Shigella
Shigella is a genus of bacteria that is Gram-negative, facultative anaerobic, non-spore-forming, nonmotile, rod-shaped and genetically closely related to E. coli. The genus is named after Kiyoshi Shiga, who first discovered it in 1897.
The causative agent of human shigellosis, Shigella causes disease in primates, but not in other mammals. It is only naturally found in humans and gorillas. During infection, it typically causes dysentery.
Shigellosis is a bacterial infection that affects the digestive system. Shigellosis is caused by a group of bacteria called Shigella. The Shigella bacterium is spread through contaminated water and food or through contact with contaminated feces. The bacteria release toxins that irritate the intestines. The primary symptom of shigellosis is diarrhea.
Salmonella
Salmonella is a genus of rod-shaped (bacillus) Gram-negative bacteria of the family Enterobacteriaceae. Salmonella species are non-spore-forming, predominantly motile enterobacteria with cell diameters between about 0.7 and 1.5 μm, lengths from 2 to 5 μm, and peritrichous flagella (all around the cell body). They are chemotrophs, obtaining their energy from oxidation and reduction reactions using organic sources. They are also facultative anaerobes, capable of generating ATP with oxygen (“aerobically”) when it is available, or when oxygen is not available, using other electron acceptors or fermentation (“anaerobically”) get its energy.
The two species of Salmonella are Salmonella enterica and Salmonella bongori. S. enterica is the type species and is further divided into six subspecies that include over 2,600 serotypes. Salmonella was named after Daniel Elmer Salmon (1850–1914), an American veterinary surgeon.
Difference Between Shigella And Salmonella In Table Form
| ELEMENTS OF COMPARISON | SHIGELLA | SALMONELLA |
| Discovery | The genus is named after Kiyoshi Shiga, who first discovered it in 1897. | Salmonella was named after Daniel Elmer Salmon (1850–1914), an American veterinary surgeon. |
| Motility | Shigella is non motile. | Salmonella is motile with peritrichous flagella. |
| Species | There are about 40 serotypes of Shigella bacteria | There are about 2,200 serotypes of Salmonella bacteria |
| Shape | Shigella is slender bacilli microbe. | Salmonella is a rod shaped microbe. |
| Differential Media | In Hektoen agar, Shigella colonies will appear green in color. | In Hektoen agar, Salmonella colonies appear in black in color. |
| H2S Production | Shigella doesn’t produce H2S. | Salmonella produces H2S. |
| Disease | Shigella causes Shigellosis. | Salmonella causes Salmonellosis. |
| Transmission | Shigella can be transmitted through contaminated food and water, personal contact even from animals. | Salmonella is transmitted by raw food while Shigella by person to person contact. |
| Major pathogen | Shigella dysenteriae | Salmonella typhi |
| Reservoir of organism | Human and primates only. | Human and animal. |
| Toxin Production | Shigella produces heat labile toxin called Shiga toxin. | Salmonella produces enterotoxin. |
| Effect on Human Intestine | Salmonella affect small and large intestine (enterocolitis). | Shigella affects colon (colitis). |
| Incubation Period | The incubation period for Shigella is 1-2 days. | The incubation period for Salmonella is 6-72 hours. |
| Dosage | Shigella requires smaller infective dosage than for Salmonella. | Salmonella requires larger infective dosage than for Shigella. |
| Bloody And Mucoid Diarrhea | Bloody and mucoid diarrhea is more likely in shigellosis than salmonellosis. | Bloody and mucoid diarrhea is more likely in shigellosis than salmonellosis. |
Similarities Between Shigella And Salmonella
- Both are facultative anaerobic and non-spore forming organisms.
- Salmonella and Shigella are different groups of Gram-negative bacteria.
- Both Salmonella and Shigella can be transmitted through contaminated food and water, personal contact or even from animals and objects (fomites).
- Salmonellosis and shigellosis are more likely to occur in children under 5 years of age and the elderly.
- Diarrhea, abdominal pain and fever are the main symptoms in both diseases.
- The symptoms of both diseases resolve within 7 days or less in most people.
- Deaths in both diseases are uncommon but are more likely to occur in children with shigellosis.