This document describes a lab exercise involving biochemical differentiation of medically important gram-negative bacilli. The exercise includes using MacConkey agar to differentiate lactose fermenters from non-fermenters. Carbohydrate fermentation tests and IMViC series tests are also used to identify bacteria species, including Shigella sonnei, Escherichia coli, Serratia marcescens, Klebsiella pneumoniae, Salmonella typhimurium, Proteus vulgaris, and Enterobacter aerogenes. Identification is done using results from the tests and charts in the lab manual.

1. Lab Exercise 17:
Biochemical Differentiation of some
Medically Important Gram-negative Bacilli

2. MacConkey Agar
Left: Shigella
- result
Right: Escherichia
+ result

3. Carbohydrate Fermentation Tests
Glucose w/ Durham Fermentation Tube

4. Carbohydrate Fermentation Tests
Sucrose Fermentation

5. Triple Sugar Iron
-/+/+

6. IMViC Series
Indole Test
broth with
tryptophan

7. Methyl Red Test
IMViC Series

8. IMViC Series
Voges-Proskauer Test
a
Leave uncapped for 15-20 minutes……..
MRVP broth

9. Citrate Utilization Test
- +
IMViC Series

10. Urease Test
Slow
positive
Negative
result (acidic)
Uninoculated
urea agar
Positive
result
(alkaline)

11. Motility Test

12. MacConkey agar
1. Which plate could have E. coli on it?
2. Which plate shows the presence of a
lactose-fermenter?
3. Which plate could have Salmonella
on it?
4. Which plate shows the presence of a
lactose non-fermenter?
Answers:
1. A 3. B
2. A 4. B
A
B

13. What is the name of the lab procedure demonstrated here?
Answer: Stabbing the butt!

14. Use the chart on p. 181 and or the
flow chart on p. 182 of your lab
manual to figure out who I am!
I M V
C
U
Answer: Shigella sonnei

15. I M V
C
U
Use the chart on p. 181 and/or the
flow chart on p. 182 of your lab
manual to figure out who I am!
Answer: Escherichia coli

16. I M V C
U
Use the chart on p. 181 and/or the
flow chart on p. 182 of your lab
manual to figure out who I am!
Answer: Serratia marcesens

17. Use the chart on p. 181 and/or the
flow chart on p. 182 of your lab
manual to figure out who I am!
I M V C
Answer: Klebsiella pneumoniae

18. Use the chart on p. 181 and/or the
flow chart on p. 182 of your lab
manual to figure out who I am!
I M V C U
Answer: Salmonella typhimurium

19. Use the chart on p. 181 and/or
the flow chart on p. 182 of your
lab manual to figure out who I am!
I M V C
U
Answer: Proteus vulgaris

20. Use the chart on p. 181 and/or the
flow chart on p. 182 of your lab
manual to figure out who I am!
I M V C
Answer: Enterobacter aerogenes
U