Molecular genotyping of multinational ovine and caprine Corynebacterium pseudotuberculosis isolates using pulsed-field gel electrophoresis.

Caseous lymphadenitis (CLA) is a chronic, suppurative disease, with a worldwide distribution, caused by Corynebacterium pseudotuberculosis. The clinical manifestation of CLA is known to vary between different countries, and has been postulated to be due to differences in the strains present in these countries. Forty-two sheep and goat isolates of C. pseudotuberculosis from Australia, Canada, Eire, The Netherlands and Northern Ireland were characterized by pulsed-field gel electrophoresis (PFGE), biotyping, antimicrobial susceptibility, and production of phospholipase D. The PFGE-determined genotypes of this multicentric collection were then compared with representative ovine and caprine isolates from a previously published panel of PFGE profiles of United Kingdom isolates. Digestion with SfiI generated 16-18 bands in the 48.5 and 290 kb range, and differentiated four distinct pulsotypes amongst the 36 ovine and 6 caprine strains which displayed remarkable homogeneity. Based on these results, it would appear that the genome of C. pseudotuberculosis is highly conserved, irrespective of the country of strain origin.

Vaccination confers significant protection of sheep against infection with a virulent United Kingdom strain of Corynebacterium pseudotuberculosis.

Using a virulent United Kingdom Corynebacterium pseudotuberculosis isolate, an ovine experimental model of caseous lymphadenitis was developed, in which the manifestation of disease was equivalent to the naturally observed infection in this country. Subsequently, the capacity of several experimental vaccines to protect against experimental challenge was determined. Sheep were immunised with a recombinant derivative of phospholipase D, deriving from the virulent UK isolate, a formalin-killed bacterin of the same strain, or a bacterin supplemented with recombinant phospholipase D. Following homologous experimental challenge, the phospholipase D and bacterin vaccines were observed to confer statistically significant protection against infection, and appeared to restrict dissemination of challenge bacteria beyond the inoculation site in the majority of animals. More importantly, the combined vaccine succeeded in providing absolute protection against infection, whereby challenge bacteria were eradicated from all vaccinates. In addition to the experimental vaccines, a commercially available CLA vaccine, unlicensed for use in the European Union, was assessed for its capacity to protect against heterologous challenge. The vaccine conferred significant protection, although the dissemination of infection beyond the inoculation site was not restricted as it had been with the previous vaccines. However, no animals immunised with this vaccine manifested infection within the lungs; thus, a potentially important route of disease transmission was eliminated. The results of this study provide information pertinent to the development of an effective caseous lymphadenitis vaccination strategy in the UK.