Search PubMed⌕ Search

Biomedical subjects

S Falkow

Publications and source records attributed to S Falkow.

At least 181 records · Page 10Linked to original sources
PubMed1988

Pilin-gene phase variation of Moraxella bovis is caused by an inversion of the pilin genes.

Moraxella bovis Epp63 can express either of two different pilin proteins, called alpha and beta. We have previously cloned and sequenced the beta-pilin gene and now report that DNAs isolated from bacteria expressing alpha pilin have hybridization patterns consistently different from those of bacteria expressing beta pilin. The phase variation between alpha- and beta-pilin gene expression appears to be associated with an inversion of about 2 kilobases of DNA, whose endpoints occur within the coding region of the expressed pilin gene. Comparisons of the beta-pilin gene sequence with those of well-studied bacterial inversion systems revealed a stretch of 58% sequence similarity (21 of 36 base pairs) between the left inverted repeat of the Salmonella typhimurium flagellar hin control region and the amino-terminal portion of the beta-pilin gene.

Bacterial Outer Membrane Proteins↗
PubMed1988

Identification of a Yersinia pestis-specific DNA probe with potential for use in plague surveillance.

A 900-base-pair DNA fragment derived from a 9.5-kilobase plasmid in Yersinia pestis hybridized specifically with Y. pestis DNA. We demonstrated the feasibility of using this DNA fragment to detect plague bacilli directly in fleas, suggesting that this Y. pestis-specific DNA probe may be used for plague surveillance in the field. Additional applications for this DNA probe may include plague diagnosis and pathogenesis research.

Animals↗
PubMed1988

The vir locus and phase-variation in Bordetella pertussis.

By a phenomenon known as phase-variation Bordetella pertussis is capable of changing between a virulent-phase in which multiple virulence-associated determinants are expressed, and an avirulent-phase in which the virulence-associated determinants are not expressed. Mutations in the vir locus of B. pertussis have a similar effect. We have examined the state of the vir locus in each of a series of strains derived one from the other by phase-variation. We have found that a single base-pair change is associated with the change between the virulent and avirulent phases. This single base-pair change corresponds to a frameshift mutation in the vir locus.

Bordetella pertussis↗
PubMed1988

Virulence factors associated with Salmonella species.

Salmonella species can cause diseases ranging in severity from acute gastroenteritis to typhoid fever. These bacteria are considered as intracellular pathogens and produce several products which are required for entry and survival in the intracellular environment, in addition to factors necessary for existence in the gastrointestinal tract and the outside environment. The virulence factors used by these bacteria to cause these diseases are complex, and only recently have we begun to characterize these factors and determine the contribution they make to Salmonella virulence.

Bacterial Adhesion↗
PubMed1987

Identification of invasin: a protein that allows enteric bacteria to penetrate cultured mammalian cells.

Bacterial strains harboring the Yersinia pseudotuberculosis inv locus were analyzed in order to investigate the mechanism of host cell penetration by an invasive pathogen. The inv locus was found to be necessary for Y. pseudotuberculosis to enter HEp-2 cells and sufficient to convert E. coli into a microorganism able to penetrate cultured cells. Both E. coli and Y. pseudotuberculosis strains harboring inv mutations were defective for entry into HEp-2 cells. Furthermore, molecular clones containing inv, and little additional DNA, converted E. coli into a microorganism that was indistinguishable from the parental Yersinia strain with regard to the entry of cultured cells. Data from in vitro protein synthesis indicated that a 103 kd protein was synthesized from inv, saturating the coding capacity of the locus. The nucleotide sequence shows an open reading frame corresponding to a protein of similar size. This protein, called invasin, is necessary for the microorganisms to penetrate HEp-2 cells, and is compartmentalized on the outer surface of the bacterium.

Adhesins, Bacterial↗
PubMed1987

Development of a tissue culture model for gonococcal invasion.

