Isolation and Identification of Effective Probiotics on <i>Staphylococcus epidermidis</i> Strains Isolated from Urine Sample

Background: The increasing prevalence of antibiotic-resistant Staphylococcusepidermidis strains underscores the urgent need for alternative therapeutic approaches. Probiotics, known for their ability to competitively exclude pathogens and modulate host immune responses, present promising potential in combating S. epidermidis infections. Objectives: This study aimed to evaluate the effectiveness of probiotics in inhibiting the growth of S.epidermidis. Methods: Staphylococcus epidermidis was isolated from urine samples of hospitalized patients in Isfahan, Iran. Probiotics were isolated from yogurt and milk. The antibacterial activity of these probiotics was assessed using agar well diffusion and broth microdilution methods. Time-kill assays and acid tolerance tests were also conducted. Anti-biofilm effects were evaluated, and the potential inhibitory mechanisms were explored through chemical analysis using high-performance liquid chromatography (HPLC). Cytotoxicity was assessed via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. Results: Two probiotic strains, Streptococcus lutetiensis OR496927.1 and Lactiplantibacillus plantarum OR496928, were successfully isolated from dairy products. Both strains exhibited cytotoxic effects on S. epidermidis isolates, with S. lutetiensis demonstrating significant activity at 1/2 minimum inhibitory concentration (MIC) and L. plantarum at 1/4 MIC. L. plantarum thrived at pH 3, while S. lutetiensis exhibited growth at both pH 3 and 4. Both probiotics showed anti-biofilm activity, though L. plantarum demonstrated stronger effects overall. The strains produced lactic, formic, and acetic acids, which were key factors in their inhibitory effects. Toxicity was observed at a concentration of 50% after 24 hours, while cell viability remained unaffected at lower concentrations. Conclusions: The findings highlight the potential of probiotics to address antibiotic-resistant S. epidermidis infections. Further research is necessary to explore their therapeutic applications and optimize treatment strategies.