Isolation,identification and characteristic analysis of Shigella from diarrhea of milk/meat calves in breeding farms in Northern Hebei Province
To identify the pathogenic bacteria causing diarrhea in milk/meat calves in livestock farms in the Northern Hebei region and analyze their biological characteristics,this study collected 273 anal swabs,feces,and diseased tissue samples from livestock farms in the Northern Hebei re-gion from 2022 to 2023.Bacterial isolation and culture,biochemical identification and PCR methods were used to isolate and identify Shigella.The pathogenicity,serotype and virulence genes of Shi-gella were detected by artificial infection test in mice,glass plate agglutination test,PCR method and K-B drug sensitivity paper method,respectively.The median lethal dose of the representative strains of its dominant serotypes was determined by artificial infection animal test and modified Koch's method.RT-PCR was used to detect five pathogens:BVDV,BRV,BCoV,BNoV and BNeV.The results showed that the detection of five viral pathogens was negative;94 strains of Shigella were isolated from collected diseased tissues,of which 52 strains were pathogenic Shigella causing disease and death in mice,with a mortality rate of over 40％in mice;52 pathogenic Shigella strains were dominated by Shigella flexneri F2a(21.2％)and F1b(25.0％),Shigella sonnei has Phase Ⅰ(19.2％)and Shigella dysentery(13.5％)as the dominant serotypes;the detection rates of 52 pathogenic Shigella virulence genes ipaH,ipa BCD,ial,Set1A,Set1B,sen,Sat and sigA were between 51.9％and 100％.The resistance rate of 52 pathogenic Shigella strains to 12 drugs such as sulfamethoxine,oxytetracycline,and doxycycline was more than 51.9％,and the resistance rate of other drugs was 5.8％-34.6％.The isolated strains showed MDR and were resistant to at least four kinds of drugs.The LD50 of the four dominant serotype representative strains HS-1(F2a),HS-2(F1b),HS-3(Shigella sonnei Ⅰ),and HS-4(Shigella dysenteriae)were 2.51 × 106,5.01 × 106,6.68 × 106 and 2.11×107 CFU/mL,respectively.This study provides a reference basis for the epidemiological investigation and prevention and control of shigellosis originating from milk and meat calves in livestock farms in the Northern Hebei region.
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