Clinical biochemistry of Escherichia coli — Which of the following reactions are typically positive for E. coli in routine identification (IMViC and basic fermentation tests)?

Introduction / Context:
In diagnostic microbiology, Escherichia coli is commonly identified by a standard panel of biochemical reactions. Recognizing the characteristic reactions for E. coli helps distinguish it from other Enterobacterales (formerly Enterobacteriaceae) during routine stool, urine, and blood culture workups.

Given Data / Assumptions:

• E. coli is a lactose and glucose fermenter.
• The classic IMViC profile for E. coli is Indole positive, Methyl red positive, Voges–Proskauer negative, Citrate negative.
• The question lists three reactions individually and asks which are usually positive.

Concept / Approach:
Glucose fermentation is a basic metabolic trait of E. coli, producing acid that changes indicator color on media and in carbohydrate broths. The indole test detects tryptophanase activity converting tryptophan to indole, which is positive in most E. coli strains. The methyl red test detects stable acid end-products from glucose fermentation (mixed-acid pathway), also typically positive in E. coli. Therefore, the integrative answer is that all listed reactions are commonly positive.

Step-by-Step Solution:

Verification / Alternative check:
Pair these results with negative Voges–Proskauer and negative Simmons citrate for the typical IMViC pattern (++--). Additional confirmatory tests include lactose fermentation on MacConkey agar and oxidase negativity.

Why Other Options Are Wrong:

• Choosing a single reaction ignores that E. coli is characteristically positive for all three listed tests.

Common Pitfalls:
Overlooking atypical strains or relying on a single test. Always interpret in combination with other markers (e.g., motility, lactose fermentation) for reliable identification.

Final Answer:
All of these