Differential Sensitivity of Lactobacillus spp. to Inhibition by Candidate Topical Microbicides

Area of Science:

• Microbiology
• Infectious Diseases
• Pharmacology

Background:

• Preclinical evaluation of vaginal microbicides involves screening against lactobacilli.
• Current consensus on which Lactobacillus species to test is lacking.
• This variability necessitates research into species-specific responses to microbicides.

Purpose of the Study:

• To determine if microbicide screening results from one Lactobacillus species are applicable to others.
• To evaluate the utility of turbidometry as a screening tool for vaginal microbicides.
• To assess the efficacy of candidate microbicides: PPCM, cellulose sulfate (CS), and polystyrene sulfonate (PSS).

Main Methods:

• Bacterial growth of Lactobacillus species was measured using both turbidometry and direct cell counts.
• Evaluated three candidate microbicides (PPCM, CS, PSS) against various Lactobacillus species.
• Compared turbidometric results with direct cell counts to assess screening method accuracy.

Main Results:

• No microbicide affected Lactobacillus gasseri growth by either measurement method.
• Turbidometry suggested inhibition of Lactobacillus jensenii and Lactobacillus crispatus by certain microbicides, but direct cell counts did not confirm this.
• Polystyrene sulfonate (PSS) and PPCM inhibited Lactobacillus crispatus and Lactobacillus acidophilus, confirmed by both methods.

Conclusions:

• Lactobacillus species exhibit different sensitivities to microbicides, making single-species screening inadequate.
• Turbidometry is a sensitive but not specific method for initial microbicide screening.
• Recommend screening candidate microbicides against multiple prevalent Lactobacillus species using turbidometry as an initial safety evaluation step.