**3. Biology of** *Salmonella*

*Salmonella* belongs to the *Enterobacteriaceae* family. On Light microscopy, they appear as Gram-negative, 0,3 to 1μm wide and 1 to 6 μm microns long (Figure 1). They are moving through peritrichous ciliature. Salmonella are mesophilic bacteria, developing at temperatures between 5.2 °C and 47 °C and optimally between 35 ° C and 37 °C, at pH between 4.5 and 9, with water activity (Aw) greater than 0.93.

Salmonella is aero-anaerobic, reduce nitrate to nitrite, can use citrate as single carbon source. She ferments glucose but not lactose or sucrose and she produce gas from glucose (except Salmonella Typhi). Hydrogen sulfide is generally produced from the mid commonly called "triple sugar". The reaction in the oxidase test is negative (Le Minor, 1984 International Commission on Microbiological Specifications for Foods, 1996, Hanes 2003). Like all bacteria stain Gram-negative envelope of Salmonella consists of three elements: the cytoplasmic membrane and outer membrane separated by a periplasmic space consists of peptidoglycan. This structure gives the bacterium its shape and rigidity and allows it to withstand a relatively high osmotic pressure in the environment (Rycroft, 2000)

#### **3.1 Habitats**

*Salmonella* can be isolated from the intestines of many animal species. They are zoonotic agents. The animals are a reservoir and release into the environment is mainly due to fecal contamination (Berends et al. 1996; Murray, 2000; Hanes, 2003). Salmonella can also survive for very long periods in the environment: a few days to 9 months in soil and surface materials Farm Building (wood, concrete, steel, iron and brick), a few months in dry foods not acidified, on stems and leaves of plants and ensiled over a year in the dust (Gray and Fedorka-Cray, 2001). These bacteria can bind to many substrates, such as, boots, brushes, shovels, wheel barrows, clothes... When cleaning and disinfection of livestock housing and feeding it must consider all inanimate material, which can cause a re-infection of the next batch. Can also be contaminated: spider webs, water, byproducts of agro-food, animal feed, the surrounding farms, fishes and birds (Berends et al., 1996). Rodents and insects can also be an important source of *Salmonella* in livestock (Letellier et al., 1999).

#### **3.1.1 Animal reservoir**

306 Salmonella – A Dangerous Foodborne Pathogen

The nomenclature of salmonella recognizes that the genre has three *Salmonella* species (Le

*Salmonella bongori*; *Salmonella enterica* or *Salmonella choleraesuis* and *Salmonella subterranea*

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

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.

*Salmonella* belongs to the *Enterobacteriaceae* family. On Light microscopy, they appear as Gram-negative, 0,3 to 1μm wide and 1 to 6 μm microns long (Figure 1). They are moving through peritrichous ciliature. Salmonella are mesophilic bacteria, developing at temperatures between 5.2 °C and 47 °C and optimally between 35 ° C and 37 °C, at pH

Salmonella is aero-anaerobic, reduce nitrate to nitrite, can use citrate as single carbon source. She ferments glucose but not lactose or sucrose and she produce gas from glucose (except Salmonella Typhi). Hydrogen sulfide is generally produced from the mid commonly called "triple sugar". The reaction in the oxidase test is negative (Le Minor, 1984 International Commission on Microbiological Specifications for Foods, 1996, Hanes 2003). Like all bacteria stain Gram-negative envelope of Salmonella consists of three elements: the cytoplasmic membrane and outer membrane separated by a periplasmic space consists of peptidoglycan. This structure gives the bacterium its shape and rigidity and allows it to withstand a

*Salmonella* can be isolated from the intestines of many animal species. They are zoonotic agents. The animals are a reservoir and release into the environment is mainly due to fecal contamination (Berends et al. 1996; Murray, 2000; Hanes, 2003). Salmonella can also survive for very long periods in the environment: a few days to 9 months in soil and surface materials Farm Building (wood, concrete, steel, iron and brick), a few months in dry foods not acidified, on stems and leaves of plants and ensiled over a year in the dust (Gray and Fedorka-Cray, 2001). These bacteria can bind to many substrates, such as, boots, brushes, shovels, wheel barrows, clothes... When cleaning and disinfection of livestock housing and feeding it must consider all inanimate material, which can cause a re-infection of the next batch. Can also be contaminated: spider webs, water, byproducts of agro-food, animal feed, the surrounding farms, fishes and birds (Berends et al., 1996). Rodents and insects can also

between 4.5 and 9, with water activity (Aw) greater than 0.93.

relatively high osmotic pressure in the environment (Rycroft, 2000)

be an important source of *Salmonella* in livestock (Letellier et al., 1999).

