Characterization of a broad-spectrum endolysin rLysJNwz and its utility against Salmonella in foods

Salmonella is a common foodborne pathogen worldwide. The use of bacteriophage-encoded endolysins as antimicrobial agents is a promising approach for controlling pathogenic contamination. In this context, a recombinant endolysin named rLysJNwz, consisting of a single domain falling with the L-alanogyl-D-glutamate peptidase-like family, was cloned, expressed, and characterized. The yield of rLysJNwz was about 25 mg/L. Synergy between 7.5 mu g/mL rLysJNwz and 0.5 mmol/L EDTA could decrease the viable counts of Salmonella NCTC 8271 by 93.28%. A synergistic effect between rLysJNwz and polymyxin B was demonstrated, exhibiting the MIC of polymyxin B decreased by twofold. Specifically, rlysJNwz had strong thermostability at temperatures (4-95 degrees C) and maintained high activity at pHs from 5.0 to 11.0. rlysJNwz was a metal ion-dependent peptidase, which activated by divalent metal ions such as Zn2+, Mn2+, or Ca2+. Moreover, it was also found that the synergism of rlysJNwz and EDTA had bactericidal activities against a broad range of Gram-negative bacteria, including several multidrug-resistant bacteria. The application of rLysJNwz combined with EDTA was evaluated on contaminated eggs and lettuce for 60 min, displaying more than 86.7% and 86.5% reduction of viable Salmonella, respectively. Hence, these results suggest that rLysJNwz is a potential antibacterial agent to control Salmonella, especially antibiotic-resistant pathogen contamination in the field of food safety.