In vitro activity of cefotiam against oxacillin-resistant Staphylococcus epidermidis strains--reevaluation of beta-lactam antibiotics efficiency on MRSE.

We evaluated the efficacy of cefotiam (CTM) against Staphylococcus epidermidis (S. epidermidis) isolated from blood culture and central venous catheters. Of the S. epidermidis strains tested, 82.3% were methicillin (MPIPC)-resistant (MPIPC MIC > or = 0.5 microg/ml) and expressed the mecA gene, and 89.2% of these MPIPC-resistant S. epidermidis (MRSE) showed less than 8.0 microg/ml CTM MIC. In vitro killing kinetics of CTM against MRSE demonstrated that strains with high CTM MIC (> or = 4.0 microg/ml) showed high MPIPC MIC (> or = 4.0 microg/ml). All strains with low CTM MIC (< or = 2.0 microg/ml) showed MPIPC MIC lower than 2.0 microg/ml. In time-kill studies, CTM had high bactericidal activity against strains with low CTM MIC (< or = 2.0 microg/ml), regardless of whether they were mecA positive. These results demonstrated that MRSE isolates with low CTM MIC (< or = 2.0 microg/ml) are not easily induced CTM resistance by CTM treatment in vitro, and indicated the possibility that beta-lactams such as CTM could be an effective antibiotic agents against beta-lactam-sensitive MRSE infections.