Heterogeneity and Diversity of mcr-8 Genetic Context in Chicken-Associated Klebsiella pneumoniae.

Increasing mobile colistin resistance, mediated by the mcr gene family, in Enterobacteriaceae has become a global concern. Among the 10 reported mcr genes, mcr-8 was first identified in Klebsiella pneumoniae, which could cause severe infections with high mortality. Information about the prevalence and genetic context of mcr-8 is still lacking. In this study, we found that mcr-8 was present in 9.83% of K. pneumoniae isolates of chicken origin. S1 nuclease pulsed-field gel electrophoresis (S1-PFGE) and Southern blotting showed that the mcr-8 gene was located on a plasmid in all of the isolates. The genetic context of the plasmids exhibited considerable diversity from the whole-genome sequence through Illumina and MinION long-read sequencing. Mutations in two-component systems may function synergistically with mcr-8, resulting in extremely high resistance to colistin. In addition to colistin resistance, these plasmids also contained genes conferring resistance to beta-lactams, tetracycline, aminoglycosides, sulfonamides, macrolides, chloramphenicol, and florfenicol. Therefore, these findings indicate that the genetic context of mcr-8 is heterogeneous and diverse and that mcr-8 and certain chromosomal mechanisms jointly contribute to high-level colistin resistance in K. pneumoniae strains, which provides new insights into the resistance mechanisms of K. pneumoniae.

Antimicrobial resistance of bacterial pathogens isolated from canine urinary tract infections.

Urinary tract infections (UTIs), many of which are caused by bacterial pathogens, are some of the most common infections in dogs. To effectively treat UTIs, it is important to identify the predominant bacterial pathogens and their susceptibility to antimicrobial agents. In this study, we collected 326 samples from cases with UTIs or other urinary system diseases at the China Agricultural University Veterinary Teaching Hospital, Beijing, from 2016-2018. In total, 129 non-duplicate bacterial isolates were recovered from 103 clinical samples. The proportion of positive female samples was higher than that of males. The predominant Gram-negative bacteria were Escherichia coli and Klebsiella spp., while Staphylococcus spp. were the predominant Gram-positive bacteria. Broth microdilution-based antimicrobial susceptibility testing showed that 39 % of E. coli and 51.5 % of Staphylococcus spp. isolates were multidrug-resistant. Specifically, E. coli isolates showed high rates of resistance to ampicillin (40.5 %), ceftazidime (59.5 %), and florfenicol (42.9 %), but limited resistance to amikacin (2.38 %), meropenem (7.14 %), and polymyxin E (7.14 %). In comparison, Staphylococcus spp. showed high rates of resistance to erythromycin (60.6 %), trimethoprim-sulfamethoxazole (54.6 %), and penicillin (45. 5 %), but low resistance rates to vancomycin (6.06 %) and nitrofurantoin (6.06 %). Pulsed-field gel electrophoresis (PFGE)-based typing identified 31 PFGE patterns among the 43 E. coli isolates. These results suggested that multiple bacterial strains, many of which are multidrug-resistant, can cause UTIs in dogs. Thus, basic antimicrobial susceptibility tests should be performed to provide guidance for the selection of first-line clinical therapeutics, and to help prevent the occurrence and spread of induced antimicrobial resistance.