| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2005: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2004: ¥2,200,000 (Direct Cost: ¥2,200,000)
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| Research Abstract |
E.coli O157:H7 vaccine candidate strain (Stx-im), which produces nontoxic mutant Shiga toxin 2, was evaluated for its safety and efficacy by using the mouse infection model reported by Shimizu et al. (Microb Pathogen 35:1-9, 2003).
When 10^3 cfu of Stx-im or wildtype virulent O157:H7 strain, both Streptomycin (SM)-resistent, were administered orally to five SM-treated mice each (6-weeks-old) and followed by Mitomycin C (MMC) i.p. injection, all mice given Stx-im were alive while 4 out of 5 mice given virulent strain died. This result proved the non-toxicity of Stx-im.
To know the period required to induce specific antibodies in mice, Stx-im (10^<10> cfu) was given orally (day 0) to 3-weeks-old mice three times with 1-week interval and the titer of anti-O157 antibody in feces and blood were monitored. The antibody was firstly detected in ileum on day 10, then in colon and feces on day 17, and in serum on day 24. The high antibody titer was kept more than 60 days.
To evaluate the efficacy of Stx-im, SM-treated 3-weeks old mice received three shots of 10^<10> cfu Stx-im with 5 days intervals. As negative controls, E.coli K12 or vehicle was used instead cf Stx-im. Mice were challenged with virulent O157:H7 strain at 6-weeks-old followed by i.p. MMC injection 18 h after the challenge Unexpectedly, no mouse died not only in vaccinated but control groups. A series of experiments have been performed and suggested two possible reasons ; SM-treatment for 3 weeks 1)reduced the sensitivity of the mice to virulent O157:H7 by growing mice faster. 2)generated SM-resistant E.coli in the intestine of the mice and such E.coli prevented the virulent O157:H7 colonizing there. It may be difficult to evaluate the efficacy of Stx-im by such mouse model. Another experiment to see the neutralizing effect of anti-O157 antibody induced by administration of Stx-im is under way.
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