Rickettsia massiliae Human Isolation

BORSA initially described nonheteroresistant strains of S. aureus with oxacillin MIC <2 mg/L, which produce ample β-lactamases and are rendered fully susceptible to PRP by β-lactamase-inhibitors (4,6). Subsequent BORSA strains described have had higher oxacillin MICs (4–8 mg/L) (4). The proportion of BORSA among clinical isolates of S. aureus varies (1.4%–12.5%) but is usually ?5% (4,10). A BORSA infection outbreak among dermatology patients with severe skin diseases has also been reported (10). Postulated resistance mechanisms include overproduction of conventional penicillinases, production of an inducible, plasmid-mediated, membrane-bound methicillinase, and in some cases, point mutations of penicillin-bindingproteins (4). The clinical importance of BORSA is unknown since early clinical/animal data suggest treatment efficacy of PRP (against strains with MIC <2 mg/L) (4,6,9). Whether BORSA with higher oxacillin MICs (4–8 mg/L) will respond equally well to PRP is less clear. Further studies into the treatment of BORSA, including pharmacokinetic considerations, are needed (4). However, high-dose β-lactam/β-lactamase inhibitor combinations (e.g., ampicillin/sulbactam), as shown in animal models, are at least as effective as PRP (9). In conclusion, our report suggests that mecA (or PBP2a) detection may help manage serious, community-acquired, non–multidrug-resistant MRSA infections because of the potential confusion between BORSA and CAMRSA.