Synergistic effect of Lactobacillus supernatant and gentamicin against biofilms of uropathogenic Escherichia coli

Background: Infection control poses a challenge due to the emergence of antibiotic-resistant bacteria and biofilm formation. Probiotics have been shown to positively affect the host, with certain strains of Lactobacilli able to prevent or alleviate inflammation and infections. Aim of the work: This work aimed to investigate the synergistic effects of gentamicin and the cell-free supernatant (CFS) of the probiotic Lactobacillus plantarum on the biofilm formation of Escherichia coli isolated from urinary tract infections (UTIs). Methods: We analyzed 422 urine samples from type 2 diabetic patients with UTIs, and identified bacterial isolates using phenotypic methods and the automated system VITEK-2. The antibiotic susceptibility test was conducted using the disc diffusion method, while the inhibitory effects of the CFS were assessed using an agar-well diffusion assay. E. coli biofilm formation was detected using a microtiter plate (MTP) method, and the minimum inhibitory concentration (MIC) was estimated via the microdilution method. Finally, the interaction between CFS and gentamicin against E. coli was tested using the checkerboard method and fractional inhibitory concentration (FIC). Results: The E. coli strains isolated from UTIs were found to be multidrug-resistant. The cell-free supernatant (CFS) exhibited a significant bactericidal effect on E. coli growth, with MICs of 12.5 U/mL for CFS and 128 μg/mL for gentamicin. The FICI for CFS and gentamicin was 0.37, suggesting a synergistic effect. Conclusion: Combining probiotics with antimicrobial agents shows promise for developing new bactericidal formulations for medical and pharmaceutical applications.