Gnotobiotic pigs were inoculated orally with wild-type or defined aroA or. W cr clp vaccine strains of Salmonella enterica serovars Typhimurium and S. Enteritidis. The parental strains were virulent, inducing severe diarrhoea, dehydration and systemic disease. The cya crp mutant was also highly virulent whereas the aroA strains were attenuated. (C) 2001 Elsevier Science Ltd. All rights reserved.