Analysis of drug resistance and detection of drug resistance gene and class I integron in porcine ExPEC

Abstract:

[Background] The long-term massive and irrational use of antibiotics has led to increasing multi-drug resistance of extraintestinal pathogenic Escherichia coli (ExPEC) isolated from pigs. [Objective] To investigate the drug resistance of ExPEC isolated from pigs and its correlation with drug resistance genes and class I integrons. [Methods] The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 54 strains of ExPEC isolated from pigs against 22 antimicrobial drugs were determined by micro-broth dilution method. The drug resistance genes were identified based on the results of drug sensitivity tests, and the distribution of drug resistance genes and class I integrons on chromosomal DNA and plasmid DNA were detected by PCR. [Results] The 54 strains of porcine ExPEC were highly resistant to penicillin, florfenicol, ampicillin and amoxicillin, of which 52 strains of porcine ExPEC were highly resistant to trimethoprim and cotrimoxazole, and their MIC values were greater than 256 μg/mL, no MBC value; and MICs to cefazolin, tetracycline, cefadroxil, daikonin, and streptomycin were 1-256 μg/mL with MBC values of 8, 16, 32, 64, 128, and 256 μg/mL, all tolerating more than 11 antimicrobial drugs, of which 17 were predominantly tolerated, accounting for 18.52%, with 47 drug resistance spectrums. We identified 20 drug resistance genes in 7 major categories, 19 drug resistance genes in chromosomal DNA except aph(3')-IIa gene were detected, with the highest detection rate of aadA1 and tetA, and all strains carried more than 5 drug resistance genes; 16 drug resistance genes in plasmid DNA except tetB, tetC, SHV and qnrA genes were detected, with the highest detection rate of floR and parC, and all strains carried more than 5 drug resistance genes. The positive detection rates of class I integrons in chromosomal DNA and plasmid DNA were 96.3% and 98.15%, respectively, and all positive strains were multi-drug resistant strains. [Conclusion] ExPEC isolated from pigs has serious multi-drug resistance, the drug resistance profiles are complex and diverse, a very high distribution of resistance genes and class I integrons in chromosomal DNA and plasmid DNA, and a correlation between the development of resistance and the presence of resistance genes, which in turn increases the risk of horizontal transfer of resistance genes.