Difference Between Pathogenic and Nonpathogenic Bacteria

The main difference between pathogenic and nonpathogenic bacteria is that the pathogenic bacteria can cause diseases while the nonpathogenic bacteria are harmless. Moreover, pathogenic bacteria possess several genes that endow the capacity to cause diseases while nonpathogenic bacteria lack such genes. Another difference between pathogenic and nonpathogenic bacteria is that the pathogenic bacteria invades the cells of the body while nonpathogenic bacteria live outside the body cells.

Pathogenic and nonpathogenic bacteria are the two main types of bacteria other organisms are in contact with. The distinction between the two can be made based on the Koch’s Postulates. However, some pathogenic bacteria may be present in normal individuals without causing a disease. Moreover, nonpathogenic bacteria may also cause diseases, becoming opportunistic pathogens in an immune-compromised host.   

Key Areas Covered

1. What are Pathogenic Bacteria
     – Definition, Examples, Pathogenic Factors
2. What are Nonpathogenic Bacteria
     – Definition, Facts, Examples
3. What are the Similarities Between Pathogenic and Nonpathogenic Bacteria
     – Outline of Common Features
4. What is the Difference Between Pathogenic and Nonpathogenic Bacteria
     – Comparison of Key Differences

Key Terms

Bacterial Diseases, Nonpathogenic Bacteria, Pathogenic Bacteria, Pathogenic Factors, Useful Bacteria

What are Pathogenic Bacteria

Pathogenic bacteria are disease-causing bacteria. Pathogenicity is the capacity of a bacteria to cause a disease. The diseases caused by pathogenic bacteria are generally called infections. Around 100 bacterial species can cause diseases in humans. Tuberculosis is the most common bacterial disease in humans. It is caused by the Mycobacterium tuberculosis.

Figure 2: Mycobacterium tuberculosis Colonies

Pathogenic Bacteria

Factors that Determine the Pathogenicity of Bacteria

1. Host susceptibility – Presence of mechanisms to fight with the infection by the host immune system
2. Pathogenic mechanisms of bacteria – Bacterial infectivity, host resistance, virulence genes, host-mediated pathogenesis (Gram-negative bacterial sepsis, tuberculosis, and tuberculoid leprosy) and intracellular growth
3. Specific virulence factors – Adherence and colonization factors, invasion factors, presence of a capsule and other surface components, endotoxins, exotoxins, and siderophores

What are Nonpathogenic Bacteria

Nonpathogenic bacteria are harmless bacteria to other organisms and they mostly live in the environment as saprophytes. Some of them are autotrophs as well. Around 99% of bacteria are nonpathogenic. They are useful to man as they can involve in manufacturing butter, cheese, alcohol, lactic acid, solvents of paints, and antibiotics.

Some nonpathogenic bacteria live on the surface of animals as normal flora. They are commensals. But, these bacteria can become opportunistic pathogens when they invade the tissues. As an example, E.coli are nonpathogenic bacteria that live in the gastrointestinal tract and can trigger an immune response in certain circumstances.

Figure 2: E. coli

Nonpathogenic Bacteria

Similarities Between Pathogenic and Nonpathogenic Bacteria

• Pathogenic and nonpathogenic bacteria are two types of bacteria other organisms are in contact with.
• Both are microorganisms that can be found in the normal flora.

Difference Between Pathogenic and Nonpathogenic Bacteria

Definition

Pathogenic bacteria refer to bacteria that can cause diseases while nonpathogenic bacteria are organisms that do not cause disease, harm or death to another organism.

Relationship with the Host

Pathogenic bacteria are parasites while nonpathogenic bacteria are commensals.

Significance

Pathogenic bacteria are harmful while nonpathogenic bacteria may be useful.

Virulence Genes

Virulence genes are present in the genome of the pathogenic bacteria while nonpathogenic bacteria do not possess virulence genes.

Adhere to tissues

Pathogenic bacteria adhere to the cells of the tissues in order to escape from the fluid flows inside the body while nonpathogenic bacteria do not adhere to the tissue.

Invasion

Pathogenic bacteria invades the cells of the body while nonpathogenic bacteria live outside the body cells.

Phagocytosis

Pathogenic bacteria resist phagocytosis by using a slick capsule, leucocidins, and other antiphagocytic mechanisms while nonpathogenic bacteria are subjected to phagocytosis.

Toxins

Pathogenic bacteria produce toxins that can alter the metabolism of the host cells while nonpathogenic bacteria do not produce toxins.

Colonization

Most of the pathogenic bacteria produce their colonies within the tissues while nonpathogenic bacteria do not produce colonies.

Conclusion

Pathogenic bacteria can cause diseases. They are very few from the whole bacterial population. They develop pathogenic factors, which help in the invasion of the host. But, nonpathogenic bacteria do not cause diseases and some of them are useful in the day to day life. The main difference between pathogenic and nonpathogenic bacteria is their disease-causing ability.  

Reference:

1. Peterson, Johnny W. “Bacterial Pathogenesis.” Advances in Pediatrics., U.S. National Library of Medicine, 1 Jan. 1996, Available Here
2. “Non-Pathogenic Microorganisms.” Biology Discussion, 16 May 2016, Available Here

Image Courtesy:

1. “TB Culture” By Photo Credit:Content Providers(s): CDC/Dr. George Kubica – Centers for Disease Control and Prevention’s Public Health Image Library (PHIL), with identification number #4428. (Public Domain) via Commons Wikimedia   
2. “Scanning electron micrograph of an E. coli colony” By Photo courtesy CDC/Janice Haney Carr. – Original CDC image is herePhil Moyer https://www.flickr.com/photos/hukuzatuna/2536878015 Photo courtesy CDC/Janice Haney Carr. (Public Domain) via Commons Wikimedia