Protection of chickens against experimental fowl typhoid using a nuoG mutant of Salmonella serotype Gallinarum

A nuoG mutation in NADH dehydrogenase I was introduced into a virulent strain of Salmonella serotype Gallinarum, the causative agent of fowl typhoid, using gene replacement with a nuoG open reading frame inactivated by insertion of DNA encoding a kanamycin resistance determinant. The S. Gallinarum nuoG mutant, named SG9NGK, was highly attenuated in chickens. SG9NGK colonized the caeca of chickens less efficiently than the S. Gallinarum parental strain, was less invasive and showed no evidence of multiplication in the liver or spleen. Using a single oral immunization with live bacteria SG9NGK reduced mortality in 2-week-old chickens following challenge with virulent S. Gallinarum from 75% to less than 8%.