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S Falkow

Publications and source records attributed to S Falkow.

At least 271 records · Page 15Linked to original sources
PubMed1979

Inhibitors of membrane transport reduce lysosomal enzyme secretion from dogfish phagocytes and their killing of sea urchin eggs.

Blood phagocytes of the dogfish Mustelus canis attack oocytes of the sea urchin Arbacia punctulata, first provoking a surrogate fertilization response and then killing the eggs. To test the hypothesis that secretion of lysosomal contents is critical in this model of phagocyte-mediated cell injury, we studied effects of agents that modify lysosomal enzyme secretion. Inhibitors of membrane transport (>0.1 mM) inhibited postphagocytic secretion of lysosomal beta-glucuronidase from dogfish phagocytes: phloretin > ethacrynate > furosemide > 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid >> pyridoxal phosphate > ouabain. The same order of activity was found for inhibition by these agents of killing of Arbacia eggs by phagocytes. Cell activation (fertilization response) and cytotoxicity were quantitated both morphologically and by measurements of enzyme (beta-glucuronidase, catalase) release. The agents neither inhibited fertilization responses of eggs to calcium ionophore A23187 nor impaired their viability. Vital staining demonstrated that ethacrynate prevented phagocytes from degranulating upon contact with zymosan particles. The data not only suggest that agents primarily known for their capacity to inhibit membrane transport systems can inhibit lysosomal enzyme secretion from phagocytes but also support the hypothesis that secretion of lysosomal contents mediates activation and killing of target cells in phagocyte-mediated tissue injury.

Animals↗
PubMed1979

The ecology of gonococcal plasmids.

Of 261 strains of Neisseria gonorrhoeae examined for plasmids, 6 were plasmid-free, 217 contained only a small multicopy 2.6 X 10(6) dalton plasmid and 38 carried a large 24.5 X 10(6) dalton plasmid. Restriction enzyme digests and DNA-DNA hybridization studies revealed that the large plasmids isolated between 1940 and 1978 share a common core of DNA sequences (70 to 100%) and represent a group of closely related molecules.

Base Sequence↗
PubMed1979

Cistrons encoding Escherichia coli heat-labile toxin.

The structure and products of the two cistrons encoding the Escherichia coli heat-labile toxin (LT) were studied. The LT deoxyribonucleic acid (DNA) region had been isolated as part of a DNA fragment from the plasmid P307, and this fragment was joined to the cloning vector pBR313. Deletion mutations of various lengths were introduced into the LT DNA region and into the adjacent DNA sequences. Analysis of the deletions indicated that the maximum size of the LT DNA region was 1.2 x 10(6) daltons. Two proteins of 11,500 daltons and 25,500 daltons had been shown to be encoded by the LT DNA region. The functions of these LT gene products were investigated. The 11,500-dalton protein had an adsorption activity for Y-1 adrenal cells, and this protein was shown to form aggregates of four or five monomers. The 25,500-dalton protein was shown to have an adenylate cyclase-activating activity. The two cistrons encoding for each of the LT proteins have been located on a genetic map of the LT DNA region. Both cistrons are probably transcribed from the same promoter.

Adenylyl Cyclases↗
PubMed1978

Some characteristics of Escherichia coli strains isolated from extraintestinal infections of humans.

Escherichia coli strains isolated from extraintestinal infections of humans possess a constellation of phenotypes not usually found in random fecal isolates, enteropathogenic strains, or the laboratory strain E. coli K12. The phenotypes found more commonly in extraintestinal strains include hemolysin production, the biosynthesis of colicin V, and the hemagglutination of human erythrocytes in the presence of D-mannose (HAh). Hemolysin is assumed to be a cytotoxic factor, colicin V is assumed to interfere with host defense mechanisms, and HAh is assumed to play a role in specific tissue adherence. In addition, greater than or equal to 50% of E. coli strains from extraintestinal infections kill allantoically inoculated 13-day-old chick embryos. Some (20%) of the fecal E. coli also kill embryos, but E. coli K12 is innocuous in this virulence model. The plasmids for hemolysin and colicin V production have been transmitted to E. coli K12 derivatives but are not sufficient to convert laboratory strains to a form virulent for the chick embryo.

Adhesiveness↗
PubMed1978

Mobilization of the Escherichia coli plasmid ColE1 (colicin E1) and ColE1 vectors used in recombinant DNA experiments.

