Which bacterium is part of the normal vaginal flora that helps resist the onset of bacterial vaginosis?

• A. Peptostreococcus sp.
• B. Peptococcus sp.
• C. Lactobacillus sp.
• D. Mobiluncus sp.

Answer: (C)

Lactobacillus species dominate healthy vaginal flora and keep the environment protective by maintaining a low pH. They produce lactic acid, which lowers the vaginal pH to about 3.8–4.5, creating an inhospitable environment for many bacteria that can cause infections. Some Lactobacillus strains also generate hydrogen peroxide, adding another layer of antimicrobial activity. When lactobacilli are abundant, this acidic, hostile environment helps resist the onset of bacterial vaginosis by suppressing overgrowth of anaerobic, BV-associated bacteria.

Mobiluncus species, in contrast, are more commonly found when BV is present rather than in normal health, so they are not the protective, inducing-resilience bacteria. Peptostreptococcus and Peptococcus are anaerobic cocci that can be present in various infections but do not define the healthy protective vaginal flora as Lactobacillus does.

So the bacterium that is part of normal vaginal flora and helps resist the onset of bacterial vaginosis is Lactobacillus species.