Biological Properties of Clinically Isolated Methicillin-Resistant Staphylococcus aureus and Its Susceptibility to Disinfectants and Antibiotics

A strain of Staphylococcus aureus was isolated from clinical material of an inpatient. The biological properties of the clinical isolate of S. aureus and its susceptibility to disinfectants and antibiotics were investigated. The clinical isolate of S. aureus was β-lactamase-positive and coagulase type-II strain, and the strain was found to produce penicillin-binding protein-2' and mec A gene, which are associated with bacterial resistance. Therefore, the clinical isolate was identified as the methicillin-resistant S. aureus (MRSA). Povidone-iodine was most rapidly bactericidal in vitro against the clinical isolate of S. aureus which was less susceptible to the other disinfectants. The clinical isolate of S. aureus was susceptible to OFLX and VCM. However, this strain was resistant to most of the antibiotics such as CMD, FOM or FMOX. In vitro antibacterial activity of the combinations of various antibiotics was evaluated by checkerboard dilution method. The fractional inhibitory concentration indices of FMOX+ CMD, FMOX+ FOM, FMOX+ FIPM, FOM+ FCMZ and F0M+ MINO were 0.51, 0.75, 0.63, 0.95 and 1.25, respectively. The effect of combination of FMOX+ CMD was superior to that of the other combinations against the clinical isolate of S. aureus. This finding suggests that combination therapy of FMOX and CMD may be useful for MRSA infections at the clinical dose.