[Postoperative mediastinitis due to methicillin resistant Staphylococcus epidermidis with low sensitivity to...

Vancomycin is the drug of choice for methicillin-resistant Staphylococcus. Antibiotherapy failure is rarely clinically related to Staphylococcus with vancomycin low susceptibility.

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.

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.