Effectiveness of bacteriocin like inhibitory substance (BLIS) extracted from Lactobacilli spp. as anti-biofilm pathogenic bacteria and yeasts: an in vitro study

Background. Bacteriocin-like inhibitory substances (BLIS) are antimicrobial peptides produced by certain strains of Lactobacillus, with the ability to inhibit the growth and biofilm formation of various bacterial and fungal pathogens. Biofilms are notoriously resistant to conventional antibiotics and represent a significant clinical challenge, especially in chronic infections and device-associated diseases. Exploring natural antimicrobial alternatives such as BLIS has become increasingly important in the context of rising antimicrobial resistance. Objective. This study aimed to investigate the in vitro antibacterial, antifungal, and anti-biofilm effects of BLIS extracted from different Lactobacillus spp., and to evaluate how physical and nutritional factors influence their production and potency. Methods. BLIS extracted from L. rhamnosus, L. acidophilus, and L. plantarum strains was tested using the agar well diffusion method and microtiter biofilm inhibition assays. Optimization steps assessed the influence of pH, carbon and nitrogen sources on BLIS production. Partial purification was performed using ammonium sulfate precipitation and dialysis. Results. This study isolated and characterized eight Lactobacillus strains (L1-L8) from probiotic dairy and healthy women, showing broad antimicrobial activity against bacterial and fungal pathogens. Strain L4 demonstrated particularly strong inhibition (12-33 mm zones) under optimal conditions (pH 4.5-5, yeast extract, glucose). Partial purification of L. rhamnosus bacteriocin revealed exceptional antimicrobial effects (46 mm zone against S. agalactiae) and potent anti-biofilm activity (90.1% reduction against S. haemolyticus). Testing showed significant biofilm inhibition (63.59-90.10%) across pathogens, with highest efficacy against Gram-positive bacteria and moderate effects on Gram-negatives, while Candida biofilms were reduced by 67.29-81.75%. Conclusion. BLIS from Lactobacillus spp. demonstrated significant in vitro anti-biofilm and antimicrobial effects, especially L. rhamnosus. These results support further exploration of BLIS as a potential therapeutic agent against biofilm-associated infections.