Isolation of carbapenem-resistant Pseudomonas spp. from food

Pseudomonas spp. are ubiquitous in nature. Carbapenem resistance in environmental isolates of members of this genus is thought to be rare but the exact resistance rate is unknown. In this study, carbapenem-resistant Pseudomonas spp. were isolated from chicken and pork samples and the mechanisms underlying the carbapenem resistance in these strains were investigated. A total of 16 carbapenem-resistant Pseudomonas aeruginosa, Pseudomonas putida and Pseudomonas otitidis isolates were recovered from eight samples of chicken and pork. The isolates exhibited meropenem minimum inhibitory concentrations (MICs) of 8 to ≥32 mg/L and imipenem MICs of <0.5-16 mg/L yet did not harbour any acquired carbapenemase genes. Meropenem resistance in various strains was found to be mediated by efflux systems only, whereas overexpression of MexAB-OprM efflux pump and lack of OprD porin were responsible for carbapenem resistance in P. aeruginosa. The intrinsic metallo-β-lactamase gene blaPOMin P. otitidis and overexpression of the TtgABC efflux system in P. putida were also responsible for carbapenem resistance in these organisms. In conclusion, this study reports for the first time the isolation of carbapenem-resistant P. aeruginosa, P. otitidis and P. putida strains from food. The resistance mechanisms of these strains are rarely due to production of carbapenemases. Further selection of such carbapenem-resistant Pseudomonas spp. in the environment and the risk by which they are transmitted to clinical settings are of great public health concern.