Staphylococcus epidermidis is a common bacterium residing on human skin and mucous membranes. While typically harmless, it can become problematic, particularly when it develops resistance to certain antibiotics. Understanding methicillin-resistant Staphylococcus epidermidis (MRSE) is becoming increasingly important due to its growing presence in healthcare environments. This resistance makes infections more challenging to treat, requiring awareness and effective management.
What is Staphylococcus epidermidis?
Staphylococcus epidermidis is a Gram-positive bacterium that appears spherical, often forming clusters. It is a member of the coagulase-negative staphylococci (CoNS) group, distinguished from Staphylococcus aureus by its inability to produce the enzyme coagulase. S. epidermidis is a facultative anaerobe, capable of growing both with and without oxygen, and is a non-motile, non-spore-forming organism.
This bacterium typically inhabits human skin, especially areas like the armpits, head, and nostrils. While S. epidermidis is generally benign, it acts as an opportunistic pathogen, causing infections primarily in individuals with weakened immune systems or those with indwelling medical devices. A key characteristic of S. epidermidis is its ability to form biofilms, protective layers that adhere to surfaces, including medical implants, making infections persistent and difficult to treat.
Understanding Antibiotic Resistance
“Methicillin-resistant” means bacteria have developed resistance to beta-lactam antibiotics, which includes methicillin, oxacillin, penicillin, and amoxicillin. This resistance primarily stems from acquiring the mecA gene. The mecA gene encodes for an altered penicillin-binding protein, PBP2a or PBP2′, which has a lower affinity for beta-lactam antibiotics.
Beta-lactam antibiotics inhibit penicillin-binding proteins, which synthesize the bacterial cell wall, leading to cell death. However, PBP2a allows the bacterium to continue building its cell wall even in the presence of these antibiotics, preventing their inhibitory effect. The mecA gene is carried on a mobile genetic element called the staphylococcal chromosome cassette SCCmec, which can be transferred between bacteria. The spread of this resistance often occurs through horizontal gene transfer, such as transduction, where bacteriophages transfer genetic material. Overuse and misuse of antibiotics contribute to the selection and proliferation of resistant strains, increasing overall antibiotic resistance.
Common Infections and Who is at Risk
MRSE commonly causes infections in healthcare settings, often involving indwelling medical devices such as catheters, prosthetic joints, pacemakers, shunts, and intravenous lines. The bacteria can colonize these devices, forming a protective biofilm.
Bloodstream infections (bacteremia) are a frequent complication, often originating from colonized medical devices. Surgical site infections are another common type, occurring during or after a surgical procedure. In more severe cases, MRSE can cause endocarditis, an inflammation of the heart’s inner lining or valves, particularly in patients with pre-existing heart valve issues or intravenous drug use history. Populations at higher risk for MRSE infections include immunocompromised individuals (such as those undergoing chemotherapy or with chronic illnesses), patients who have undergone surgery, and neonates.
Identifying and Treating MRSE
Diagnosing MRSE infections involves collecting a sample from the patient, such as blood, tissue, or a tip from an infected medical device. These samples are then sent to a laboratory for culture and sensitivity testing. Rapid testing methods, including molecular techniques like polymerase chain reaction (PCR) to detect the mecA gene, can provide results within hours, though traditional culture methods may take up to 48 hours.
Treating MRSE infections is challenging because standard beta-lactam antibiotics are ineffective. Alternative antibiotics are employed, with vancomycin frequently used as a first-line agent. Other effective options include linezolid and daptomycin. If medical devices are the infection source, their removal or replacement is often necessary, as antibiotics may struggle to penetrate biofilms.
Stopping the Spread of MRSE
Preventing MRSE spread involves several practices, especially in healthcare settings. Rigorous hand hygiene is a cornerstone of prevention, requiring healthcare workers to wash hands or use alcohol-based rubs before and after patient contact. This significantly reduces bacterial transmission.
Proper sterilization of medical equipment and thorough cleaning of hospital rooms and surfaces are also important. Healthcare workers use appropriate personal protective equipment, such as gloves and gowns, when caring for patients with MRSE. Judicious use of antibiotics helps curb the development and spread of resistance. Educating patients about personal hygiene and adherence to treatment protocols also prevents MRSE transmission.