Postbiotic approach to antibiotic resistance: antibacterial and antibiofilm potential of Lactobacillus salivarius supernatant.

The rapid rise in antibiotic resistance is making infections, particularly those caused by ESBL-positive and biofilm-forming Escherichia coli isolates, increasingly difficult to treat. Therefore, interest in alternative biotherapeutic approaches based on probiotic or postbiotic sources is increasing. Although there are many reports on the antibacterial and antibiofilm effects of probiotics in the current literature, the efficacy of Lactobacillus salivarius supernatant (LS-S) on ESBL-positive and biofilm-forming clinical E. coli isolates has not been studied sufficiently. The aim of this study was to evaluate the antibacterial and antibiofilm effects of LS-S against ESBL-positive E. coli isolates in vitro and to compare it with other probiotic-derived findings in the literature. Antibacterial activity was determined by modified disk diffusion and agar well diffusion methods, and growth inhibition was assessed over time using a microplate assay. Biofilm inhibition was measured using a quantitative biofilm assay, and the results were analyzed statistically. LS-S produced average inhibition zones of 16.0 ± 3.9 mm (disk) and 18.8 ± 3.3 mm (well) in ESBL-positive E. coli isolates. Microplate assay results showed that inhibition reached 20% at 3 h, 65–70% at 6–12 h, and 87% at 24 h. In biofilm analyses, biofilm formation was suppressed in all isolates, with inhibition exceeding 40% detected in 13 isolates (43.3%), and the highest efficacy was found to be 73.1%. The data obtained demonstrate that LS-S has the capacity to inhibit both planktonic growth and biofilm development. These findings demonstrate that postbiotic-based biotherapeutics are promising candidates for infection control in the era of antibiotic resistance and highlight the need for in vivo and translational studies for clinical applications.