Abstract
A PCR-aided monitoring of verotoxin-producing Escherichia coli (VTEC) was performed over the period of 12 months by using fresh feces collected monthly from 5 dairy cows that had been identified as VTEC carriers. The PCR products were confirmed to be verotoxin genes by Southern hybridization using a gene fragment of verotoxin 2 as a probe. Although seasonal variation of VTEC shedding seemed to depend on each cow, several factors may have influenced the frequency of detection. Shedding of VTEC tended to be reduced during grazing from the middle of May up to the beginning of October. Only one cow was positive for VTEC in August. Dry-off was also suggested to have a depressive effect on VTEC shedding, i.e. 3 of 4 dry cows showed no shedding of VTEC. Contrary to these factors, winter or indoor rearing tended to increase VTEC with only 5/24 samples being negative during the period from November to April. Total VFA concentration was higher (p<0.05) in VTEC-positive feces than in VTEC-negative feces, while fecal pH and VFA proportions were not different. Partial sequences of verotoxin genes from feces of 4 VTEC-positive cows were nearly identical (99-100%), suggesting that gut bacteria sharing the same gene were distributed among the cows. The present results indicate that grazing and dry-off could be factors which reduce VTEC shedding, while winter/indoor rearing may be a factor which increases the shedding, possibly through on-farm interactions.
Highlights
Verotoxin-producing Escherichia coli (VTEC) has attracted much attention since outbreaks of food-borne pathogenic VTEC have occurred all over the world (Gilgen et al, 1998; Sanz et al, 1998)
The present results indicate that grazing and dry-off could be factors which reduce VTEC shedding, while winter/indoor rearing may be a factor which increases the shedding, possibly through on-farm interactions. (Key Words : Dairy Cattle, Feces, Verotoxin Genes, Escherichia coli, PCR Detection, Diet Change)
The sequence of vt2 gene used as a probe and the sequences of verotoxin genes detected in feces from cows A-D during the winter indoor rearing period (JanuaryApril, 2002) in the present study were submitted to the DDBJ data base under the following accession numbers: Probe, AB259615; A1, A2, B1, B2, B3, B4, C1, D1, D2, Table 1
Summary
Verotoxin-producing Escherichia coli (VTEC) has attracted much attention since outbreaks of food-borne pathogenic VTEC have occurred all over the world (Gilgen et al, 1998; Sanz et al, 1998). Winter or indoor rearing tended to increase VTEC with only 5/24 samples being negative during the period from November to April.
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