Susceptibility of 497 clinical isolates of Gram-negative anaerobes to trovafloxacin and eight other antibiotics

Trovafloxacin is a novel investigational trifluoronaphthyridone antibiotic with broad-spectrum activity against Gram-positive and Gram-negative organi sms. Its in-vitro activity and those of eight other antimicrobial agents we re evaluated against 497 clinical isolates of Gram-negative anaerobic bacte ria by the agar dilution method. Trovafloxacin had excellent activity, with a minimum inhibitory concentration (MIC) range of <0.03-4 mu g/ml, against all species. Out of the 497 isolates tested, 496 (99.5%) were inhibited by a concentration of less than or equal to 2.0 mu g/ml of trovafloxacin; the remaining two strains were inhibited by a concentration of 4.0 mu g/ml. Th e MIC(50)s and MIC(90)s were 0.12 mu g/ml and 1.0 mu g/ml, respectively. Me ropenem, imipenem and piperacillin/tazobactam were also very active. Overal l, at the MIC(90)s, trovafloxacin was as active as meropenem, slightly more active than metronidazole and imipenem, twice as active as amoxicillin-cla vulanic acid, five times more active than piperacillin-tazobactam and 68 ti mes more active than clindamycin. About 21% of the isolates were resistant to cefoxitin, 30% to clindamycin and 40% to piperacillin. Five species in t he Bacteroides fragilis group of isolates were highly resistant to metronid azole (MIC >128 mu g/ml). In general, the relatively more resistant species were the B. vulgatus, B. ovatus, B. thetaiotaomicron, and B, fragilis sens u stricto, in that order. All the isolates of the B, fragilis group and abo ut 50% of the Prevotella spp. were beta-lactamase positive, Trovafloxacin c ertainly holds promise as an alternative drug for therapy of anaerobic infe ctions.