Postoperative mediastinitis due to methicillin resistant Staphylococcus epidermidis with low sensitivity to vancomycin

BACKGROUND: Vancomycin is the drug of choice for methicillin-resistant Staphylococcus. Antibiotherapy failure is rarely clinically related to Staphylococcus with vancomycin low susceptibility. CASE REPORT: A surgical cure of an aortic stenosis in a neonate was complicated by a Staphylococcus mediastinitis. After initiation of antibiotherapy with vancomycin and rifampin and surgical debridement, there was a rapid improvement. Few days later, failure of therapy was obvious. Despite continuous infusion of vancomycin, with a serum level of 29 mg/L, blood cultures were positive again to Staphylococcus. There was no endocarditis or inadequate surgical drainage. Susceptibility of the Staphylococcus was tested, looking for a tolerant strain. The vancomycin minimum bactericidal concentration was 30 mg/L (above usual value 2 to 8 mg/L), while the minimum inhibitory concentration was 3.75 mg/L. A higher dosage of vancomycin associated with fusidic acid was rapidly efficient, and total recovery was achieved. CONCLUSION: In case of failure of vancomycin therapy, despite correct serum levels, the susceptibility of the Staphylococcus strain has to be determined. A low susceptibility strain prescribes more prolonged combination of two antibiotics.