Genomic signatures of experimental adaptation to antimicrobial peptides inStaphylococcus aureus

Abstract

ObjectivesThe evolution of resistance against antimicrobial peptides has long been considered unlikely due to their mechanism of action, yet experimental selection with AMPs results in rapid evolution of resistance in several species of bacteria. Although numerous studies have utilized mutant screens to identify loci that determine AMP susceptibility, there is a dearth of data concerning the genomic changes which accompany experimental evolution of AMP resistance.MethodsUsing genome re-sequencing we analysed the mutations which arise during experimental evolution of resistance to the cationic AMPs iseganan, melittin and pexiganan, as well as to a combination of melittin and pexiganan, or to the aminoglycoside antibiotic streptomycin.ResultsAnalysis of 17 independently replicated Staphylococcus aureus selection lines, including unselected controls, showed that each AMP selected for mutations at distinct loci. We identify mutations in genes involved in the synthesis and maintenance of the cell envelope. This includes genes previously identified from mutant screens for AMP resistance, and genes involved in the response to AMPs and cell-wall-active antibiotics. Furthermore, transposon insertion mutants were used to verify that a number of the identified genes are directly involved in determining AMP susceptibility.ConclusionsStrains selected for AMP resistance under controlled experimental evolution displayed consistent AMP-specific mutations in genes which determine AMP susceptibility. This suggests that different routes to evolve resistance are favored within a controlled genetic background.

Genomic signature of experimental adaptation ofStaphylococcus aureusto a natural combination of insect antimicrobial peptides

“…We have previously shown that evolution of resistance towards the AMP melittin in S. aureus JLA513 is associated with nonsense mutations in ytrA . Here we find that the most frequent ytrA mutation is identical to the stop-gain mutation described in S. aureus JLA513 12 . In S. aureus , the ytr operon is induced by cationic AMPs 32 and encodes a putative GntR-family repressor (YtrA) as well as two ABC transporters.…”

“…While our assessment is based on the Jaccard-Distance, it is noteworthy that all strains have one of two resistance-associated mutations. This is much lower than the variation observed in a previous study in S. aureus against a panel of antimicrobial peptides originating from different organisms 12 .…”

“…In a recent experimental evolution study investigating S. aureus resistance evolution against three different AMPs from different organisms (melittin, pexiganan and iseganan 11 ), we found a range of mutations associated with resistance 12 . These mutations did not segregate by AMP.…”

Genomics of experimental adaptation of Staphylococcus aureus to a natural combination of insect antimicrobial peptides

“…In a recent experimental evolution study investigating S. aureus resistance evolution against three different AMPs from different organisms (melittin, pexiganan and iseganan) 12 , we found a range of mutations associated with resistance 13 . These mutations were not specific for different AMPs.…”

Evolution of defence cocktails: Antimicrobial peptide combinations reduce mortality and persistent infection

“…Such defence cocktails often contain a high abundance of AMPs that are not known to be effective against the infectious agent, (Barribeau, Sadd, du Plessis, & Schmid‐Hempel, ; Makarova et al., ; Yokoi, Ito, Minakuchi, Toshiharu, & Miura ), despite the capacity of the insect immune system to mount‐specific immune responses (Kounatidis & Ligoxygakis, ). Also, the expression of AMPs comes at a metabolic cost (Johnston, Dobson, & Rolff, ; Poulsen, Bot, Nielsen, & Boomsma, ).…”