What is the Difference Between Salmonella and Shigella

The key difference between Salmonella and Shigella is that Salmonella species cause salmonellosis in humans while Shigella species cause shigellosis in humans.

Salmonella and Shigella are two bacterial genera that are gram-negative in nature. This means their cells contain a high amount of peptidoglycan layer, which is a mesh-like substance that provides structure and strength. These bacterial species are also facultative anaerobes and bob-spore-forming organisms. Bacterial species of these two genera cause serious human infections as well. Therefore, they are human pathogens.

1. Overview and Key Difference
2. What is Salmonella
3. What is Shigella
4. Similarities – Salmonella and Shigella
5. Salmonella vs Shigella in Tabular Form
6. Summary – Salmonella and Shigella

What is Salmonella?

Salmonella is a genus of rod-shaped gram-negative bacteria of the family Enterobacteriaceae. This genus has two bacterial species, including Salmonella enterica and Salmonella bongori. Salmonella enterica is further subdivided into six subspecies that include over 2600 serotypes. Moreover, Salmonella was named after Daniel Elmer Salmon (1850-1914), an American veterinary surgeon. Salmonella species are non-spore-forming and motile enterobacteria with cell diameters between 0.7 and 1.5μm, and lengths from 2 to 5μm. They have peritrichous flagella around the cell body, allowing them to move. These bacterial species are chemotrophs obtaining their energy from oxidation and reduction reactions through organic sources. Salmonella are also facultative anaerobes capable of generating ATP with oxygen when the oxygen is available or using other electron acceptors or fermentation when oxygen is not available.

Salmonella and Shigella - Side by Side Comparison

Figure 01: Salmonella

Salmonella genus has bacterial species that cause salmonellosis in humans. Bacterial species of this genus are intracellular pathogens. Therefore, certain serotypes can cause human illness. Salmonella serotypes that cause human illness can be divided into two main groups: typhoidal and nontyphoidal. Typhoidal serotypes can only be transferred from human to human and can cause food-borne infection, typhoid fever, and paratyphoid fever. Typhoid fever is due to Salmonella invading the bloodstream and spreading throughout the body, invading organs and secreting endotoxins. Furthermore, nontyphoidal serotypes are zoonotic and can be transferred from animal to human and from human to human. However, they usually invade only the gastrointestinal tract and cause salmonellosis.

What is Shigella?

Shigella is a genus of bacteria that is gram-negative, facultatively anaerobic, non-spore-forming, non-motile, and rod-shaped. They are genetically closely related to E. coli. This genus is named after Kyoshi Shiga, who discovered it in 1897.

Figure 02: Shigella

The bacterial species of this genus are the causative agents of human shigellosis. Shigella species cause disease in primates but not in other mammals. These species are only naturally found in humans and gorillas. Shigella species normally cause dysentery. Shigella is one of the leading bacterial causes of diarrhoea worldwide, causing an estimated 80 to 165 million cases. The number of deaths caused by Shigella species is around 74000 to 600000 per year. Moreover, Shigella species are one of the top four pathogens that cause moderate to severe diarrhoea in African and South Asian children.

What are the Similarities Between Salmonella and Shigella?

Salmonella and Shigella are two genera that contain bacterial species that are gram-negative in nature.
Both genera belong to the family Enterobacteriaceae.
They contain a high amount of peptidoglycan layer in the cell wall, a mesh-like substance that provides structure and strength.
The bacterial species of these two genera are also facultative anaerobes and bob-spore forming organisms.
The bacterial species that belong to these two genera cause serious human infections as well.

What is the Difference Between Salmonella and Shigella?

Salmonella is a genus of bacteria that causes salmonellosis in humans, while Shigella is a genus of bacteria that causes shigellosis in humans. Thus, this is the key difference between Salmonella and Shigella. Furthermore, Salmonella bacterial species are rod-shaped while Shigella bacterial species are slender shaped.

The below infographic presents the differences between Salmonella and Shigella in tabular form for side by side comparison.

Summary – Salmonella vs Shigella

Salmonella and Shigella are two bacterial genera that are gram-negative. They belong to the family Enterobacteriaceae. The bacterial species that belong to these two genera cause serious human infections. Salmonella causes salmonellosis in humans, while Shigella causes shigellosis in humans. So, this is the key difference between Salmonella and Shigella.