Antibiotic Resistance in Community-Associated MRSA

Summary and Comment |
March 28, 2007

Antibiotic Resistance in Community-Associated MRSA

  1. Daniel J. Diekema, MD, MS

Clindamycin, tetracycline, and mupirocin resistance are emerging in community-associated MRSA.

  1. Daniel J. Diekema, MD, MS

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is an important cause of disease worldwide. Previous studies have shown that >80% of CA-MRSA in the U.S. is susceptible to clindamycin and tetracycline. Now, investigators report increasing resistance to these antibiotics in CA-MRSA isolates collected in Boston.

Pulsed-field gel electrophoresis (PFGE) and antibiotic susceptibility testing were performed on all MRSA isolates collected at a single Boston ambulatory care center from May 2004 through November 2005. Of the 123 isolates examined, 102 had PFGE patterns consistent with CA-MRSA strain type USA300. Among these USA300 isolates, resistance rates were high to erythromycin (96%), levofloxacin (85%), clindamycin (57%), and tetracycline (30%). Eighteen isolates (18%) were resistant to all four of these oral antibiotics. Twelve of the 18 were tested further and found to have high-level mupirocin resistance. Two major USA300 subtypes were represented (0114 and 0247), and most of the antimicrobial resistance was found among the USA300-0247 isolates. The resistance genes detected among multidrug-resistant isolates (tetK, ermC, and mupA) are typically found on plasmids. All isolates were susceptible to trimethoprim-sulfamethoxazole, linezolid, doxycycline, and rifampin.


Although these data are from a single center, they suggest that multiple-drug resistance is now emerging in CA-MRSA. Because the resistance genes involved are plasmid-mediated, they could spread quickly. The spread of multidrug-resistant CA-MRSA limits options both for oral therapy and for use of mupirocin decolonization during CA-MRSA outbreaks.


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