2014, Number 2
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ABSTRACTBackground: Recently the susceptibility cutoff point of S. aureus to vancomycin was reduced 4 to 2 mg/mL due to poor response, now questions whether a further reduction should be done.
Objective: To review the frequency of isolations of methicillin and vancomycin resistant strains of S. aureus in our hospital.
Material and method: A retrospective, cross-sectional and descriptive study was done; within 3 years we isolated strains of S. aureus and MICs to vancomycin were obtained with the MicroScan system (Dade-Behring, Sacramento, CA) according to the Clinical and Laboratory Standards Institute.
Results: Seven (13.2%) out of 53 MSSA and 17 (19.1%) out of 89 MRSA strains gave vancomycin MIC of 2 µg/mL, MIC was not greater in any case. From these 24 samples, 10 (41.6%) were from subcutaneous abscesses, 8 (33.3%) from bronchial lavage, 4 from blood cultures and two from joint fluid.
Conclusions: The resistance in our isolates of S. aureus to methicillin is high, and important the coexistence of meticyline-resistant and -susceptible S. aureus with vancomycin MICs of 2 µg/mL. We found no strains with MICs ≥ 4 µg/mL. The laboratory must be aware of the strains with vancomycin MIC › 2 µg/mL, and this information should be confirmed in cases of severe infections.
Rybak M, Lomaestro B, Rotschafer JC, et al. Therapeutic monitoring of vancomycin in adult patients: a consensus review of the American Society of Health-System Pharmacists, the Infectious Disease Society of America, and the Society of Infectious Diseases Pharmacists. Am J Health Syst Pharm 2009;66:82-98.
Satola SW, Lessa FC, Ray SM, Bulens SN, et al. Clinical and laboratory characteristics of invasive infections due to methicillin-resistant Staphylococcus aureus isolates demonstrating a vancomycin MIC of 2 micrograms per milliliter: lack of effect of heteroresistant vancomycinintermediate S. aureus phenotype. J Clin Microbiol 2011; 49:1583-1587.