The Regulatory Mechanism Of BasSR,McbR And AI-2 On The Pathogenicity And Antibiotic Resistance In Avian Pathogenic Escherichia Coli

Avian pathogenic Escherichia coli(APEC),which is typical extraintestinal pathogenic Escherichia coli(ExPEC),leads to the highly morbidity and mortality of poultry.APEC can cause localized or systemic extraintestinal infections in chickens,ducks,geese and other birds,with a complex syndrome characterized by multiple organ lesions like airsacculitis,pericarditis,peritonitis,polyserositis,arthromeningitis,osteomyelitis,perihepatitis and septicemia.APEC is responsible for severe economic losses for the poultry industry worldwide.Antibiotic is a traditional treatment method,however,the abuse and misuse of antibiotics has contributed to the improvement of antibiotic-resistance level and the expansion of antibiotic-resistance spectrum in Escherichia coli(E.coli),and the emergence of multidrug-resistant E.coli.It is reported that the regulatory networks involved in the pathogenicity and multidrug resistance of E.coli are quorum sensing system,two-component system,the second messenger c-di-GMP and transcriptional regulator protein family.Until now,the molecular regulatory mechanism of above four regulatory networks on the pathogenicity and multidrug resistance of APEC isolated from poultry with colibacillosis has not been intensively studied.In this study,we explored that the regulatory mechanisms of above four regulatory systems on the pathogenicity and multidrug resistance of APEC.The main results are as follows:1.AI-2 increases the susceptibility of APEC to trimethoprim-sulfamethoxazole by down-regulating the transcription of the folate synthetase encoding genes folA and folC,and the folic acid synthesis-related genes luxS,metE and metH.This regulation is in a folate synthesis dependent pathway but not in the LsrR-dependent manner.2.The transcriptional regulator McbR increases biofilm formation by up-regulating the transcription of the biofilm-associated genes bcsA,fliC,wcaF and fimA,and McbR activates the expression of stress proteins YciF and YciE by directly binding to the promoters of yciG and yciF in APEC,and then enhance the resistance of APEC to hydrogen peroxide and tert-butyl hydrogen peroxide.4.BasSR two-component system enhances the resistance and pathogenicity of APEC to the host by up-regulating the transcription of biofilm-associated genes bcsA,csgA,fliC,fimA,motA and wcaF,and virulence-associated genes ais,entC,opgC,fepA and gfcE.This regulation is achieved by binding to the promoter regions of the biofilm-and virulence-related genes,including aisy opgC and fepA.5.c-di-GMP phosphodiesterase YfgF could regulate the biofilm formation of E.coli and the resistance E.coli to hydrogen peroxide.Both LsrR and BasSR regulate the expression of YfgF by directly binding to the promoter region of yfgF,and then affect c-di-GMP concentrations,and further regulate the biofilm formation of APEC and the resistance of APEC to hydrogen peroxide.In conclusion,this study revealed that the molecular mechanism of LsrR,BasSR,YfgF,and McbR on regulating the pathogenicity and multidrug resistance of APEC using antimicrobial activity assays,biofilm formation assays,crystal violet staining experiments,animal model experiments,real-time reverse-transcription(RT)-PCR experiments,electrophoretic mobility shift assays(EMSA)and transcriptional profiling.Therefore,this study might provide new clues for the prevention and treatment of APEC infection in poultry.