Study On Correlation Of Virulence And Resistance Of Escherichia Coli Isolated From Dairy Cows With Mastitis In Liaoning Province

Escherichia coli(E.coli)can cause various animal diseases,and pose great threaten to animal husbandry industry and human health.The drug resistance of E,coll is common currently and sets great difficulties in the prevention and treatment of infections caused by this bacteria.Resistance in bacteria can lead to the changes including bacterial virulence,and studies about effect of drug resistance in E.coli on virulence have got an increasing concern recently.In this study.we aimed to investigate about the influence of drug resistance of E.coli from dairy cows with clinical mastitis in Liaoning on virulence,and this will be beneficial for preventing and curing mastitis in this area.The polymerase chain reaction(PCR)was hired to detect the virulence distribution of 79 E.coli isolates from dairy cows with mastitis of Liaoning,and the phylogenytic group and the characteristics of virulence distribution were also analyzed in this study.The results showed that 59.5%of all isolates belonged to phylogenetic group A,and followed by 27.9%of phylogenetic B1,phylogenetic group B2 and D shared with the same ratio at 6.3%.The investigation about virulence distribution indicated that ten of twenty-two virulence genes were detected,the virulence genes were as following:fimH(89.9%),ECs3703(88.6%),ompC(100%),ompF(73.4%).colV(5.1%),irp2(2.5%),fyuA(2.5%).eaeA(1.3%),ler(1.3%)and iucD(1.3%).We found that phylogenetic group A were the mostly detected group,and contained more virulence genes in comparison with other groups.Besides,real time quantitative PCR(RT-PCR)was used to detect the mRNA expression levels of virulence genes ompF and ECs3703 in E.coli isolates with four different resistant phenotypes.The results showed that the mRNA expression levels of ompF decreased in E.coli isolates when the antibiotic resistance increased.The mRNA expression level of ompF in isolates which were resistant to two antibiotics was significantly lower(P<0.05)when compared with the antibiotic-sensitive goups.Furthermore,the mRNA expression level of ompF in isolates which were resistant to four or six antibiotics were significantly different(P<0.01)than that in the antibiotic-sensitive group.Although the mRNA expression level of ECs3 703 gene was not significantly different between antibiotic resistant isolates and antibitotic susceptible isolates.However,the mRNA expression level of ECs3703 gene in isolates resistant to six classes of antimicrobial agents showed significantly decreased(P<0.05)in comparison with the control group.In order to evaluate the virulent,the isolates were divided into four groups according to their resistant phenotype,including Group I(susceptible to antimicrobial agents),Goup II(resistant to two classes of antimicrobial agents).Group III(resistant to four classes of antimicrobial agents)and Group IV(resistant to four classes of antimicrobial agents).Group I,?,? and ? possessed morality rates with 72.22%,61.11%,33.33%and 16.67%respectively.The motality rates in Group III and IV were obviously lower than that in Group II.Our results indicated that E.coli isolates resistant to tetracyclines,?-lactams,fluoroquinolones,aminoglycosides,Amphenicols and macrocodes showed decreased virulent to mice as the drug resistance increased.In our study,we analyzed the virulence genes distribution and effect of drug resistance on its pathogenicity in E.coli from dairy cows with clinical mastitis.This study will provide theoretical basis for preventing and controlling clinical mastitis in dairy cows in this area.