In Vitro Activity of Ceftolozane-Tazobactam against Anaerobic Organisms Identified during the ASPECT-cIAI Study

The in vitro activities of ceftolozane-tazobactam, meropenem, and metronidazole were determined against anaerobic organisms isolated from patients with complicated intraabdominal infections (cIAI) in global phase III studies. Ceftolozane-tazobactam activity was highly variable among different species of the Bacteroides fragilis group, with MIC90 values ranging from 2 to 64 mu g/ml. More-potent in vitro activity was observed against selected Gram-positive anaerobic organisms; however, small numbers of isolates were available, and, therefore, the clinical significance of these results is unknown. Variable activity of ceftolozanetazobactam against anaerobic organisms necessitates use in combination with metronidazole for the treatment of cIAI.