Salmonella (non-typhoidal)

Salmonella is a bacterium belonging to the family Enterobacteriaceae.

There are two main species: Salmonella bongori and Salmonella enterica, and the latter has six subspecies.

One of the subspecies is enterica, which has over 2500 serotypes that can be divided into two main groups based on the clinical symptoms they cause- so typhoidal or non-typhoidal Salmonella.

The non-typhoidal group, can infect humans and animals and cause a variety of disease states.

But, the most common serotype, Salmonella enteritidis, causes intestinal inflammation, called gastroenteritis, or commonly called “food poisoning”.

OK, but generally, Salmonella are encapsulated gram-negative, rod bacteria – meaning, they have a polysaccharide layer outside the cell envelope and look like little red or pink sticks on a gram stain.

They’re facultative intracellular pathogens, meaning they can live both outside or inside of its host’s cells.

And have flagella, making them motile, but don’t form spores.

They’re also facultative anaerobes, so they can undergo respiratory and fermentative metabolism; and they can ferment glucose but not lactose; are oxidase negative, and produce hydrogen sulfide gas.

And while a variety of media can be used to selectively identify Salmonella, among them is Triple Sugar Iron agar which produces a black precipitate when hydrogen sulfide is produced.

Now, once Salmonella is ingested and reaches the distal ileum of the small intestine, it tends to target the epithelial layer of the mucosal lining where it uses surface appendages to adhere to microfold cells, or M-cells.

And these M-cells eat, or phagocytose, the bacteria from the intestinal lumen and spit it out into the underlying Peyer’s patches - a type of mucosal immune tissue that extends into the submucosa.

When encountering non-typhoidal Salmonella, the immune system responds strongly by releasing proinflammatory cytokines that recruit additional immune cells, particularly neutrophils.