Salmonella typhimurium SR-11 mutants with cya::Tn10 or crp::Tn10 mutations were found to be avirulent and immunogenic for BALB/c mice. Fusaric acid-resistant derivatives with deletions of the Tn10 and adjacent DNA sequences were constructed in S. typhimurium SR-11 strains with or without the virulence plasmid pStSR100. These delta cya delta crp strains grew more slowly than wild-type strains. They possessed wild-type ability to attach to, invade, and persist in gut-associated lymphoid tissue for up to a week but exhibited a diminished ability to reach mesenteric lymph nodes and the spleen. Mice 4 to 8 weeks old were resistant to oral infection with 10(9) cells of several different delta cya and delta cya delta crp strains (the equivalent to 10(4) 50% lethal doses of wild-type S. typhimurium SR-11) and 30 days after immunization became resistant to oral challenge with 10(3) to 10(4) 50% lethal doses of wild-type S. typhimurium SR-11.

Salmonella typhimurium deletion mutants lacking adenylate cyclase and cyclic AMP receptor protein are avirulent and immunogenic.

The question of how bacteria are able to overcome species barriers and adapt to new hosts is central to the understanding of both the origin of infectious diseases and the emergence of new pathogens. The analysis of virulence factors used by different Salmonella serotypes can serve as a powerful

https://iai.asm.org/content/iai/66/10/4579.full.pdf

Evolution of Host Adaptation in Salmonella Enterica

Targeted delivery of antibiotics using liposomes and nanoparticles: research and applications.

We investigated the role of the 100-kilobase (kb) plasmid of Salmonella typhimurium in the virulence of this organism for mice. Three strains, LT2-Z, SR-11, and SL1344, which possessed 100-kb plasmids with identical restriction enzyme digestion profiles, were cured of their respective 100-kb plasmids after Tnmini-tet was used to label plasmids. Curing wild-type virulent strains SR-11 and SL1344 raised peroral 50% lethal doses from 3 x 10(5) and 6 x 10(4) CFU, respectively, to greater than 10(8) CFU. Both wild-type strains had intraperitoneal 50% lethal doses of less than 50 CFU, whereas the intraperitoneal 50% lethal doses for cured SR-11 and SL1344 were less than 50 and 400 CFU, respectively. Reintroduction of the Tnmini-tet-labeled, 100-kb plasmid restored wild-type virulence. Invasion from Peyer's patches to mesenteric lymph nodes and spleens after peroral inoculation was the stage of pathogenesis most affected by curing S. typhimurium of the 100-kb plasmid. Wild-type S. typhimurium replicated in spleens of mice inoculated intravenously to a greater extent than did plasmid-cured derivatives. Wild-type and cured strains equally adhered to and invaded Henle-407, HEp-2, and CHO cells; furthermore, the presence of the 100-kb plasmid was not necessary for replication of S. typhimurium within CHO cells. The 100-kb plasmid had no effect on phagocytosis and killing of S. typhimurium by murine peritoneal macrophages in vitro and in vivo. Similarly, wild-type and plasmid-cured strains were resistant to killing by 90% normal human, rabbit, and guinea pig sera. All wild-type and plasmid-cured S. typhimurium strains possessed complete lipopolysaccharide, as determined by silver staining solubilized cells in sodium dodecyl sulfate-polyacrylamide gels. We have confirmed the role of the 100-kb plasmid of S. typhimurium in virulence, primarily in invasion to mesenteric lymph nodes and spleens after peroral inoculation of mice. Involvement of the 100-kb plasmid in infection of mesenteric lymph nodes and spleens suggests a role for the plasmid in the complex interaction of S. typhimurium with cells of the reticuloendothelial system.

Plasmid-associated virulence of Salmonella typhimurium.

