Assessment of phage-mediated inhibition of Salmonella Typhimurium treated with sublethal concentrations of ceftriaxone and ciprofloxacin.

This study was designed to evaluate the synergistic effect of phage (P22) and antibiotic on the inhibition of Salmonella Typhimurium exposed to ceftriaxone (CEF) and ciprofloxacin (CIP). The effect of phage and antibiotic treatments was evaluated by plaque size, disk diffusion, antibiotic susceptibility and phage multiplication assays. The sequential treatment effect of phage and antibiotic was carried out in different treatment order and time for 12 h at 37°C. P22 plaque sizes were increased by 28 and 71%, respectively, in the presence of CEF and CIP. The clear zone sizes in disk diffusion assay were significantly increased to >37 mm in the presence of CEF and CIP compared to the control (28-31 mm). Pre-treatment with P22 enhanced the antimicrobial effect of CIP, showing >2 log reduction after a 12 h incubation. Phage P22 combined with antibiotics (CEF and CIP) effectively inhibited the growth of S. Typhimurium depending on the treatment order and time. These results provide useful information for understanding the synergistic effect of phage and antibiotic treatment which can be an effective option to control antibiotic resistant pathogens.