Antimicrobial Peptide Exposure Selects for Resistant and Fit Stenotrophomonas maltophilia Mutants That Show Cross-Resistance to Antibiotics

Abstract

Antimicrobial peptides (AMPs) are essential components of the innate immune system and have been proposed as promising therapeutic agents against drug-resistant microbes. AMPs possess a rapid bactericidal mode of action and can interact with different targets, but bacteria can also avoid their effect through a variety of resistance mechanisms. Apart from hampering treatment by the AMP itself, or that by other antibiotics in the case of cross-resistance, AMP resistance might also confer cross-resistance to innate human peptides and impair the anti-infective capability of the human host. A better understanding of how resistance to AMPs is acquired and the genetic mechanisms involved is needed before using these compounds as therapeutic agents. Using experimental evolution and whole-genome sequencing, we determined the genetic causes and the effect of acquired de novo resistance to three different AMPs in the opportunistic pathogen Stenotrophomonas maltophilia, a bacterium that is intrinsically resistant to a wide range of antibiotics. Our results show that AMP exposure selects for high-level resistance, generally without any reduction in bacterial fitness, conferred by mutations in different genes encoding enzymes, transporters, transcriptional regulators, and other functions. Cross-resistance to AMPs and to other antibiotic classes not used for selection, as well as collateral sensitivity, was observed for many of the evolved populations. The relative ease by which high-level AMP resistance is acquired, combined with the occurrence of cross-resistance to conventional antibiotics and the maintained bacterial fitness of the analyzed mutants, highlights the need for careful studies of S. maltophilia resistance evolution to clinically valuable AMPs. IMPORTANCE Stenotrophomonas maltophilia is an increasingly relevant multidrug-resistant (MDR) bacterium found, for example, in people with cystic fibrosis and associated with other respiratory infections and underlying pathologies. The infections caused by this nosocomial pathogen are difficult to treat due to the intrinsic resistance of this bacterium against a broad number of antibiotics. Therefore, new treatment options are needed, and considering the growing interest in using AMPs as alternative therapeutic compounds and the restricted number of antibiotics active against S. maltophilia, we addressed the potential for development of AMP resistance, the genetic mechanisms involved, and the physiological effects that acquisition of AMP resistance has on this opportunistic pathogen.

E. faecalisacquires resistance to antimicrobials and insect immunity via common mechanisms

“…However, recent work has shown that this low level of peptide redundancy is typical of most bacterial infections in Drosophila (Carboni et al, 2022; Hanson et al ., 2019). In vitro experiments have shown that mammalian cationic antimicrobial peptides can select antimicrobial resistance in Stenotrophomonas maltophilia ; our experiments indicate that this is not restricted to cationic antimicrobial peptides and can take place in response to intact immune responses in vivo (Blanco et al, 2020).…”

“…E. faecalis has been isolated from many insects, including the gut and hemolymph of wild Drosophila ( 1, 4-6 ). Unlike mammals, insect immune responses are often described as being strongly dependent on inducible antimicrobial peptides as immune effectors; in vitro selection experiments with other bacteria have borne out the possibility that antimicrobial peptides can select resistance to other antibiotics ( 7, 8 ). However, intact immune systems—in insects as in other animals—are complex, typically deploying a variety of semiredundant effectors against any given infection, so the actual selective pressure experienced by infecting organisms is not necessarily simple.…”

“…faecalis has been isolated from many insects, including the gut and hemolymph of wild Drosophila (1,(4)(5)(6). Unlike mammals, insect immune responses are often described as being strongly dependent on inducible antimicrobial peptides as immune effectors; in vitro selection experiments with other bacteria have borne out the possibility that antimicrobial peptides can select resistance to other antibiotics (7,8).…”

A Synthetic Cyclized Antimicrobial Peptide with Potent Effects against Drug-Resistant Skin Pathogens

“…To determine whether CD4-PP-sensitive isolates could quickly develop resistance, random clinical isolates of S. aureus , MRSA, and GAS were subcultured in TSB media supplemented with CD4-PP at MIC for 1 week, whereafter the MIC was repeated for these isolates using the methods as described previously. 31 …”

Analyzing resistome in soil and Human gut: a study on the characterization and risk evaluation of antimicrobial peptide resistance

“…AMP resistance can emerge under selective pressures and be acquired through horizontal transfer ( Arcilla et al, 2016 ). Furthermore, resistance to an AMP may compromise the efficacy of other AMPs and impact immunoregulatory functions in humans ( Joo et al, 2016 ; Blanco et al, 2020 ). These factors pose limitations on the widespread use of AMPs across various domains.…”