Abstract: 【Objective】 The purpose of this experiment was to understand the prevalence,drug sensitivity and the presence of virulence genes of Proteus mirabilis causing calf diarrhea in Inner Mongolia region. 【Method】 A total of 89 diarrhea samples from calves were collected for bacterial isolation and culture.The isolates were identified through Gram staining microscopy,biochemical identification,and specific gene ureR PCR amplification,and the pathogenicity test was carried out in mice.The drug sensitivity test of the isolates was conducted using K-B method,and the carriage status of virulence genes and drug resistance genes in the isolates was detected by PCR. 【Result】 The isolates showed black center and colorless colony on SS agar medium，and showed migratory growth on BHIA medium.From 89 diarrhea samples of calves,14 suspected bacterial strains were isolated. The biochemical identification results showed that the isolates reacted positively with hydrogen sulfide,lysine,and ornithine,and negatively with adonitol,indole and raffinose.The PCR amplification using the specific gene ureR primer of Proteus mirabilis resulted in a band with a fragment size of 225 bp.After sequencing and splicing of the amplification products,comparative analysis was conducted.The results indicated that all 14 isolates were Proteus mirabilis,with an isolation rate of 15.7%.The results of pathogenicity test and virulence gene detection in mice showed that the isolates were all pathogenic,and the detection rates of virulence genes zapA, urec, pmfA, rsbA,ucaA and atfA ranged from 64.3% to 100%,among which 9 isolates carried 6 virulence genes,accounting for 64.3%.The results of the drug sensitivity test showed that the isolates exhibited multi-drug resistance,with a multi-drug resistance rate of up to 92.9%.Among them,the resistance rates to tetracycline,polymyxin B,and compound sulfamethoxazole were relatively high,with resistance rates ≥78.6%.They were sensitive to amikacin and ceftriaxone,with sensitivity rates ≥71.4%.The results of the drug resistance gene detection showed that the isolates were found to carry aminoglycoside resistance genes aadA25,strA and strB,quinolone resistance genes qnrA and qnrS,β-lactam resistance genes bla_TEM and bla_OXA-1,tetracycline resistance genes tetA and tetB,chloramphenicol resistance gene floR,and sulfonamide resistance genes Sul1 and Sul3.Among them,the detection rate of addA25 and Sul1 genes was the highest (100%). 【Conclusion】 14 strains of Proteus mirabilis from the diarrhea samples of calves in Inner Mongolia was isolated in this study.All the isolates were pathogenic and carried multiple virulence genes.There was a certain correlation between the drug resistance phenotypes and drug resistance genes.Amikacin and ceftriaxone were recommended for clinical treatment.

Key words: calf diarrhea; Proteus mirabilis; virulence gene; drug sensitivity test; drug resistance gene