Intrinsic resistance of Enterococcus faecalis strains to φEf11 phage endolysin is associated with the presence of φEf11 prophage

The use of bacteriophage-encoded murein hydrolases (endolysins) is being actively explored as a means of controlling multidrug-resistant pathogens. Previously, we isolated and characterized one such enzyme, the phage phi Ef11 ORF28 lysin, which demonstrated profound antimicrobial activity against many strains of Enterococcus faecalis. Although the lysin is eminently active against many vancomycin-resistant enterococal (VRE) strains, and displays lower minimum inhibitory concentrations than vancomycin against vancomycin-sensitive strains, there is a subset of E. faecalis strains that is not affected by the lysin. Currently, there is no explanation for the disparate sensitivity to ORF28 lysin among E. faecalis strains. In the present investigation, we show that the intrinsic insensitivity of the insusceptible strains to the lysin is associated with the presence of a phi Ef11 prophage. Of the strains harboring phage phi Ef11 genes (N = 28), 68% were insensitive to the lysin, whereas 91% of the strains (N = 75) lacking detectable phi Ef11 genes demonstrated lysin sensitivity. Furthermore, curing a lysin-resistant, lysogenic E. faecalis strain resulted in a lysin-sensitive derivative, whereas lysogenizing a wild-type non-lysogenic strain converted it from lysin sensitivity to lysin resistance. Our results suggest that lysin resistance comes about through lysogenic conversion of non-lysogenic, lysin-sensitive strains.

Automated summary

The study explores the use of bacteriophage-encoded murein hydrolases as a means of controlling multidrug-resistant pathogens. It is found that the sensitivity of E. faecalis strains to the lysin is associated with the presence of a phi Ef11 prophage, indicating that lysin resistance comes about through lysogenic conversion of non-lysogenic, lysin-sensitive strains.