The in vitro activities of quinupristin/dalfopristin (Synercid), ampicillin
, erythromycin, clarithromycin, vancomycin, teicoplanin, ciprofloxacin and
tetracycline were examined and compared against 526 gram-positive bacteria.
The minimal inhibitory concentrations (MICs) for quinupristin/dalfopristin
against Staphylococcus aureus, including methicillin-resistant strains, we
re low (MIC90 = 0.5 mg/l), and were comparable with those of vancomycin and
teicoplanin. This compound was superior to the macrolides and highly activ
e against Streptococcus pneumoniae (both penicillin-sensitive and penicilli
n-resistant strains), with MIC90 = 2 mg/l. It was also active against other
streptococci, with MIC90 = 4 mg/l. However, this agent is less active agai
nst enterococci (MIC90 = 32 mg/l). Quinupristin/dalfopristin showed high ac
tivity against gram-positive anaerobes, including Clostridium spp., Peptoco
ccus spp. and Peptostreptococcus spp., with MIC90 less than or equal to2 mg
/l. Quinupristin/dalfopristin was also investigated for its post-antibiotic
effect (PAE) and bactericidal kinetics against nine strains of gram-positi
ve organisms, including staphylococci, enterococci and pneumococci. Exponen
tially growing (log phase) cultures were exposed to quinupristin/dalfoprist
in at 2 x MIG. Growth kinetics was evaluated using viable counting. The dru
g was uniformly bactericidal against pneumococci and staphylococci within 2
and 8 h of exposure, respectively. The killing activity against enterococc
i was weak; there was little or no reduction in bacterial count over 24 h o
f incubation. PAEs ranging from 2.13 to 3.28 h, 0.92 to 3.02 h and 1.89 to
7.07 h were produced on the tested pneumococci, staphylococci and enterococ
ci, respectively. This study showed that quinupristin/dalfopristin is a pro
mising agent active against gram-positive bacteria. The prolonged PAEs also
suggest that the drug could be used intermittently at more widely spaced d
osing intervals against grampositive organisms. Copyright (C) 2001 S. Karge
r AG, Basel.