"Methicillin-resistant" Staphylococcus aureus: reassessment by controlled trial in burns unit

Area of Science:

• Microbiology
• Clinical Pharmacology
• Dermatology

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant challenge in burn wound infections.
• Heteroresistant strains of S. aureus exhibit variable resistance patterns, complicating treatment decisions.

Purpose of the Study:

• To evaluate the efficacy of oral flucloxacillin in treating burn infections caused by methicillin-resistant Staphylococcus aureus (MRSA).
• To determine the optimal temperature for in vitro sensitivity testing of MRSA to guide flucloxacillin treatment.

Main Methods:

• A controlled trial involving 34 patients with burn wounds yielding MRSA.
• Patients received oral flucloxacillin (250 mg q6h for 4 days) or were controls.
• In vitro sensitivity testing was performed at 30°C and 37°C using diffusion and dilution methods.

Main Results:

• S. aureus was eradicated in 9 of 17 patients treated with flucloxacillin, compared to none of the controls.
• Strains previously considered methicillin-resistant were found to be moderately sensitive to flucloxacillin at 37°C.
• Diffusion sensitivity tests at 37°C more accurately predicted clinical response to flucloxacillin than tests at 30°C.

Conclusions:

• Oral flucloxacillin can be effective against specific MRSA strains in burn infections.
• The term 'heteroresistant' is proposed for S. aureus strains showing moderate sensitivity to flucloxacillin at 37°C.
• In vitro sensitivity testing at 37°C is crucial for guiding flucloxacillin therapy in staphylococcal infections.