Metabolic end products: Coliform bacteria ferment carbohydrates to produce which organic acids?

Introduction / Context:
Coliforms (such as Escherichia coli and Enterobacter spp.) are Gram-negative rods used as indicators of fecal contamination. Their fermentation profiles are fundamental in food and water microbiology, determining gas and acid production from sugars like lactose and glucose.

Given Data / Assumptions:

• Focus on carbohydrate fermentation end products.
• Typical coliform metabolism includes mixed-acid and butanediol pathways, depending on species.
• We consider common acids observed in tests and literature.

Concept / Approach:

Classic mixed-acid fermentation (e.g., E. coli) yields a mixture that can include lactic, acetic, succinic, and formic acids, plus ethanol and CO2/H2. Therefore, each of lactic acid, acetic acid, and formic acid can be produced by coliforms, making “All of these” the comprehensive choice.

Step-by-Step Solution:

Verification / Alternative check:

Methyl red (MR) test positivity in E. coli reflects stable acid production. Gas formation in Durham tubes and formate lyase activity support the presence of formic acid derivatives. Enterobacter (Voges–Proskauer positive) shifts toward 2,3-butanediol but can still produce the listed acids in smaller amounts.

Why Other Options Are Wrong:

• Single-acid choices are incomplete because coliforms do not produce only one of these acids.

Common Pitfalls:

• Assuming uniform fermentation across all coliforms; metabolic profiles vary, but the listed acids are broadly representative outputs.
• Confusing coliforms with strictly lactic acid bacteria, which primarily yield lactic acid only.

Final Answer:

All of these