Characteristics of plasmids in KPC-2-producing Serratia marcescens / 中华微生物学和免疫学杂志

ABSTRACT

Objective:To analyze the characteristics of plasmids in KPC-2-producing Serratia marcescens ( S. marcescens) isolates. Methods:Four carbapenem-resistant S. marcescens strains were isolated from four patients admitted to the hepatobiliary ward of Affiliated Cancer Hospital of Zhengzhou University in 2016. BD Phenix-100 was used to identify the strains and detect the minimum inhibitory concentrations (MICs). Homology analysis was performed using pulsed-field gel electrophoresis (PFGE). The modified Hodge test was used to detect the phenotypes of carbapenemase. PCR and gene sequencing were used to detect the types of carbapenem resistance genes. The transferability of plasmids was detected by conjugation test. The characteristics of plasmids were analyzed by genomic alignment method after whole genome sequencing. DNAMAN V9 software was used to compare the amino acid sequences of the replication initiation proteins. A phylogenetic tree was constructed with neighbor-joining method using MEGA7.0. Results:All of the four S. marcescens strains were resistant to carbapenem antibiotics. They were highly homologous according to PFGE. Hodge test results were all positive and the carbapenemase genotype was blaKPC-2. Conjugation test results were positive. The plasmid was a circular DNA of 42 742 bp in length. It had the similar skeleton of incX6 plasmid and the similar amino acid sequence of replication initiation protein. Moreover, it and incX6 plasmid were at the same node in the phylogenetic tree. The blaKPC-2 was located in the core of drug resistance, which was composed of insertion elements including Tn3 family transposons, recombinant enzyme genes, △ISKpn6 and ISKpn27. Conclusions:The plasmid was incX6-like. The blaKPC-2 gene was located in the transposon of △Tn6296. More attention should be paid to the bacteria carrying KPC-2 in incX plasmids.