Understanding Salmonella Vs Shigella: 10 General Differences

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Characteristics of Salmonella

Salmonella species are predominantly motile enterobacteria found in the digestive tracts of humans and animals especially reptiles. Food and water can also be contaminated with the bacteria if they come in contact with the feces of infected people or animals.

Salmonella is a facultative bacteria. What this means is that, it can survive with or without oxygen. Obligate bacteria, on the other hand, can only survive under specific conditions.

Salmonella is  a gram negative bacteria, this means that their cells contain high amount of peptidoglycan, a mesh-like substance that provide structure and strength. Salmonella is a rod-shaped bacteria or bacillus. However, unlike other strains of bacilli, salmonella does not produce spores. On MacConkey agar, salmonella colonies appear colorless and transparent, though they sometimes have dark centers. A colony is a group of bacteria that are growing together. Salmonella in humans causes Enteric fever, typhoid and gastroenteritis.

Characteristics of Shigella

There are four shigella species, that is, Shigella dysenteriae, Shigella flexneri, shigella boydii and Shigella sonnei. Shigella sonnei is the most common infectious form in North America and the developed world.

Shigella are gram-negative rods that are non-motile and non-spore –forming. Shigella is not only a human disease but it has been found in some primates. In medical laboratory, individual shigella species are often accomplished through slide agglutination using absorbed rabbit antisera.  Isolation with MacCkongey’s , Hektoen Enteric Agar or salmonella-shigella agar are used as deferential media.

Salmonella Vs. Shigella In Tabular Form

BASIS OF COMPARISON     SALMONELLA SHIGELLA
Shape Salmonella is a rod shaped microbe.     Shigella is a slender shaped microbe.  
Motility Salmonella is motile with peritrichous flagella.     Shigella is non-motile in nature.
Differential Media (Hektoen Agar) Salmonella colonies in Hektoen Agar appear black in color.     Shigella colonies in Hektoen Agar will appear green in color.
Human Organs Highly Likely To be Affected Salmonella affects both large and small intestines.     Shigella mainly affects the large intestine.
Toxic Production Salmonella produces enterotoxin.     Shigella produces heat labile toxin referred to as Shiga toxin.
Causes Salmonella mainly causes Salmonellosis.     Shigella mainly causes Shigellosis.
H2H Production Salmonella produces H2S.     Shigella doesn’t produce H2S.
Reservoir of the Microbe Human and animals are the main reservoir of Salmonella. Human and primates are the only reservoir of Shigella.
Major Pathogen Salmonella typhi.     Shigella dysenteriae.
Common Mode of Transmission Raw food, contaminated food and  water     Person to person contact
Dosage Salmonella requires large dosage.     Shigella requires small dosage

What Are Some Of The Similarities Between Salmonella and Shigella?

  1. Both Shigella and Salmonella are facultative anaerobes and bob-spore forming organisms.
  2. Both Salmonella and Shigella are gram negative.