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Genomic Insights into Staphylococcus aureus Isolates Exhibiting Diminished Daptomycin Susceptibility
Natalia Gómez-Casanova1,2, Mª Nieves Gutiérrez-Zufiaurre1,3, Ana Mª Blázquez de Castro1,3
1Research Group on Clinical Microbiology and Parasitology and Antimicrobial Resistance (IIMD-16), Instituto de Investigación Biomédica de Salamanca (IBSAL), Universidad de Salamanca, CSIC, Hospital Universitario de Salamanca, 37007 Salamanca, Spain.
Daptomycin resistance in Staphylococcus aureus involves complex genetic mutations, particularly in the mprF gene. Understanding these genetic changes is crucial for developing new strategies against multidrug-resistant bacteria.
Area of Science:
- Microbiology
- Genetics
- Infectious Diseases
Background:
- Daptomycin is a critical antibiotic for treating multidrug-resistant gram-positive bacterial infections.
- Mechanisms of daptomycin resistance and its genetic underpinnings are not fully understood.
- Previous studies linked mutations in genes like mprF, walkR, rpoB, and rpoC to daptomycin resistance.
Purpose of the Study:
- To investigate mutations in 11 previously identified genes associated with daptomycin non-susceptibility in clinical Staphylococcus aureus isolates.
- To compare the mutation profiles in clinical isolates with the reference strain S. aureus ATCC 25923.
- To elucidate the role of specific genes in the development of daptomycin resistance.
Main Methods:
- Studied nine daptomycin-non-susceptible Staphylococcus aureus clinical isolates (daptomycin MIC >1 mg/L).
- Assessed susceptibility to daptomycin and other antibiotics (vancomycin, linezolid, oxacillin, telavancin, dalbavancin).
- Amplified and sequenced 11 target genes (walkR, agrA, cls1, cls2, fakA, pnpA, clpP, prs, rpoB, rpoC, mprF) using PCR and compared sequences to S. aureus ATCC 25923 via BLAST.
Main Results:
- No mutations were found in walkR, pnpA, prs, and clpP genes.
- Most isolates (except MSa5) exhibited significant mutations (13-25 amino acid changes) in the mprF gene.
- Mutations were also frequently observed in rpo genes, cls genes, and fakA.
- Isolate MSa5 showed a single mutation (P314T) in mprF.
- High polymorphism was noted in mprF and cls1 across most isolates.
Conclusions:
- Daptomycin non-susceptibility in clinical Staphylococcus aureus arises from diverse combinations of mutations, differing from the reference strain.
- The mprF gene is a major site of mutation contributing to daptomycin resistance.
- cls1 and mprF genes display substantial polymorphism in daptomycin-resistant isolates, highlighting their importance.
- Further research is needed to fully understand the complex genetic landscape of daptomycin resistance.
