LysM: a bacterial self-encoded peptidoglycan hydrolase as an antimicrobial and anti-biofilm agent for Gram-negative nosocomial pathogens

Abstract

Agents with both anti-biofilm property and broad-spectrum antimicrobial activity are urgently needed, especially for drug-resistant nosocomial pathogens. Here, we report a bacterial genome-encoded glycoside hydrolase, named LysM, with lytic activity against multiple Gram-negative nosocomial pathogens and little toxicity to human cells. 3D structural modelling and site-directed mutagenesis indicates that LysM is a peptidoglycan-specific glycoside hydrolase. In combination with EDTA, exogenous LysM induces explosive bacterial cell lysis, exhibits potent bactericidal activity, and eliminates 24 h-old biofilms formed by Gram-negative ESKAPE group pathogens with the highest activity on three nosocomial pathogens, namely Pseudomonas aeruginosa, Acinetobacter baumannii, and Enterobacter cloacae, all of which contain LysM homologs in their genome. More strikingly, LysM supplied in growth media without EDTA, also inhibits the growth of several nosocomial pathogens. Single-cell tracking analysis reveals that LysM completely prevent biofilm formation of P. aeruginosa by reducing bacterial surface-adherence and extending the doubling time. A LysM-based cocktail consisting of LysM, EDTA, and matrix exopolysaccharide-degrading glycosidase PslG, shows potent anti-biofilm activity against P. aeruginosa, including drug-resistant clinical isolates, both in vitro and in human airway organoids (HAOs) biofilm infection model. In addition, LysM enhances the efficacy of many antibiotics from all major classes, including colistin, tobramycin, ciprofloxacin, and tetracycline. Our findings not only provide a clinical candidate for the treatment of nosocomial infections but also open a new path for antimicrobial discovery and anti-biofilm strategies, as homologues of LysM are present in the genomes of many bacteria and phages.