Study On The Epidemic Characteristics And Transmission Mechanism Of The Drug-resistant FosA3 Gene Of Escherichia Coli Isolates From Pigs

Escherichia.coli(E. coli) is a component of the normal intestinal flora in the animal and human body, and widely distributed in nature. But it was considered to be a non-pathogenic bacterium. In recent years, diarrhea, sepsis and dairy cow’s mastitis caused by E. coli often occurred and colibacillosis seriously restricts the development of animal husbandry industry. E. coli is easy to produce drug resistance to a lot of kinds of antibiotics and resistance can be disseminated to other susceptible bacteria by plasmids posing serious challenges to the clinical anti-infective therapy. Fosfomycin is only used in human clinic, and which is not be applied to veterinary clinic in almost all countries including China. However, in recent years, the bacteria of animal origin displayed fosfomycin resistance in China and the frequency of fosfomycin resistance has increased in prevalence in recent years. The current study confirmed that fosA3 gene is the major mechanism mediating fosfomycin resistance. But the epidemic characteristics and transmission mechanism of the drug-resistant gene fosA3 in Escherichia.coli is unclear in China. Since, the epidemiologic characterization and transfer mechanism of fosA3 in E. coli are urgently examined.In this study, 54 fosA3-producing E. coli isolates were isolated in E. coli from Foshan City of Guangdong Province. PFGE was successfully performed on 54 E. coli isolates carrying fosA3 gene, and 34 different XbaI PFGE patterns were identified. The fosA3 gene was confirmed on plasmid through plasmid extraction, PCR amplification of fosA3 gene using plasmid as the template, filter mating and southern blotting. Results showed that fosA3 gene from most of 34 isolates was located on ca.97 kb plasmid. Sequence analysis showed that plasmids carrying fosA3 were IncFII and IncN type plasmid, and fosA3 gene was surrounded by two insertion sequence IS26. All transconjugants and original strains were tested for their MICs of selected nine antibiotics. A total of 34 fosA3-producing E. coli isolates were resistant to cefotaxime, tetracycline, doxycycline, chloramphenicol and fosfomycin. The resistant rate of the 34 E. coli isolates for gentamicin, florfenicol, was more than 70%. All of transconjugants of these isolates showed significant differences to fosfomycin, cefotaxime, gentamicin, tetracycline, amikacin, chloramphenicol, florfenicol and doxycycline. During amplification of chloramphenicol resistance gene, we have detected cfr and floR gene, detection of related resistant genes of β-lactam antibiotics, mainly blaCTX-M-1, blaCTX-M-9 and blaTEM gene were found, detection of related resistant genes of aminoglycoside antibiotics, mainly rmtA and rmtB gene were sensed, and detection of related resistant genes of tetracycline antibiotic, tetR gene was found in transconjugants.This study preliminarily explores the propagation mechanism of fosA3 gene in E.coli from pigs, providing a theoretical basis for clinical guidelines and rational drug to control its rapid spread.