| Postweaning edema disease is an important disease in piglets, which is caused by shiga-toxin2e-producing Escherichia coli (STEC). The preliminary diagnosis for the disease is mainly based on the clinical symptoms and postmortal dissection. To establish a rapid diagnostic method for the disease, one pair of primers were designed according to the published sequences for the shiga-toxin2e (Stx2e) gene and the PCR was established using DNAs from known Stx2e+and Stx2e-E.coli as the template, the result of which showed that an expected amplicon of454bp was detectable in Stx2e+E. coli only. Five rectal swab samples and15duodenum samples were collected from the affected and died piglets with edema symptoms, respectively. After culture at37℃for4-6h in LB, PCR detection showed that19samples were STEC-positive, indicating that the PCR is a specific method for quick diagnosis of edema disease in piglets.Diarrhea in piglets is also an important disease in industrial pig farms with pathogenic Escherichia coli as the main causative agent. The preliminary diagnosis of this disease is mainly based on clinical symptoms and postmortal dissection. To establish a multiplex PCR method for quick diagnosis of the disease, four pairs of primers were designed according to the published sequences for the enterotoxin ST1, ST2, LT1and high pathogenicity island (HPI) genes. The specificity of the PCR was confirmed by using the reference E. coli strains with expected amplicons of183-,360-,282-and280-bp detected from ST1+, ST2+, LT-1+ETEC and HPI+E.coli, respectively. A total of200feces samples were obtained from the affected and died piglets with diarrheic simptoms. Following cultivation at37℃for4-6h in LB, all of the cultures were detected using the PCR, the result of which showed that52.5%,7.25%and6.5%were HPI-, HPI-plus ETEC-and ETEC-positive, respectively.To further investigate the association of HPI+E. coli with diarrhea in piglets, a total of164rectal swab samples were obtained for PCR detection. The results showed that58.18%was HPI+E. coli among110samples from the diarrheic piglets, compared to44.44%among54samples from healthy piglets. Among600isolates from the diarrheic piglets,25isolates were HPI-positive,4(16%) isolates were F6-positive,2(8%) were F4-positive,2(8%) were F4-plus F6--positive and only1(4%) isolate was F6-, LTa-and STb-positive. While among480isolates from healthy pilets, only20isolates were HPI-positive E. coli,1(5%) isolate was LTa-and STb-positive, without F4-and F6-positive E.coli detected. Furthermore,0138was the most prevalent serotype among all of the E.coli isolates from diarrheic and healthy piglets. Based on these and published data, it can be concluded that HPI+E. coli is an opportunistic pathogen for diarrhea in postweaning piglets.To develop an efficient autogenus vaccine against diarrhea in piglets, a total of40fecal samples were collected from the diarrheic piglets in a pig farm in Jiangsu provine, and submitted to PCR detection for ETEC and HPI-positive E. coli. The results showed that25(62.5%) were HPI+E. coli,5(12%) were ETEC and HPI+E. coli, and2(5%) were ETEC. Two predominant E. coli strains were selected to make an autogenus inactivated vaccine with aluminum hydroxide as the adjuvant. The results of sow immunization and diarrhea statistics showed that the incidence of diarrhea was23.9%in46piglets born by the sows immunized with the autogenus vaccine, compared to28.9%and55.5%in45piglets born by the sows immunized with a commercial trivalent inactivated vaccine and born by unimmunized sows, respectively. In the adhesion inhibition assay, the whey antibodies from the immunized and control sows at day1post parturition were able to inhibit the adhesion of K88+and987P+E.coli to porcine enterocytes. From day7post parturition, however, the whey antibodies from the sows of three groups were unable to inhibit the adhesion of K88+E. coli to porcine enterocytes, while the whey antibodies from the immunized sows could inhibit the adhesion of987P+E.coli to porcine enterocytes. |
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