Characterization of NDM-1-producing carbapenemase in Acinetobacter spp.and E.coli isolates from diseased pigs

In recent years,the mobile metallo-β-lactamase(MBL)genes have been found to correspond to one of the most important resistance characters identified in Gramnegative bacteria,severely affecting clinical chemotherapy and threatening public health.The prevalence of mobile MBL genes and their flanking regions in Gram-negative bacteria from diseased pigs in China was investigated.A total of 334 lung samples from diseased pigs were screened for Gram-negative bacteria classified as non-susceptible to meropenem(MIC≥4mg·L^(–1)).Six isolates,including three Escherichia coli,two Acinetobacter baumanii and one A.calcoaeticus,exhibitedMBL production and carried the blaNDM-1 gene.S1-PFGE and Southern blot analysis showed that the blaNDM-1 gene was located on the chromosome of one A.baumanii isolate and on plasmids of various sizes in the other five isolates.MIC testing using broth microdilution revealed that all blaNDM-1-carrying isolates and some of their transconjugants exhibited resistance to almost allβ-lactams tested.Whole genome sequencing revealed that the flanking region of the blaNDM-1 gene from all porcine isolates had high levels of similarity with the corresponding regions in human isolates.One porcine E.coli isolate carrying blaNDM-1 was typed as ST48,a common sequence type in human E.coli isolates.These results suggest the possibility of human-tofood animal transfer of blaNDM-1-producing E.coli,highlighting the need for surveillance of carbapenemase producers among bacteria from food animals.In addition,the prudent use of antimicrobial agents to decrease the opportunities for co-selection of carbapenemase genes in food animals is also urgently needed.