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Biomedical subjects

S Falkow

Publications and source records attributed to S Falkow.

At least 343 records · Page 19Linked to original sources
PubMed1969

Polynucleotide sequence relationships among members of Enterobacteriaceae.

Polynucleotide relationships were examined among many representatives of the Enterobacteriaceae by means of agar, membrane filter, and hydroxyapatite procedures. The amount of deoxyribonucleic acid (DNA) that reassociated was dependent, especially in interspecific reactions, on the annealing temperature. In only three cases: Escherichia coli-Shigella flexneri, Salmonella typhimurium-S. typhi, and Proteus mirabilis-P. vulgaris, was relative interspecific duplex formation 80% or higher. In most cases interspecies DNA duplex formation was 40% or less of that obtained from intraspecies DNA reassociation reactions. The stability of E. coli-S. flexneri DNA duplexes formed at either 60 or 75 C was virtually identical to that of homologous E. coli DNA duplexes, and the degree of interspecies duplex formation was minimally affected by the temperature increase (86% at 60 C; 77% at 75 C). The thermal stability of DNA duplexes formed at 60 C between DNA from E. coli and DNA from strains of Aerobacter aerogenes, S. typhimurium, S. typhi, and P. mirabilis was about 12 to 14 C below that of reassociated E. coli DNA. At 75 C, the formation of the interspecific DNA duplexes was markedly decreased, but the stability of the DNA able to reassociate at this temperature approximated that of reassociated E. coli DNA. The degree of reassociation and the thermal stability of E. coli-S. flexneri DNA duplexes suggests relatively little evolutionary divergence in these organisms. The other enterobacteria tested, however, have diverged to a point where less than one-half of their DNA can reanneal with E. coli DNA at 60 C and less than 10% reacts at 75 C. The degree of divergence between various enterobacteria does not appear to be uniform along the DNA molecule. Ribosomal ribonucleic acid (RNA)-specific sequences are conserved among most enterobacteria. An examination of messenger RNA relatively specific for the lactose operon suggests that specific chromosomal genes may diverge more or less than the genome as a whole.

Carbon Isotopes↗
PubMed1966

Protection of monkeys against experimental shigellosis with a living attenuated oral polyvalent dysentery vaccine.

Formal, Samuel B. (Walter Reed Army Institute of Research, Washington, D.C.), T. H. Kent, H. C. May, A. Palmer, and E. H. LaBrec. Protection of monkeys against experimental challenge with a living attenuated oral polyvalent dysentery vaccine. J. Bacteriol. 91:17-22. 1966.-Virulent strains of Shigella flexneri 1b, S. flexneri 3, and S. sonnei I were mated with an Hfr strain of Escherichia coli K-12, and hybrids were selected for the xylose marker. One hybrid strain of each of the serotypes was chosen for study of their biological characteristics. Their capacity to cause a fatal enteric infection in starved guinea pigs was reduced, they failed to cause dysentery when fed to monkeys, they caused keratoconjunctivitis in the guinea pig eye, and they penetrated HeLa cells. Two doses of a polyvalent oral vaccine composed of S. flexneri 1b, 2a, and 3, and S. sonnei I hybrid strains were fed to groups of monkeys at an interval of 4 to 7 days, and they, together with controls, were challenged 10 days after the last dose with one or another of the virulent parent dysentery strains. A significant degree of protection was afforded in all vaccinated groups with the exception of one group challenged with S. flexneri 6, a component not included in the vaccine. When animals were challenged with virulent S. flexneri 2a 1 month after oral vaccination, they were also protected. The vaccine produced a rise in serum antibody, but we were not able to detect coproantibody in saline extracts of feces from animals which received the vaccine.

Animals↗
PubMed1965

Protection of Monkeys Against Experimental Shigellosis with Attenuated Vaccines.

Formal, Samuel B. (Walter Reed Army Institute of Research, Washington, D.C.), E. H. LaBrec, Amos Palmer, and Stanley Falkow. Protection of monkeys against experimental shigellosis with attenuated vaccines. J. Bacteriol. 90:63-68. 1965.-Two Shigella flexneri 2a strains of reduced virulence were used as oral vaccines to protect monkeys against experimental challenge. One strain, a spontaneous mutant, had lost its ability to cause disease and was unable to penetrate the intestinal epithelium and reach the lamina propria. The other strain was a hybrid obtained by mating virulent S. flexneri 2a with Escherichia coli. This hybrid strain retained the capacity to penetrate the intestinal epithelium but was not able to maintain itself in the lamina propria. Five oral doses of the nonpenetrating mutant strain were required to render monkeys resistant to experimental challenge, but a single dose of the hybrid strain sufficed to protect the animals. There was some evidence that a degree of specificity was involved in the induced resistance, although neither vaccine evoked a consistent serum antibody or a detectable coproantibody response.

