Difference Between Epidermidis and Aureus

The key difference between epidermidis and aureus is that Staphylococcus epidermidis is a non-haemolytic bacterium while Staphylococcus aureus is a haemolytic bacterium.

Epidermidis and aureus are species names of two bacteria in the bacterial genus Staphylococcus. They cause the most common medical device-mediated infections. Therefore, it is very important to understand their characteristics and the difference between epidermidis and aureus. Causatives, drug resistance, virulent factors, and identifying characteristics are different between S. aureus and S. epidermidis.

CONTENTS

1. Overview and Key Difference
2. What is Epidermidis 
3. What is Aureus
4. Similarities Between Epidermidis and Aureus
5. Side by Side Comparison –  Epidermidis vs Aureus in Tabular Form
6. Summary

What is Epidermidis?

Epidermidis is a facultative anaerobe. It is also a gram-positive coccus. The bacterium appears as a bunch of grapes-like colonies composed of round, small, and white colour raised colonies. They are non-haemolytic in blood agar. Similar to other staphylococci, S. epidermidis is also catalase positive. However, S. epidermidis reacts negatively to the coagulase test and oxidase test. Furthermore, S. epidermidis shows a positive response for the nitrate reductase test and urease test.

Epidermidis is usually infected through catheters and implants since S. epidermidis biofilms are able to grow on plastic devices placed inside the bodies. Furthermore, this bacterium commonly lives on the skin and mucosa as a commensal bacterium. However, it is not pathogenic unless the host has a weak immune system. In case of an infection, it is not easy to stop them through antibiotics. But it is also not impossible. The severe infections can go as high as up to deathly endocarditis.

What is Aureus?

Aureus is also a facultative anaerobic gram-positive coccus of the genus Staphylococcus. Similar to S. epidermidis, S. aureus also appears as a bunch of grapes-like colonies. However, unlike S. epidermidis colonies, S. aureus produces large, smooth, and round colonies, which are golden in colour. Furthermore, unlike S. epidermidis, S. aureus shows haemolysis during their growth in blood agar. Also, this bacterium reacts positively to the catalase test, which is important to identify them from Enterococci and Streptococci. One of the most important characteristics of S. aureus is that this bacterium is coagulase positive. S. aureus synthesizes coagulase enzyme that causes clot formation. Thus, this feature is helpful in order to differentiate them from other Staphylococcus species.

Aureus is a part of the normal skin flora and the nose as well. However, this bacterium is resistant to most antibiotics. The bacteria can produce enterotoxins, and these enzymes are the virulent factors that cause a vast range of diseases. Enterotoxins can destroy the mucosal cells of the intestine by changing the permeability of the apical membrane. Additionally, their infections can spread through contact with pus from infected wounds, direct skin contact, or clothes and towels, etc. They have a vast range of pathogenicity from simple pimples to deathly endocarditis.

What are the Similarities Between Epidermidis and Aureus?

• Epidermidis and aureus are two bacterial species belonging to the same bacterial genus Staphylococcus.
• They are facultative anaerobes.
• Also, both are gram-positive.
• Additionally, they are commensal bacteria.
• Furthermore, they are spherical bacteria. Hence, they are cocci.
• Moreover, they cause the most common medical device-mediated infections.
• They are positive for the catalase test.
• Importantly, both their infections can become severe as endocarditis.

What is the Difference Between Epidermidis and Aureus?

Epidermidis is a nonhaemolytic bacterium while S. aureus is a haemolytic bacterium on blood agar. So, this is the key difference between epidermidis and aureus. Furthermore, a significant difference between epidermidis and aureus is that the S. epidermidis colonies are small, round and white in colour while S. aureus colonies are large, smooth and golden in colour. Also, another significant difference between epidermidis and aureus is that the S. epidermidis is coagulase negative while S. aureus is coagulase positive.

In addition, S. epidermidis produces biofilms while S. aureus produces enterotoxins. S. aureus is more virulent than S. epidermidis. Moreover, S. aureus is resistant to a vast range of antibiotics while S. epidermidis is not. Therefore, this also adds to the difference between epidermidis and aureus.

Below infographic summarizes the difference between epidermidis and aureus.

Summary – Epidermidis vs Aureus

Staphylococcus is a genus of gram-positive bacteria comprising over 40 species. Among them, S. epidermidis and S. aureus are two bacterial species which are facultative anaerobes and clinically important. Both species are part of the normal human flora. They become opportunistic pathogens in immune-compromised people. S. epidermidis is a nonhaemolytic bacterium while S. aureus is a haemolytic. Therefore, this is the key difference between epidermidis and aureus. Also, another difference between epidermidis and aureus is that S. epidermidis reacts negatively to coagulate test while S. aureus reacts positively to the coagulase test. In addition, S. epidermidis is able to produce biofilms of plastic surfaces while S. aureus is able to produce enterotoxins. Furthermore, S. aureus shows resistance against a vast range of antibiotics while S. epidermidis is not. Thus, this is a summary of the difference between epidermidis and aureus.

Reference:

1. “Staphylococcus Epidermidis.” Wikipedia, Wikimedia Foundation, 4 Feb. 2019, Available here.
2. Taylor, Tracey A. “Staphylococcus Aureus.” StatPearls [Internet]., U.S. National Library of Medicine, 27 Oct. 2018, Available here.

Image Courtesy:

1. “Staphylococcus epidermidis 01” By Janice CarrContent Providers(s): CDC/ Segrid McAllister – Centers for Disease Control and Prevention’s Public Health Image Library (PHIL), (Public Domain) via Commons Wikimedia
2. “Staphylococcus aureus VISA 2” By CDC/ Matthew J. Arduino, DRPH, Photo Credit: Janice Haney Carr – from the Centers for Disease Control and Prevention’s Public Health Image Library (PHIL) (Public Domain) via Commons Wikimedia