Search PubMed⌕ Search

Biomedical subjects

H de Barjac

Publications and source records attributed to H de Barjac.

46 records · Page 3Linked to original sources
PubMedDate not supplied

Bacillus sphaericus asporogenous mutants: morphology, protein pattern and larvicidal activity.

Asporogenous mutants from Bacillus sphaericus strains 2297 and 1593-4, blocked at different stages of the sporulation process, were isolated. Two mutants (2297 Aspo30A and 2297 Aspo34) which were blocked early in sporulation did not possess any crystalline inclusions and were poorly toxic to Culex pipiens mosquito larvae. Other mutants (2297 Aspo115, 2297 Aspo24 and 1593-4 Aspo12) which were blocked at later stages synthesized crystal-like inclusions next to the forespores, and were highly toxic to mosquito larvae. Electrophoretic protein analysis of alkali extracts from mutants and wild type strains confirmed the absence of toxic crystal-related proteins in early-blocked mutants and their presence in later ones. Western blots with antisera directed against the crystal proteins confirmed those observations.

Animals↗
PubMedDate not supplied

Another Bacillus sphaericus serotype harbouring strains very toxic to mosquito larvae: serotype H6.

Ten isolates of Bacillus sphaericus from Ghana, very toxic to mosquito larvae, have been identified as belonging to serotype H6. These isolates can be represented by the head-group strain IAB59. They form crystals at the sporulation stage. Their larvicidal effect on Culex pipiens and Anopheles stephensi larvae is as high as that of the most toxic strains already known, e.g. 1593 and 2362 (serotype H5a,5b) and 2297 (serotype H25). Spore-crystal extracts of all these strains contain a 43-Kd polypeptide immunologically related to the 43-Kd polypeptide from strain 2362 described by other authors.

Animals↗
PubMedDate not supplied

Clostridium bifermentans serovar malaysia: sporulation, biogenesis of inclusion bodies and larvicidal effect on mosquito.

Sporulation of Clostridium bifermentans serovar malaysia, which has a larvicidal activity towards mosquitoes, was examined by electron microscopy. Parasporal inclusion bodies lacking a crystalline structure were first detected at t5 (5 h after the end of exponentional growth). Also, the presence of "brush-bottle"-like appendages appearing first at t5 was noted; these remained attached to the spores when released after sporangium lysis. Larvicidal activity assayed on Anopheles stephensi larvae appeared at t0 and increased rapidly to a maximum between t5 and t8. However, a decrease in bacterial toxicity occurred with sporangium lysis.

Animals↗
PubMedDate not supplied

[Biochemical and serological characterization of "Bacillus sphaericus" strains, pathogenic or non-pathogenic for mosquitoes (author's transl)].

A biochemical and serological study of 35 Bacillus sphaericus strains including some pathogenic for mosquito larvae, is reported. A classification of these, and a differentiation of the pathogenic strains, cannot be made on the basis of the 78 phenotypic characters which have been determined by conventional methods. Numerical analysis of the results given by the auxanograms on 160 substrates, gives good results. An even more valuable approach is the flagellar agglutination technique, which clearly distinguishes the pathogenic from the non-pathogenic strains and furthermore can specifically differentiate strains among the pathogenic isolates.

Animals↗
PubMedDate not supplied

[Action of crystals of Bacillus thuringiensis var. israelensis on the midgut of Aedes aegypti L. larvae, studied by electron microscopy].

Ingestion of Bacillus thuringiensis var. israelensis crystals by Aedes aegypti larvae is followed by midgut epithelium disruption. Earliest ultrastructural changes consist of an enlargement of intra- and intercellular spaces in the basal region of the cell. Endoplasmic reticula disintegrate by forming spherical structures which increase in size during intoxication. Mitochondria are transformed at first into a condensed form, then become swollen with the disappearance of internal cristae. In the cardia cells, which secrete the peritrophic membrane, the Golgi apparatus may produce electron-dense secretion vesicles; in this event, the peritrophic membrane assumes an abnormal configuration. Before complete breakdown, a cellular hypertrophy is observed: few cells become balloon-like. At the same time, the microvilli decrease in size, widen and then disappear after a few hours exposure to crystal delta-endotoxin.

Aedes↗
PubMedDate not supplied

[Electron microscope study of "Bacillus thuringiensis" var. "Israelensis" sporulation and crystal biogenesis (author's transl)].

The sporulation and crystal development of Bacillus thuringiensis serotype H-14 was described for a wild spore- and crystal-forming strain and for a mutant crystal but non spore-forming strain. The special nature of the israelensis var. consisted in the composite structure of the crystal, made of a number of components differing in size, shape and electron density. The components were formed in a single inclusion or sometimes separately inside the same bacterial cell.

Bacillus thuringiensis↗
PubMedDate not supplied

[Specificity and active principle of Bacillus thuringiensis var. israelensis].

Bio-assays of B. thuringiensis var. israelensis on larvae of Drosophila melanogaster, Musca domestica, Culicoides sp. and Chironomus plumosus are negative except in the last case, but only with doses much higher than those which are lethal for mosquito larvae. Tests on mollusks (Biomphalaria glabrata) and golden fishes are also negative. The specificity of action of the H 14 serotype, limited to a few Diptera families, should be mainly related to the special characteristics of its crystals, which are proved to be the only active material by studying the larvicidal power of isolated crystals and of spore-free or crystal-free mutants. The amino-acid composition is one of these characteristics, being similar qualitatively but different quantitatively, when compared with the composition of the other studied H serotypes.

Animals↗
PubMedDate not supplied

[pH variations in the midgut of Aedes aegypti in relation to Bacillus thuringiensis var. israelensis (serotype H14) crystal intoxication].

After feeding Aedes aegypti larvae with B. thuringiensis var. israelensis crystals the very alkaline pH (greater than or equal to 10) of the anterior midgut remains stable during the first twenty minutes, in spite of important cytological damage. Thereafter, the pH drops to surround the neutrality and the death occurs. These results are discussed according to the knowledge on the action of B. thuringiensis var. israelensis.

Aedes↗
PubMedDate not supplied

Comparison between bacteriophage typing and serotyping for the differentiation of Bacillus sphaericus strains.

Eleven bacteriophages were isolated using mosquito pathogenic strains of B. sphaericus as hosts. The phage morphology and host range on five DNA homology groups including 16 mosquito pathogenic and 32 non-pathogenic strains were determined. the same bacterial strains were studied serologically for their flagellar agglutination by antisera representing eight serotypes: six antisera prepared against the reference strains for the DNA homology groups and two others against selected mosquito pathogenic strains. Two new serotypes have been determined among the non-pathogenic strains. Both phage typing and serotyping identified subgroups within the IIA homology group which contains the mosquito pathogens. The same bacterial strains were found in the subgroups established by both methods. These subgroups often paralleled difference in the level of toxicity of the strains for mosquito larvae.

Bacillus↗