The antimicrobial potential of Lactobacillus acidophilus on pathogenic bacteria causing diarrhea

Object: Lactobacillus acidophilus is a nonpathogenic member of gastrointestinal tract and it is widely used in fermented dairy products. This study aimed to assess the antimicrobial potential of two strains of L. acidophilus on some pathogenic bacteria frequently causing diarrhea or gastroenteritis.Methods: The antibacterial activity cell free supernatant (CFS) of two control standard strains of L. acidophilus (L. acidophilus-la5 and L. acidophilus against fie control standard strains of bacteria causing diarrhea; Enterotoxogenic Escherichia coli (ETEC), Enterohaemorrhagic E. coli O 157:H7(EHEC) Salmonella typhimurium Shigella flxeneri and Staphylococcus aureus were determined using agar well diffusion method. The sensitivity of the pathogenic bacteria to the CFS of each L. acidophilus in relation to time was determined by standard plate count .The antibiotic susceptibility tests of 20 antibiotics against tested organisms with and without CFS were assessed by disc diffusion method. The minimum inhibitory concentration (MIC) of ciproflxacin with and without CFS was determined by tube dilution method.Results: Both Lactobacilli strains decrease the colony count of tested strains by more than 90% after 60 min contact time. Both Lactobacilli strains signifiantly improve the antibacterial effect of tested antibiotics against ETEC, S. typhimurium and S. aureus, and S. flxeneri (P< 0.05). The MIC of ciproflxacin alone against all tested strains was 15.625 μg/ml, while when combined with both Lactobacilli CFSs, the MIC decreased signifiantly to 0.488 μg/ml for ETEC, S. typhimurium, and S. flxeneri and to 0.977 μg/ml for EHEC and S. aureus (P= 0.000).Conclusion: living L. acidophilus strains could be used in prevention and treatment of diarrhea caused by certain bacterial pathogens, either in fermented milk/ yoghurt or as mediations