Tuesday, July 26, 2011

MRSE: The other Staph


Staph biofilm, Source: CDC

Drug-resistant Staphylococcal infections usually bring to mind MRSA (methicillin-resistant Staphylococcus aureus), but another bacterial strain is also resistant to methicillin treatment, Staphylococcus epidermidis. The infection is known as MRSE (methicillin-resistant Staphylococcus epidermidis). This strain was the original methicillin-resistant hospital strain of Staph.

S. epidermidis are Gram-positive, coagulase-negative cocci that can survive on dry surfaces for long periods of time. This bacterium is a leading cause of hospital-based (nosocomial) infections, particularly when a foreign body is introduced into the body, such as catheters and implants, due to its ability to form biofilm. The bacterial strain exists normally on human skin and mucous membranes, but a breach in the body’s defenses can open the door to infection. MRSE is commonly resistant to multiple antibiotics, including the penicillins as well as methicillin.

Urinary catheter use

Urinary catheter use is the primary source of nosocomial infections. In the 1980s, S. epidermidis was the most common bacteria isolated from catheters, but in recent years S. aureus (MRSA) has become the more common Staph strain associated with this route of infection (the same can be said for central lines and subsequent infection). Preventative measures have included antimicrobial ointments and new catheter materials to prevent biofilm formation, but the bacteria can contaminate the catheter from the skin of the patient or health care worker, and even from tap water used to clean the catheter or body. Catheter coatings, such as bacteriophages, have been investigated as another method of active prevention.

Symptoms of catheter-associated urinary tract infections include: cloudy urine, bloody urine, foul-smelling urine, leakage around the catheter, pelvic pressure or pain, and common symptoms of infection, including fever, fatigue, chills, and vomiting. Like any other bacterial infection, antibiotics are used for treatment. Since at least the early 1990s, vancomycin has been the only antibiotic to which methicillin-resistant Staph strains are still sensitive for treatment. However, new antibiotics like ciprofloxacin may be effective against MRSE.


Inflammation of the inside of the eye, known as endophthalmitis, can also be caused by Staph infection. Generally, the bacteria enter the ocular cavity from the blood and it may appear as secondary to infection elsewhere in the body. The eye may appear simply to have white nodules, or it can appear cloudy and red, with vision greatly affected. Infection can spread to the surrounding tissues. The condition is treated with aspiration of the infected fluid and antibiotics, generally vancomycin in the case of MRSE, local (via drops or intravitreal) or systemic depending on the extent of infection. Topical steroids, particularly dexamethasone, are also considered helpful.

Cardiac symptoms and treatment

Endocarditis is inflammation of the lining of the heart chambers and valves, known as the endocardium, and is most often caused by bacterial infection. Symptoms are weakness, swelling of the limbs and extremities, paleness, fever, fatigue, chills, night sweats, abnormal urine color, and muscle aches among others. The bacteria may enter due to cardiac catheters, dialysis, or other medical devices.

Vancomycin treatment is, again, the standard antibiotic treatment. However, research published in The Journal of Infectious Diseases in 1993 found that amoxicillin plus clavulanate was just as effective in treating experimental MRSE endocarditis. Researchers at Johns Hopkins in 2007 found that linezolid can also be used to treat endocarditis caused by MRSE.


Meningitis is inflammation of the lining of the spinal cord and brain (known as the meninges). If MRSE infects the central nervous system, it can cause acute infective meningitis (known as Staphylococcal meningitis). When the condition does occur, it is usually with prosthetic use. Symptoms may escalate quickly over 12 to 24 hours and include confusion, fever, rash, nausea or vomiting, severe headache, stiff neck, and light sensitivity.

Treatment is chosen after confirming the infectious agent behind the meningitis via spinal tap, gram stains, and antigen tests. For MRSE, dexamethasone is sometimes used to decrease inflammation, and antibiotic treatment normally consists of vancomycin, but this drug does not penetrate well into the cerebrospinal fluid unless the disease has progressed to severe inflammation. A 2003 study found that linezolid may also be an option for treating this condition when low-level inflammation is present. Removal of the device responsible for infection is also an option to remove the source.


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