Investigating the antibacterial activity of L. casei and L. acidophilus against common agents of nosocomial infections

Background: The emergence of antibiotic resistance in nosocomial pathogens has become a great concern with rising reports of cases worldwide. Interestingly, the application of probiotics and their products for inhibition and bacterial replacement has been the focus of many investigations within the recent years. Objective: This study was performed to evaluate the antibacterial effect of L. casei & L. acidophilus against a number of known nosocomial bacteria in an attempt to introduce a replacement therapy. Methods: This study was carried out in bacteriology department of Shiraz Medical School in 2008. Lactobacilli strains were isolated from the local dairy (FARS) products and identified through routine microbiological methods using chemical (sugar) test. According to the results of a previous study, these two strains were tested for antibiotic resistance using disk diffusion method. Later, the supernatant of a 72-hour culture of each strain was tested for inhibitory affect on standard bacterial strains including S. aureus, E. coli, K. pneumonia, P. aeruginosa, and the spore- forming bacterium B. subtilis in two active and inactive forms. Findings: Review of the antibiotic results showed that both L.casei and L.acidophilus were resistant to all antibiotics used except the Tobramycin and Vancomycin which were demonstrated to have antibacterial activities against L.acidophilus. Additionally, when investigating the antibacterial activity of these two strains, it was revealed that except for B. subtilis, significant inhibition zones were found around the colonies of pathogenic bacteria both in active and inactive forms. Conclusion: According to the result of the present study it was demonstrated that the two strains of lactobacilli have a good resistance against the routine antibiotics although their antibacterial activity on growth of some usual nosocomial pathogens is limited in inactivated form when in conditions in which acid and H2O2 are available, they can act as good inhibitors of bacterial growth.