Acid tolerance: Which of the following bacteria are capable of growth at acidic pH and are therefore associated with acid-tolerant or acidophilic behavior?

Introduction / Context:
pH preference is a key ecological and diagnostic trait. While many pathogens prefer neutral pH, some bacteria thrive in acidic environments, influencing their habitats, roles in food fermentation, and survival in the host.

Given Data / Assumptions:

• We are contrasting acid-tolerant organisms with those that prefer neutral or alkaline pH.
• Lactobacilli are well-known for acid production and tolerance.
• Other listed genera are enteric or aquatic pathogens with different pH preferences.

Concept / Approach:

Lactobacillus species are lactic acid bacteria used in yogurt, sauerkraut, and other fermented foods; they tolerate and generate acidic conditions. In contrast, Vibrio cholerae prefers alkaline environments, and many Shigella and Salmonella strains are neutrophiles even though they can survive transient acid stress.

Step-by-Step Solution:

Verification / Alternative check:

Food microbiology texts document lactobacilli thriving at lower pH; they both produce lactic acid and tolerate acidic environments better than many pathogens.

Why Other Options Are Wrong:

Vibrio cholerae: alkaline-tolerant; selected at pH around 8.5.

Shigella, Salmonella: generally neutrophilic growth optima; acid exposure is a stressor, not a preferred condition.

Common Pitfalls:

Confusing survival under acid stress with growth preference; assuming all pathogens thrive across broad pH ranges without selective advantage.

Final Answer:

Lactobacilli