Staphylococcus Epidermidis: Infection, Transmission & Diseases

Staphylococcus epidermidis is a Gram-positive bacterium that colonizes human skin and mucous membranes as a saprophage. The bacterium is not pathogenic to humans with intact immune systems. However, it can colonize polymeric plastic surfaces of implanted devices, such as catheters and artificial heart valves, forming a biofilm and causing the most serious nosocomial infections.

What is Staphylococcus epidermidis?

The Gram-positive and plasma-coagulase-negative bacterium Staphylococcus epidermidis feeds as a saprophage on dead skin cells and other degradation products of skin and mucous membranes. The fact that the bacterium is plasma coagulase-negative means that it cannot produce a substance that activates prothrombin when it enters the body, so the bacterium cannot surround itself with a protective shield of the body’s own proteins, as some related species do. For people with an intact immune system, Staphylococcus epidermidis is therefore not pathogenic. However, the bacterium has the unpleasant property of being able to attach itself easily to implanted objects with polymeric plastic surfaces. It then forms a multilayer, well-adherent, biofilm protected with a membrane-like glycocalyx of exopolysaccharides. When the bacteria attach to endoprostheses, artificial heart valves, and catheters, they can cause serious nosocomial inflammation. Staphylococcus epidermidis can therefore be described as facultative pathogenic. Often, such infections are difficult to treat when they involve a multidrug-resistant strain of the bacterium that is insensitive to most antibiotics.

Occurrence, distribution, and characteristics

The Staphylococcus epidermidis bacterium is nearly spherical in shape and, as its name suggests, colonizes human skin and mucous membranes, where it is nearly ubiquitous. The bacterium forms a large part of the site flora (normal flora) of the skin. The bacteria can also be found on food and in water. An effective and complete protection against an external contact with the bacteria or also against an oral intake is practically not possible and also not necessary. The bacterium does have properties and functions that are useful for humans. Its facultative pathogenicity consists in its ability to colonize invasively introduced materials with polymeric surfaces and to protect itself by a membrane-like structure, so that the bacterium cannot be reached by the immune system or by antibiotics. There are also strains in hospitals that are resistant to penicillin and methicillin, as well as some other antibiotics. They are therefore counted among the dangerous multidrug-resistant germs that are difficult to combat.

Importance and function

The Staphylococcus epidermidis bacteria feed on exfoliating horny cells and other waste products from the body. The bacteria therefore dominate the composition of the site flora of the skin. The site flora normally represents a stable, dynamic equilibrium resulting from a complex interaction of different microorganisms. For example, Staphylococcus epidermidis is also capable of effective defense reactions against competing bacteria such as Staphylococcus aureus. The bacterium with high and feared pathogenicity can attack the immune system via destruction of phagocytes and cause life-threatening infections. Staphylococcus epidermidis can synthesize an enzyme that destroys the protective biofilm of Staphylococcus aureus and prevents the bacterium from building a new protective film. Staphylococcus epidermidis also knows how to involve the body’s own immune system in the complex defense process via appropriate stimulation. These effects were demonstrated by Japanese researchers in 2010 for the area of the nasal mucosa. In the nasal mucosa, Staphylococcus epidermidis normally exerts a particularly dominant “predominance”. In this case, the bacterium exerts an active, immune-supportive, important defense against infection, although it is classified as facultative pathogen. The effective defense against the Staphylococcus aureus bacterium, by certain strains of Staphylococcus epidermidis, is almost certainly the reason why some people appear to be immune to dangerous Staphylococcus aureus infection.

Diseases and ailments

The greatest danger posed by the otherwise harmless and even beneficial bacterium Staphylococcus epidermidis is its ability to colonize artificial objects inserted into the body, such as endoprostheses, catheters, or artificial heart valves, and to settle in a protective, membrane-like biofilm. In particular, objects with surfaces made of polymer plastics or metal are preferred by the bacterium for colonization. The colonization of the objects can trigger a so-called foreign body infection, with a sometimes serious course. Approximately 70 to 80 percent of all foreign body infections are caused by the bacterium Staphylococcus epidermidis. Such infections are particularly feared in hospitals, as they are usually caused by bacterial strains with multi-resistance to penicillin, methicillin and other antibiotics and embody typical nosocomial infections. If food is contaminated with the bacterium and provides good conditions for it to multiply, eating it can cause nausea, vomiting, diarrhea and cramps. However, this is not an infection in the classical sense, because Staphylococcus cannot normally survive in the digestive tract. Thus, it is basically food poisoning, since the symptoms of illness are caused by the toxins that the bacterium has already produced in the food before it is eaten. Usually, the symptoms subside relatively quickly once the contaminated food has left the body through the accelerated digestive passage. In individuals with weakened or artificially suppressed (suppressed) immune systems, Staphylococcus epidermidis can cause wound infections, boils, sinusitis, and other inflammatory conditions. The biggest problem with an emerging Staphylococcus epidermidis infection is the fact that the bacterium retreats into “hiding places” where it is not noticed by the immune system and therefore not fought. As soon as conditions are favorable for the bacterium to re-infect, it re-establishes itself and creates new foci of inflammation – often chronic – that are difficult to fight because of multiresistance.