Q
QuestionMicrobiology

E. coli and Enterobacter aerogenes are small Gram-negative rods. How can you differentiate them?
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Step 1:
I'll solve this microbiology problem by providing a clear, step-by-step differentiation between E. coli and Enterobacter aerogenes.

Step 2:
: Biochemical Characteristics

- E. coli and Enterobacter aerogenes are both Gram-negative, rod-shaped bacteria - Key differences can be identified through specific biochemical tests

Step 3:
: Lactose Fermentation

\text{Lactose Fermentation Test: } E. \text{ coli } (+), E. \text{ aerogenes } (+/-)
- E. coli: Rapidly ferments lactose, producing acid and gas - Enterobacter aerogenes: Slower lactose fermentation

Step 4:
: Indole Production

\text{Indole Test: } E. \text{ coli } (+), E. \text{ aerogenes } (-)
- E. coli: Positive indole test (produces indole from tryptophan) - Enterobacter aerogenes: Negative indole test

Step 5:
: Methyl Red Test

\text{Methyl Red Test: } E. \text{ coli } (+), E. \text{ aerogenes } (-)
- E. coli: Strongly positive (produces mixed acids) - Enterobacter aerogenes: Negative or weak positive

Step 6:
: Habitat and Clinical Significance

- E. coli: Primarily found in intestinal tract, common cause of UTIs - Enterobacter aerogenes: Found in water, soil, and human gastrointestinal tract - Both can cause opportunistic infections

Final Answer

1. Indole test 2. Lactose fermentation rate 3. Methyl Red test 4. Specific biochemical characteristics