Novel Selective Inhibition of Lactobacillus iners by Lactobacillus-Derived Bacteriocins

Area of Science:

• Microbiology
• Bacteriology
• Pharmacology

Background:

• Lactobacillus iners is frequently linked to vaginal dysbiosis and bacterial vaginosis (BV), posing risks for gynecological and obstetric health.
• Unlike other protective vaginal lactobacilli, L. iners can coexist with BV-associated bacteria and may contribute to dysbiosis recurrence after treatment.

Purpose of the Study:

• To identify natural inhibitors of Lactobacillus iners from human Lactobacillus strains.
• To characterize the inhibitory compounds and assess their selectivity against key vaginal lactobacilli.

Main Methods:

• Screening of cell-free supernatants from 78 Lactobacillus strains for L. iners inhibitory activity.
• Purification and identification of active peptides from Lactobacillus paragasseri K7.
• Determination of Minimum Inhibitory Concentrations (MICs) and assessment of synergistic effects.
• Testing bacteriocin selectivity against major vaginal Lactobacillus species and in a simulated BV environment.

Main Results:

• Lactobacillus paragasseri K7 produced class IIb bacteriocins, gassericin K7A and gassericin K7B, with potent L. iners inhibitory activity.
• The GasK7B α peptide showed the highest individual potency (MIC: 23 ng/ml), while the GasK7B α and β peptide combination exhibited synergistic inhibition (MIC: 2 ng/ml).
• K7 bacteriocins selectively inhibited all tested L. iners strains (100%) but <20% of L. crispatus, L. jensenii, and L. gasseri strains.
• Combined treatment with metronidazole and K7 bacteriocins eradicated L. iners and Gardnerella vaginalis in coculture without affecting L. crispatus.

Conclusions:

• Potent, selective bacteriocins targeting L. iners have been identified from Lactobacillus paragasseri K7.
• These bacteriocins demonstrate potential as novel therapeutic agents for bacterial vaginosis and dysbiosis.
• The selective action spares beneficial vaginal lactobacilli, offering a promising approach to restoring vaginal microbiome balance.