Investigation of the bactericidal effects of vancomycin and quinupristin/dalfopristin on Staphylococcus aureus isolates

The present study aimed to determine the correlation between the bactericidal activity of vancomycin and quinupristin/dalfopristin (Q/D) on Staphylococcus aureus isolates and their minimal inhibition concentrations. The in-vitro susceptibilities of the 99 S. aureus isolates to vancomycin and Q/D were investigated by agar dilution. Thirty methicillin-resistant S. aureus (MRSA) and 30 methicillin-susceptible S. aureus (MSSA) vancomycin and Q/D susceptible isolates were involved in time-kill studies. While both MRSA and MSSA isolates were susceptible to vancomycin, 96% of both isolates were determined as susceptible to Q/D. In the time-kill test, after 6 h of incubation vancomycin exhibited a bactericidal activity of 90% on MRSA and 100% on MSSA isolates. On the other hand, in the same incubation period Q/D was 47% and 93% bactericidal for MRSA and MSSA isolates, respectively. After 24 h of incubation, while vancomycin was bactericidal for all MRSA and MSSA isolates, Q/D exhibited a bactericidal activity of 93% on MRSA isolates and 97% on MSSA isolates.