Bacteriocins of Listeria monocytogenes and Their Potential as a Virulence Factor.

Sangmi Lee

doi:10.3390/toxins12020103

Abstract

Intestinal microbiota exerts protective effects against the infection of various bacterial pathogens, including Listeria monocytogenes, a major foodborne pathogen whose infection can lead to a disease (listeriosis) with a high fatality rate. As a strategy to mitigate the action of the intestinal microbiota, pathogens often produce antimicrobial proteinaceous compounds such as bacteriocins. In this review, we summarize the information currently available for the well-characterized L. monocytogenes bacteriocin listeriolysin S, with the emphasis on its intriguing mode of action as a virulence factor, which promotes the infection of L. monocytogenes by changing the composition of the intestinal microbiota. We then discuss another intriguing L. monocytogenes bacteriocin Lmo2776 that specifically inhibits the inflammogenic species, Prevotella copri, in the intestinal microbiota, reducing superfluous inflammation while weakening virulence. In addition, we describe relatively less studied phage tail-like Listeria bacteriocins (monocins) and elaborate on the possibility that these monocins could be involved in enhancing pathogenicity. In spite of the burgeoning interest in the roles played by the intestinal microbiota against the L. monocytogenes infection, our understanding on the virulence factors affecting the intestinal microbiota is still lacking, calling for further studies on bacteriocins that could function as novel virulence factors.

Highlights

Listeria monocytogenes is the only species in genus Listeria that causes a disease in humans via contaminated foods [1,2,3]
We describe Lmo2776, another well-characterized L. monocytogenes bacteriocin involved in bacterial pathogenicity, as well as high-molecular-weight bacteriocins produced by L. monocytogenes that have been far less studied while discussing their possible roles in pathogenicity
As a result of comprehensive research on L. monocytogenes pathogenesis, we have witnessed a considerable surge in our understanding on various virulence factors of L. monocytogenes, including the latest appreciation on the important role of the microbiota to defend against L. monocytogenes infection in the intestine

Summary

Introduction

Listeria monocytogenes is the only species in genus Listeria that causes a disease (listeriosis) in humans via contaminated foods [1,2,3]. LLS is a bacteriocin that possesses post-translationally modified amino acids and belongs to a subgroup of the family of thiazole/oxazole-modified microcins (TOMMs), which have been identified in various Gram-positive pathogens including Streptococcus pyogenes (SLS), Staphylococcus aureus (staphylolysin S; STS), and Clostridium botulinum (botulysin S or clostridiolysin S; BTS) [22,23,24,25,26,27,28] Among these related bacteriocins, LLS displays the highest similarity to STS in the organization of the gene cluster and amino acid sequence of the encoded proteins, whereas SLS more closely corresponds to BTS [22,23,24,25,29]. 28.2%–53.8% identity to the corresponding sts gene products but 18%–24.7% to the proteins in the SLS-associated gene (sag) operon (data not shown) [25,29] Most studies on this TOMM subgroup have been conducted on SLS, a constitutively expressed bacteriocin that is a potent hemolytic factor and a eukaryotic toxin [27,30,31]. The white triangle represents the promoter PllsA that was predicted by BPROM (http://www.softberry.com/berry.phtml?topic=bprom&group=programs&subgroup=gfindb) [37]

LLS as a Virulence Factor

Monocins

Findings

Conclusions