Protection against experimental fowl typhoid by parenteral administration of live SL5828, an aroA-serC (aromatic dependent) mutant of a wild-type Salmonella Gallinarum strain made lysogenic for P22 sie

A wild-type strain of Salmonella enterica serotype Gallinarum, lysogenized with P22 sie (super-infection-exclusion defective) was greatly attenuated f or newly hatched or 21-day-old chickens. An aroA transductant of the lysoge nic strain and an aroA-serC tetracycline-sensitive deletion or deletion-inv ersion mutant of the latter were equally attenuated. Intramuscular administ ration of the aroA-serC strain to 21-day-old chickens protected them agains t oral challenge with 10(6) colony forming units of a highly virulent Galli narum strain (no deaths in the 30 vaccinated chickens versus 14 of 30 in th e control group). There was evidence of protection in the contents, mucosa and lymphoid tissue of the alimentary tract, in addition to that which occu rred in the liver and spleen. A weak serological response was detected by e nzyme-linked immunosorbent assay, indicating that use of such a strain is c ompatible with serological monitoring and would be a useful adjunct to cont rol schemes for fowl typhoid.