Enterococcus spp. as a Producer and Target of Bacteriocins: A Double-Edged Sword in the Antimicrobial Resistance Crisis Context

Abstract

Enterococcus spp. are one of the most frequent producers of bacteriocins (enterocins), which provides them with an advantage to compete in their natural environment, which is the gut of humans and many animals. The enterocins' activity against microorganisms from different phylogenetic groups has raised interest in Enterococcus spp. in different contexts throughout the last decades, especially in the food industry. Nevertheless, some species can also cause opportunistic life-threatening infections and are frequently multidrug-resistant (MDR). Vancomycin-resistant Enterococcus (VRE), in particular, are an ongoing global challenge given the lack of therapeutic options. In this scenario, bacteriocins can offer a potential solution to this persistent threat, either alone or in combination with other antimicrobials. There are a handful of studies that demonstrate the advantages and applications of bacteriocins, especially against VRE. The purpose of this review is to present a current standpoint about the dual role of Enterococcus spp., from important producers to targets needed to be controlled, and the crucial role that enterocins may have in the expansion of enterococcal populations. Classification and distribution of enterocins, the current knowledge about the bacteriocinome of clinical enterococci, and the challenges of bacteriocin use in the fight against VRE infections are particularly detailed.

Keywords: VRE; alternatives to antibiotics; antimicrobial resistance; bacteriocins; enterocins; enterococci; gut microbiota; multidrug-resistant infections.

Figure 1

Timeline of important events in the history of bacteriocins. Enterocins specifically described in clinical enterococci isolates so far are included as blue lines: dark blue indicates enterocins produced by E. faecium and light blue by E. faecalis; the years indicated correspond to the first mention of a given enterocin, either the year of isolation or, whenever unknown, the year of bacteriocin description/publication (marked with * in the latter case). The year corresponding to the appearance of the most clinically relevant antibiotic resistance in enterococci appear as red lines. Abbreviations: LAB, lactic acid bacteria; VRE, vancomycin-resistant enterococci; Bac, bacteriocin; Ent, enterocin.

Figure 2

Advantages and limitations of bacteriocins. Words in bold indicate that such a bacteriocin feature can be an advantage or a limitation, according to different contexts. Arrows pointing down mean “less”. Arrows pointing simultaneously up and down mean “are related”.