Staphylococcus Epidermidis

Staphylococcus epidermidis is one of the most prevalent microorganisms found on the human skin and in the mucous membranes, however, it is a typically overlooked bacterium because there is very little that is known about it.

Though it is not as aggressive as its cousin Staphylococcus aureus, Staphylococcus epidermidis is the most frequent cause for nosocomial pathogens, especially among newborns, the elderly, and anyone who has a compromised immune system. These infections are usually associated with intravascular catheters and other indwelling medical devices (“Staphylococcus epidermidis”). S.epidermidis produces a biofilm that grows on medical devices and then microorganisms are able to attach to themselves to the biofilm.

It is also resistant to common antibiotics which make it difficult to treat which is why it is very important for hospitals to prevent infection by keeping a sterile environment and to follow aseptic techniques at all times (“Staphylococcus epidermidis”). Staphylococcus epidermidis is a gram-positive bacterium, whose species belongs to the genus Staphylococcus. It was an unknown species until 1884, when microbiologist, Fredrich Julius Rosenbach, distinguished it from Staphylococcus aureus.

He had discovered that S. epidermidis grew in white colonies, whereas S. aureus grew in yellow colonies. As a result of those findings, he had initially named it Staphylococcus albus (Horak). When viewed under the microscope, S. epidermidis can usually be found growing in round, grape-like clusters, but it may also grow in chains or pairs. Just like most members of this genus, S. epidermidis is non-motile and they do not form spores.

It is a facultative anaerobe that is able to grow by aerobic respiration or by formation (Horak). S.epidermidis is a coagulase-negative strain of the Staphylococcus species and is not able to utilize mannitol, which can easily distinguish it from S. aureus. It is also positive for urease and it is sensitive to novobiocin. When placed in phenol red broth, S. epidermidis is able to use lactose and glucose, but it does not produce gas (Horak). It presents itself as small, white colonies on tryptic soy agar plates and does not actively hemolyze the red blood cells in blood agar. When exposed to hydrogen peroxide, it will bubble up meaning that it is also catalase positive.

Incubation time is normally at 37°C for 18-24 hours (Horak). Staphylococcus epidermidis predominantly colonizes the armpits, head, and nostrils. It is also well equipped with genes that provide protection from harsh conditions encountered in its natural habitat (“Staphylococcus epidermidis”). S. epidermidis is considered a true opportunistic pathogen that is normally harmless to a healthy person; however, newborns, the elderly, and patients with compromised immune systems are at risk for infection (“Staphylococcus epidermidis”).

Infections are both nosocomial and community acquired and they do pose more of a threat to hospital patients because hospitals carry more aggressive strains of it due to the constant use of antibiotics and disinfectants (“Staphylococcus epidermidis”). S. epidermidis has the ability to cause infection by producing a biofilm that can adhere to indwelling medical devices such as catheters, joint and vascular prosthesis, prosthetic valves, pacemakers, and cerebrospinal fluid shunts. Once the biofilm has formed, it makes it harder to treat because it protects the cells that are inside the biofilm from antibiotics and the immune system.

The biofilm is also able to release a host immune response to the antigens so that it prevents it from being removed, which could result in tissue damage (“Staphylococcus epidermidis). The organisms that cause infection may originate from many different sources, including the skin around the site of insertion, airborne contamination, colonies already forming on the medical device before it’s implanted, and microorganisms that are shed from health care workers (McCann, Gilmore, and Gorman 1551-1570).

The reason that S.epidermidis is such a successful pathogen within the hospital setting is because of its highly adaptive nature, inherent genetic variability, and intrinsic genetic flexibility. All of those things make it able to better withstand hostile external environments (McCann, Gilmore, and Gorman 1551-1570). S. epidermidis can cause infection in many different locations of the body and no matter where the infection started, the symptoms of the infection may be similar, such as having a fever, being fatigued, having pain in the area that the implant is in, breathing rapidly, or having a high pulse rate (Horak).

The clinical presentation and symptoms of infection are depended upon where the site of insertion is and what type of medical device was used (McCann, Gilmore, and Gorman 1551-1570). Just like its cousin S. aureus, there is now a methicillin-resistant Staphylococcus epidermidis (MRSE) strain that has popped up. This same strain was also the original methicillin-resistant hospital strain of Staphylococcus (Prater). MRSE is resistant to many types of antibiotics, including penicillin and methicillin. It can also cause many types of infections.

Catheter infections along with catheter-associated urinary tract infections can cause bloody and/or foul-smelling urine, leakage around the catheter, and pelvic pain (Prater). It can cause endocarditis, which is an infection of the heart valves and parts of the inside lining of the heart muscle. MRSE is also responsible for causing infections such as cause meningitis and septicemia. Vancomycin, an antibiotic, is the best course of treatment for those that are fighting MRSE infections (Prater).

Treating an infection that has been caused by S.epidermidis is very difficult because the resistance towards antibacterial agents has been increasing. This is because of the frequent overuse of antibiotics, medications being prescribed when they shouldn’t be, and patients not taking their antibiotics as directed (McCann, Gilmore, and Gorman 1551-1570). And because antimicrobial treatment has little or no effect against the populations of biofilm that has colonized on medical devices, it is often necessary to surgically remove and replace the device.

If that is not a viable option, then the patient would require intermittent antibiotic therapy for the rest of their life (McCann, Gilmore, and Gorman 1551-1570). Though Staphylococcus epidermidis is normally harmless, once it gets into the bloodstream, the infections can be hard to treat but rarely fatal and it could lead to sepsis and endocarditis. Being able to diagnose the infection quickly is very important in getting the right treatment. There are many tests that microbiologists can perform on it once they receive an isolated clinical specimen to find the identity such as a gram stain to check if gram positive or gram negative.

They could do a catalase test to distinguish between Staphylococcus and Streptococcus or Enterococcus, or they could do a coagulase test to distinguish between S. aureus or S. epidermidis. The biofilm produced by S. epidermidis can protect pathogens from disinfectants inside the body, helping it cause disease by releasing microorganisms which can have an effect on the immune system (Horak). Since it is mostly found in hospital settings, it is very important for hospitals to prevent contamination and infection by maintaining a sterile environment. The most common treatment for infection is to remove and replace the infected device.

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