Penicillin-Binding Proteins and Associated Protein Mutations Confer Oxacillin/Cefoxitin Tolerance in Borderline...

Area of Science:

• Microbiology
• Molecular Biology
• Antimicrobial Resistance

Background:

• Borderline oxacillin-resistant Staphylococcus aureus (BORSA) strains are clinical isolates with mild oxacillin resistance, lacking mecA/mecC genes.
• BORSA is a risk factor for developing resistance to multiple antibiotics.
• Understanding the mechanisms of BORSA resistance is crucial for effective treatment strategies.

Purpose of the Study:

• To characterize BORSA isolates and their derivatives.
• To investigate the role of penicillin-binding proteins (PBPs) and their regulatory regions in oxacillin and cefoxitin tolerance in BORSA.
• To identify genetic mutations associated with increased antibiotic resistance in BORSA.

Main Methods:

• Antibiotic susceptibility testing, including Minimum Inhibitory Concentrations (MICs) and TDtest.
• Mutation analysis of genes encoding PBPs (pbp1, pbp2, pbp3, pbp4) and related proteins (gdpP, yjbH), including the pbp4 promoter region.
• Spontaneous selection of derivative strains with increased oxacillin resistance.

Main Results:

• Eight BORSA isolates harbored the blaZ gene, with predicted hyperproduction of penicillinase.
• Four derivative strains exhibited higher oxacillin MICs compared to parent isolates.
• Mutations in pbp1, pbp2, pbp3, pbp4, gdpP, and yjbH genes, and the pbp4 promoter were identified in BORSA isolates and derivatives, correlating with oxacillin/cefoxitin tolerance.

Conclusions:

• Mutations in PBPs and their regulatory regions contribute to oxacillin and cefoxitin tolerance in BORSA strains.
• The blaZ gene and penicillinase hyperproduction are present in some BORSA isolates.
• Genetic alterations in PBPs are a significant mechanism for acquired antibiotic resistance in BORSA.