Unusual susceptibility of methicillin-resistant Staphylococcus aureus to erythromycin, clindamycin, gentamicin, and tetracycline at 30 degrees C but not at 35 degrees C

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Abstract
To determine the percentage of MRSA [methicillin-resistant S. aureus] isolates that would be missed if only 1 temperature were used, methicillin resistance and susceptibility of 2397 S. aureus isolates were evaluated by agar dilution at 30.degree. and 35.degree. C. Of the clinical isolates, 93% showed matching MIC [minimum inhibitory concentrations] of methicillin at both temperatures. Another 6.8% (162) showed different MIC at 30.degree. and 35.degree. C, with 60 of the 162 isolates (2.5% of all isolates studied) being resistant to methicillin at 30.degree. C but suceptible at 35.degree. C (temperature-discrepant MRSA). MIC of other antimicrobial agents, measured at 35.degree. C, revealed an unusual pattern of suceptibility of these temperature-discrepant MRSA isolates. In contrast to previously reported resistance of MRSA at 35.degree. C to erythromycin clindamycin, gentamicin and tetracycline, the temperature-discrepant MRSA isolates were susceptibile to these agents. This resistance pattern may be of value in identifying questionable MRSA isolates when only 1 incubation temperature is used.