BACKGROUND AND AIMS The gastrointestinal microflora exerts a barrier effect against enteropathogens. The aim of this study was to examine if bifidobacteria, a major species of the human colonic microflora, participates in the barrier effect by developing antimicrobial activity against enterovirulent bacteria. METHODS Antibacterial activity was examined in vitro against a wide range of Gram negative and Gram positive pathogens. Inhibition of Salmonella typhimurium SL1334 cell association and cell invasion was investigated in vitro using Caco-2 cells. Colonisation of the gastrointestinal tract in vivo by bifidobacteria was examined in axenic C3/He/Oujco mice. Antimicrobial activity was examined in vivo in axenic C3/He/Oujco mice infected by the lethal S typhimurium C5 strain. RESULTS Fourteen human bifidobacterium strains isolated from infant stools were examined for antimicrobial activity. Two strains (CA1 and F9) expressed antagonistic activity against pathogens in vitro, inhibited cell entry, and killed intracellular S typhimurium SL1344 in Caco-2 cells. An antibacterial component(s) produced by CA1 and F9 was found to be a lipophilic molecule(s) with a molecular weight of less than 3500. In the axenic C3/He/Oujco mice, CA1 and F9 strains colonised the intestinal tract and protected mice against S typhimurium C5 lethal infection. CONCLUSION Several bifidobacterium strains from resident infant human gastrointestinal microflora exert antimicrobial activity, suggesting that they could participate in the “barrier effect” produced by the indigenous microflora.

https://gut.bmj.com/content/gutjnl/47/5/646.full.pdf

Bifidobacterium strains from resident infant human gastrointestinal microflora exert antimicrobial activity

Summary The growth pattern of Salmonella enterica subsp. enterica serotype Typhimurium (Typhimurium) was studied in mice to examine the role of the 60-Mdal virulence-associated plasmid in the pathogenesis of mouse typhoid. After repeated subcultures at 45°C, isogenic variants harbouring the virulence-associated plasmid (strains C52, TM122 and TM332) or having lost this large plasmid (strains C53, TM123 and TM333) were obtained from three parental strains (strains C5, TM 12 and TM33, respectively). Plasmid plP1350, present in strain C52, was tagged by Tn10 and transferred by successive conjugations to strains C53, TM123 and TM333. The behaviour of these three Typhimurium lines was studied in C57BL/6, DBA2, 136132 (C57BL/6 x DBA2 F1 hybrid) and OF, mice after oral infection, subcutaneous injection into the hind footpad or intravenous inoculation. The kinetics of organ colonization were followed at intervals after injection by enumeration of viable bacteria in caecum, mesenteric or popliteal lymph node, spleen, liver, kidney and lung depending on the route of infection. Strains harbouring virulence plasmid and their cured derivatives did not differ significantly in their ability to colonize caecal content and to translocate to draining lymph nodes. Elimination of the virulence plasmid was correlated with a significant reduction in the ability of cured variants to colonize spleen and liver. Reintroduction of the virulence plasmid into plasmidless variants restored the virulence to the level originally observed. These data demonstrate that a 60-Mdal plasmid in Typhimurium strains is necessary to ensure colonization of spleen and liver of experimentally infected mice.

Virulence-associated plasmids of Salmonella serotype Typhimurium in experimental murine infection.

Summary All studied isolates of Salmonella serotypes abortusovis (16 strains), enteritidis (30 strains), paratyphi C (29 strains), and 2 out of 10 isolates of serotype newport harboured large 54–76-Kb plasmids. No such plasmids were found in the following serotypes: agona, bovismorbificans, heidelberg, infantis, panama, paratyphi A, paratyphi B, saintpaul, senftenberg and typhi. These plasmids and the virulence-associated plasmids of Salmonella serotypes typhimurium and dublin were compared at the molecular level. Plasmids from the same serotype usually showed similar Hin dIII endonuclease patterns. Plasmids from different serotypes displayed markedly different cleavage patterns. Using the 3 H-labelled plasmid from serotype typhimurium strain C5 as a probe, nitrocellulose filter hybridization showed that all these plasmids shared homologous sequences distributed throughout the plasmid molecule. With the S1-nuclease method, all plasmids were 61 to 88% related to the virulence plasmid of serotype typhimurium strain C5. The large plasmids in Salmonella serotypes abortusovis, enteritidis, paratyphi C, newport and the virulence-associated plasmids in serotypes typhimurium and dublin thus constitute a single group of homology and represent a family of related plasmids. We suggest that this plasmid group may contribute to the pathogenic potential of host serotypes.