Minor and Popoff, 1987, Reeves et al. Nov.1989):

(Shelob olina et al., 2004).

*Salmonella enterica* subsp. *salamae*.

**3. Biology of** *Salmonella*

**3.1 Habitats** 

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 various problems to humans, from various sources.

#### **3.1.2 Salmonella and human**

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

#### **3.2 Mechanisms of virulence**

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.

Use Thyme Essential Oils for the Prevention of Salmonellosis 309

The O antigen is an antigen of the wall. O antigens are carried by chains specific lipopolysaccharide (LPS). The O antigen has properties immunizing is a complex containing a protein, a polysaccharide and a phospholipid compound. We distinguish 67 O factors depending on the nature of the sugars used in the construction of oligosaccharide units of the polysaccharide (Humbert et al., 1998). O antigens are composed of a lipid fraction called lipid A is responsible for toxic effects, or basal part of the core and the support of the specific polysaccharide (Gledel and Corbion, 1991). Antigens are classified as major factors O and O factors accessories. The major factors are related to the presence of certain sugars (abequose for O: 4, tyvélose for O: 9) (Humbert et al., 1998). The somatic antigen is stable and it is resistant to alcohol and phenol for two

It is a polymer of flagellin (structural protein of flagella). This antigen is thermolabile, destroyed by heat at 100 ° C by the action of alcohol and by proteolytic enzymes. It is resistant to formalin and loses their agglutinability by antibodies in the presence of alcohol and phenol. Optimum development is achieved on soft liquid media after spending eight hours at 37 ° C (Dumas, 1958). The vast majority of serovars has two genetic systems, and can alternately express two different specificities for their flagellar antigen. It is said that the

It is an antigen of the envelope; it was identified in three types of serovar: Typhi, Paratyphi C and Dublin, but all strains of these serotypes do not necessarily have this antigen (Humbert et al., 1998). This antigen is considered a surface antigen (Dumas, 1958), it is distinct from the somatic antigen and the flagellar antigen. The Vi antigen makes germs inagglutinable by antibodies O when it is abundant. It does not develop if the cultures are carried out below 25 ° C and above 40 ° C. Heating at 100 ° C destroys the germs and become agglutinating antibodies by O. It is likely glucidolipidopolypeptidique. In addition to these antigens exists in the genus Salmonella, the protein structures from surface pilis pilis which differentiate into common (occurring in mannose-dependent haemagglutination) and sexual pilis (involved in bacterial conjugation) and whose presence

*Salmonella* Typhi, Paratyphi A, B, C are preferably isolated in the blood and feces of typhoid (Dumas, 1958). The *Salmonella* that cause food poisoning or acute gastroenteritis are still being sought in the feces and in food. The detection of *Salmonella* may be direct (bacteriological method) or indirect (serological technique) according to (Humbert et al., 1998). The microbiological analysis of a food is to highlight the microorganisms responsible for the alteration of merchantability and / or health. The analytical methods vary with the type of food, the potential danger it presents, and conservation features, consumption (raw or cooked) and the desired type of germ. Food is supportive environments for the development of a multitude of germs, some of which are pathogenic. Faced with the task of

flagellar antigens of Salmonella are two-phase (Humbert et al., 1998).

**5.1 Somatic O antigen (Ag O)** 

**5.2 Flagellar antigen (Ag H)** 

**5.3 The virulence antigen (Vi Ag)** 

**6.1 Isolation of salmonella** 

is encoded by plasmids (and Gledel Corbion, 1991).

**6. Isolation and identification of salmonella** 

and a half hours at a 100 ° C (Dumas, 1958).

To survive in the inflammatory process and the development of bactericidal proteins produced by PMN, a set of genes must be activated, especially those in the complex PhoPQ.
