Surveillance Of Antimicrobial Resitance And Detection Of Integron Gene Cassettes Among Escherichia Coli Isolates From Food-animals In Sichuan Province

With the worldwide use of antimicrobial agents in veterinary medicine, the incidence of resistance and multidrug-resistance among pathogenic bacteria has been increasing, which attracts global attentions. Surveillance of antimicrobial resistance is very urgent to clinical medicine. The traditional method used in surveillance of resistance is to test resistant phenotype. With the development of molecular biological technology, PCR technology have been extensivly used in detection of resistant genotype and novel resistant mechanism.In this study, The samples of colibacillosis were collected from food animals in different farms in Sichuan province, E.coli isolates were identified by conventional test. Antimicrobial susceptibility of these isolates was examined using the broth microdilution method and the results interpreted according to Clinical and laboratory standards institute (CLSI). Multiplex PCR was used to detect 3 different classes of integron in multi-resistant strains, and PCR-sequencing method was used to analysis gene cassettes. The study was classified into two parts as follows.1. Surveillance of different antimicrobial resistance among E.coli isolates from food animals.The samples of colibacillosis were collected from food animals, including chickens, ducks, cattles and pigs, in different farms in Sichuan province,705 isolates were identified in the study. Antimicrobial susceptibility of these isolates to 25 different agents indicated: The resistance of 705 isolates to 25 agents were different, more than 100% of the 705 E.coli isolates were resistant to TMP, Trimethoprim-sulfamethoxazole and Rifampin respectively; Then, above 70% of isolates were resistance to Ampicillin,Tetracyline, Chloramphenicol and Fluoroquinolone,respectively. Isolates exhibited relatively low resistant level toβ-lactams, resistane rate of Cephazolin,Ceftiofur and Ceftriaxone, was 34.34%,41.30% and 26.25%, respectively. However, the medium rates of 3 kinds ofβ-lactams were very high, which indicated that the resistant changing trends was ascendant; All of isolates showed different susceptible level to Amikacin, susceptible rates exceeded 67%.Multidrug-resistance was very serious among isolates, All of 705 isolates exhibited multiple resistance to 15-24 antimicrobial agents. The rate of resistant strains to 23 agents was at most, then to 21 agents. Resistant rate of Avian strains was the most serious among different animal isolates; Although the resistant levels of the partial agents were different in isolates from different locals, however, resistant patterns among E.coli isolates from different geographical origins was similar.2. Detection of integron-gene cassettes among Escherichia coli isolates from food-animalsMultiplex PCR was used to detect 3 different classes of integron in 327 isolates. The results of multiplex PCR indicated 294 of 327 isolates harbored intI1 integrase genes, the detection rate of intI1 was 89.91%, intI2 and intI3 genes were not discoveried in the study. Amplification of Gene cassettes in 81 intI1-positive strains choosed randomly was carried out. The results showed that amplicons of 845bp-2731bp were yielded in 67 intI1-positive strains. The sequencing of gene cassettes indicated that 6 kinds of gene cassettes were harbored in 67 strains. The gene cassettes arrays were dfrA17+aadA5,dfrA17, aadA22, dhfrAI+aadA2, dfrA17+orfF+aadA2 and aacA4+catB3+dfrA1, which were encoding resistant to TMP+Sulfonamides, Aminoglycosides and chloramphenicol, respectively. aadA22, which was novel gene encoding resistant to Aminoglycosides, was first acquired in avian E.coli strains from Sichuan province. The study of aadA22 gene will be carried out in future.