Caractérisation phénotypique et moléculaire des salmonelles isolées à partir des aliments et d’origine humaine responsables de gastro-entérites

Abstract

Salmonella bacteria are of the main causes of food contamination and therefore a major etiology of human gastroenteritis. The phenotypic and molecular evolution of these bacteria has not stopped, allowing to the latter to adapt to each step of pathogenesis, including: environmental conditions, host response and control methods. Emergence of antibiotic-multi resistant salmonella strains, which is often the cause of treatment failure that significantly exacerbated the situation.With regard to this development, an arsenal of biological techniques have been developed to study the phenotypic and molecular diversity of this bacterium in order of support and monitor to better adapt the means of prevention and control. The undertaken work as part, first the objective of assessing the phenotypic variability of 37Salmonella isolated from food (serotype diversity, biochemical characterization and sensitivity to antibiotics) and visualize the molecular (genetic) variability using various techniques: ADN16S sequencing, MLST (Multi-Locus SequenceTyping), MLVA(Multiple- Locus VNTR Analysis) by identifying and exploring the genetic materials whose expression is essential for metabolism and necessary for the adaptation of Salmonella to their environment. A second approach was also conducted. It consisted of a comparative study of 39 humanorigin Salmonella responsible for gastroenteritis during the same period. Results obtained with food borne isolates revealed a serotype diversity with predominance of Salmonella Enteritidis accompanied by biochemical variability in antibiotic susceptibility resistance to nalidixic acid, ofloxacin and non-wild phenotypes to the ciprofloxacin, trimethoprim/sulfamithoxazol and betalactamines observed with some serovars that reflect the development of resistance mechanisms poorly expressed or silent. Compared with serovars of human origin, a variety of serotype and predominance of the sames pecies was observed. A complexity and heterogeneity of the biochemical characteristics and profiles of antibiotic sensitivities more advanced than those of food-isolates. MLST technic seem to be little discriminating between the seven selected markers between strains of the same serotype. For its part, MLVA technique has confirmed high discriminating power between the Salmonella until intra-serotype level. Different clones were visualized (06) genotypes were obtained from (06) serotypes. The intra-serotype variability reflects the impact of environmental factors and the diversity of reservoirs (animal or human) and sources of contamination.