Analysis of an IncR plasmid carried by carbapenem-resistant Klebsiella pneumoniae: A survey of swine Klebsiella pneumoniae in Jilin Province.

OBJECTIVES: This study was conducted in Jilin Province to investigate the mechanism involved in the antibiotic resistance and pathogenicity of Klebsiella pneumoniae. METHODS: Lung samples were collected from large-scale pig farms in Jilin Province. Antimicrobial susceptibility and mouse lethality assays were carried out. K. pneumoniae isolate JP20, with high virulence and antibiotic resistance, was chosen for whole-genome sequencing. The complete sequence of its genome was annotated, and the virulence and antibiotic resistance mechanism were analysed. RESULTS: A total of 32 K. pneumoniae strains were isolated and tested for antibiotic resistance and pathogenicity. Among them, the JP20 strain showed high levels of resistance to all tested antimicrobial agents and strong pathogenicity in mice (lethal dose of 1.35 × 1011 CFU/mL). Sequencing of the multidrug-resistant and highly virulent K. pneumoniae JP20 strain revealed that the antibiotic resistance genes were mainly carried by an IncR plasmid. We speculate that extended-spectrum ß-lactamases and loss of outer membrane porin OmpK36 play an important role in carbapenem antibiotic resistance. This plasmid contains a mosaic structure consisting of a large number of mobile elements. CONCLUSION: Through genome-wide analysis, we found that an lncR plasmid carried by the JP20 strain may have evolved in pig farms, possibly leading to multidrug resistance in the JP20 strain. It is speculated that the antibiotic resistance of K. pneumoniae in pig farms is mainly mediated by mobile elements (insertion sequences, transposons, and plasmids). These data provide a basis for monitoring the antibiotic resistance of K. pneumoniae and lay a foundation for an improved understanding of the genomic characteristics and antibiotic resistance mechanism of K. pneumoniae.

Antibacterial activity and cytotoxicity of a novel bacteriocin isolated from Pseudomonas sp. strain 166.

Pseudomonas sp. strain 166 was isolated from soil samples from Changbai Mountains. A novel bacteriocin PA166 from Pseudomonas sp. 166 was purified using ammonium sulfate, dextran gel chromatography column and Q-Sepharose column chromatography successively. The molecular mass of bacteriocin PA166 was found to be 49.38 kDa by SDS-PAGE and liquid chromatography-mass spectrometry (MS)/MS. Bacteriocin PA166 showed stability at a wide range of pH (2-10), and thermal stability (40, 60, 80 and 100°C). The bacteriocin PA166 antimicrobial activity was slightly inhibited by Ca2+ , K+ and Mg2+ . The minimum bactericidal concentrations of bacteriocin PA166 against five Pasteurella multocida strains ranged from 2 to 8 µg ml-1 . Bacteriocin PA166 showed low cytotoxicity and a higher treatment index (TI = 82.51). Fluorescence spectroscopy indicated that bacteriocin PA166 destroyed the cell membrane to exert antimicrobial activity. In summary, bacteriocin PA166 had strong antibacterial activity, high TI and low toxicity, and hence could serve as a potential clinical therapeutic drug.