Increasing prevalence of bacteriocin carriage in a 6-year hospital cohort of <i>E. faecium</i>

Vancomycin-resistant enterococci (VRE) are important pathogens in hospitalized patients; however, the factors involved in VRE colonization of hospitalized patients are not well characterized. Bacteriocins provide a competitive advantage to enterococci in experimental models of colonization, but little is known about bacteriocin content in samples derived from humans and even less is known about their dynamics in the clinical setting. To identify bacteriocins which may be relevant in the transmission of VRE, we present a systematic analysis of bacteriocin content in the genomes of 2,248 patient-derived <i>E. faecium</i> isolates collected over a 6-year period from a single hospital system. We used computational methods to broadly search for bacteriocin structural genes and a functional assay to look for phenotypes consistent with bacteriocin expression. We identified homology to 15 different bacteriocins, with 2 having a high presence in this clinical cohort. Bacteriocin 43 (bac43) was found in a total of 58% of isolates, increasing from 8% to 91% presence over the 6-year collection period. There was little genetic variation in the bac43 structural or immunity genes across isolates. The enterocin A structural gene was found in 98% of isolates, but only 0.3% of isolates had an intact enterocin A gene cluster and displayed a bacteriocin-producing phenotype. This study presents a wide survey of bacteriocins from hospital isolates and identified bac43 as highly conserved, increasing in prevalence, and phenotypically functional. This makes bac43 an interesting target for future investigation for a potential role in <i>E. faecium</i> transmission.IMPORTANCEWhile enterococci are a normal inhabitant of the human gut, vancomycin-resistant <i>E. faecalis</i> and <i>E. faecium</i> are urgent public health threats responsible for hospital-associated infections. Bacteriocins are ribosomally synthesized antimicrobial proteins and are commonly used by bacteria to provide a competitive advantage in polymicrobial environments. Bacteriocins have the potential to be used by <i>E. faecium</i> to invade and dominate the human gut leading to a greater propensity for transmission. In this work, we explore bacteriocin content in a defined clinically derived population of <i>E. faecium</i> using both genetic and phenotypic studies. We show that one highly active bacteriocin is increasing in prevalence over time and demonstrates great potential relevance to <i>E. faecium</i> transmission.