Serious streptococcal infections produced by isolates resistant to streptogramins (quinupristin/dalfopristin): Case reports from the SENTRY antimicrobial surveillance program

The emergence and sustained prevalence of Gram-positive organisms resistant to antimicrobials has been of interest for over a decade. Quinupristin/dal fopristin (formerly RP 59500 or Synercid(R)) is a new injectable streptogra min combination that has been reported to have activity against Gram-positi ve organisms, even those with documented MLS, resistance. However, the two case reports presented here illustrate three well-documented Streptococcus spp. strains (S. mitis, S. pneumoniae) to be resistant to quinupristin/dalf opristin (MICs at 3, 8, and 12 mu g/ml) following referral as routine isola tes in the SENTRY Antimicrobial Surveillance Program. The S. pneumoniae ple ural fluid isolate was cross-resistant to erythromycin. Both bacteremic S. mitis strains were resistant to macrolides (erythromycin, azithromycin, cla rithromycin), lincosamides (clindamycin), and fluoroquinolones. Patient his tories indicated no prior use of MLS class antimicrobials for the S. mitis case, but the patient having the S. pneumoniae isolate did receive prior tr eatment of erythromycin and clindamycin. All isolates had modestly increase d penicillin MICs of 0.12 mu g/ml. The mode of resistance to quinupristin/d alfopristin was not evident (sat A-negative by PCR); and these cases illust rate the existence of streptogramin-resistant isolates before the introduct ion of this antimicrobial class into human clinical practice. (C) 2000 Else vier Science Inc. All rights reserved.