Virulence Factors of *Salmonella Typhi*

*Noor S.K. Al-Khafaji, Ali M.K. Al-Bayati and Hussein O.M. Al-Dahmoshi*

### **Abstract**

S. Typhi is an enteric bacillus which belongs,to the genus *Salmonella* in the family Enterobacteriacaea and it is a multi–organs pathogen which inhibits the lymphatic tissues of the small intestine, liver, spleen, and blood stream of infected humans. S. Typhi has a mixture of features that make it an efficient pathogen. This species contains an endotoxin that is characteristic of Gram-negative organisms, as well as the virulence-enhancing Vi antigen. Many of the S. Typhi virulence factors are clustered in some areas of the chromosome known as *Salmonella* pathogenicity islands (SPI), such as adhesion, invasion, and toxin genes. A protein known as invasin that permits non-phagocytic cells is also produced and excreted by the bacterium., Where it is capable of intracellular living. The oxidative burst of leukocytes may also be inhibited, making innate immune reaction ineffective.

**Keywords:** S. Typhi-virulence factors -endotoxin, enterotoxin, cytotoxin

### **1. Introduction**

It was quite a long time before typhoid fever was differentiated from other febrile disorders. Pierre Louis was the first who used the word " typhoid " and give the classical picture of typhoid in 1829 and described in detail post-mortem finding, especially the enlargement and ulceration of peyer's patches. However, he did not clearly differentiate between typhoid and typhus. In 1837, Gerhard was the first who clearly differentiate typhoid from typhus fever and William Budd described the contagious nature of the disease and Incriminated transmission of facially polluted water supplies in 1873 [1].

In 1873, William Budd, a physician in Bristol who was interested in cholera and intestinal fever, showed that typhoid fever could be transmitted by a particular toxin found in the excrement and that this propagation was responsible for the contamination of water by the feces of patients. Each case was linked to another anterior case, according to Budd. A significant number of doctors and scientists have attempted to discover the nature of the disease-causing microorganism and have experienced considerable difficulty in isolating the bacillus. It was Karl Joseph Eberth, Rudolf Virchow's doctor and pupil, who discovered the bacillus in the abdominal lymph nodes and the spleen in 1879. In 1880 and 1881, he reported his findings. The genus '*Salmonella*' was named after Daniel Elmer Salmon, an American veterinary pathologist, who was the administrator of the USDA (United States Department of Agriculture) research program. His discovery was then tested and confirmed by German and English bacteriologists, including Robert Koch., Thus, despite the fact

that a number of scientists had contributed to the quest [2, 3], the organism was named after him. *Salmonella* has thus become new scientific knowledge and thus the mechanisms of infection and the presence of healthy carriers have been relatively nascent [4]. Recent reports suggest that there are approximately 20 million cases of typhoid each year, resulting in deaths of 100,000-200,000 [5]. Karl J. Eberth, who isolated the bacterium from spleen parts and lymph nodes from a patient who died of typhoid fever and discovered the typhoid agglutinins and their diagnostic application, first isolated S. Typhi in 1880. In 1881, Robert Koch succeeded in cultivating the bacterium. However the isolation of typhoid bacillus from other enteric bacteria was unclear due to the lack of differential characters [6, 7].

*Salmonella* is a genus of rod shaped (bacillus) gram negative bacteria related to family Enterobacteriaceae. They have two species which are *Salmonella enterica* and *Salmonella bongori*. *S. enterica* is the kind species and is further divided into sex subspecies [8]. that contain over 2,600 serotypes [9]. *Salmonella* species are non spore forming, predominantly motile enterobacteria for cell diameters between on 0.7 and 1.5 μm, lengths for 2 to 5 μm, and peritrichous flagella (all concerning the cell body [10]. exceptions *S. Gallinarum* and *S. Pullorum* [11, 12]. The bacterial strain was named after the American pathologist, Dr. Daniel Elmer Salmon, who collaborated with Smith. The *Salmonella* nomenclature is controversial and still changing. The Centers for Disease Control and Prevention (CDC) is currently using the *Salmonella* nomenclature system suggested by the World Health Organization (WHO) Collaborating Centre as a nomenclature system.: Species: *Salmonella enterica* serotype Typhi. [13].
