Phage infection and sub-lethal antibiotic exposure mediate Enterococcus faecalis type VII secretion system dependent inhibition of bystander bacteria.

Anushila Chatterjee,Julia L E Willett,Gary M Dunny,Breck A Duerkop,Melanie Blokesch

doi:10.1371/journal.pgen.1009204

Anushila Chatterjee, Julia L E Willett + Show 3 more

Open Access

https://doi.org/10.1371/journal.pgen.1009204

Copy DOI

Abstract

Bacteriophages (phages) are being considered as alternative therapeutics for the treatment of multidrug resistant bacterial infections. Considering phages have narrow host-ranges, it is generally accepted that therapeutic phages will have a marginal impact on non-target bacteria. We have discovered that lytic phage infection induces transcription of type VIIb secretion system (T7SS) genes in the pathobiont Enterococcus faecalis. Membrane damage during phage infection induces T7SS gene expression resulting in cell contact dependent antagonism of different Gram positive bystander bacteria. Deletion of essB, a T7SS structural component, abrogates phage-mediated killing of bystanders. A predicted immunity gene confers protection against T7SS mediated inhibition, and disruption of its upstream LXG toxin gene rescues growth of E. faecalis and Staphylococcus aureus bystanders. Phage induction of T7SS gene expression and bystander inhibition requires IreK, a serine/threonine kinase, and OG1RF_11099, a predicted GntR-family transcription factor. Additionally, sub-lethal doses of membrane targeting and DNA damaging antibiotics activated T7SS expression independent of phage infection, triggering T7SS antibacterial activity against bystander bacteria. Our findings highlight how phage infection and antibiotic exposure of a target bacterium can affect non-target bystander bacteria and implies that therapies beyond antibiotics, such as phage therapy, could impose collateral damage to polymicrobial communities.

Highlights

Enterococci constitute a minor component of the healthy human microbiota [1]
We provide direct evidence of how phage infection of a clinically relevant pathogen triggers an intrinsic type VII secretion system (T7SS) antibacterial response that restricts the growth of neighboring bacterial cells that are not susceptible to phage infection
Phage induction of T7SS activity is a stress response and in addition to phages, T7SS antagonism can be induced using sub-inhibitory concentrations of antibiotics that facilitate membrane or DNA damage. Together these data show that a bacterial pathogen responds to diverse stressors to induce T7SS activity which manifests through the antagonism of neighboring non-kin bystander bacterial cells

Summary

Introduction

Enterococci, including Enterococcus faecalis, are nosocomial pathogens that cause a variety of diseases, including sepsis, endocarditis, surgical-site, urinary tract and mixed bacterial infections [2, 3]. Multi-drug resistant (MDR) enterococci can outgrow to become a dominant member of the intestinal microbiota, resulting in intestinal barrier invasion and blood stream infection [7, 9]. The ongoing evolution of MDR enterococci in healthcare settings [4,5,6, 10, 11] and their ability to transmit antibiotic resistance among diverse bacteria [9, 12,13,14,15], emphasize the immediate need for novel therapeutic approaches to control enterococcal infections. Our understanding of how phages interact with bacteria and the bacterial response to phage infection is limited

Methods

Results

Discussion

Conclusion