Synthetic antimicrobial peptides as enhancers of the bacteriolytic action of staphylococcal phage endolysins

Ana Gouveia,Helena Veiga,Daniela Pinto,Carlos São-José,Wilson Antunes,Mariana G Pinho

doi:10.1038/s41598-022-05361-1

Abstract

Bacteriophage endolysins degrade the bacterial cell wall and are therefore considered promising antimicrobial alternatives to fight pathogens resistant to conventional antibiotics. Gram-positive bacteria are usually considered easy targets to exogenously added endolysins, since their cell walls are not shielded by an outer membrane. However, in nutrient rich environments these bacteria can also tolerate endolysin attack if they keep an energized cytoplasmic membrane. Hence, we have hypothesized that the membrane depolarizing action of antimicrobial peptides (AMPs), another attractive class of alternative antibacterials, could be explored to overcome bacterial tolerance to endolysins and consequently improve their antibacterial potential. Accordingly, we show that under conditions supporting bacterial growth, Staphylococcus aureus becomes much more susceptible to the bacteriolytic action of endolysins if an AMP is also present. The bactericidal gain resulting from the AMP/endolysin combined action ranged from 1 to 3 logs for different S. aureus strains, which included drug-resistant clinical isolates. In presence of an AMP, as with a reduced content of cell wall teichoic acids, higher endolysin binding to cells is observed. However, our results indicate that this higher endolysin binding alone does not fully explain the higher susceptibility of S. aureus to lysis in these conditions. Other factors possibly contributing to the increased endolysin susceptibility in presence of an AMP are discussed.

Highlights

Bacteriophage endolysins degrade the bacterial cell wall and are considered promising antimicrobial alternatives to fight pathogens resistant to conventional antibiotics
Application of endolysins as enzybiotics against Gram-positive bacteria is usually considered facilitated, since these lack the outer membrane that in Gram-negative bacteria and mycobacteria hinders enzybiotic access to the CW8,9. Despite lacking this cell wall (CW) protecting barrier, a few studies have shown that Gram-positive bacteria can restrict or tolerate endolysin attack to certain extent. This was observed for several bacterial species/endolysin pairs, with endolysin tolerance being favored in media that supported bacterial growth, but abolished upon membrane proton-motive force (PMF) collapse by the holin or by ionophores mimicking its action[10,11,12]
By using a PMF-disrupting antimicrobial peptides (AMPs) and a staphylococcal endolysin as models, we have explored the capacity of the AMP to enhance the lytic power of the endolysin against the high priority, Gram-positive pathogen S. aureus[24], including methicillin resistant S. aureus (MRSA) clinical strains, under growth supporting conditions

Summary

Introduction

Bacteriophage endolysins degrade the bacterial cell wall and are considered promising antimicrobial alternatives to fight pathogens resistant to conventional antibiotics. One of the measures to tackle the problem relies on the development of alternative antimicrobials capable of acting on drug-resistant bacteria, preferentially with new modes of action that minimize the emergence of resistance Among such alternatives in the pipeline are endolysins[4], which are enzymes (enzybiotics) that destroy the bacterial cell wall (CW)[5]. Application of endolysins as enzybiotics against Gram-positive bacteria is usually considered facilitated, since these lack the outer membrane that in Gram-negative bacteria and mycobacteria hinders enzybiotic access to the CW8,9 Despite lacking this CW protecting barrier, a few studies have shown that Gram-positive bacteria can restrict or tolerate endolysin attack to certain extent. This phenomenon seems to recapitulate the natural context of phage infection, where endolysins only act after the holin-mediated PMF dissipation (lysis mechanisms reviewed in Ref.[8])

Methods

Results

Conclusion