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Category: Clinical Microbiology; Bacterial Pathogenesis
Mechanisms of Salmonella enterica Serotype Typhimurium Intestinal Colonization, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555817619/9781555813239_Chap21-1.gif /docserver/preview/fulltext/10.1128/9781555817619/9781555813239_Chap21-2.gifAbstract:
The serotype associated most frequently with Salmonella, a diarrheal disease, is Salmonella enterica serotype Typhimurium. Serotype Typhimurium infection in calves is an excellent model for the intestinal pathology, host response, and disease syndrome observed in humans. The interaction of S. enterica serotype Typhimurium with the intestinal mucosa in calves and humans results in the recruitment of neutrophils whose presence is the histopathologic hallmark for the acute phase of Salmonella-induced enterocolitis. This neutrophilic infiltrate is associated with necrosis of the upper mucosa in large areas of the terminal ileum and colon. Serotype Typhimurium initiates interaction with epithelial cells by causing the formation of membrane ruffles, a process that results in bacterial internalization. This invasion process is mediated by a type III secretion system (T3SS-1) encoded by genes located on Salmonella pathogenicity island 1. The main function of the T3SS-1 is to translocate effector proteins into the cytosol of a host cell. Persistence of serotype Typhimurium in the mesenteric lymph nodes has also been described for apparently healthy cattle. The lipopolysaccharide (LPS) of serotype Enteritidis does not contain the O4 antigen but instead carries a tyvelose branch (O9 antigen) as the immunodominant epitope on the trisaccharide backbone of its O-antigen repeat unit.
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Comparison of the amino acid sequences deduced from fimbrial genes of S. enterica serotype Typhimurium strain LT-2 ( 69 ) with orthologues present in serotype Typhi strain CT-18 (Ty) ( 92 ), serotype Enteritidis phage type 4 (En) (http://www.sanger.ac.uk/Projects/Salmonella/ and http://www.salmonella.org/), E. coli K-12 strain MG1655 (K12) ( 11 ), and E. coli O157:H7 strain EDL933 (EHEC) ( 93 ). Serotype Typhimurium genes are indicated by arrows. Genes whose deduced amino acid sequences show homology to fimbrial chaperones and outer membrane fimbrial usher proteins are indicated as hatched and black arrows, respectively. The percent identity of deduced serotype Typhimurium amino acid sequences to orthologues (defined by the same location on the genome, as indicated by homology of flanking DNA regions) present in serotype Typhi, serotype Enteritidis, E. coli K-12, and E. coli O157:H7 are indicated below each arrow. Asterisks indicate that sequences were modified prior to the alignment to correct for truncations, frameshift mutations, or stop codons. NP, gene not present.
Comparison of the amino acid sequences deduced from fimbrial genes of S. enterica serotype Typhimurium strain LT-2 ( 69 ) with orthologues present in serotype Typhi strain CT-18 (Ty) ( 92 ), serotype Enteritidis phage type 4 (En) (http://www.sanger.ac.uk/Projects/Salmonella/ and http://www.salmonella.org/), E. coli K-12 strain MG1655 (K12) ( 11 ), and E. coli O157:H7 strain EDL933 (EHEC) ( 93 ). Serotype Typhimurium genes are indicated by arrows. Genes whose deduced amino acid sequences show homology to fimbrial chaperones and outer membrane fimbrial usher proteins are indicated as hatched and black arrows, respectively. The percent identity of deduced serotype Typhimurium amino acid sequences to orthologues (defined by the same location on the genome, as indicated by homology of flanking DNA regions) present in serotype Typhi, serotype Enteritidis, E. coli K-12, and E. coli O157:H7 are indicated below each arrow. Asterisks indicate that sequences were modified prior to the alignment to correct for truncations, frameshift mutations, or stop codons. NP, gene not present.