Abstract: In order to study the serotyping,phylogenetic clustering and virulence gene distribution of Escherichia coli isolated from dairy cow manure with diarrhea in dairy cows,147 fresh feces of dairy cows with diarrhea symptoms were collected from some dairy farms in Shandong Province.The isolated strain was confirmed to be pathogenic Escherichia coli by routine bacterial isolation and culture,biochemical test and PCR amplification of bacterial 16S rDNA molecular biology technology.The serotype,phylogenetic clustering and virulence gene of the isolated strain were further detected,and the distribution of virulence gene in the phylogenetic clustering was analyzed.The results showed that 62 strains of Escherichia coli were identified and 9 pathogenic serotypes were identified.Among them,intestinal invasion（EIEC）,intestinal pathogenicity（EPEC）,and enterotoxigenic（ETEC） E.coli serotypes accounted for 17.74%,24.19%,and 19.35%,respectively.The dominant serotyping were O125∶K70（B15） and O124∶K72.18 strains belonged to group A,12 strains belonged to group B1,15 strains belonged to group B2,9 strains belonged to group D,and 8 strains could not determine the phylogenetic clustering.The distribution rates of virulence genes ibeB,mat and fimC were high,which were 100.00%,95.16% and 91.94%,respectively.At least 4 virulence gene and 9 virulence gene combinations were distributed in all strains.The correlation analysis between virulence gene and phylogenetic clustering showed that the distribution rate of ibeB in the four groups was 100%,and 17 virulence gene were detected in group B1.The results showed that the serotyping and phylogenetic clustering of pathogenic Escherichia coli in dairy cow with diarrhea in some areas of Shandong Province were diverse,carrying a variety of virulence gene,which should be paid attention to and strengthened monitoring and prevention and control.

Key words: dairy cow manure, Escherichia coli, serotyping, phylogenetic clustering, virulence gene