In vitro activity of quinupristin/dalfopristin in comparison with five antibiotics against worldwide clinical isolates of staphylococci

Objective To evaluate the in vitro activity of quinupristin/dalfopristin (Q /D), a streptogramin combination, in comparison with five antibiotics again st worldwide clinical isolates of staphylococci. Methods A multicenter in vitro study was performed using the E test during a period of 3 months (April to June) in 1997 on fresh, clinically significa nt, non repetitive strains of staphylococci from patients hospitalized in 2 3 different hospitals in 18 countries tested. Results A total of 2132 staphylococcal isolates including methicillin resis tant (MR), methicillin susceptible (MS) S. aureus (1003 MS, 462 MR), S. epi dermidis (169 MS, 251 MR), S. haemolyticus (28 MS, 46 MR), S, hominis (28 M S,16 MR), and coagulase negative staphylococci (86 MS, 43 MR) were analyzed . Q/D was highly active against all species tested. MIC90 (mg/L) ranged from 0.5 to 2 depending on the species. Strains had MIC less than or equal to1 m g/L in 97.6%. For S. aureus, S, epidermidis, S. hominis and other coagulase -negative staphylococci no differences in MIC90 were observed for MS or MR. One dilution difference was observed for S. haemolyticus, which overall wa s the less susceptible species. Erythromycin resistance was observed among 57-87% of MR-strains and was lower among MS-strains (18-56%). Erythromycin resistance had no or little influence on MIC of Q/D. In comparison to vanco mycin, Q/D was two to four times more active. Conclusions The streptogramin combination Q/D showed an excellent in vitro activity against all staphylococcal species tested regardless of the resist ance pattern to other drug classes, particularly resistance to methicillin. Q/D was two to four times more active than vancomycin and MIC values varie d from 0.5-2 according to the species. The synergy of Q/D was well conserve d in macrolide-resistant strains.