Efficacy of ceftolozane/tazobactam, alone and in combination with colistin, against multidrug-resistant Pseudomonas aeruginosa in an in vitro biofilm pharmacodynamic model.

•Alternative therapies were tested in a PK/PD biofilm model by multidrug-resistant/extensively drug-resistant (MDR/XDR) Pseudomonas aeruginosa•Ceftolozane/tazobactam alone had little anti-biofilm efficacy•Colistin alone had notable efficacy, but it was influenced by resistance•Ceftolozane/tazobactam-colistin was the best therapy for meropenem-resistant strains•Meropenem-colistin was the most effective combination for MDR/XDR susceptible strains