Carbapenems and piperacillin/tazobactam for the treatment of bacteremia caused by extended-spectrum β-lactamase–producing Proteus mirabilis

This study was intended to delineate the role of carbapenems and piperacillin/tazobactam in treating bacteremia caused by extended-spectrum β-lactamase (ESBL)–producing Proteus mirabilis. We performed a multicenter and retrospective study of the patients with ESBL-producing P. mirabilis bacteremia. The outcomes of the patients treated by piperacillin/tazobactam or a carbapenem for at least 48 hours and the MICs of the prescribed drugs for these isolates were analyzed. Forty-seven patients with available clinical data were included. The overall 30-day mortality rate was 29.8%. All available isolates (n = 44) were susceptible to ertapenem, meropenem, and doripenem, and 95.6% were susceptible to piperacillin/tazobactam; however, only 11.4% of the isolates were susceptible to imipenem. Among the 3 patients infected with isolates exhibiting non-susceptibility to imipenem (MIC ≥2 mg/L) who were treated with imipenem, none died within 28 days. The 30-day (14.3% versus 23.1%, P = 0.65) or in-hospital (19.1% versus 30.8%, P = 0.68) mortality rate of 21 patients treated by a carbapenem was lower than that of 13 treated by piperacillin/tazobactam. However, among those treated by piperacillin/tazobactam, the mortality rate of those infected by the isolates with lower piperacillin/tazobactam MICs (≤0.5/4 mg/L) was lower than that of the isolates with MICs of ≥1/4 mg/L (0%, 0/7 versus 60%, 3/5; P = 0.045). ESBL-producing P. mirabilis bacteremia is associated with significant mortality, and carbapenem therapy could be regarded as the drugs of choice. The role of piperacillin/tazobactam, especially for the infections due to the isolates with an MIC ≤0.5/4 mg/L, warrants more clinical studies.