Lactobacillus species, a group of beneficial bacteria commonly found in the human microbiota (especially in the gut and vagina), are widely studied for their role in supporting and preventing bacterial infections. There is moderate scientific evidence indicating that certain strains of Lactobacillus can help restore or maintain healthy microbial balance, which is associated with resistance to pathogenic bacterial colonization. This mechanism is particularly well-documented in the context of recurrent bacterial vaginosis and urinary tract infections, where supplementation with specific Lactobacillus strains may reduce recurrence rates. The proposed mechanisms include competitive exclusion of pathogens, production of antimicrobial compounds (e.g., lactic acid, bacteriocins), and modulation of the local immune response.

However, it is important to note that not all Lactobacillus strains have the same effects, and many studies specify the use of particular strains (such as L. rhamnosus GR-1, L. reuteri RC-14, or L. crispatus). The use of “Lactobacillus (unspecified)” is therefore less precise, and effectiveness can vary significantly depending on the strain and the type of infection. Most of the supportive evidence is of moderate quality (hence the rating of 3), with some clinical trials and systematic reviews supporting the adjunctive use of Lactobacillus-containing probiotics for certain bacterial infections, though more high-quality, strain-specific research is still needed.