In-Vitro Study the Antibacterial Activity of Bacteriocin against Stenotrophomonas Maltophilia and Evaluation its Synergism with some Antibiotics

The core of the study is to screen the inhibitory effect of bacteriocin producing Lactobacillus acidophilus against isolated S. maltophilia and examine whether the combination of bacteriocin with antibiotics showed synergistic or antagonistic interaction. The majority of isolates were resistant to two antibiotics and the isolate coded S19 was resistant to the three antibiotics used, which is consider as multi-drugs resistant isolate and used for the synergy test. Initially, minimum inhibitory concentrations (MICs) of Ceftazidime (CAZ), Imipenem (IMP) and Minocycline (MIN) were determined using exponentially growing cultures of S. maltophilia. The MICs of antimicrobial were 64, 32 and 128μg/ml, respectively. When antimicrobial and bacteriocin combined in the checkerboard microtiter test, a synergistic effect was observed and the MICs decreased dramatically. All of the three antimicrobials with bacteiocin combinations showed synergy against the resistant S. maltophilia isolate (S19).A combination of Imipenem plus bacteiocin showed the highest synergistic effect among the combinations. FIC index of a combination of Imipenem, Ceftazidime and Minocyclin with bacteriocin, were 0.249, 0.093 and 0.312 for S. maltophilia isolate respectively. Antagonistic activity was not found in any of the combinations. In conclusion in the presence of bacteriocin, a lower Ceftazidime, Imipenem and Monocycline concentrations were needed to fully inhibit S. maltophilia .Checkerboard assay was appropriate method to calculate the MIC and combination testing of the bacteriocin and antibiotic as well as the fractional inhibitory concentration index (FICI) was applicable to aid in an interpretation of the combination testing results.