Detection Of Class Ⅰ Integron And Antimicrobial Resistance Analysis Of The Pathogenic E.coli Isolated From Minjiang River Basin

With widespread and uncontrolled overuse of antibiotics, the problems of drug resistance, especially multi-drug resistance in pathogenic bacteria has been expanded seriously. As a new drug-resistant mechanism, integron-cassett system, which has the ability of capturing and expressing foreign genes, has attracted more and more attention. Gene cassette with resistance genes is a minor-movable deoxyribonuc1eic acid (DNA) molecule, and usually is transcribed with a integron. Integron is a conservative and movable transposon-like DNA element, which can make a horizontal transmission of drug resistance gene and contribut greatly to the diffusion of drug resistance gene among bacteria and the production of multidrug resistance.In present study antibiotic resistance of Escherichia coli strains isolated from Minjiang river basin and their correlation with class I integrons as well as the gene cassettes harbored were investigated using PCR, RFLP and sequencing. Two hundered E. coli isolates recovered from 7 sampling sites within Minjian river were randomly selected to test their antimicrobial susceptibility to the 20 antibiotics following NCCLS.The results showed that there were 41.8% (209/500) E. coli isolates carrying Classâ… integron. All the isolates tested in this study were found to resist different kinds of antibiotics, ranging from 2 to 16 antibiotics. The drug-resistance of E. coli isolates carrying Classâ… integron exhibited stronger than that of the integron-negative isolates, implying the positive correlation between the integron and antibiotic resistance. About 37.5% (15/40) of the integron-positive strains carried gene cassettes in variable regions of class 1 integron. Upon sequencing, 4 different gene cassettes were identified, including genes encoding for resistance to aminoglycosides (aadA1), to trimethoprim and aminoglycosides (dfrA1+aadA1), rifampin ADP-ribosylating transferase and dihydrofolate reductase (arr-3+dfrA27), tetracycline resistance (TetR) family, with dfrA and aadA being predominant gene cassettes.Our data clearly indicated that integrons were likely important, both in terms of mechanisms of multiple-antibiotic-resistance and in the dissemination of resistance genes. Classâ… integrons are widespread in E.coil isolates in Minjiang river.And a priority should be given to control the discharge of wastewater from urban and animal farms and to restrict the use of antibiotics in human and veterinary medicine, and feed additives as well.