Epidermidis vs Aureus
Epidermidis and aureus are the species names of the two bacteria in the Genus: Staphylococcus. They cause the most common medical device mediated infections. Therefore, it is very important to understand their characteristics and the differences between them. The causativeness, drug resistance, virulent factors, and identifying characteristics are different between aureus and epidermidis.
Staphylococcus Aureus
It is a facultative anaerobic gram-positive coccus, which appears as a bunch of grapes-like colonies. They produce large, smooth, and round colonies, which are golden in colour. They have shown haemolysis during their growth in blood agar. They react positively to catalase test, which is important to identify them from enterococci and streptococci. In addition, they are coagulase positive, i.e. S. aureus can produce coagulase enzyme that causes clot formation, and which is a significant character to differentiate them from other Staphylococcus species. They are common on skin as commensal bacteria, and in the nose as well. However, aureus is resistant to most of the antibiotics. The bacteria can produce enterotoxins, and these enzymes are the virulent factors 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 wound, direct skin contact, or clothes and towels… etc. They have a vast range of pathogenicity from simple pimples to deathly endocarditis.
Staphylococcus Epidermidis
Epdermidis is also a facultative anaerobic gram-positive coccus; they appear as bunch of grapes-like colonies composed of round, small, and white colour raised colonies. They are non-haemolytic in blood agar, but catalase positive like many of the staphylococci. However, epidermidis react negatively to coagulase test and oxidase test, but are positive for nitrate reductase test, urease test. They usually infect through the catheters and implants because their biofilms are able to grow on plastic devices placed inside bodies. Epidermidis 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 not impossible, but the severity can go as high as up to deathly endocarditis.
Comparison between Aureus and Epidermidis
| Staphylococcus aureus | Staphylococcus epidermidis | |
| Colony morphology |
Large, smooth, and golden in colour |
Small, round, and white in colour |
| In blood agar | Haemolytic | Non-haemolytic |
| Coagulase test |
Positive |
Negative |
| Virulent factors | Enterotoxins | Biofilms |
| Disease causativeness |
Highly infectious and has a vast range from superficial to systemic illnesses including intoxications |
Not highly infectious, but sometimes severity can go very higher |
| Antibiotic resistance | Very high | Less prominent compared to aureus |
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