Factors affecting virulence of Shigella flexneri: avirulent strain with altered metablism of succinate, fumarate, and malate

Alterations in the pathogenicity of Escherichia coli K-12 after transfer of plasmid and chromosomal genes from Shigella flexneri

A 140-megadalton plasmid (pWR110), which has previously been associated with virulence in Shigella flexneri, was transferred to Escherichia coli K-12. Segments of S. flexneri chromosomal material were then transferred to the plamid-bearing K-12 strains. The virulence of these transconjugant hybrids was assessed in the HeLa cell model, in ligated rabbit ileal loops, or in the Sereny test. A K-12 strain which harbored only pWR110 invaded HeLa cells, produced minimal lesions in the rabbit ileal mucosa, and was negative in the Sereny test. Plasmid-containing K-12 hybrids which had incorporated various shigella chromosomal regions gave differential reactions in the rabbit ileal loops and in the Sereny test. Analysis of these transconjugants indicated that three regions were linked with virulent phenotypes. These included the his region (when the genes responsible for O-antigen synthesis were cotransferred) and the kcp locus (linked to the lac-gal region). Either of these chromosomal regions was sufficient to allow invasion of the rabbit ileal mucosa. In addition to both of these regions, another shigella chromosomal segment linked to the arg and mtl loci was necessary for fluid production in the rabbit ileal loop and for a positive Sereny reaction. Thus, derivatives of an E. coli K-12 strain, constructed by the stepwise conjugal transfer of a large plasmid and three chromosomal segments from S. flexneri, appeared to contain the necessary determinants for full pathogenicity in a variety of laboratory models.

Influence of D,L-ureidosuccinic acid dihydrazide on some biological properties of Pseudomonas pseudomallei and of Salmonella typhimurium

The changes induced in strains of Pseudomonas pseudomallei and Salmonella typhimurium under the action of D.L-ureidosuccinic acid dihydrazide were characterized. A decrease of the speed of multiplication in vitro and of the oxygen consumption was established. The virulence of the strains was reduced and their susceptibility to phagocytosis in vitro was increased.

Mutation in Shigella flexneri resulting in loss of ability to penetrate HeLa cells and loss of glycerol kinase activity

A colonial variant of a virulent Shigella flexneri 2a has lost both virulence and glycerol kinase activity. It also has several other altered characteristics: lowered ability to oxidize tricarboxylic acid cycle intermediates, increased electrophoretic mobility, and decreased sensitivity to sodium lauryl sulfate. Genetic analysis has revealed that the gene governing glycerol kinase activity in Shigella has a different chromosomal locus than that from Escherichia coli. Furthermore, transduction of the Shigella glycerol kinase gene (glp K) into the avirulent Shigella strain can restore the ability to penetrate HeLa cells, whereas the gene from E. coli cannot. About half of the glp K mutants lose this ability, and only about half of the revertants of an avirulent glp K mutant regain it. This indicates that more than one gene affects glycerol kinase activity in Shigella, only one of which is associated with penetration. Glycerol kinase activity is closely correlated with changes in electrophoretic mobility, but does not appear to have any relationship to sodium lauryl sulfate sensitivity nor to the oxidation of tricarboxylic acid cycle intermediates.