| Infectious coryza is an acute respiratory disease caused by Avibacterium paragallinarum.Infectious coryza in chickens has a short incubation period,acute onset and rapid spread.It is an infectious disease that can cause acute or subacute respiratory diseases in chickens.The disease has great harm to both breeding chickens and laying hens,which can hinder the growth of broilers,reduce the meat quality,reduce the laying rate of laying hens,and bring huge economic losses to the breeding industry.At present,the most conventional treatment for infectious coryza is the use of antibiotics,but it also brings a series of serious drug resistance problems.At present,there are few reports on the drug sensitivity and drug resistance of Avibacterium paragallinarum in China.Therefore,exploring the changes in the sensitivity of Avibacterium paragallinarum to antibiotics plays an important role in the prevention and treatment of Infectious coryza.In this study,in the second half of 2021,samples of chickens with infectious rhinitis were collected from eight provinces(autonomous regions and municipalities)including Beijing,Anhui,Hebei,Jiangxi,Liaoning,Shandong and Shaanxi,and the collected samples were isolated and identified.The collected samples were identifed by PCR biomolecular and biochemical characterization.After detennination,the isolated strains were serologically identified by hemagglutination inhibition test,and the virulence of the isolated strains was verified again by animal regression test The results showed that the isolated strains were all Avibacterium paragallinarum,and it was found that most of the strains were serotypes A and C in all Avibacterium paragallinarum strains.The results of animal regression test showed that the pathogenic strain was still Avibacterium paragallinarum.The distribution results of antimicrobial susceptibility of 4 strains of Avibacterium paragalliarum preserved in the unknown specific years of the 20th century and all strains preserved and isolated from 2013 to 2021 showed that more than 80%of the strains were sensitive to erythromycin(82.1%),azithromycin(99.1%),ceftiofur(96.6%)and spectinomycin(91.5%).More than 80%of the resistant strains were resistant to ampicillin(100.0%),clindamycin(96.6%),cotrimoxazole(83.7%),nalidixic acid(8.9%)and tetracycline(94.9%).From the sensitivity of all strains to 18 kinds of antibiotics,the sensitivity of Avibacterium paragallinarum to compound sulfamethoxazole,nalidixic acid,ceftiofur,cefalexin,gentamicin,neomycin and kanamycin changed from sensitivity in the 20th century to moderate resistance or resistance in 2013,and the resistance phenotype continued until 2021.The resistance phenotypes of the other 11 antibiotics did not change much.The detection of drug resistance genes showed that a strain of Avibacterium paragallinarum carrying tet(X4)gene was isolated,but no unknown plasmid was extracted.The resistance mechanism and plasmid of Avibacterium paragallinarum need to be further studied.This study provides reference data for clinical treatment of Avibacterium paragallinarum and related research on drug resistance genes. |