The Escherichia coli Co1E1 plasmid, which codes for production of colicin E1, is inherently nontransferable (nonconjugative) by bacterial mating. Co1E1 can be transmitted at mating by a process called mobilization if Co1E1 is coresident with a transfer plasmid. Mobilization is governed in part by a Co1E1 gene called mob. Co1E1 is mob+. Several Co1E1 derivatives employed in recombinant DNA experiments, notably pBR313 and pBR322, are mob-. These cloning vehicles are mobilized at markedly reduced frequency relative to Co1E1. E. coli K12 carrying either pBR313 or pBR322 represents a useful host vector system for recombinant DNA experiments and affords a significant degree of biological containment.

Bacteriocin Plasmids↗
PubMed1978

Association of hemolysin production, hemagglutination of human erythrocytes, and virulence for chicken embryos of extraintestinal Escherichia coli isolates.

One hundred forty-two strains of Escherichia coli isolated from extraintestinal infections were examined for colicin V (ColV) and hemolysin (Hly) production. For comparison, 20 strains isolated from the feces of normal individuals and 12 enteropathogenic strains of E. coli were tested for these properties. Thirty-five to 59% of extraintestinal isolates were Hly+, but only one fecal strain was Hly+. Colicin V biosynthesis was found for 12% of blood culture isolates, 7% of urine culture isolates and 16% of the strains from other extraintestinal infections. None of the fecal isolates was ColV+. Selected strains were tested for virulence in 13-day-old chicken embryos; these same strains were tested for their ability to hemagglutinate chicken or human erythrocytes. Of 22 extraintestinal isolates, 13 (59%) killed greater than or equal to 60% of the embryos within 72 h. Only one of eight normal fecal isolates and two of three enteropathogenic strains tested were virulent. About 80% of the virulent strains were Hly+. The most striking finding, however, was the hemagglutination of human erythrocytes by virulent extraintestinal isolates. It seems possible that the hemagglutination property reflects a specific common adherence factor.

Animals↗
PubMed1978

Characterization of plasmids that encode for the K88 colonization antigen.

K88 antigen, and important virulence factor in porcine enteropathogenic Escherichia coli (EEC), can be transferred along with the ability to ferment the trisaccharide raffinose (Raf). The plasmids from a number of EEC strains that encode these two properties were isolated and characterized. In most strains the K88 and Raf genes were found on a single nonconjugative plasmid approximately 50 x 10(6) daltons in size. This plasmid core was conserved with only slight variation among the strains tested. In some transconjugants, larger conjugative plasmids were observed that were apparently recombinants between the Raf/K88 plasmid and a transfer fa(tor. Occasionally plasmids carrying only the raffinose fermentation genes arose by deletion of a deoxyribonucleic acid segment of about 20 x 10(6) daltons that included the K88 antigen gene(s).

Animals↗
PubMed1978

Characterization of an Escherichia coli plasmid encoding for synthesis of heat-labile toxin: molecular cloning of the toxin determinant.

P307 is a plasmid isolated from a strain of Escherichia coli that was responsible for an outbreak of diarrheal disease in piglets. This 60 X 10(6)-dalton plasmid was subsequently shown to encode for the synthesis of a heat-labile toxin (LT). Using recombinant DNA technology, we isolated a 7.8 X 10(6)-dalton DNA fragment that contains the LT gene(s). This fragment was generated using an EcoRI partial digestion of P307 DNA, and the fragment was joined to a small multicopy plasmid, RSF2124. E. coli strains harboring the chimeric plasmid produced greater amounts of LT than did the same strains containing P307. The LT genes were also isolated on a 5.8 X 10(6)-dalton DNA fragment made by BamHI digestion, and we identified an EcoRI recognition sequence that is located in a position essential for LT synthesis.

Animals↗
PubMed1978

Method for the genetic labeling of cryptic plasmids.

A recently developed method for detecting transposition was employed to genetically "label" conjugative plasmids such as F and Ent P307, which do not normally exhibit a readily identifiable phenotype.

Conjugation, Genetic↗
PubMed1978

Plasmid-mediated chromosomal gene transfer in Neisseria gonorrhoeae.

An indigenous Neisseria gonorrhoeae conjugative plasmid, pLE2450, was tested for its ability to mediate chromosomal gene transfer between gonococcal strains. Plasmid-mediated chromosomal transfer was detected at a low frequency and can be used to establish certain linkage relationships between amino acid and antibiotic resistance markers.

Chromosomes, Bacterial↗