Multicenter survey of the changing in vitro antimicrobial susceptibilitiesof clinical isolates of Bacteroides fragilis group, Prevotella, Fusobacterium, Porphyromonas, and Peptostreptococcus species

In vitro surveys of antimicrobial resistance among clinically important ana erobes are an important source of information that can be used for clinical decisions in the choice of empiric antimicrobial therapy, This study surve yed the susceptibilities of 556 clinical anaerobic isolates from four large medical centers using a broth microdilution method. Piperacillin-tazobacta m was the only antimicrobial agent to which all the isolates were susceptib le. Similarly, imipenem, meropenem, and metronidazole were highly active (r esistance, <0.5%), whereas the lowest susceptibility rates were noted for p enicillin G, ciprofloxacin, and clindamycin, For most antibiotics, blood is olates were less susceptible than isolates from intra-abdominal, obstetric- gynecologic, and other sources, All isolates of the Bacteroides fragilis gr oup were susceptible to piperacillin-tazobactam and metronidazole, while re sistance to imipenem and meropenem was low (<2%), For these same isolates, resistance rates (intermediate and resistant MICs) to ampicillin-sulbactam, cefoxitin, trovafloxacin, and clindamycin were Il, 8, 7, and 29%, respecti vely. Among the individual species of the B.fragilis group, the highest res istance rates were noted among the following organism-drug combinations: fo r clindamycin, Bacteroides distasonis and Bacteroides ovatus: for cefoxitin , Bacteroides thetaiotaomicron, B, distasonis, and Bacteroides uniformis; f or ampicillin-sulbactam, B, distasonis, B, ovatus, and B, uniformis; and fo r trovafloxacin, Bacteroides vulgatus, For the carbapenens, imipenem resist ance was noted among B.fragilis and meropenem resistance was seen among B. fragilis, B. vulgatus, and B. uniformis, With few exceptions all antimicrob ial agents were highly active against isolates of Prevotella, Fusobacterium , Porphyromonas, and Peptostreptococcus, These data further establish and c onfirm that clinically important anaerobes can vary widely in their antimic robial susceptibilities, Fortunately most antimicrobial agents were active against the test isolates. However, concern is warranted for what appears t o be a significant increases in resistance to ampicillin-sulbactam and clin damycin.