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Biomedical subjects

S Kamoun

Publications and source records attributed to S Kamoun.

32 records · Page 2Linked to original sources
PubMed1992

Rapid generation of directed and unmarked deletions in Xanthomonas.

We have devised a rapid four-step procedure for the generation of directed and unmarked chromosomal deletions in bacteria, based on the use of a novel cloning vector containing the Bacillus subtilis sacB gene that encodes levansucrase and confers sucrose sensitivity, which can be used for counter-selection. Using this technique, we describe the construction of a 6.5 kb directed and unmarked deletion in a phytopathogenicity region of the chromosome in Xanthomonas campestris. This procedure allows rapid and easy transfer of a wide variety of mutant allelic DNA to the bacterial chromosome, and should be adaptable to various bacteria besides Xanthomonas spp.

Bacillus subtilis↗
PubMed1991

[Brucella endocarditis on Starr aortic valve prosthesis].

The authors report the case of a 22 year old patient with brucella endocarditis on a Starr-Edwards aortic valve prosthesis implanted 5 years previously. Six blood cultures were positive for Brucella melitensis biovar I. Antibiotic therapy associating Rifampicin and Tetracycline and then Rifampicin and Ofloxacine did not prevent abscess formation and valve dehiscence. The poor haemodynamic status and persistent infection led to replacement of the valve prosthesis. Culture of the infected prosthesis grew a colony of brucella melitensis resistant to fluoro-quinolones. Valve replacement and antibiotic therapy led to clinical improvement and constant apyrexia with a 12 month follow-up. Brucella endocarditis on a valve prosthesis is a very rare occurrence. The combination of valve replacement and antibiotic therapy is usually required.

Adult↗
PubMed1990

Phenotypic Switching Affecting Chemotaxis, Xanthan Production, and Virulence in Xanthomonas campestris.

The chemotaxis towards sucrose and yeast extract of nine strains of Xanthomonas campestris representing pathovars campestris, armoraciae, translucens, vesicatoria, and pelargonii was analyzed by using swarm plates. Unexpectedly, each of these strains formed small or reduced swarms typical of nonmotile or nonchemotactic bacteria. With time, however, chemotactic cells appeared on the swarm plates as blebs of bacteria. These cells were strongly chemotactic and were concomitantly deficient in exopolysaccharide production. The switch from the wild type (exopolysaccharide producing and nonchemotactic) to the swarmer type (exopolysaccharide deficient and chemotactic) appeared irreversible ex planta in bacteriological medium. However, in radish leaves swarmer-type strains of X. campestris pv. campestris were able to revert to the wild type. Swarmer-type derivatives of two X. campestris pv. campestris wild-type isolates showed reduced virulence and growth in the host plants cauliflower and radish. However, exocellular complementation of X. campestris pv. campestris Hrp (nonpathogenic) mutant was achieved by coinoculation with a swarmer-type strain.

Journal Article↗
PubMed1990

A plant-inducible gene of Xanthomonas campestris pv. campestris encodes an exocellular component required for growth in the host and hypersensitivity on nonhosts.

Using Tn4431, a transposon that allows transcriptional fusions to a promoterless luciferase (lux) operon, we have isolated a nonpathogenic mutant of Xanthomonas campestris pv. campestris, i.e., JS111, that does not incite any of the black rot symptoms on all tested cruciferous host plants (J. J. Shaw, L. G. Settles, and C. I. Kado, Mol. Plant Microbe Interact. 1:39-45, 1988). In the study reported here, we determined that in contrast to the wild-type strain, JS111 is unable to induce a hypersensitive necrotic response on nonhost plants such as datura, tomato, and cucumber, suggesting that JS111 is a nonpathogenic, nonhypersensitive Hrp mutant. JS111 displayed culture growth rates, exopolysaccharide production, and protease, pectate lysase, cellulase, amylase, and phosphatase activities comparable to those of the wild-type strain. However, the growth of JS111 in host leaves was markedly attenuated. Coinoculation of JS111 with the wild-type strain in cauliflower or radish leaves rescued the growth deficiency of the mutant to normal levels. The locus mutated in JS111 was cloned and named hrpXc, and transcriptional and genetic complementation analyses of the hrpXc locus were conducted. The regulation of hrpXc expression was also investigated in vitro and in planta, using fusions to a lux or chloramphenicol acetyltransferase reporter gene. The hrpXc gene was found to be strongly induced in radish leaves. This is the first report and analysis of a hrp locus from a Xanthomonas species.

Chromosome Mapping↗
PubMed1989

Two chromosomal loci involved in production of exopolysaccharide in Agrobacterium tumefaciens.

The chromosomal locus pscA (exoC) of Agrobacterium tumefaciens LBA4301 has been cloned by complementation of the avirulent and exopolysaccharide (EPS)-deficient mutant LBA4301 pscA. We have also identified a new locus, termed psdA (polysaccharide depression) and located 16 kilobases from pscA in the A. tumefaciens chromosome, that negatively affects EPS production when it is present in more than one copy in A. tumefaciens LBA4301. Subcloning, transposon mutagenesis, and transcriptional analysis have been conducted for both loci and indicate that pscA and psdA are transcribed in the same orientation. Acidic-EPS assays showed that psdA depresses succinoglycan production and that its negative effect increases with the copy number of the gene. Virulence tests of psdA transconjugants on Datura stramonium showed no visible alteration in virulence, while LBA4301 pscA was totally avirulent.

Chromosome Mapping↗
PubMed1987

[Parasite burden and immune response in kala-azar].

The parasite-burden, which is indicative of the macrophage activity, was determined before treatment in 84 kala azar cases (L. infantum) and compared to non specific immune response parameters (serum IgG, and IgM), to the specific antibody levels as detected by immunofluorescence and IgG and IgM-ELISA, as well as to rheumatoid factor titers. In 57 cases presenting with less than 3 months from the first appearance of symptoms and despite some individual variations, high parasite-burden levels were accompanied with high specific and non specific immune response parameters and inversely. The data suggest that, during kala azar, low and high immune responders could be distinguished in the humans in the way it was demonstrated by Biozzi in mice. Data collected from 27 cases with more than 3 months duration showed a poor correlation. However, at highest antibody levels, some decreasing in parasite-burden was noticed. The prognostic value of the parasite-burden determination is emphasized. Genetic studies of populations would improve control measures.

Antibodies↗
PubMedDate not supplied

A gene encoding a host-specific elicitor protein of Phytophthora parasitica.

Extracellular elicitor proteins (elicitins) from Phytophthora species induce local and distal defense responses specifically in plants of the Solanaceae and Cruciferae. Based on elicitin amino acid sequences, elicitin-coding sequences from P. parasitica were amplified by the polymerase chain reaction. A genomic clone containing a complete elicitin gene, parA1, was isolated and sequenced. Elicitin was confirmed to be encoded as a precursor protein containing a 20-amino acid signal peptide that is processed before secretion. Bacterial expression of the cloned elicitin gene as a translational fusion protein containing glutathione S-transferase yielded a biologically active protein capable of inducing a hypersensitive response in tobacco, suggesting that fungus-specific postranslational modifications of elicitin are not required for its activity. Southern blot analysis indicated that elicitin genes occur as a multigene family (at least two to 10 copies) in P. parasitica, P. capsici, P. citricola, P. citrophthora, P. cryptogea, P. drechsleri, P. megasperma, and P. palmivora. Some isolates of P. parasitica that did not produce elicitins still contained elicitin-coding sequences but did not accumulate elicitin mRNA.

Algal Proteins↗