Neisseria gonorrhoeae invasion of the human endometrial cell line HecIB was monitored by electron microscopy. Within six hours postinfection, the gonococci have attached to the surface of some HecIB cells and are embraced by microvilli. Gonococci subsequently enter the HecIB cells in membrane bound vesicles but by eight hours, gonococci can be seen free in the cytoplasm. At twelve hours post-infection some HecIB cells are observed containing hundreds of internalized bacteria. At twenty-four hours gonococci appear in large clusters embedded in a matrix of cellular debris, which are possibly the remains of lysed infected cells. In contrast, N. lactamica is adherent to the monolayer but noninvasive.

Adenocarcinoma↗
PubMed1987

The frequency of expression of pyelonephritis-associated pili is under regulatory control.

The Escherichia coli urinary tract isolate C1212 contains two pyelonephritis-associated pili (pap) DNA sequences designated here as pap-17 and pap-21. Each of these pap sequences encodes antigenically-distinct pilin monomers, pilin-17 and pilin-21, respectively. Most individual strain C1212 cells isolated from a single bacterial colony expressed pilin-21. Only a small fraction (5%) of strain C1212 cells expressed pilin-17. Most of the latter population simultaneously expressed pilin-21, but a low percentage of cells expressed pili composed of pilin-17 alone. In contrast, almost every E. coli K-12 cell containing multicopy pap-17 expressed pilin-17 at the cell surface. These results indicated that the regulation of pilin-17 expression observed for strain C1212 was lost when pap-17 was in the multicopy state. Transfer of pap-17 to a single copy vector resulted in a pilin-17 expression frequency lower than strain C1212 (1%). Using E. coli K-12 containing single copy pap-17, we found that the frequency of pilin-17 expression increased about 15-fold when pap-21 was present in multiple copies in trans. Subcloning of pap-21 showed that a 2.2 kilobase-pair DNA sequence adjacent to, but not including, the pilin-21 structural gene was sufficient for activation of pilin-17 expression.

Bacterial Outer Membrane Proteins↗
PubMed1987

Construction and characterization of Bordetella pertussis toxin mutants.

Pertussis toxin is one of the major virulence determinants produced by Bordetella pertussis. The DNA encoding the structural genes for pertussis toxin was cloned in Escherichia coli, and pertussis toxin subunit S4 was expressed under the control of the tac promoter. Mutations were introduced into the cloned toxin genes, and a conjugative shuttle vector system was devised for delivering the mutations from E. coli back into B. pertussis. The mutations were introduced by allelic exchange into the chromosome of B. pertussis resulting in a series of B. pertussis strains which were isogenic except at the loci encoding the structural genes for pertussis toxin. These B. pertussis strains were utilized to study the biogenesis of pertussis toxin. Polar mutations in the S1 gene led to a lack of detectable S2 or S4 subunits in whole-cell lysates, suggesting a polycistronic arrangement for these genes. Mutations in the S5 subunit gene resulted in a truncated S1 subunit, while mutations in the S4 gene resulted in a lack of detectable S2 subunit, suggesting that physical relationships among the toxin subunits are directly reflected in the stable biogenesis of the subunits.

Alleles↗
PubMed1987

Comparison of the ability of enteroinvasive Escherichia coli, Salmonella typhimurium, Yersinia pseudotuberculosis, and Yersinia enterocolitica to enter and replicate within HEp-2 cells.

