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La sexualite et la genetique microbienne et le destin des maladies infectieuses

Frappier, Armand; Sonea, Sorin (1966). La sexualite et la genetique microbienne et le destin des maladies infectieuses Canadian Journal of Public Health , vol. 57 , nº 10. p. 447-452.

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Résumé

The discoveries of molecular biology have changed the concepts of infection and parasitism. It is well known that the smallest parasite may be a carrier of a smaller parasite: which means that infection and even contagion may spread among the cells of bacteria and perhaps viruses by means of smaller parasites.

This can be produced by the following mechanisms, most of them recently discovered:

(1) Transformation is the acquisition of hereditary characteristics through the penetration of the deoxyribonucleic acid of a donor bacterium to a susceptible bacterial cell. This may acquire a new favourable propert as, for instance, virulence for some pneumococcus types.

(2) Conversion may be produced in bacteria "infected" with temperate phages which we may consider either infectious agents or genetic elements. It may confer on the bacteria the capacity to synthesize a toxin (the diphteric toxin, the erythrogenic toxin and alpha or delta staphylococcus hemolysins). It may also alter the bacterial surface, changing the phage typing pattern of Salmonellae or Staphylococci, and also the surface antigens of different Enterobacteriaceae. Temperate phases being replicating units which act as genetic determinants and being able to exist as an infectious and autonomous particle free in the bacterial cytoplasm, or as a fixed attachment to a bacterial chromosome, with possibilities of changing from one ^phase to the other, are considered as the best example of a new class in microbiology: the episomes. Malignant cells may be produced by a similar mechanism, with animal viruses playng a possible role of temperate phages.

(3) Bacterial traduxction is the transfer by a bacteriophage of a gragment of one bacterial chromosome to another chromosome in a different bacterial cell. Resistance to antibiotics and a few characteristics associated with virulence have been experimentally "transducted".

(4) Conjugation is a transfer of genetic material between two closely related but not identical bacterial cells through a conjugation "canal" physically uniting the two bacterial cells. The genetic material transmitted may be a plasmid which is an extrachromosomal autonomous particle, or an episome which is able to alternate, with a low frequency, between an autonomous, extrachromosomal phase and an integrated, chromosomal phase when it is part of the bacterial choromosome. By conjugation the episomes may transfer attached genetic material responsible for many characteristics favourable to pathogens. Multiple drug resistance is transmitted by the R. episome in many gram negative bacteria, particularly in Shigellae and in enteropatogenic E. coli. Penicillinase production in staphylococci seems to be due to the presence of plasmids. Hereditary changes in the antigenic structure and in virulence of Salmonellae and Shigellae have been described as due to hybridization produced by the sex factor (F or Hjr). New "species" are appearing and taxonomy is nore more what it used to be. Bacteriocines, and particularly the colicines produced by E. coli cells, are antibiotic substances which kill nonparental strains and are already used in therapeutics. They are synthesized by bacteria under the control of episomes.

Thus, it has been possible to study a new menacing submicroscopic "reservoir" of genetic particles, similar to some viruses and in part to a fertilizing element, which constitutes an extremely rich genetic pool in which different pathogenic bacteria may obtain new characteristics able to help them to adjust to the adverse conditions of our tissues, mostly when reinforced with chemotherapy.

This genetic pool has probably been in existence since bacteria evolved, but it was more efficient in the soil than in the highly selective climate in which pathogens used to survive. Overcrowding, hospital infections and the introduction of selective action of antibiotics seem to have revitalized this fertility pool which gives a permanent choice of hereditary weapons to be picked up or discharged by pathogenic bacteria or the candidates for pathogenicity.

Research in the particular field of the bacterial genetics of pathogens may bring also a few answers. Some episomes seem to immunize the bacteria to infection by related but not identical episomes. Plasmids and episomes are sensitive to acridines which may cure the bacteria of these infectious heredity factors. Other substances also show some anti-episomic or anti-plasmid prperties. Therefore, the same methods used to prevent or cure bacterial infections seem to be adjustable to the new problems generated by the multiple possibilities of bacterial sexuality and parasexuality.

Type de document: Article
Informations complémentaires: Recueil de tiré-à-part de la bibliothèque: A0352
Mots-clés libres: génétique; infectieuse; maladie; microbien; microbienne; sexualité
Centre: Centre INRS-Institut Armand Frappier
Date de dépôt: 06 févr. 2020 15:49
Dernière modification: 06 févr. 2020 15:49
URI: http://espace.inrs.ca/id/eprint/8284

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