Vaccination of chickens with a Salmonella enteritidis aroA live oral Salmonella vaccine.

A mouse-virulent strain of Salmonella enteritidis, Se795 (LD50 less than 10 organisms for mice), was non-virulent for 12-day-old chickens given 10(6) cfu intravenously; the organisms were cleared from liver and spleen by day 14 as measured by direct plating and by day 21 by enrichment. An Se795aroA mutant, CU58, was also cleared from liver and spleen by day 14 after intravenous inoculation of 10(7) cfu. Day-old chicks vaccinated orally with either one dose of 10(9) CU58 at 1 day of age, 10(7) at 1 and 14 days, or 10(5) at 1 and 7 days followed by 10(9) at 14 and 21 days of age, were challenged orally with a nalidixic acid resistant variant of the virulent phage type 4 S. enteritidis strain 109. All vaccinated groups showed a reduction in faecal shedding of the challenge. Chickens given four doses of CU58 showed a significant reduction of cfu in liver, spleen and faeces following intravenous challenge with virulent strain 109. Intramuscular vaccination with 10(9) cfu of Aro strain CU58 at 1 day of age gave no protection against oral challenge with virulent strain 109. Serum antibody production to LPS (ELISA) was minimal in all vaccinated birds. The results indicate that oral vaccination with Aro- S. enteritidis can confer protection to day old chicks against virulent S. enteritidis.