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Daptomycin selects for genetic and phenotypic adaptations leading to antibiotic tolerance in MRSA.

ABSTRACT: Objectives:Daptomycin non-susceptibility in Staphylococcus aureus can emerge via the accumulation of single or multiple mutations, each resulting in a slight increase in the daptomycin MIC. The daptomycin-non-susceptible phenotype may include other features such as daptomycin tolerance. This study identifies S. aureus genomic regions that frequently develop mutations following prolonged daptomycin exposure but have not been previously associated with daptomycin non-susceptibility. Methods:Sequence variations in the same eight loci independently observed following 28?day parallel serial passages of S. aureus J01 in daptomycin were introduced in isolation into S. aureus J01. MICs were determined by microbroth dilution. Daptomycin killing and tolerance were determined by kill curve analysis. Results:Single mutations in snoF, hmp1, sspA, rimP, hepT, rsh, map1 and amaP had only a modest impact on the daptomycin MIC (?2-fold). In contrast, individual mutation in several of these regions resulted in pronounced changes to daptomycin tolerance. Conclusions:This study demonstrates that less characterized mutations in S. aureus following daptomycin exposure do not result in significant daptomycin susceptibility changes, but rather allow for enhanced survival characteristics during treatment. This sheds new light on genetic adaptations that may play a role in persistent infection. Further studies are needed to elucidate the prevalence of these mutations in clinical isolates.

SUBMITTER: Berti AD

PROVIDER: S-EPMC6054297 | biostudies-literature | 2018 Aug

REPOSITORIES: biostudies-literature

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Daptomycin selects for genetic and phenotypic adaptations leading to antibiotic tolerance in MRSA.

Berti Andrew D AD Shukla Neehal N Rottier Aaron D AD McCrone J Sue JS Turner Hannah M HM Monk Ian R IR Baines Sarah L SL Howden Benjamin P BP Proctor Richard A RA Rose Warren E WE

The Journal of antimicrobial chemotherapy 20180801 8

<h4>Objectives</h4>Daptomycin non-susceptibility in Staphylococcus aureus can emerge via the accumulation of single or multiple mutations, each resulting in a slight increase in the daptomycin MIC. The daptomycin-non-susceptible phenotype may include other features such as daptomycin tolerance. This study identifies S. aureus genomic regions that frequently develop mutations following prolonged daptomycin exposure but have not been previously associated with daptomycin non-susceptibility.<h4>Met ...[more]

PMID: 29718242

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Project description:Methicillin-resistant Staphylococcus aureus (MRSA) is a major threat to human health, as the US mortality rate outweighs those from HIV, tuberculosis, and viral hepatitis combined. In the wake of the COVID-19 pandemic, antibiotic resistant bacterial infections acquired during hospital stays have increased. Instead of designing and deploying new antibiotics which MRSA would quickly develop resistance to, adjuvants are a key strategy to combatting these bacteria. We have evaluated several small molecule adjuvants that have strong potentiation with β-lactam antibiotics and have now investigated at the molecular level how the lead adjuvant exerts its effects. We hypothesized that the expression levels of key resistance genes would decrease once cotreated with a β-lactam antibiotic (oxacillin) and the adjuvant (compound 8). Furthermore, bioinformatic analyses would reveal biochemical pathways enriched in differentially expressed genes. RNA-seq analysis showed 176 and 233 genes significantly up and downregulated, respectively, upon cotreatment with oxacillin and compound 8. We identified four subclusters of genes that were regulated in similar patterns in response to drug treatment. Many of these genes displayed a similar pattern of expression where they were unaffected by compound 8 treatment alone, upregulated upon antibiotic challenge, and downregulated again upon cotreatment. GO categories that were significantly enriched among downregulated genes involved carbohydrate utilization and/or transport. Most of the biochemical pathways enriched with significantly downregulated genes involved carbohydrate utilization, such as the citric acid cycle (p=6.4x10-6) and the phosphotransferase system (p=1.8x10-5). The most populated pathway was S. aureus infection (p=3.0x10-3). Creating a network of affected gene products helped uncover potential master regulators for further investigation. This study revealed a dramatic impact of our lead adjuvant on the transcriptome that is consistent with a pleiotropic effect. These results point to this adjuvant as having potential broad therapeutic use in combatting MRSA infections.

