Salmonella-Epidemiology, Pathogenesis, diseases, and Treatment
Salmonella belongs to the Enterobacteriaceae family, are gram-negative rods, facultative anaerobes, oxidase negative, have peritrichous flagella.
Its antigenic structure contains lipopolysaccharide that has outer somatic O polysaccharides, a common antigen is corepolysaccharides and lipid A i.e., an endotoxin.
The isolates that are responsible for human gastrointestinal diseases belong to the species Salmonella enterica.
More than 2500 unique O serotypes are present.
E.g., of Serotypes of S. enterica, are S. Typhi, S. Typhimurium, S. enteritidis, S. paratyphi.
Salmonella usually colonizes in animals such as livestock, rodents, poultry (especially eggs), reptiles, birds, domestic animals, and humans.
Transmission is carried by an animal to animal spread, and from animal reservoirs to humans.
The infective dose is 1000 or more to cause disease by Salmonella species.
People who consume antacids regularly can be infected in the small inoculum.
Salmonella is a major cause of foodborne intestinal infections, poultry products i.e., eggs act as vehicles of infection for gastroenteritis.
In the U.S, per year 40,000 to 50,000 cases are reported, the peak of infections varies seasonally especially in summer.
Children less than 5 yrs, adults above 20- 30, and older people above 70 are susceptible to the highest rate of infections.
On account, 5% of fully recovered patients from Salmonella gastroenteritis can shed organisms even after 20 weeks.
Salmonella is ingested through contaminated food, and passes through the stomach, gets attached to the small intestine mucosal membrane, and invades into microfold cells (M cells), in Peyer patches, and also enterocytes.
Bacteria multiply in endocytic vacuoles
The bacteria can also transport across the cytoplasm and get released into the blood.
Virulence Factors: Attachment, engulfment, and replication are regulated by two clusters of genes on pathogenicity islands I & II
Genes encode by pathogenicity I for salmonella secreted invasion proteins (Ssps) & type III secretion system (helps to injects proteins inside the host cells).
Pathogenicity island II encodes for evasion of bacteria through host immune response & also second type III secretion system.
Inflammatory response mediates the release of the prostaglandins and triggers the cAMP which causes hyper fluid secretion
The four forms of Salmonella infection are gastroenteritis, septicemia, enteric fever, and asymptomatic colonization.
It’s a common form of Salmonellosis.
Appears in 6- 48 hrs, after consumption of salmonella-contaminated food or water.