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.