| Aeromonas is regarded as an important pathogen of freshwater animals. However, little is known about genetics of antimicrobial resistance in Aeromonas spp. in Chinese aquaculture. The aim of this study was to investigate the presence of class 1 integron and characterize multidrug resistant Aeromonas spp. isolated from integrated farms. Three hundred and seventeen Aeromonas strains were isolated from fish, pond water, sediments geese feces and pig feces. These samples were collected from 5 livestock-fish integrated farms in Foshan and Zhaoqing of Guangdong province. All strains were evaluated for resistance to 20 antimicrobials of 7 classes by two fold dilution method. Genomic DNA was extracted with the Omega DNA mini kit. All the isolates were screened for the presence of intI1. All the intI1-positive strains were also amplified sulI, qacEΔ1 fragment and gene cassette region by PCR. Gene cassettes arrays were analyzed by BLAST. Percentages of isolates resistant to 20 antimicrobials were variable. Resistance was most prevalent for ampicillin, sulfamonomethoxine and nalidixic acid. Among 317 Aeromonas isolates, 50(15.77%) isolates were positive for intI1. The incidence of class 1 integron was more prevalent in Aeromonas from fish and pig than that from environmental sources. Comparing the resistance phenotypes represented in integron-positive and integron-negative strains, the results showed that the resistance rates of trimethoprim/sulfamethoxazole, doxycycline, enrofloxacin, neomycin and florfenicol among integron-positive isolates are higher than those from integron-negative strains. All of the integron-positive strains were resistant to more than three classes of agents. There were 16 different gene cassettes encoding resistance to aminoglycosides(aadA1, aadA2, aac6-Ⅱ, aacA4), trimethoprim(drfA1, dfrA12, dfrA15, dfrA17, dfrB4), β-lactams(blaOXA-10, blaOXA-21), chloramphenicl(catB3, catB8), rifampicin(arr-2, arr-3) and plasmid-mediated quinolone resistance(PMQR) gene aac(6’)-Ib-cr. Most of the integron-positive isolates carrying gene cassettes mentioned above corresponded to the resistance profile of antimicrobial agents such as trimethoprim, streptomycin, chloramphenicol. It indicated that there were a close relationship between class 1 integron and multi-drug resistance in Aeromonas isolates. ERIC-PCR showed that 50 integron-positive isolates were grouped into 16 molecular typing. Two different strain 5S33 and 5W13 from pond water and sediment have same ERIC-PCR patterns. Similar result also showed in the strain 7F9-1 and 7F9-2 which isolated from fish. Most of the integron-positive isolates carried same gene cassettes arrays have same molecular typing. The isolates carring aac(6’)-Ib-cr- arr-3 gene cassettes arrays strains were clusted in group E and group F, and all of which had similar plasmid pattern. It is concluded that class 1 integron mediated multi-drug resistance was widespread in Aeromans from different origins of livestock-fish integrated farms. Further study on resistance mechanism should be undertaken and provide a basis for rational usage of antimicrobial agents in Chinese aquaculture. |