Salmonella typhimurium, enteroinvasive Escherichia coli, Yersinia pseudotuberculosis, and Yersinia enterocolitica possess the ability to enter intestinal epithelial cells. We used a quantitative tissue culture model employing HEp-2 cells to compare the abilities of these bacteria to enter epithelial cells. S. typhimurium and Yersinia species were highly infective for HEp-2 cells but were unable to replicate extensively intracellularly. Enteroinvasive E. coli exhibited low infectivity but replicated extensively intracellularly. The growth of enteroinvasive E. coli led to destruction of the HEp-2 monolayer, whereas Yersinia spp. and S. typhimurium were maintained intracellularly for prolonged periods without damage to the monolayer. The ability of enteroinvasive E. coli to enter HEp-2 cells required prior growth at 37 degrees C; neither S. typhimurium nor Yersinia spp. exhibited this temperature dependence for cell entry. An E. coli K-12 derivative containing a 230-kilobase plasmid from enteroinvasive E. coli was constructed. This derivative shared all the invasive characteristics of the parental enteroinvasive strain, suggesting that determinants required for cell entry and intracellular multiplication were at least partially plasmid encoded. An HB101 derivative containing a cloned invasion determinant from Y. pseudotuberculosis was constructed in our laboratory. HEp-2 monolayers were coinfected with these two K-12 derivatives to compare invasion determinants from enteroinvasive E. coli with those of Y. pseudotuberculosis in a common genetic background. Results from these experiments suggest that these organisms reside within separate intracellular compartments.

Cells, Cultured↗
PubMed1987

Cloning of the recA gene of Neisseria gonorrhoeae and construction of gonococcal recA mutants.

Interspecific complementation of an Escherichia coli recA mutant was used to identify recombinant plasmids within a genomic cosmid library derived from Neisseria gonorrhoeae that carry the gonococcal recA gene. These plasmids complement the E. coli recA mutation in both homologous recombination functions and resistance to DNA damaging agents. Subcloning, deletion mapping, and transposon Tn5 mutagenesis were used to localize the gonococcal gene responsible for suppression of the E. coli RecA- phenotype. Defined mutations in and near the cloned gonococcal recA gene were constructed in vitro and concurrently associated with a selectable genetic marker for N. gonorrhoeae and the mutated alleles were then reintroduced into the gonococcal chromosome by transformation-mediated marker rescue. This work resulted in the construction of two isogenic strains of N. gonorrhoeae, one of which expresses a reduced proficiency in homologous recombination activity and DNA repair function while the other displays an absolute deficiency in these capacities. These gonococcal mutants behaved similarly to recA mutants of other procaryotic species and displayed phenotypes consistent with the data obtained by heterospecific complementation in an E. coli recA host. The functional activities of the recA gene products of N. gonorrhoeae and E. coli appear to be highly conserved.

Cloning, Molecular↗
PubMed1986

A common plasmid of Chlamydia trachomatis.

A 7.4-kb plasmid is a common and perhaps essential component of the Chlamydia trachomatis genome. This plasmid occurs as 10 copies per chlamydial chromosomal equivalent. It is unable to replicate in Escherichia coli. Complete plasmid genomes from eight serovars of C. trachomatis have been isolated in E. coli as cloned sequences ligated to pBR322. Restriction enzyme cleavage site mapping indicates that these plasmids are closely related. Homologous plasmid sequences have also been detected by DNA hybridization in all of the 200 clinically isolated strains of C. trachomatis which have been examined. DNA sequences homologous to the C. trachomatis plasmid were not found in eucaryotic DNA nor in a plasmid of similar size isolated from C. psittaci. C. trachomatis plasmid genes are expressed in vivo and the plasmid encoded gene products may play a role in the intracellular growth of this organism. Plasmid encoded genes were also expressed from the cloned C. trachomatis plasmid in E. coli minicells and using an E. coli S-30 in vitro transcription translation extract.

Chlamydia trachomatis↗
PubMed1986

The construction of a cloning vector designed for gene replacement in Bordetella pertussis.

We report here the construction of a plasmid cloning vector, pRTP1, designed to facilitate exchange of cloned and chromosomal alleles of the human bacterial pathogen Bordetella pertussis. pRTP1 provides the ability to successively select two homologous recombination events within the cloned sequences. The first is by selection for maintenance of the ampicillin-resistance gene on the plasmid which is unable to replicate autonomously after transfer via conjugation. The second selection, via streptomycin (Sm) selection, is against the maintenance of vector sequences which contain a gene encoding the Sm-sensitive allele of the gene for ribosomal protein S12 thus rendering an otherwise Sm-resistant strain Sm-sensitive. We demonstrate the use of this vector to introduce an unmarked mutation, constructed in vitro, into the chromosomal locus encoding pertussis toxin.

