Pathogenicity of SG 9R, a rough vaccine strain against fowl typhoid.
SG 9R, a rough vaccine strain of Salmonella gallinarum, has been used for the prevention of fowl typhoid and paratyphoid in the world despite the presence of residual virulence. SG 9R-like rough strains have been recently isolated from fowl typhoid cases; however, molecular markers to differentiate SG 9R from field strains are not well-characterized and the molecular mechanisms of SG 9R residual virulence are unclear. Therefore, we analyzed LPS biosynthesis (rfa gene cluster) and virulence genes (spv, SPI-2) of both SG 9R and S. gallinarum rough field strains. SG 9R carried a unique nonsense mutation in rfaJ (TCA to TAA) and a shared rfaZ mutation (G-deletion) by rough and smooth S. gallinarum strains. SG 9R also carried intact SPI-2 and spvC, B, A, and R (except deleted spvD). SG 9R-like rough strains (n=10) carried identical mutations in virulence-related genes to SG 9R. SG 9R and SG 9R-like rough strains did not demonstrate significant mortality or liver lesions under normal conditions. However, fowl typhoid was successfully reproduced in the present study by SG 9R inoculation to 1-day-old male brown layer chicks per os following starvation. Therefore, the LPS defect may be one of the major mechanisms of SG 9R attenuation, and the possession of intact SPI-2, spvC, B, A, and R virulence genes may be associated with residual SG 9R virulence.
Zoonotic Disease Institute, Seoul National University, Shillim-Dong, Gwanak-Gu, Seoul, Republic of Korea. kwonhj01@snu.ac.kr
Hyuk-Joon
HJ
Kwon
Sun-Hee
SH
Cho
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics; D001428:Bacterial Vaccines / Q000009:adverse effects* / Q000235:genetics / Q000276:immunology*; D053898:Biosynthetic Pathways / Q000235:genetics; D001715:Bird Diseases / Q000382:microbiology / Q000517:prevention & control*; D008070:Lipopolysaccharides / Q000096:biosynthesis; D008297:Male; D012475:Salmonella / Q000235:genetics / Q000276:immunology* / Q000472:pathogenicity*; D012481:Salmonella Infections, Animal / Q000382:microbiology / Q000517:prevention & control*; D014774:Virulence; D037521:Virulence Factors / Q000235:genetics
D001426:Bacterial Proteins; D001428:Bacterial Vaccines; D008070:Lipopolysaccharides; D037521:Virulence Factors