Characterization of the expression of Salmonella Type III secretion system factor PrgI, SipA, SipB, SopE2, SpaO, and SptP in cultures and in mice.
BACKGROUND
The type III secretion systems (T3SSs) encoded by Salmonella pathogenicity island 1 and 2 (SPI-1 and SPI-2) are important for invasion of epithelial cells during development of Salmonella-associated enterocolitis and for replication in macrophages during systemic infection, respectively. In vitro studies have previously revealed hierarchical transport of different SPI-1 factors and ordered synergistic/antagonistic relationships between these proteins during Salmonella entry. These results suggest that the level and timing of the expression of these proteins dictate the consequences of bacterial infection and pathogenesis. However, the expression of these proteins has not been extensively studied in vivo, especially during the later stages of salmonellosis when the infection is established.


RESULTS
In this study, we have constructed bacterial strains that contain a FLAG epitope inserted in frame to SPI-1 genes prgI, sipA, sipB, sopE2, spaO, and sptP, and investigated the expression of the tagged proteins both in vitro and in vivo during murine salmonellosis. The tagged Salmonella strains were inoculated intraperitoneally or intragastrically into mice and recovered from various organs. Our results provide direct evidence that PrgI and SipB are expressed in Salmonella colonizing the spleen and cecum of the infected animals at early and late stages of infection. Furthermore, this study demonstrates that the SpaO protein is expressed preferably in Salmonella colonizing the cecum but not the spleen and that SptP is expressed preferably in Salmonella colonizing the spleen but not the cecum.


CONCLUSIONS
These results suggest that Salmonella may express different SPI-1 proteins when they colonize specific tissues and that differential expression of these proteins may be important for tissue-specific aspects of bacterial pathogenesis such as gastroenterititis in the cecum and systemic infection in the spleen.
Division of Infectious Diseases, School of Public Health, University of California, Berkeley, CA 94720, USA. haogong@berkeley.edu
Hao
H
Gong
Jing
J
Su
Yong
Y
Bai
Lu
L
Miao
Kihoon
K
Kim
Yonghua
Y
Yang
Fenyong
F
Liu
Sangwei
S
Lu
D000818:Animals; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D002432:Cecum / Q000382:microbiology; D015169:Colony Count, Microbial; D005260:Female; D015964:Gene Expression Regulation, Bacterial; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D016513:Mice, SCID; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism; D016254:Mutagenesis, Insertional; D017027:Protein Tyrosine Phosphatases / Q000235:genetics / Q000378:metabolism; D012481:Salmonella Infections, Animal / Q000382:microbiology*; D012486:Salmonella typhimurium / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D013154:Spleen / Q000382:microbiology
D001426:Bacterial Proteins; D020662:Guanine Nucleotide Exchange Factors; D008565:Membrane Proteins; D008840:Microfilament Proteins; C118287:SipA protein, Salmonella; C436324:SopE2 protein, Salmonella typhimurium; C101106:SpaO protein, Salmonella sp.; C419942:Spi1 protein, Salmonella; C094579:invasion protein B, Salmonella typhimurium; D017027:Protein Tyrosine Phosphatases; C439890:sptP protein, Salmonella typhimurium