Molecular relationships between virulence plasmids of Salmonella serotypes typhimurium and dublin and large plasmids of other Salmonella serotypes.

Summary A collection of 31 strains received as Agrobacterium tumefaciens and A. radiobacter was subjected to detailed phenotypic and genomic studies. These strains were recovered from plants, soil, water and clinical specimens. Type strains of A. tumefaciens, A. radiobacter, A. rhizogenes and A. rubi were also included. The strains were tested for their ability to use 169 organic compounds as sources of carbon and energy. In addition, 11 conventional characters were studied for each strain. Relatedness among the strains was assessed by determining the extent of reassociation in heterologous DNA preparations. S1 nuclease and diethylaminoethyl-cellulose filters were used to separate reassociated from non-reassociated nucleotide sequences, and to determine the thermal stability of related nucleotide sequences. The resultant data revealed the following points: 1) regardless of their phytopathogenic effects, 3-ketolactose-producing A. tumefaciens and A. radiobacter strains group into one species; this species contains 9 taxa which can be differentiated from each other by phenotypic and genomic characters; 2) clinical isolates did not induce tumours on plants and clustered in three taxa of this species; the clinical and ecological significance of these organisms is not known; 3) the present classification of the genus Agrobacterium is based on phytopathogenicity and does not reflect the phylogenetic relationships amongst these bacteria; as proposed previously by several workers, the genus Agrobacterium should be divided into 3 species on the basis of phenotypic and genomic characteristics. Different aspects of the classification and nomenclature of Agrobacterium are discussed.

Position taxonomique de souches de Agrobacterium d'origine hospitalière

A collection of 31 strains received as Agrobacterium tumefaciens and A. radiobacter was subjected to detailed phenotypic and genomic studies. These strains were recovered from plants, soil, water and clinical specimens. Type strains of A. tumefaciens, A. radiobacter, A. rhizogenes and A. rubi were also included. The strains were tested for their ability to use 169 organic compounds as sources of carbon and energy. In addition, 11 conventional characters were studied for each strain. Relatedness among the strains was assessed by determining the extent of reassociation in heterologous DNA preparations. S1 nuclease and diethylaminoethyl-cellulose filters were used to separate reassociated from non-reassociated nucleotide sequences, and to determine the thermal stability of related nucleotide sequences. The resultant data revealed the following points: regardless of their phytopathogenic effects, 3-ketolactose-producing A. tumefaciens and A. radiobacter strains group into one species; this species contains 9 taxa which can be differentiated from each other by phenotypic and genomic characters; clinical isolates did not induce tumours on plants and clustered in three taxa of this species; the clinical and ecological significance of these organisms is not known; the present classification of the genus Agrobacterium is based on phytopathogenicity and does not reflect the phylogenetic relationships amongst these bacteria; as proposed previously by several workers, the genus Agrobacterium should be divided into 3 species on the basis of phenotypic and genomic characteristics. Different aspects of the classification and nomenclature of Agrobacterium are discussed.

I. Miras

Papers

Virulence-associated plasmids of Salmonella serotype Typhimurium in experimental murine infection.

Molecular relationships between virulence plasmids of Salmonella serotypes typhimurium and dublin and large plasmids of other Salmonella serotypes.

Position taxonomique de souches de Agrobacterium d'origine hospitalière

Taxonomic position of Agrobacterium strains of hospital origin