Influence of codon usage on the immunogenicity of a DNA vaccine against tetanus.

Two related DNA vaccine vector plasmids, harbouring either wild-type (pcDNA3/ntetC) or synthetic codon optimised (pcDNA3/stetC) DNA encoding fragment C (TetC) of tetanus toxin were constructed. COS-7 cells transformed with pcDNA3/stetC reproducibly expressed higher levels of TetC than similar cells transformed with pcDNA3/ntetC. BALB/c mice immunised intramuscularly with pcDNA3/stetC produced significantly higher levels of anti-TetC antibodies in their serum in the weeks following vaccination compared to mice immunised with pcDNA3/ntetC, even when differences in the CpG content between the two sequences were controlled for using non-expressing DNA.

Vaccination for control of Salmonella in poultry.

Salmonella spp. are facultative intracellular pathogens causing localised or systemic infections, in addition to a chronic asymptomatic carrier state. They are of worldwide economic and public health significance. In poultry, which represent important sources of cheap protein throughout the world, fowl typhoid and pullorum disease continue to cause economic losses in those parts of the world where the poultry industries are continuing to intensify and where open sided housing is common. A number of serotypes that cause human gastro-enteritis are also increasing. The costs or impracticality of improvements in hygiene and management together with the increasing problems of antibiotic resistance suggest that vaccination in poultry will become more attractive as an adjunct to existing control measures. However, our understandings of the immunology of Salmonella infections in poultry is rudimentary and much poorer than that of equivalent infections in mice and live vaccine development for poultry has therefore been largely empirical. In addition to the killed Salmonella vaccines which have been used over the past few years with variable efficacy, a number of live vaccines have become available and some new vaccines will appear on the market over the next few years. These new vaccines should fulfil the criteria of efficacy, safety and compatibility with existing systems for monitoring infection before they are released on to a mass market. In this review we attempt to summarise the current understanding of Salmonella immunology in poultry together with the progress that has been made in poultry vaccine development.

Protection of chickens against experimental fowl typhoid using a nuoG mutant of Salmonella serotype Gallinarum.

A nuoG mutation in NADH dehydrogenase I was introduced into a virulent strain of Salmonella serotype Gallinarum, the causative agent of fowl typhoid, using gene replacement with a nuoG open reading frame inactivated by insertion of DNA encoding a kanamycin resistance determinant. The S. Gallinarum nuoG mutant, named SG9NGK, was highly attenuated in chickens. SG9NGK colonized the caeca of chickens less efficiently than the S. Gallinarum parental strain, was less invasive and showed no evidence of multiplication in the liver or spleen. Using a single oral immunization with live bacteria SG9NGK reduced mortality in 2-week-old chickens following challenge with virulent S. Gallinarum from 75% to less than 8%.

Identification of Salmonella typhimurium genes required for colonization of the chicken alimentary tract and for virulence in newly hatched chicks.

From a collection of 2,800 Tn5-TC1 transposon mutants of Salmonella typhimurium F98, 18 that showed reduced intestinal colonization of 3-week-old chicks were identified. The sites of transposon insertion were determined for most of the mutants and included insertions in the lipopolysaccharide biosynthesis genes rfaK, rfaY, rfbK, and rfbB and the genes dksA, clpB, hupA, and sipC. In addition, identification was made of an insertion into a novel gene that encodes a protein showing similarity to the IIC component of the mannose class of phosphoenolpyruvate-carbohydrate phosphotransferase systems, which we putatively called ptsC. Transduction of most of the transposon mutations to a fresh S. typhimurium F98 genetic background and construction of defined mutations in the rfbK, dksA, hupA, sipC, and ptsC genes of S. typhimurium F98 supported the role in colonization of all but the pts locus. The virulence of the rfbK, dksA, hupA, sipC, and ptsC defined mutants and clpB and rfaY transductants in 1-day-old chicks was tested. All but the ptsC and rfaY mutants were attenuated for virulence. A number of other phenotypes associated with some of the mutations are described.

Influence of genes encoding proton-translocating enzymes on suppression of Salmonella typhimurium growth and colonization.

Twenty-four-hour-old, aerobically grown, Luria-Bertani broth cultures of Salmonella typhimurium F98 suppressed the growth of a spectinomycin-resistant (Spcr) derivative of the same strain inoculated at 10(3) CFU ml(-1). This growth suppression is genus specific and RpoS independent, and it is not solely a result of nutrient depletion (P. A. Barrow, M. A. Lovell, and L. Zhang-Barber, J. Bacteriol. 178:3072-3076, 1996). Mutations in three genes are shown here to significantly reduce growth suppression under these conditions. The mutations were located in the nuo, cyd, and unc operons, which code for the NADH dehydrogenase I, cytochrome d oxidase, and F0F1 proton-translocating ATPase complexes, respectively. When cultures were grown under strictly anaerobic conditions, only the unc mutant did not suppress growth. Prior colonization of the alimentary tract of newly hatched chickens with the S. typhimurium F98 wild type or nuo or cyd mutants suppressed colonization by an S. typhimurium F98 Spcr derivative inoculated 24 h later. In contrast, the S. typhimurium unc mutant did not suppress colonization. The nuo and unc mutants showed poorer growth on certain carbon sources. The data support the hypothesis that growth suppression operates because of the absence of a utilizable carbon source or electron acceptor.