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S FALKOW

Publications and source records attributed to S FALKOW.

At least 19 recordsLinked to original sources
PubMed1965

RESTORATION OF VIRULENCE TO A STRAIN OF SHIGELLA FLEXNERI BY MATING WITH ESCHERICHIA COLI.

Formal, Samuel B. (Walter Reed Army Institute of Research, Washington, D.C.), E. H. LaBrec, H. Schneider, and Stanley Falkow. Restoration of virulence to a strain of Shigella flexneri by mating with Escherichia coli. J. Bacteriol. 89:835-838. 1965.-Three spontaneous avirulent variants of Shigella flexneri 5 were isolated and employed as genetic recipients in matings with Escherichia coli K-12. The various hybrid classes isolated from these matings were subsequently examined for their ability to induce keratoconjunctivitis and to kill pretreated guinea pigs. All hybrids derived from two of the variants remained avirulent. A majority of the mal(+) hybrids of the third avirulent variant were observed to be restored to complete virulence.

Amino Acids↗
PubMed1965

ABORTIVE INTESTINAL INFECTION WITH AN ESCHERICHIA COLI-SHIGELLA FLEXNERI HYBRID STRAIN.

Formal, Samuel B., (Walter Reed Army Institute of Research, Washington, D.C.), E. H. LaBrec, T. H. Kent, and S. Falkow. Abortive intestinal infection with an Escherichia coli-Shigella flexneri hybrid strain. J. Bacteriol. 89:1374-1382. 1965.-The mechanism of the apparent loss of virulence of an Escherichia coli-Shigella flexneri hybrid strain was studied. The parent Shigella strain caused a fatal enteric infection when fed to starved guinea pigs, and signs of dysentery followed its oral administration to monkeys. The hybrid strain failed to produce any apparent symptoms when fed to either of these species. The parent strain was shown to invade the intestinal mucosa of starved guinea pigs. This caused a severe inflammatory reaction in the lamina propria, which progressed to ulceration of the intestinal epithelium and resulted in death of the animal. The hybrid strain also invaded the intestinal mucosa and produced an inflammatory reaction. In this case, the inflammatory reaction subsided, the intestine returned to normal within 4 days after challenge, and the animal survived. Both fluorescent-antibody techniques and in vivo growth studies have shown that the hybrid strain can not maintain itself in the intestinal mucosa. Preliminary studies have indicated that a similar situation also exists in the monkey. It is concluded that the virulence of dysentery bacilli rests not only in the capacity to reach the lamina propria, but also in the ability to multiply in this region.

Animals↗
PubMed1964

TRANSFER OF EPISOMIC ELEMENTS TO PROTEUS. I. TRANSFER OF F-LINKED CHROMOSOMAL DETERMINANTS.

Falkow, Stanley (Walter Reed Army Institute of Research, Washington, D.C.), J. A. Wohlhieter, R. V. Citarella, and L. S. Baron. Transfer of episomic elements to Proteus. I. Transfer of F-linked chromosomal determinants. J. Bacteriol. 87:209-219. 1964.-F-linked lac(+) genes may be transferred from Escherichia coli to several species of Proteus by conjugation. Usually the transferred genetic elements are markedly unstable in Proteus, but repeated plating permits the selection of relatively stable Proteus lac(+) strains. Proteus strains carrying F-linked lac(+) markers are heterogenotes and limited donors for lac(+). In addition, both the fertility and lac(+) property may be eliminated from Proteus by treatment with acridine orange. Escherichia and Proteus possess very different overall deoxyribonucleic acid (DNA) base compositions. In CsCl density gradients of DNA extracted from Proteus lac(+) strains, the acquisition of Escherichia genes by Proteus may be correlated with the addition of a physically recognizable high molecular weight, native DNA fraction of Escherichia base composition. Proteus lac(+) strains synthesize a beta-galactosidase which is indistinguishable from E. coli enzyme by several criteria. Despite this specificity, the regulatory functions of Escherichia lac(+) genes appear to be impaired in Proteus.

