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Published on: September 5, 2013
A chromosomal location of the mupA gene in Staphylococcus aureus expressing high-level mupirocin resistance
E E Udo1, N Al-Sweih, B C Noronha
1Department of Microbiology, Faculty of Medicine, Kuwait University, PO Box 24923, Safat 13110, Kuwait. edet@hsc.kuniv.edu.kw
Objectives:
To investigate the genetic location of the mupA gene in high-level mupirocin-resistant Staphylococcus aureus isolates.
Materials And Methods:
Antibiotic resistance was detected by disc diffusion. The Etest was used to determine mupirocin MIC. The presence of mupA was detected by PCR using specific primers. Curing, transfer experiments, pulsed-field gel electrophoresis (PFGE) and DNA hybridization were used to study the genetic location of mupA.
Results:
The isolates had mupirocin MICs > 1024 mg/L and were resistant to methicillin, gentamicin, kanamycin, streptomycin, erythromycin, tetracycline, ciprofloxacin, cadmium acetate, propamidine isethionate and ethidium bromide. They carried two plasmids of approximately 26 and 2.8 kb. Curing and transfer experiments demonstrated that the 26 kb plasmid encoded resistance to cadmium acetate, propamidine isethionate and ethidium bromide. Loss of mupirocin resistance corresponded to the loss of a 40 kb DNA fragment from a 175 kb SmaI chromosomal fragment. The mupA gene was detected only in the genomic DNA of the mupirocin-resistant strains and in their derivatives cured of the 26 kb plasmid. A labelled mupA probe hybridized to the 175 kb SmaI fragment only in the mupirocin-resistant isolates.
Conclusion:
The absence of mupA on any of the plasmids and its detection only in the chromosomal DNA of the parents and in their derivatives cured of the 26 kb plasmid strongly supports a chromosomal location for mupA in these isolates.
Insights
High-level mupirocin resistance in Staphylococcus aureus is linked to the mupA gene. This gene is located on the chromosome, not plasmids, in resistant isolates.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Staphylococcus aureus is a significant pathogen.
- High-level mupirocin resistance is an emerging clinical concern.
- The genetic basis for this resistance, particularly the mupA gene, requires clarification.
Purpose of the Study:
- To determine the genetic location of the mupA gene in Staphylococcus aureus isolates exhibiting high-level mupirocin resistance.
Main Methods:
- Antibiotic resistance profiling using disc diffusion and Etest.
- Polymerase Chain Reaction (PCR) to detect the mupA gene.
- Plasmid curing, transfer experiments, pulsed-field gel electrophoresis (PFGE), and DNA hybridization to elucidate gene location.
Main Results:
- Resistant isolates showed high minimum inhibitory concentrations (MICs) for mupirocin (>1024 mg/L) and resistance to multiple other antibiotics.
- The mupA gene was detected exclusively in the genomic DNA of resistant strains and their derivatives.
- Experiments indicated that the mupA gene was associated with a chromosomal DNA fragment, not plasmids.
Conclusions:
- The mupA gene conferring high-level mupirocin resistance in these Staphylococcus aureus isolates is chromosomally located.
- This finding differentiates it from plasmid-mediated resistance mechanisms.
- Understanding the genetic location is crucial for tracking and managing resistance spread.
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