Carbapenem-resistant and cephalosporin-susceptible Pseudomonas aeruginosa: a notable phenotype in patients with bacteremia Shuang Li,1,* Xiaojiong Jia,1,* Congya Li,1 Hua Zou,1 Hang Liu,1 Yuanbiao Guo,2 Liping Zhang1 1Department of Laboratory Medicine, The First Affiliated Hospital of Chongqing Medical University, Chongqing, China; 2Medical Research Center, The Second Chengdu Hospital Affiliated to Chongqing Medical University, Chengdu, China *These authors contributed equally to this work Purpose: Pseudomonas aeruginosa is recognized as a major cause of severe and potentially life-threatening infection. However, P. aeruginosa isolates with the phenotype of being carbapenem resistant and cephalosporin susceptible (Carb-R/Ceph-S) have not been thoroughly characterized to date. The aim of this study was to assess the mechanisms, risk factors, and clinical impact of Carb-R/Ceph-S P. aeruginosa bacteremia on mortality.Patients and methods: We conducted a retrospective case–case–control study of the risk factors and clinical outcomes of hospitalized patients with Carb-R/Ceph-S P. aeruginosa bacteremia from 2011 to 2017 in Chongqing, China. Case patients infected with Carb-R/Ceph-S P. aeruginosa, carbapenem-susceptible and cephalosporin-susceptible (Carb-S/Ceph-S) P. aeruginosa, and controls with no P. aeruginosa bacteremia were compared at a ratio of 1:1:2. Real-time reverse transcription polymerase chain reaction was performed to assess resistance mechanisms. A multivariate logistic regression model was performed to investigate several potential predictors for mortality.Results: We collected 63 Carb-R/Ceph-S P. aeruginosa isolates during the study period. None of these isolates possessed carbapenemase or extended-spectrum β-lactamase-encoding genes. The overall 30-day mortality rate was 27.0%. Real-time reverse transcription polymerase chain reaction analysis showed that an overexpression of efflux systems and decreased expression of OprD were associated with Carb-R/Ceph-S P. aeruginosa. Multivariate analysis indicated that 30-day readmission, central venous catheters, and exposure to carbapenems were unique independent predictors for acquiring Carb-R/Ceph-S P. aeruginosa bacteremia. Additionally, hematologic malignancy was a peculiar predictor for Carb-S/Ceph-S P. aeruginosa bacteremia. Notably, total parenteral nutrition was the only common factor of both Carb-R/Ceph-S and Carb-S/Ceph-S groups compared to controls. In a multivariate analysis for the outcome, intensive care unit admission and septic shock were identified as the independent predictors for mortality.Conclusion: Our findings can potentially improve the ability of physicians to identify the high-risk patients, and carbapenems were noted to potentially increase the risk of Carb-R/Ceph-S P. aeruginosa. Additionally, cephalosporin should be considered a valuable therapeutic option for such cases of bacteremia. Keywords: Pseudomonas aeruginosa, carbapenem resistance, bacteremia, risk factor