Emergence of Ceftolozane-Tazobactam-Resistant Pseudomonas aeruginosa during Treatment Is Mediated by a Single AmpC Structural Mutation.

Ceftolozane-tazobactam is a cephalosporin-β-lactamase inhibitor combination that exhibits potent in vitro activity against Pseudomonas aeruginosa, including strains that are resistant to other β-lactams. The emergence of ceftolozane-tazobactam resistance among clinical isolates of P. aeruginosa has rarely been described. Here we characterized ceftolozane-tazobactam-resistant P. aeruginosa strains recovered from a patient who was treated with this agent for 6 weeks for a recurrent wound infection. The results showed that the resistance was mediated by a single AmpC structural mutation.