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Mupirocin resistance in methicillin-resistant Staphylococcus aureus from a veterans hospital
M H Naguib1, M T Naguib, D J Flournoy
1Laboratory Service, Veterans Affairs Medical Center, Oklahoma City, OK 73104.
Abstract:
679 clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) which occurred from 1986 and 1992 were retrospectively tested to determine the frequency of mupirocin resistance. With disk agar diffusion screening, 26 of 679 MRSA had zones of inhibition of < 18 mm using a 5 micrograms mupirocin disk. Minimal inhibitory concentrations (MICs) by agar dilution on the 26 suspect MRSA revealed that 9 were resistant. Of these 9, 1 had a MIC of 6.25, 4 of 12.5, 1 of 25, 1 of 500 and 2 of > 1,000 micrograms/ml. Although the overall incidence of mupirocin resistance was low in our hospital, 5 of the 9 resistant isolates occurred in 1992 and may signal a much more serious threat in the future.
Insights
Mupirocin resistance in methicillin-resistant Staphylococcus aureus (MRSA) is low but increasing. Nine of 679 MRSA isolates were resistant, with a concerning rise in cases during 1992, signaling a potential future threat.
Area of Science:
- Clinical microbiology
- Infectious diseases
- Antimicrobial resistance
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) is a significant healthcare-associated pathogen.
- Mupirocin is a crucial topical antibiotic for treating MRSA infections.
- The emergence of mupirocin resistance in MRSA is a growing public health concern.
Purpose of the Study:
- To determine the frequency of mupirocin resistance among clinical MRSA isolates.
- To analyze trends in mupirocin resistance over time.
Main Methods:
- Retrospective analysis of 679 MRSA isolates collected between 1986 and 1992.
- Disk agar diffusion screening using a 5 µg mupirocin disk.
- Agar dilution method to determine Minimal Inhibitory Concentrations (MICs) for suspect isolates.
Main Results:
- Twenty-six out of 679 MRSA isolates (3.8%) showed zones of inhibition < 18 mm, suggesting potential resistance.
- Nine isolates (1.3% of total) were confirmed resistant to mupirocin, with MICs ranging from 6.25 to >1,000 µg/ml.
- A notable increase in resistant isolates was observed in 1992, with 5 out of 9 resistant strains identified that year.
Conclusions:
- The overall incidence of mupirocin resistance in this MRSA cohort was low.
- The increasing trend of mupirocin resistance, particularly in recent years (1992), warrants close monitoring.
- This rise may indicate a developing threat that could compromise future MRSA treatment strategies.