Salmonella vs. Shigella

What's the Difference?

Salmonella and Shigella are both types of bacteria that can cause gastrointestinal infections in humans. However, there are some key differences between the two. Salmonella is a genus of bacteria that includes various species, with Salmonella enterica being the most common cause of salmonellosis. It is typically transmitted through contaminated food or water and can cause symptoms such as diarrhea, fever, and abdominal cramps. On the other hand, Shigella is a genus of bacteria that causes shigellosis, a highly contagious infection. Shigella is primarily spread through person-to-person contact or by consuming contaminated food or water. Symptoms of shigellosis include severe diarrhea, fever, and stomach cramps. While both bacteria can cause similar symptoms, Shigella tends to cause more severe and persistent diarrhea compared to Salmonella.


Gram StainNegativeNegative
Oxygen RequirementFacultative anaerobeFacultative anaerobe
PathogenicityCauses salmonellosisCauses shigellosis
TransmissionFoodborne, waterborne, and contact with infected animalsFecal-oral route, person-to-person contact
Common SymptomsFever, diarrhea, abdominal crampsFever, diarrhea, abdominal cramps
Common SerotypesS. enterica serotype Typhimurium, S. enterica serotype EnteritidisS. sonnei, S. flexneri, S. boydii, S. dysenteriae

Further Detail


Salmonella and Shigella are two types of bacteria that can cause gastrointestinal infections in humans. While they share some similarities, they also have distinct characteristics that set them apart. In this article, we will delve into the attributes of Salmonella and Shigella, exploring their morphology, pathogenicity, symptoms, transmission, and treatment.


Both Salmonella and Shigella are gram-negative bacteria, meaning they have a thin peptidoglycan layer in their cell walls. However, Salmonella is rod-shaped (bacillus) and typically measures 2-5 micrometers in length, while Shigella is also rod-shaped but slightly shorter, ranging from 0.5-0.8 micrometers. Salmonella possesses peritrichous flagella, allowing it to be motile, whereas Shigella is non-motile.


Salmonella and Shigella are both pathogenic bacteria, capable of causing diseases in humans. Salmonella infections, known as salmonellosis, are primarily caused by two species: Salmonella enterica and Salmonella bongori. These bacteria invade the intestinal epithelial cells, leading to inflammation and subsequent symptoms such as diarrhea, abdominal cramps, fever, and vomiting.

On the other hand, Shigella infections, also called shigellosis, are caused by four species: Shigella dysenteriae, Shigella flexneri, Shigella boydii, and Shigella sonnei. Shigella bacteria invade the colon's epithelial cells, resulting in severe diarrhea, often accompanied by blood and mucus, abdominal pain, and fever.


While both Salmonella and Shigella infections primarily affect the gastrointestinal tract, there are some differences in the symptoms they produce. Salmonella infections typically manifest as non-bloody diarrhea, which can range from mild to severe. Other common symptoms include abdominal cramps, fever, and vomiting. The onset of symptoms usually occurs within 12-72 hours after exposure and can last for 4-7 days.

On the other hand, Shigella infections often present with more severe symptoms. The hallmark symptom of shigellosis is bloody diarrhea, often accompanied by tenesmus (a constant feeling of needing to pass stool) and abdominal cramps. Fever is also common. The incubation period for Shigella infections is shorter, usually ranging from 1-3 days, and the illness duration is typically 5-7 days.


Both Salmonella and Shigella can be transmitted through the fecal-oral route, primarily via contaminated food or water. Salmonella can be found in various animal products, such as poultry, eggs, and dairy, as well as fruits and vegetables contaminated during cultivation or processing. Person-to-person transmission can also occur, particularly in settings like daycare centers or nursing homes.

Similarly, Shigella can be transmitted through contaminated food and water, but it is more commonly spread through person-to-person contact. Shigella bacteria are highly infectious, and even a small number of organisms can cause illness. Poor hygiene practices, such as inadequate handwashing after using the toilet, contribute to the rapid spread of Shigella infections within households and communities.


Both Salmonella and Shigella infections are usually self-limiting and resolve without specific treatment. However, in severe cases or for individuals at higher risk, medical intervention may be necessary. Rehydration therapy, including oral rehydration solutions or intravenous fluids, is crucial to prevent dehydration caused by diarrhea and vomiting.

Antibiotics can be used to treat severe or complicated cases of salmonellosis and shigellosis. However, due to increasing antibiotic resistance, susceptibility testing is essential to guide appropriate antibiotic selection. In some cases, antimicrobial therapy may be contraindicated, especially for mild or uncomplicated infections, to avoid promoting further resistance development.


Salmonella and Shigella are two distinct types of bacteria that can cause gastrointestinal infections in humans. While they share similarities in terms of being gram-negative, pathogenic, and transmitted through the fecal-oral route, they also have notable differences in morphology, symptoms, and transmission methods. Understanding these attributes is crucial for effective prevention, diagnosis, and treatment of Salmonella and Shigella infections.

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