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

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

Answer: (C)

Lactobacillus species are the key bacteria in a healthy vaginal microbiome. They keep the environment hostile to BV-associated bacteria by producing lactic acid, which lowers the vaginal pH to around 3.5–4.5, creating an acidic environment that inhibits many potential pathogens. Some Lactobacillus strains also generate hydrogen peroxide and bacteriocins, giving an extra antimicrobial edge. By dominating the niche and consuming available nutrients, they prevent overgrowth of opportunistic bacteria that can lead to bacterial vaginosis.

Other bacteria like Mobiluncus tend to appear when BV is present rather than prevent it, and Peptostreptococcus/Peptococcus are not the protective, dominant vaginal flora.