A Novel Mechanism of Killing Antibiotic-Resistant Enterococci

Abstract

The enterococci are a tenacious genus of bacteria that are both commensals of nearly all land animals and hospital-associated antibiotic-resistant pathogens due to their unusual ability to tolerate antibiotics, disinfectants, desiccation, and starvation. When pathogenic strain Enterococcus faecalis V583 was grown together with commensal strain E. faecalis OG1RF, the commensal unexpectedly killed the pathogen. Previous work determined that two mobile elements in the pathogen, pheromone-responsive plasmid pTEF2 and novel integrative conjugative element NovICE, were necessary for this killing phenomenon. We created a strain of E. faecalis with pTEF2 and EF0150, the gene from NovICE necessary and sufficient for killing, fixed in place with antibiotic resistance genes, and generated pheromone-killing resistant mutants. 130 mutants were sequenced and computationally analyzed for the mutations that conferred resistance. These results identify candidates for the necessary factor on pTEF2 for the killing phenomenon and suggest possibilities as to the mechanism of killing downstream of the interaction of EF0150 and the factor from pTEF2. In addition to further illuminating how pheromone-responsive plasmid pTEF2 compares to the model enterococcal sex pheromone pCF10 and shedding light on the tradeoffs of mobile element accretion for pathogens, this work contributes to our understanding of a novel mechanism of killing enterococci, identified as a “serious threat” by the CDC, and could lead to the creation of a therapeutic based on this new target.