In Vitro Activities of Linezolid, Meropenem, and Quinupristin-Dalfopristin against Group C and G Streptococci, Including Vancomycin-Tolerant Isolates

Abstract

The in vitro activities of meropenem, linezolid, quinupristin-dalfopristin, vancomycin, and penicillin against 130 clinical isolates of group C and G streptococci, including vancomycin-tolerant isolates, were evaluated. Meropenem, linezolid, quinupristin-dalfopristin, vancomycin, and penicillin MICs at which 90% of the isolates were inhibited were 0.06, 2.0, 0.25, 0.5, and <0.016 g/ml, respectively. Meropenem, linezolid, quinupristindalfopristin, and penicillin were active against group C and G streptococci, including vancomycin-resistant strains.There is increasing interest in the role of Lancefield group C streptococci (GCS) and group G streptococci (GGS) as emerging nosocomial and opportunistic pathogens (18,20). The spectrum of human infection caused by these organisms includes primary and secondary bacteremia in healthy and immunocompromised hosts as well as cellulitis, endocarditis, skin and wound infections, meningitis, arthritis, osteomyelitis, pneumonia, abscesses, puerperal infections, and pharyngitis (2,4,6,18,20).The majority of GCS and GGS strains demonstrate in vitro susceptibility to penicillins, vancomycin, erythromycin, and cephalosporins (3, 17). Antimicrobial tolerance, defined as a minimum bactericidal concentration (MBC) 32 or more times greater than the MIC, among GCS and GGS has been reported for penicillin and other agents (12,15,16). A high rate of vancomycin tolerance among GGS isolated from patients with invasive infections was previously reported (21). We have evaluated the in vitro activities of novel agents, including linezolid and quinupristin-dalfopristin, which are active against gram-positive organisms, and meropenem, a cell wall-active carbapenem, against GGS and GCS, including vancomycintolerant isolates.( MATERIALS AND METHODSA total of 130 clinical isolates of GCS and GGS (48 and 82 isolates, respectively) were obtained from patients in the United States and Finland. Isolates from Finland were collected from January 1992 through December 1995 from throat swabs and infected human material. Isolates in the United States were collected from December 1991 to March 1996 from sterile sites from patients at the Christiana Hospital in Newark, Del.Isolate identification was performed using the API 20S Strep Strip (bioMerieux Vitek, Hazelwood, Mo.). Serotyping for GCS and GGS was performed using the PathoDx agglutination kit (Remel, Lenexa, Kans.).MICs of penicillin, vancomycin, linezolid, meropenem, and quinupristin-dalfopristin were determined using National Committee for Clinical Laboratory Standards (NCCLS) broth microdilution methods (9). Tests were performed in cation-adjusted Mueller-Hinton broth with lysed horse blood (lot 5517; Remel). Dilutions tested ranged from 16 to 0.016 g/ml for all drugs. Plates were prepared on-site (50 l per well), and antibiotic powders were supplied by the respective manufacturers. Microtiter plates were prepared to include a positive growth control well and a medium sterility well. The plates were stored at Ϫ70°C until use, and they were thawed ...

Streptococcus canis infections in humans: Retrospective study of 54 patients

“…18,19 New molecules such as linezolide have been shown in vitro to have excellent efficacy on the group G streptococci. 20 Linezolide could therefore constitute a therapeutic alternative in patients with a contraindication to betalactamine and/or glycopeptides in severe streptococcal G infections including S. canis, providing validation studies in vivo prove conclusive.…”

Invasive group G streptococcal infection in a paediatric patient

“…Other antibiotics with activity against group G streptococci include other β-lactam agents, carbapenems, linezolid, quinupistin-dalfopristin and vancomycin 3 5 17. Oxacillin and nafcillin are not effective therapeutic agents.…”

The oxazolidinones

“…Against 1531 strains of Streptococcus pneumoniae with varying resistance to penicillin, including 329 that were fully resistant, the MIC 90 for linezolid was consistently 2 µg/mL [12••]. Linezolid possesses clinically useful activity against vancomycin-tolerant strains of group C and G streptococci, rapidly growing mycobacteria, and gram-positive anaerobes including Clostridium difficile [13][14][15]. A single case report of the successful treatment of a patient with disseminated Mycobacterium chelonae infection (resistant to clarithromycin) with linezolid would appear to underline its potential usefulness as an addition to the limited agents available to treat rapidly growing mycobacteria [16].…”