Generation of aromatic-dependent Salmonella havana and evaluation of its immunogenic potential in mice and sheep

Current perspectives in salmonellosis

Salmonellosis remains an important human and animal problem worldwide and, despite extensive research effort, many of the details of its pathogenesis are not known. While there have been recent advances in some aspects of pathogenesis, other areas are not understood. The host adaptation shown by several serotypes and the recent dramatic changes in the predominance of particular serotypes are examples. Molecular techniques using in vitro model systems have identified several genes involved in adhesion and invasion, though their function and even their relevance to disease remain poorly defined. Similarly, several potential toxins have been identified and the genes cloned, although their significance is far from clear. Some of the essential genes on the large virulence plasmids have been defined, and these are known to be necessary for the establishment of systemic infection. Two of these genes are regulatory, but the function of the other genes is unknown. A general theme has been the identification of gene systems involved in regulation of virulence. New vaccines, based on 'rational attenuation' are being designed, and these have also been used to carry heterologous antigens; such vaccines are currently undergoing trials. The improved understanding of the pathogenesis of salmonellosis may also provide a model of wide applicability to a more general understanding of bacterial pathogenesis. New techniques, including the polymerase chain reaction, are being applied to diagnose salmonellosis.

The development of oral vaccines against parasitic diseases utilizing live attenuated Salmonella

Genetically defined, live attenuated Salmonella vaccines are proving useful both as oral vaccines against salmonellosis and for the development of multivalent vaccines based on the expression of heterologous antigens in such strains. Several candidate attenuated S. typhi strains are at present being evaluated as new single dose oral typhoid vaccines in human volunteers. The emergence of such a vaccine will facilitate the development of multivalent vaccines for humans. Many antigens from different infectious organisms have been expressed in attenuated Salmonella. A focus of this work has been on developing vaccines against parasitic diseases. This review will summarize the efforts that have been made in this area.