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 μg/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 ceftolozane-tazobactam against anaerobic organisms necessitates use in combination with metronidazole for the treatment of cIAI.