In vitro Activity and Post-Antibiotic Effect of Quinupristin/Dalfopristin (Synercid)

Abstract

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, were low (MIC₉₀ = 0.5 mg/l), and were comparable with those of vancomycin and teicoplanin. This compound was superior to the macrolides and highly active against Streptococcus pneumoniae (both penicillin-sensitive and penicillin-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 against enterococci (MIC₉₀ = 32 mg/l). Quinupristin/dalfopristin showed high activity against gram-positive anaerobes, including Clostridium spp., Peptococcus spp. and Peptostreptococcus spp., with MIC₉₀ ≤2 mg/l. Quinupristin/dalfopristin was also investigated for its post-antibiotic effect (PAE) and bactericidal kinetics against nine strains of gram-positive organisms, including staphylococci, enterococci and pneumococci. Exponentially growing (log phase) cultures were exposed to quinupristin/dalfopristin at 2 × MIC. Growth kinetics was evaluated using viable counting. The drug was uniformly bactericidal against pneumococci and staphylococci within 2 and 8 h of exposure, respectively. The killing activity against enterococci was weak; there was little or no reduction in bacterial count over 24 h of 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 enterococci, respectively. This study showed that quinupristin/dalfopristin is a promising agent active against gram-positive bacteria. The prolonged PAEs also suggest that the drug could be used intermittently at more widely spaced dosing intervals against gram-positive organisms.

The Emergence of Glycopeptide-Resistant <i>Enterococcus faecium </i>in a University Hospital in Southwestern Greece

“…The GRE isolated in this study were resistant to ampicillin, erythromycin and ciprofloxacin, a phenotype already reported from different hospitals [1,6,15,16]. Resistance to linezolid was not detected, while the isolation of GRE resistant to quinupristin/dalfopristin in this collection is not common, as rare isolates with higher MIC levels to this combination have been identified [17].…”

Cell surface hydrophobicity and adherence of a strain of group B streptococci during the post-antibiotic effect of penicillin

“…A number of in vitro studies have quantified the PAE induced by numerous antibiotics in a variety of Gram-positive 10,19,20,21,23,30 and Gram-negative bacteria 19,20,21,32 .…”

Efficacy of Quinupristin-Dalfopristin against Methicillin-Resistant <i>Staphylococcus aureus</i> and Vancomycin-Insensitive <i>S. aureus</i> in a Model of Hematogenous Pulmonary Infection

“…The MICs for Q-D against S. aureus, including methicillin-resistant strains, were low (MIC 90 = 0.5 mg/l), and were comparable with those of VCM and teicoplanin [10]. Auckenthaler et al [11] investigated the susceptibility of 2,132 staphylococci to Q-D. Q-D was active against 97.6% of all strains at !1 mg/l, and the MIC 90 value was 0.5-2 mg/l [11].…”