Acridines↗
PubMed1964

RECIPIENT ABILITY OF SALMONELLA TYPHOSA IN GENETIC CROSSES WITH ESCHERICHIA COLI.

Johnson, E. M. (Walter Reed Army Institute of Research, Washington, D.C.), Stanley Falkow, and L. S. Baron. Recipient ability of Salmonella typhosa in genetic crosses with Escherichia coli. J. Bacteriol. 87:54-60. 1964.-Salmonella typhosa strain 643WS(r) was mated with Escherichia coli Hfr strains W1895 and Hayes, with single marker selection for the E. coli genes lac(+) (lactose utilization) and ara(+) (arabinose utilization). Four classes of Salmonella hybrids were obtained, each class possessing one marker derived from one E. coli parent. In a series of eight genetic crosses, in which each hybrid class was remated with each of the Hfr strains, recipient ability of the hybrids was increased only when their substituted E. coli genetic section matched the lead region of the Hfr chromosome. Data obtained from replica plating indicated that the S. typhosa 643WS(r) population is probably homogeneous with respect to its initial ability to mate with E. coli. Transfer of the F-lac element was found to occur only slightly less efficiently from an E. coli F' donor to S. typhosa than it did to an E. coli F(-) strain. This indicated that E. coli is able to conjugate almost as effectively with S. typhosa as it does intraspecifically. However, failure to detect beta-galactosidase production by merozygotes derived from an E. coli Hfr W1895 x S. typhosa mating indicated that transfer of chromosomal lac(+) may be impaired.

Arabinose↗
PubMed1964

CHROMOSOME TRANSFER KINETICS OF SALMONELLA HFR STRAINS.

Johnson, E. M. (Walter Reed Army Institute of Research, Washington, D.C.), Stanley Falkow, and L. S. Baron. Chromosome transfer kinetics of Salmonella Hfr strains. J. Bacteriol. 88:395-400. 1964.-The kinetics of chromosome transfer of an Hfr strain of Salmonella typhosa and an Hfr strain of S. typhimurium were examined in interrupted matings with multiply auxotrophic S. typhimurium recipients. The S. typhosa Hfr, TD-7, was found to transfer the pro-A, met-A, arg (A, C, F, or H), and ile markers at 8, 32, 36, and 51 min, respectively, after contact with the recipient strain. Comparison of these entry times with those of the analogous Escherichia coli Hfr P4X-6 for the same markers showed the gene order to be identical. However, the TD-7 entry times were considerably extended over those of P4X-6, which transfers these markers of E. coli F(-) strains at, respectively, 5, 20, 22.5, and 28 min. A similar extension of the entry times was noted with the S. typhimurium Hfr, SR-305, which transfers the markers in the reverse order, ile-met-A-pro-A, at 3 to 4, 18, and 46 min, respectively. Examination of P4X-6/Salmonella Hfr entry time ratios showed them to be constant at 0.63 for the earlier markers transferred by both TD-7 and SR-305. These data suggest that the physical length of the Salmonella chromosome is the same as that of E. coli, and that the rate of chromosome transfer of the Salmonella Hfr strains to S. typhimurium recipients is only 0.63 that of P4X-6 to E. coli F(-) strains under the same physical conditions.

Amino Acids↗
PubMed1964

CHARACTERIZATION OF AN HFR STRAIN OF SHIGELLA FLEXNERI.

Schneider, Herman (Walter Reed Army Institute of Research, Washington, D.C.), and Stanley Falkow. Characterization of an Hfr strain of Shigella flexneri. J. Bacteriol. 88:682-689. 1964.-A Hfr Shigella flexneri, strain 69, was obtained by terminal marker selection in a cross between Hfr Escherichia coli and S. flexneri. The chromosome of this Hfr Shigella bears gross homology to the E. coli chromosome: it can conjugate with both Shigella and E. coli; its order of gene transmission is the same as E. coli; and interrupted matings show that distance between gene loci is the same as for E. coli. The kinetics of transfer of the pro(+), thr(+) + leu(+), and arg(+) loci by Hfr S. flexneri differ from Hfr E. coli, and may indicate that function of the sex factor, F, derived from E. coli, is modified when integrated into the Shigella chromosome.

