Salmonella Enterica

Salmonella spp. are Gram-negative pathogenic bacteria that infect a wide variety of mammalian, avian and reptile hosts. Infection with this highly versatile pathogen can lead to different clinical outcomes including asymptomatic carriage, gastroenteritis, or severe, life-threatening systemic disease, known as enteric fever. The nature and the severity of the disease is depended upon the infecting serovar as well as the infected host species and its immunological status. 

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Non-typhoid Salmonella enterica (NTS) serovars are a predominant cause of foodborne illnesses worldwide. The majority of cases present as gastroenteritis, which is mostly a mild to moderate, self-limited inflammatory infection of the intestines. However, about 5% of these illnesses may be invasive, and manifest as bacteremia or other extra-intestinal infections. There are an estimated 93.8 million cases of gastroenteritis due to NTS infections each year, resulting in approximately 155,000 deaths. In addition, the estimated global annual burden of enteric fever due to typhoidal Salmonella infections is over 27 million cases, resulting in more than 200,000 deaths.

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NTS is considered a zoonotic pathogen and many of these serovars are also capable of colonizing the intestines of food-producing animals and contaminate the avian reproductive tract and the laid egg. The routes of transmission include consumption of contaminated food from animal sources, particularly eggs, poultry, ground meat and dairy products as well as contaminated fresh fruits and vegetables.
 
The two hallmarks of Salmonella enterica pathogenesis are the invasion of non-phagocytic cells such as epithelial cells of the intestinal mucosa, and their ability to survive and replicate inside infected phagocytic cells. Both mechanisms, as well as many of the virulence determinants used by S. enterica, are directly linked to genes encoded within large horizontally acquired regions of the chromosome termed Salmonella Pathogenicity Islands (SPIs).