| Escherichia coli(Escherichia coli,E.coli)is traditionally considered to be an opportunistic bacterium,usually found in both humans and animals as a part of intestinal tract microbiota.Pathogenic E.coli can cause diarrhea and inflammation of the intestinal mucosa,causing its death in severe cases.E.coli developed resistance under the pressure of antibiotic selection,making it an important place for the storage and exchange of drug resistance genes.Giant panda is a valuable wild animal resource in China.The leading cause of death of pandas is various diseases,of which enteric disease is the most common.So far,there have been reports on the resistance of E.coli in the intestines of giant pandas,but there is little information available with the regard to the prevalence about mobile genetic elements in E.coli of the giant panda.Therefore,this study investigated the antibiotics resistance,mobile genetic elements and integron gene cassettes of E.coli in captive giant pandas,laying a foundation for further exploring the antibiotics resistance mechanism of intestinal E.coli in giant pandas,which is of great significance for the conservation and research of giant pandas in China.In this study,84 feces samples of captive giant pandas were collected from the Chengdu Research Base of Giant Panda Breeding in Sichuan Province,China,and 84 non-repetitive E.coli isolates(one isolate per feces)originated from the giant pandas in present study.The KirbyBauer disc diffusion method was used to test the susceptibility of 84 strains of E.coli against 22 antimicrobial agents.The results showed that 84 isolates showed different levels of resistance to 22 antimicrobial agents.E.coli isolates had high resistance to aztreonam(86.90%),amoxicillin-clavulanic acid(80.95%),ampicillin(69.05%),doxycycline(61.90%),tetracycline(48.81%)and amoxicillin(46.43%),and the resistance rates were 86.90%,80.95%,69.05%,61.90%,48.81% and 46.43%,respectively.In addition,73.81%(n= 62)of the isolates demonstrated multi-drug resistant(MDR),and the most frequent resistance pattern observed was that of ampicillin/amoxicillin-clavulanic acid.Significant difference in resistance to florfenicol were observed between isolates in different ages(P<0.01).There was no significant difference in the antibiotics resistance rate in different genders(P>0.05).At the same time,21 kinds of mobile genetic elements were amplified by PCR on 84 isolates of E.coli.The results showed that eleven kinds of mobile genetic elements were detected,and four kinds of mobile genetic elements were detected.Mobile genetic elements detected rates of E.coli isolates were as the following: merA(64.30%),followed by tbrC(47.62%)and tnpA/Tn21(35.71%),intI1(32.14%),IS1133(29.76%).Of the 84 these isolates,there were 36 mobile genetic elements combinations,in which the merA gene is predominant.However,13 isolates were not detected any mobile genetic elements.We further detected if E.coli isolates carrying integrase genes also carried the gene cassettes in variable regions.The results showed these isolates contained six distinct gene cassettes in class 1 integron,including: dfrA17+aadA5(2 isolates),aadA2(1 isolate),dfrA12+aadA2(1 isolate),dfrA1+aadA1(1 isolate),dfrA1(1 isolate)and aadA1(1 isolate).Highly significant differences in resistance to chloramphenicol,florfenicol and amoxicillinclavulanic acid were observed among the intI1-positive and intI1-negitive isolates(P<0.01);significant differences in resistance to ampicillin,tetracycline and compound sulfamethoxazole were observed among the intI1-positive and intI1-negitive isolates(P<0.05).In addition,three intI2-positive isolates were not amplified the integron gene cassette in this study;There was no significant difference in the antibiotics resistance rate among the intI2-positive and intI2-negitive isolates(P>0.05).The results of this study showed that 84 isolates showed different levels of resistance to 22 antimicrobial agents in captive giant pandas,as well as the isolates demonstrated multi-drug resistant;eleven kinds of mobile genetic elements were detected;and the strains mainly carried class 1 integrons,a few strains carried class 2 integrons,and the integron-gene cassettes were mainly aadA and dfrA which mediated aminoglycosides and trimethoprim resistant;the resistant phenotype of E.coli does not correspond to the gene cassette it carries.Antimicrobial resistance that mediated by gene cassettes is partially related to the resistant phenotype of E.coli. |
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