A Novel Enterococcus Phage Endolysin Lys22 with a Wide Host Range Against Mixed Biofilm of Enterococcus faecalis, Staphylococcus aureus, and Acinetobacter baumannii

The global surge in multidrug-resistant (MDR) bacterial pathogens has created an urgent imperative for innovative antimicrobial strategies. <i>Enterococcus faecalis</i>, <i>Staphylococcus aureus</i>, and <i>Acinetobacter baumannii</i> demonstrate remarkable antibiotic resistance and dominate hospital-acquired infections. These bacteria often form biofilms, a complex community structure that shields them from immune system phagocytosis, resists antibiotic penetration, and enhances their survival in hostile environments. In clinical cases, these bacteria often form mixed biofilms and lead to treatment failures. Phages and their derivatives have emerged as promising candidates in the fight against drug-resistant bacteria. Lys22, an endolysin derived from an enterococcus phage, has been cloned and demonstrated to possess a broad host range, effectively targeting <i>E. faecalis</i>, various <i>Staphylococcus</i> species, and <i>A. baumannii</i>. When applied to the biofilms formed by these bacteria, Lys22 was found to significantly inhibit both simple and complex biofilms in vitro. Virulent genes, including <i>agrA</i>, <i>sarA</i>, and <i>icaA</i> in <i>S. aureus</i>; <i>asa1</i>, <i>cylA</i>, and <i>gelE</i> in <i>E. faecalis</i>; and <i>OmpA</i> and <i>lpsB</i> in <i>A. baumannii</i> were also downregulated by Lys22. Notably, Lys22 also exhibited a robust protective effect against dual or triple infections involving <i>E. faecalis</i>, <i>S. aureus</i>, and <i>A. baumannii</i> in a zebrafish embryos model, highlighting its potential as a therapeutic agent in combatting multi-bacterial infections.