Cytotoxicity assessment and antimicrobial effects of cell-free supernatants from probiotic lactic acid bacteria and yeast against multi-drug resistant Escherichia coli.

The antibacterial, antibiofilm, and cytotoxicity activity of cell-free supernatants (CFSs) from probiotics including Lactobacillus plantarum, Bifidobacterium bifidum, and Saccharomyces cerevisiae against multi-drug resistant Escherichia coli evaluated in current research. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the CFSs were determined by analyzing inhibition zone formation using agar disk diffusion for antibacterial activity, microtiter plate for biofilm analysis, and auto-aggregation were done. CFSs substances were analyzed by GC-MS. The MTT assay on HEK293 cells investigated CFS's influence on cell viability. CFSs were examined for biofilm-related virulence genes including aggR and fimH using real-time PCR. All CFSs had bacteriostatic and bactericidal effects. The B. bifidum exhibited the highest antibiofilm activity compared to the others. B. bifidum, L. plantarum, and S. cerevisiae produce 19, 16, and 11 mm inhibition zones against E. coli respectively. GC-MS indicated that Hydroxyacetone, 3-Hydroxybutyric acid and Oxime-methoxy-phenyl dominated CFSs from L. plantarum, B. bifidum, and S. cerevisiae CFSs, respectively. The MTT test demonstrated a cell viability rate of over 90%. Statistically, adding all CFSs lowered the relative expression of both aggR and fimH virulence genes.