Journal Article↗
PubMed1965

Nucleic acid homologies of selected bacteria, L forms, Mycoplasma species.

Rogul, M. (Walter Reed Army Institute of Research, Washington, D.C.), Z. A. McGee, R. G. Wittler, and Stanley Falkow. Nucleic acid homologies of selected bacteria, L forms, and Mycoplasma species. J. Bacteriol. 90:1200-1204. 1965.-The molar per cent of guanine plus cytosine (G + C) in the deoxyribonucleic acids (DNA) of Proteus mirabilis, strain 9, and its stable L form was determined by thermal denaturation and found to be approximately 39.5% G + C. The DNA homologies of this bacterium and its L form were estimated by the agar-column technique and were equivalent in their abilities to anneal and form specific duplexes. The next series of comparisons were performed between two Mycoplasma species and their often suggested bacterial parent. The G + C ratios of M. gallisepticum (32.7%), M. gallinarum (28.1%), and Haemophilus gallinarum (41.9%) varied to a high degree. In the homologous system, the denatured DNA of H. gallinarum trapped in agar bound approximately 40% of its sheared, denatured, and H(3)-labeled DNA. In comparison, the nucleic acids of M. gallinarum and M. gallisepticum were incapable of binding the labeled DNA of H. gallinarum. These findings provided evidence that the two strains of Mycoplasma were not derived from H. gallinarum.

Carbon Isotopes↗
PubMed1962

EPISOMIC ELEMENT IN A STRAIN OF SALMONELLA TYPHOSA.

Falkow, Stanley (Walter Reed Army Institute of Research, Washington, D.C.) and L. S. Baron. Episomic element in a strain of Salmonella typhosa. J. Bacteriol. 84:581-589. 1962.-An episomic element, F(0)-lac(+), has been identified in a strain of Salmonella typhosa isolated from a natural habitat. The F(0)-lac(+) element is transferred at high frequency as a single unit of transmission and replication without linkage to any other genetic character. Cells receiving F(0)-lac(+) are heterogenotes as if F(0)-lac(+) is not integrated as part of the linear structure of the chromosome, but rather replicates autonomously or in some other association with the genome. Evidence from complementation tests and transduction experiments is presented that the lac genes carried by F(0) are identical or at least markedly similar to the lac genes of Escherichia coli K-12. The F(0) transmission factor cannot be precisely identified but it does not appear to be phage or colicin. F(0) does exhibit mutual repression with the sex factor, F, of E. coli, and immunological experiments indicate some relationship between F and F(0).

Journal Article↗
PubMed1962

GENETIC HOMOLOGY BETWEEN ESCHERICHIA COLI K-12 AND SALMONELLA.

Falkow, Stanley (Walter Reed Army Institute of Research, Washington, D.C.), Robert Rownd, and L. S. Baron. Genetic homology between Escherichia coli K-12 and Salmonella. J. Bacteriol. 84:1303-1312. 1962.-Recombinant analysis and interrupted mating procedures, in conjunction with molecular hybridization experiments, demonstrated that the genetic homology between Escherichia and Salmonella is incomplete. The most likely explanation of this incomplete homology is imperfect pairing between the deoxyribonucleic acid molecules of the two species. Despite the inhomologies, there is ample evidence that the order and distance of the genetic characters on the Salmonella chromosome are identical to those of Escherichia.

Journal Article↗
PubMedDate not supplied

Salmonella-induced macrophage death: the role of caspase-1 in death and inflammation.

Salmonella typhimurium invades host macrophages and can induce either an almost immediate cell death or establish an intracellular niche within the phagocytic vacuole. Rapid cell death depends on the Salmonella pathogenicity island SPI1 and the host protein caspase-1, a member of the pro-apoptotic caspase family of proteases. Caspase-1-dependent cell death leads to the activation of the potent pro-inflammatory cytokines interleukin (IL)-1beta and IL-18 to produce bioactive cytokines. Animal studies indicate that the activation of these cytokines is necessary for efficient colonization of the mouse gastrointestinal tract. Salmonella that reside in the phagocytic vacuole do not cause this early cell death and can trigger a macrophage death at a much later time point. This late-phase cell death is dependent on SPI2-encoded genes and ompR.

Animals↗
PubMedDate not supplied

Identification of the protein encoded by the transposable element Tn3 which is required for its transposition.

Protein products have now been identified which account for the entire coding capacity of the transposable element Tn3. Mutations in Tn3 have allowed us to map the genes encoding each of these peptides and to identify their role in transposition. We have found that only a single Tn3-encoded peptide is required for transposition. Expression of this peptide is repressed by the product of a second gene, which is itself autogenously regulated.

Bacterial Proteins↗