A study on the resistance mechanism of Morganella morganii to carbapenems

Abstract

Abstract: Objective To investigate resistance mechanisms to carbapenems and transmission modes of 3 Morganella morganii isolates (M1， M2 and M3) isolated from patients in surgical intensive care unit (SICU). Methods The susceptibility of antimicrobial agents was detected by agar dilution method. The molecular epidemiological characteristics of the isolates were analyzed by enterobacterial repetitive intergenic consensus (ERIC)-polymerase chain reaction (PCR). The encoding genes of beta-lactamases were analyzed by specific PCR amplification. The transitivity and homology of plasmids were detected by plasmid conjugation and restriction endonuclease analysis. Genetic environments around bla_KPC were analyzed by sequencing. The changes of outer membrane permeability were analyzed by the electrophoresis of outer membrane protein. Results The bla_KPC-2 was detected by PCR in all 3 isolates and their transconjugants. M1 and M2 were the same clonal type. Carbapenem-resistance was successfully transfered by conjugation experiments. The bla_KPC-2 was located on dissimilar plasmids with quite different restriction profiles. The genetic environments around bla_KPC-2 were the same. The 3 original Morganella morganii isolates showed a loss of 38 000 outer membrane proteins, and additional 36 000 outer membrane proteins appeared compared with the Morganella morganii isolates susceptible to carbapenems. Conclusions The bla_KPC-2is detected in the 3 Morganella morganii isolates belonging to 2 clonal types . This gene encoded by dissimilar plasmids is likely located on the same mobile genetic elements by which bla_KPC-2 is possibly transferred between different plasmids. The KPC-2-producing and lack of outer membrane proteins together cause these 3 Morganella morganii isolates resistant to carbapenems possibly.

Key words: Morganella morganii, Carbapenem, Beta-lactamase, Drug resistance

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