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Susceptibility of calves to challenge with Salmonella typhimurium 4/74 and derivatives harbouring mutations in htrA or purE

Institute for Animal Health, Compton, Berkshire RG20 7NN, UK¹
Biochemistry Section, Glasgow Veterinary School, Bearsden Rd, Glasgow G61 1QH, UK²
Department of Biochemistry, Imperial College of Science, Technology and Medicine, London SW7 2AZ, UK³

Author for correspondence: Bernardo Villarreal-Ramos. Tel: +44 1635 578 411. Fax: +44 1635 577 263. e-mail: Bernardo.Villarreal{at}bbsrc.ac.uk

Salmonella typhimurium 4/74 is highly virulent for cattle after oral challenge, causing severe diarrhoea, which is sometimes associated with systemic spread of the micro-organism. Although susceptible to oral challenge, groups of cattle were found to be relatively resistant to subcutaneous challenge with this strain. The virulence of S. typhimurium 4/74 harbouring mutations in htrA and purE was also assessed in cattle. Although S. typhimurium 4/74 htrA and purE are attenuated following oral challenge in mice, cattle were highly susceptible to oral challenge with these mutants. As with the parent S. typhimurium 4/74 strain, cattle exhibited greater susceptibility to oral compared to subcutaneous challenge with S. typhimurium htrA and purE mutants. Following subcutaneous challenge with sublethal levels of S. typhimurium 4/74, calves produced significant levels of antibodies to S. typhimurium soluble extract. No correlation was detected between interferon gamma levels in sera and susceptibility to infection by any route. The concentrations of the acute-phase-associated protein haptoglobin were increased in the sera of five of six cattle inoculated subcutaneously, although increases in concentration were smaller in cattle inoculated orally.

Keywords: Salmonella, cattle, htrA, purine

Abbreviations: STSE, Salmonella typhimurium soluble extract; PBS-T, phosphate buffered saline/Tween 20; IFN, interferon gamma