What is the Difference Between E coli and Salmonella

The main difference between E Coli and salmonella is that E. coli is a type of commensal bacteria that commonly lives in the lower intestine of warm-blooded animals whereas Salmonella is a facultative, intracellular pathogen in both warm-blooded and cold-blooded animals. Although most E. coli strains are harmless, some can cause serious food poisoning through food contamination. Salmonella, on the other hand, can cause typhoid fever, and paratyphoid fever through food-borne infection.

E. coli and Salmonella are Gram-negative bacteria of the family Enterobacteriaceae. Generally, they are rod-shaped, non-spore-forming, facultative anaerobes. Their pathogenic species use the faecal-oral contamination route for spreading. 

Key Areas Covered 

1. What is E. coli
     – Definition, Characteristics, Importance
2. What is Salmonella
     – Definition, Characteristics, Importance
3. What are the Similarities Between E. coli and Salmonella
     – Outline of Common Features
4. What is the Difference Between E. coli and Salmonella
     – Comparison of Key Differences  

Key Terms 

Commensal, E. coli, Gram-Negative Bacteria, Intracellular Pathogen, Salmonella, Warm-blooded Animals

Difference Between E coli and Salmonella - Comparison Summary

What is E. coli

E. coli (Escherichia coli) is a Gram-negative bacterium of the family Enterobacteriaceae. Therefore, it is a rod-shaped bacterium that is a facultative anaerobe. Thus, E. coli can switch between aerobic respiration and fermentation according to the presence and absence of oxygen. It is also a type of coliform bacteria. The two main characteristic features of a coliform bacterium include living in the intestine as an ecological resident and the ability to ferment lactic acid, producing gas.

Difference Between E coli and Salmonella

Figure 1: Gram Staining of Gram-Negative E. coli and Gram-Positive Staphylococcus 

Furthermore, E. coli is a commensal that produces beneficial effects such as the production of vitamin K2. It also prevents the colonization of the pathogenic bacteria in the intestine. It is a harmless, normal part of the microbiota of the gut. E. coli is expelled into the environment along with the faecal matter. In rare cases, food contamination can allow some serotypes of E. coli to cause serious food poisoning. 

What is Salmonella 

Salmonella is a pathogenic bacterium in the family Enterobacteriaceae. It is a rod-shaped, Gram-negative bacterium and a facultative anaerobe. Along with E. coli, Salmonella is a type of campylobacteria that occurs in the gut of the infected individuals. In addition to these, the common symptoms of campylobacter bacteria infections include diarrhoea, stomach pain or cramps, flu-like symptoms, nausea, and vomiting. Generally, campylobacter bacteria appear in 1-10 days of infection, and the symptoms last for less than 10 days.

Main Difference - E coli vs Salmonella

Figure 2: Salmonella Typhimurium – Gram Staining

Moreover, there are two species of Salmonella. They are Salmonella enterica and Salmonella bongori. The former infects warm-blooded animals while the latter infects cold-blooded animals, particularly reptiles. Moreover, nontyphoidal Salmonella can be invasive and cause paratyphoid fever, which requires immediate treatment with antibiotics. In contrast, typhoid subtypes of Salmonella cause typhoid and paratyphoid fever. Most importantly, typhoid fever can generate life-threatening conditions such as hypovolemic shock and septic shock as the typhoid form invades the bloodstream and the septic form invades organs and secretes endotoxins. 

Similarities Between E. coli and Salmonella  

  • E. coli and  Salmonella are two types of bacteria that belong to the family Enterobacteriaceae.  
  • Both are rod-shaped, non-spore-forming, Gram-Negative bacteria.  
  • Moreover, they are facultative anaerobes that can switch between fermentation and aerobic respiration according to the absence or presence of oxygen.    
  • They mainly live in the intestine of animals.  Both can also cause diseases in animals. Therefore,  they are campylobacter bacteria that appear 1-10 days of infection.  
  • Both types of bacteria are present in faeces and later contaminate food and water. 

Difference Between E. coli and Salmonella 


E. coli refers to a bacterium commonly found in the intestines of humans and other animals; some strains can cause severe food poisoning, while Salmonella refers to a bacterium that occurs mainly in the gut, especially a serotype causing food poisoning. 

Type of the Host

E. coli commonly lives in the lower intestine of warm-blooded animals, while Salmonella lives in both warm-blooded and cold-blooded animals.  


E. coli is about 2.0 μm long and 0.25–1.0 μm in diameter, while Salmonella is about 2 to 5 μm long and 0.7 and 1.5 μm in diameter. 

Coliform or Non-Coliform

Moreover, E. coli is a type of coliform bacteria, while Salmonella is a type of non-coliform bacteria. 

Mode of Living

E. coli is a type of commensal bacteria, while Salmonella is an intracellular pathogen. 

Effect on the Host

While E. coli is typically harmless and produces vitamin K2, Salmonella is pathogenic. 

Type of Diseases Caused 

Some E. coli strains can cause serious food poisoning through food contamination, while Salmonella can cause typhoid fever and paratyphoid fever through food-borne infection. 

Appearance of Symptoms 

The symptoms of E. coli appear in 2-10 days after infection, while the symptoms of Salmonella appear 6-72 days after infection.  


E. coli is a type of Gram-negative, rod-shaped bacteria that live in the intestine of animals. Therefore, it is a facultative anaerobe and produces vitamin K2. It is a commensal, usually harmless to the host. However, some strains can cause food poisoning. Salmonella is also a type of Gram-negative, rod-shaped bacteria that belong to the same family. However, it is an intracellular pathogen that causes typhoid and paratyphoid fever. Hence, the main difference E Coli and Salmonella is their mode of living. 


1. Felson, Sabrina. “E. Coli Bacteria Infection: Symptoms, Treatment, Causes & Prevention.” WebMD, WebMD, 15 Dec. 2018, Available Here.
2. “Campylobacter, E.Coli and Salmonella.” HealthEd, Available Here.

Image Courtesy:

1. “Gram stain 01” By Y tambe – Y tambe’s file (CC BY-SA 3.0) via Commons Wikimedia    
2. “Salmonella Typhimurium Gram” By Y tambe – Own work (CC BY-SA 3.0) via Commons Wikimedia   

About the Author: Lakna

Lakna, a graduate in Molecular Biology and Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things. She has a keen interest in writing articles regarding science.

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