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

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.

Extreme genetic diversity in the type VII secretion system of Listeria monocytogenes suggests a role in bacterial antagonism

“… Streptococcus intermedius produces at least three antibacterial toxins, of which TelB is an NADase and TelC a lipid II phosphatase [30]. Moreover, recent reports indicate that the T7b systems of Bacillus subtilis and Enterococcus faecalis also have antibacterial activity [38, 39], indicating that bacterial antagonism is a common feature of several Firmicutes T7SSs.…”

A type VII secretion system in Group B Streptococcus mediates cytotoxicity and virulence

“…1c). We performed BLAST analysis to compare the CJB111 EsxA1 against orthologs in other species in which the T7SS has been studied: Mtb (H37Rv) 47 , S. aureus (USA300 strain FSRP357) 13 , Enterococcus faecalis (OG1RF) 29 , L. monocytogenes (EGD-e) 49 , Bacillus subtilis (PY79) 50 , Streptococcus intermedius (B196) 30 , Streptococcus suis (GZ0565) 51 , and Streptococcus gallolyticus (TX20005) 31 . CJB111 EsxA1 shared the least identity with Mtb EsxA (13%) and was more similar to S. aureus EsxA (49% identical) than to S. intermedius or E. faecalis EsxAs (33% and 32% identical, respectively), despite the fact that Streptococcus and Enterococcus are more phylogenetically similar overall 52 .…”

“…Thus, the effect of the T7SS on a bacterium's interaction with other normal flora or on fitness within the host may be strain-or EssC subtype-specific.Despite large variation in EssC subtypes and their cognate putative effectors between strains and bacterial species, genomic analyses indicate that T7SSb loci encode relatively conserved core components (including the N-terminus of EssC) as well as WXG100 protein EsxA, a widely studied T7SS substrate 12,17,26,27 . Increasing numbers of reports have shown a role for the T7SSb and/or EsxA in the pathogenesis of several Gram-positive bacteria 12,[28][29][30][31] ; however, T7SSb has not yet been characterized in the important pathogen Streptococcus agalactiae (also known as Group B Streptococcus, GBS). GBS is a β-hemolytic streptococcal species and the leading etiologic agent of bacterial meningitis in neonates [32][33][34] .…”

“…Additional common substrates of the T7SS include LXG-domain containing polymorphic toxins, which encode a conserved N-terminus similar in structure to WXG100 proteins but with an extended variable C-terminal toxin domain 72 . These toxins have been described in S. intermedius 30,73 , S. aureus 14,16 , and E. faecalis 29 and mediate interbacterial competition and/or host toxicity. CJB111 encodes a putative LXG toxin just downstream of the T7SS core machinery locus that has not yet been characterized.…”

Characterization of an Enterococcus faecalis Bacteriophage vB_EfaM_LG1 and Its Synergistic Effect With Antibiotic

“…Currently, numerous phages against pathogens had been characterized; however, there are only 63 sequenced E. faecalis bacteriophage deposited in NCBI (Chatterjee et al, 2021), which is relatively understudied compared with phages that infect other pathogens, such as Pseudomonas aeruginosa or Staphylococcus aureus phages (De Smet et al, 2017). More phages need to be characterized to provide more therapeutic options for treating the multidrug-resistant E. faecalis.…”