**2. Taxonomy**


Use Thyme Essential Oils for the Prevention of Salmonellosis 307

Serotypes can be classified according to the target animal species. First, some are exclusively adapted to humans, causing serious and very specific diseases. This is essentially *Salmonella* Typhi, Paratyphi, and Sendai, causative agents of typhoid and paratyphoid fevers (Bäumler et al. 1998; Hu and Kopecko, 2003). Second, a number of serotypes can attract animals. Among these are: Choleraesuis, Typhisuis pigs, Abortusequi in horses, sheep Abortusovis, Gallinarum, specific poultry... Finally, most Salmonella serotypes can cross the species barrier. They are present in many animal species, usually in a latent or subclinical diseasecausing, and can reach the man, either through food, which is the most common way, either by direct or indirect contact. Any salmonella, with rare exceptions, is potentially dangerous to humans. United States, Salmonella has been associated with collective poisoning from reptiles, which are used as pets (Center for Disease Control, 1999, Mitchell and Shane, 2000). This shows that Salmonella are capable of multiple adjustments and can cause new and

The specific agents of salmonellosis in humans (Salmonella Typhi, Paratyphi, and Sendai) are the agents of typhoid and paratyphoid fevers. Worldwide, the human deaths caused by typhoid fever are estimated at 600,000 per year (Hu and Kopecko, 2003). The cases are mainly listed in the Third World. In developed countries, cases are usually du to imported food. Five percent of patients infected with S. Typhi become chronic carriers, asymptomatic (Mermin et

A considerable number of genes (of the order of hundreds) must be mobilized by Salmonella to counteract the defense mechanisms of the host. All Salmonella serotypes can in theory cause a systemic infection in humans with decreased immune status, although most will generate a febrile diarrhea, vomiting, abdominal pain and in elderly or immunodéfiscients bacteremia, the septicemia and extra intestinal locations, especially vascular (Bäumler et al., 2000). When there is localization of the infection, Salmonella often remain confined to the mesenteric lymph nodes. The first defense mechanisms used by the host are made by the acidity of the stomach and bile salts in the small intestine, which exert a bactericidal effect. Once in the small intestine, Salmonella must as soon as possible adhere to the intestinal mucosa. They will cross at the lymphoid follicles of the ileum (Peyer's patches, located at the bottom of intestinal crypts). At this point in the gut, the epithelium is characterized by the presence among the enterocytes, M cells and the absence of cells secreting mucus. It seems that the fimbriae (adhesins) must be present to allow recognition and binding of Salmonella to Peyer's patches (Dibb-Fuller et al. 1999; Thorns and Woodward, 2000, Vimal et al., 2000).These fimbriae play a critical role in the pathology and the fact that some serotypes are specifically tailored to a particular species. Entry into the Peyer's patches requires the presence of secretion systems of type III. They are encoded by sets of pathogenicity genes ("pathogenicity islands"), known as SPI-1 and SPI-2 (China and Goffaux, 1999; Bäumler et al. 2000; Cornelis, 2000; Jones et al. 2002; Doublet et al., 2005). SPI-1 is normally necessary for passage through M cells of the intestinal mucosa, whereas SPI-2 is involved in the systemic nature of the infection (Hueck, 1998). Subsequent to penetration of salmonella in M cells, the latter will be killed by apoptosis, leading to transmigration across mucosal inflammatory cell type polymorphonuclear (PMN) and acute gastroenteritis.

al., 1999). This poses enormous problems if they are employed by food companies.

**3.1.1 Animal reservoir** 

various problems to humans, from various sources.

**3.1.2 Salmonella and human** 

**3.2 Mechanisms of virulence** 

The nomenclature of salmonella recognizes that the genre has three *Salmonella* species (Le Minor and Popoff, 1987, Reeves et al. Nov.1989):

*Salmonella bongori*; *Salmonella enterica* or *Salmonella choleraesuis* and *Salmonella subterranea* (Shelob olina et al., 2004).

The second most important species includes six subspecies (Grimont et al., 2000): *Salmonella enterica* subsp. *Arizonae; Salmonella enterica* subsp. *Diarizonae; Salmonella enterica* subsp. *Enterica; Salmonella enterica* subsp. *Houtenae; Salmonella enterica* subsp. *Indica* and *Salmonella enterica* subsp. *salamae*.

With this division into species and sub-species actually, 2541 serotypes are recognized officially. These result from multiple combinations of somatic O polysaccharide in nature, flagellar H antigens, protein in nature and, finally, capsular (Vi). Genetic determinants of these factors are stable enough to perform reliable epidemiological surveys. The type of classification based on the O and H antigens is called the Kauffmann-White scheme (Grimont et al., 2000). Names of serotypes should necessarily be written in capitalized block characters (not italics): *Salmonella enterica* subsp. *enterica* serotype Typhimurium. However, the following simplifications are allowed: *Salmonella* Typhimurium or *S*. Typhimurium.