Bordetella pertussis↗
PubMed1986

Use of nucleic acid probes for the detection of sexually transmitted infectious agents.

Deoxyribonucleic acid sequences specific for a pathogen of interest can be isolated from a variety of microorganisms. Such DNA probes can be exploited to detect infectious agents directly in infected patient material despite the presence of large numbers of other organisms and host DNA. This technology is dependent upon the recognition of a specific nucleotide sequence present in DNA extracted from a clinical sample by a radiolabeled or nonisotopically labeled DNA probe. We have isolated several DNA probes for the detection of pathogenic Neisseria which include a plasmid species unique to the gonococcus, as well as several cloned genes that detect both the gonococcus and the meningococcus. In addition, we characterized a unique plasmid of Chlamydia trachomatis that has proved to be quite useful as a DNA probe for the detection of this pathogen in cervical secretions and, by in situ hybridization, in Papanicolaou smears. Deoxyribonucleic acid hybridization as a diagnostic tool is still in its infancy. It holds a number of advantages over conventional methods of pathogen detection and serves as an alternative, as well as a complement, to available immunologic methods.

Bacterial Outer Membrane Proteins↗
PubMed1986

An unusual Neisseria isolated from conjunctival cultures in rural Egypt.

Seven isolates of an unusual Neisseria sp. were obtained from eye cultures of children in two rural Egyptian villages. These Neisseria utilized only glucose, they exhibited a positive reaction when tested with antisera to crude antigen from Neisseria meningitidis and N. gonorrhoeae, and they did not react with the fluorescent antibody tests for N. gonorrhoeae or with the monoclonal antibodies used to serotype gonococci. The Egyptian isolates had colony morphology more typical of meningococci than gonococci and showed opaque and transparent colony variants. On SDS-PAGE, the major outer-membrane proteins had different patterns than those noted for comparable proteins of meningococci and gonococci; heat-modifiable outer-membrane proteins were present. Four of the six isolates examined had cryptic plasmids of 2.8 megadaltons, which were slightly larger than the cryptic plasmid of N. gonorrhoeae. These plasmids were homologous to the gonococcal cryptic plasmid, but had different restriction enzyme fragment patterns. The DNA from the Egyptian isolates, like DNA from N. meningitidis but unlike DNA from N. gonorrhoeae, could be cut with the restriction enzyme HaeIII. The frequency of transformation into a temperature-sensitive mutant of N. gonorrhoeae was 0.2 for the Egyptian isolates and 0.1 for N. meningitidis, a frequency that was 5-10-fold lower than that for the N. gonorrhoeae control isolates. Whole-cell DNA from the Egyptian isolates showed 68%-73% homology with N. gonorrhoeae and 57%-63% with N. meningitidis. On the basis of our observations, the Egyptian isolates are distinct from N. meningitidis and may represent a variant of N. gonorrhoeae. We suggest that the isolates be called Neisseria gonorrhoeae ssp. kochii.

Bacterial Proteins↗
PubMed1986

Chromosomal map position of genes encoding P adhesins in uropathogenic Escherichia coli.

Escherichia coli isolates from upper urinary tract infections frequently express adherence to human uroepithelium and D-mannose-resistant hemagglutination of human erythrocytes. Such adherence is usually associated with P pili encoded by the pap operon(s). In this paper, we report approximate chromosomal map positions for two copies of the pap operon. Only one copy expressed an adhesin capable of D-mannose-resistant hemagglutination, although both expressed P-related antigen.

Adhesins, Escherichia coli↗