphylococcus)
do not ferment mannitol (red/pink medium)
Staphylococcus
ferments
mannitol
(yellow)(yellow)
Micrococcus does not
ferment mannitol
(pink)

13. Levine Eosin-Methylene Blue (EMB)
Agar
Gram negatives
(growth)
Gram positive
(growth inhibited)
SELECTIVE MEDIUM

14. Levine Eosin-Methylene Blue (EMB)
Agar
Nonlactose
fermenters
Lactose
fermenter
DIFFERENTIAL MEDIUM

15. High acid producers on EMB
e.g. E. coli
blue-black colonies or metallic sheen

16. Levine Eosin-Methylene Blue (EMB)
Agar
Lactose fermenter
(low acid producer:
pink colonies)
Non-lactose fermenter Lactose fermenter
(high acid producer:
black colonies)
Gram positive
(growth inhibited)

17. Brilliant Green Agar
SELECTIVE
DIFFERENTIAL
•
Growth of all gram positive and
many gram negative bacteria
inhibited
• Growth of many Salmonella species
occurs

18. Brilliant Green Agar
DIFFERENTIAL
Differentiates lactose fermenters lactose fermenters from
nonlactose fermenters

19. Brilliant Green Agar
Non-lactose fermenter Lactose fermenter
SalmonellaE. coliE. coli

20. Catalase Test
Many bacteria produce the enzyme catalase.
H
2
O
2
H
2
O + O
2
catalase
hydrogen
peroxide
oxygen
(gas)

21. Catalase Test
bubbles (gas)
Catalase positive organism