Chromosomes↗
PubMed1964

TRANSFER OF EPISOMIC ELEMENTS TO PROTEUS. II. NATURE OF LAC+ PROTEUS STRAINS ISOLATED FROM CLINICAL SPECIMENS.

Falkow, Stanley (Walter Reed Army Institute of Research, Washington, D.C.), J. A. Wohlhieter, R. V. Citarella, and L. S. Baron. Transfer of episomic elements to Proteus. II. Nature of lac(+)Proteus strains isolated from clinical specimens. J. Bacteriol. 88:1598-1601. 1964.-Strains of Proteus mirabilis exhibiting the unusual property of utilizing lactose (lac(+)) have been reported in clinical material. A genetic examination discloses that the lac(+) determinants in these Proteus strains are associated with an infectious element, P, which is distinct from the sex factor of Escherichia coli K-12. The composite genetic element, P-lac, is readily transmissible to other enteric species and possesses properties which conform to those of an episomic element of the transfer variety. CsCl density-gradient studies of deoxyribonucleic acid (DNA) extracted from lac(+)P. mirabilis indicate that the P-lac(+) element did not arise in this species, but was acquired from an organism possessing a markedly different DNA base composition.

Amino Acids↗
PubMed1963

VIRULENCE OF ESCHERICHIA-SHIGELLA GENETIC HYBRIDS FOR THE GUINEA PIG.

Falkow, Stanley (Walter Reed Army Institute of Research, Washington, D.C.), H. Schneider, L. S. Baron, and S. B. Formal. Virulence of Escherichia-Shigella hybrids for the guinea pig. J. Bacteriol. 86:1251-1258. 1963.-Genetic recombination studies between donor Escherichia coli and recipient Shigella flexneri 2a strains were employed to examine alterations in the virulence of Shigella hybrids for guinea pigs. The genetic studies indicated that several chromosomal regions of E. coli and S. flexneri are grossly homologous. The frequency of recombination between E. coli and Shigella was decreased, however, in comparison with E. coli x E. coli matings. Moreover, the predominant Shigella hybrid classes acquired only the selected genetic marker, and extensive transfer of the Escherichia genome was detected only occasionally. The virulence studies made use of hybrids with well-defined single markers as well as those with overlapping chromosomal regions. Analysis of over one-half of the chromosome revealed only one chromosomal region, located between the rha(+) and xyl(+) genes, which was essential for virulence. However, hybrids which had received the E. coli pili antigen and fuc(+)-nic(+) determinants exhibited an intermediate virulence. Hybrids carrying a full complement of Shigella genes and the rha(+)-xyl(+)Escherichia region as a persistent exogenote (partial diploids) were of intermediate virulence. These partial diploids may return to complete virulence by elimination of the Escherichia chromosomal fragment or become avirulent by incorporation of this fragment.

Animals↗
PubMed1962

Deoxyribonucleic acid base composition of Proteus and Providence organisms.

Falkow, Stanley (Walter Reed Army Institute of Research, Washington D.C.), I. R. Ryman, and O. Washington. Deoxyribonucleic acid base composition of Proteus and Providence organisms. J. Bacteriol. 83:1318-1321. 1962.-Deoxyribonucleic acids (DNA) from various species of Proteus and of Providence bacteria have been examined for their guanine + cytosine (GC) content. P. vulgaris, P. mirabilis, and P. rettgeri possess essentially identical mean GC contents of 39%, and Providence DNA has a GC content of 41.5%. In marked contrast, P. morganii DNA was found to contain 50% GC. The base composition of P. morganii is only slightly lower than those observed for representatives of the Escherichia, Shigella, and Salmonella groups. Aerobacter and Serratia differ significantly from the other members of the family by their relatively high GC content. Since a minimal requirement for genetic compatibility among different species appears to be similarity of their DNA base composition, it is suggested that P. morganii is distinct genetically from the other species of Proteus as well as Providence strains. The determination of the DNA base composition of microorganisms is important for its predictive information. This information should prove of considerable value in investigating genetic and taxonomic relationships among bacteria.

Bacteria↗