General overview
Staphylococcus epidermidis (S. epidermidis) is a gram positive, coagulase negative, facultative anaerobic bacteria found in human normal flora. It is a normal skin commensal and less commonly found in mucosal flora. Other names used for this organism are Micrococcus epidermidis, Albococcus epidermidis, and Staphylococcus epidermidis albus.
S. epidermidis infections are almost always nosocomial infections. This organism is transmitted by self-inoculation or by contact with infected patients and hospital personnel. Though this bacterium is a part of normal human flora, it can cause bacteremia by entering to the blood stream.
Moreover, S. epidermidis is an opportunistic pathogen that cause infection in debilitated or compromised patients at the site of implants. It commonly infects prosthetic heart valves, intravenous catheters. It causes endocarditis in patients with prosthetic valves, intravenous catheter infections, cerebrospinal fluid shunt infections, catheter-associated peritonitis and endocarditis.
Furthermore, it causes neonatal sepsis, osteomyelitis, wound infections, vascular graft infections, and mediastinitis.
Ability to produce polysaccharide glycocalyx, namely slime is an important virulence factor of the bacterium. It is helpful to adhere to prosthetic valves and other implant materials. Formation of a multi-layered biofilm, essential for the pathogenesis of device-related S. epidermidis infection.
Usually it is non haemolytic and forms white colour colonies on blood agar. The colonies are 1-2 mm in diameter. On chocolate agar S. epidermidis shows white colour colonies.
epidermidis is catalase positive, coagulase negative organism and does not ferment Mannitol. It tolerates salts, survives drying and highly antibiotic resistant. Clinically significant two coagulase negative staphylococci are distinguished by sensitivity testing to antibiotic, Novobiocin (5 μg disc). S epidermidis sensitive for Novobiocin. There it does not have improved serological tests or any skin tests developed for the diagnosis of any acute infection.
Treatment
S. epidermidis is highly antibiotic resistant. Most strains produce Beta lactamase. However, most strains are sensitive to beta lactamase resistant drugs such as Nafcillin. These strains are called Methicillin sensitive Staphylococcus epidermidis (MSSE).
Some strains are Methicillin/ Nafcillin resistant (MRSE) due to altered penicillin binding proteins. The drug of choice for this organism is Vancomycin.
Commonly the strains are resistant to Penicillin, Penicillinase-stable Penicillins, Gentamicin, Erythromycin and Chloramphenicol. Vancomycin or Teicoplanin should be used for systemic infections caused by this organism.
For the treatment of infections related to the central nervous system or device related infections associated with biofilms, it is occasionally used Rifampicin in combination with a Glycopeptide. Daptomycin and Linezolid may have a impact as a newer agent but scientists are waiting for clinical data to confirm their efficacy.
Other important features
People who are working in hospital setups are more likely to have antibiotic resistant to this organism.
There is no vaccine against S. epdermidis. There is considerable interest in the development of antimicrobial-impregnated devices such as central intravascular catheters, prosthetic heart valves, which will be helpful in the prevention of infections caused by this organisms.
Moreover, use of materials that are less prone to adherence by S. epidermidis and subsequent biofilm formation will be helpful in the prevention of diseases.
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