Assessment of bacteriophage-encoded endolysin as a potent antimicrobial agent against antibiotic-resistant Salmonella Typhimurium

This study was designed to evaluate the potential of using newly purified Salmonella phage-encoded endolysin LysPB32 as novel antibiotic alternative. The endolysin LysPB32 was characterized by analyzing pH and thermal stability, lytic spectrum, antimicrobial activity, and mutant frequency against Salmonella Typhimurium KCCM 40253 (STKCCM), S. Typhimurium ATCC 19585 (STATCC), S. Typhimurium CCARM 8009 (STCCARM), Klebsiella pneumoniae ATCC 23357 (KPATCC), K. pneumoniae CCARM 10237 (KPCCARM), Pseudomonas aeruginosa ATCC 27853 (PAATCC), Listeria monocytogenes ATCC 1911 (LMATCC), Staphylococcus aureus ATCC 25923 (SAATCC), and S. aureus CCARM 3080 (SACCARM). The molecular weight of LysPB32 is 17 kDa that was classified as N-acetyl-beta-Dmuramidase. The optimum activity of LysPB32 against the outer membrane (OM) permeabilized STKCCM, STATCC, and STCCARM was observed at 37 degrees C and pH 6.5. LysPB32 had a broad spectrum of muralytic activity against antibiotic-sensitive STKCCM (41 mOD/min), STATCC (32 mOD/min), and SBKACC (25 mOD/min) and antibioticresistant STCCARM (35 mOD/min) and KPCCARM (31 mOD/min). The minimum inhibitory concentrations (MICs) of polymyxin B against STKCCM, STCCARM, and STATCC were decreased by 4-, 4-, and 8-folds, respectively, when treated with LysPB32. The combination of LysPB32 and polymyxin B effectively inhibited the growth of STKCCM, STCCARM, and STATCC after 24 h of incubation at 37 degrees C, showing 4.9-, 4.4-, and 3.3-log reductions, respectively. The mutant frequency was low in STKCCM, STCCARM, and STATCC treated with combination of LysPB32-polymyxin B system. The results suggest the LysPB32-polymyxin system can be a potential candidate for alternative therapeutic agent to control antibiotic-resistant pathogens.