Project description:BackgroundUnderstanding drivers of antibiotic resistance evolution is fundamental for designing optimal treatment strategies and interventions to reduce the spread of antibiotic resistance. Various cytotoxic drugs used in cancer chemotherapy have antibacterial properties, but how bacterial populations are affected by these selective pressures is unknown. Here we test the hypothesis that the widely used cytotoxic drug methotrexate affects the evolution and selection of antibiotic resistance.MethodsFirst, we determined methotrexate susceptibility (IC90) and selective abilities in a collection of Escherichia coli and Klebsiella pneumoniae strains with and without pre-existing trimethoprim resistance determinants. We constructed fluorescently labelled pairs of E. coli MG1655 differing only in trimethoprim resistance determinants and determined the minimum selective concentrations of methotrexate using flow-cytometry. We further used an experimental evolution approach to investigate the effects of methotrexate on de novo trimethoprim resistance evolution.FindingsWe show that methotrexate can select for acquired trimethoprim resistance determinants located on the chromosome or a plasmid. Additionally, methotrexate co-selects for genetically linked resistance determinants when present together with trimethoprim resistance on a multi-drug resistance plasmid. These selective effects occur at concentrations 40- to >320-fold below the methotrexate minimal inhibitory concentration.InterpretationOur results strongly suggest a selective role of methotrexate for virtually any antibiotic resistance determinant when present together with trimethoprim resistance on a multi-drug resistance plasmid. The presented results may have significant implications for patient groups strongly depending on effective antibiotic treatment.FundingPJJ was supported by UiT The Arctic University of Norway and the Northern Norway Regional Health Authority (SFP1292-16/HNF1586-21) and JPI-EC-AMR (Project 271,176/H10). DIA was supported by the Swedish Research Council (grant 2017-01,527). The publication charges for this article have been funded by a grant from the publication fund of UiT The Arctic University of Norway.

Project description:Daptomycin remains as one of the main treatment options for Methicillin-Resistant Staphylococcus aureus (MRSA). Sporadic resistance cases reported in patients treated with either daptomycin or glycopeptides are a growing concern. In a previous study, we described a clinical case of a patient with a community-acquired MRSA infection resistant to daptomycin and with intermediate resistance to vancomycin who developed a recurrent infection with a susceptible isogenic strain. In the present work, we further investigated the sequential events to determine whether the switch from a daptomycin resistance to a susceptible phenotype was due to a phenomenon of resistance reversion or recurrent infection with a susceptible strain. Pairwise competition experiments showed that the susceptible clinical recurrent SA6850 strain had increased fitness when compared to the resistant counterpart SA6820 strain. In fact, although we have demonstrated that reversion of daptomycin resistance to daptomycin susceptible can occur in vitro after serial passages in drug-free media, phylogenetic analysis suggested that the in vivo process was the result of a recurrent infection with a previous susceptible isolate carried by the patient rather than a resistance reversion of the strain. Whole genome sequence of evolved strains showed that daptomycin resistance in MRSA is associated with a high fitness cost mediated by mutations in mprF gene, revealed as a key element of the biological cost. Moreover, we determined that daptomycin resistance-associated fitness cost was independent of vancomycin intermediate resistance phenotype, as demonstrated in additional clinical MRSA vancomycin susceptible strains. This study highlights important observations as, despite daptomycin offers a useful treatment option for the patients with persistent infections, it has to be carefully monitored. The high fitness cost associated to daptomycin resistance may explain the reduced dissemination of daptomycin resistance and the absence of daptomycin reported outbreaks.

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Daptomycin selects for genetic and phenotypic adaptations leading to antibiotic tolerance in MRSA.

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Daptomycin selects for genetic and phenotypic adaptations leading to antibiotic tolerance in MRSA.

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