Recent case reports of vancomycin treatment failures in the United States, Japan, and France have prompted a retrospective analysis of 42 cases of septicemia caused by epidemic methicillin-resistant Staphylococcus aureus strain 15 (EMRSA-15), which is the most prevalent epidemic strain of methicillin-resistant S. aureus in the United Kingdom; all cases occurred in a teaching hospital in Manchester, United Kingdom, between 1994 and 1998. Mortality was lowest (4%) in patients with rifampin-susceptible isolates treated with vancomycin and rifampin. It rose to 38% in patients who were treated with both antibiotics but in whom the organism became resistant to rifampin during therapy, and it reached 78% in patients who had rifampin-resistant isolates or in whom rifampin was contraindicated (P<.0001; Fisher exact test, 2-tailed). All isolates were susceptible to vancomycin by conventional laboratory testing, but susceptibility was lost by growth in vancomycin in vitro, becoming resistant at a minimum inhibitory concentration of 8 mg/L. This was associated with accumulation of cell-wall material. The deoxyribonucleic acid fingerprint remained unchanged. This study suggests that rifampin played a key role in the prevention of deaths caused by an epidemic strain of methicillin-resistant S. aureus that readily gave rise to a subpopulation with reduced susceptibility to vancomycin.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.