What is an example of a MARCONS (Methicillin-resistant coagulase-negative Staphylococcus)?

Methicillin-Resistant Coagulase-Negative Staphylococci (MRCoNS)

Methicillin-resistant coagulase-negative staphylococci (MRCoNS) are primarily represented by Staphylococcus epidermidis, which is the most common species causing healthcare-associated infections, particularly in patients with indwelling medical devices. 1

Common Examples of MRCoNS

• Staphylococcus epidermidis is the most frequently isolated MRCoNS, accounting for the majority of catheter-related bloodstream infections and prosthetic device infections 1
• Staphylococcus haemolyticus is another common MRCoNS species that has been associated with bloodstream infections 2
• Staphylococcus lugdunensis, while technically a CoNS, behaves more virulently than other CoNS species and should be managed similarly to S. aureus due to its ability to cause endocarditis and metastatic infections 1, 3
• Other MRCoNS species include S. hominis, S. warneri, S. capitis, and S. saprophyticus (though the latter is primarily associated with community-acquired urinary tract infections) 4, 5

Clinical Significance and Epidemiology

• Approximately 55-75% of nosocomial CoNS isolates are methicillin-resistant 4
• MRCoNS account for approximately 30% of all nosocomial bloodstream infections, with the majority related to catheter-associated sepsis 4
• MRCoNS are particularly problematic in specific patient populations:
  • Preterm neonates 6
  • Patients with implanted medical devices 1
  • Immunocompromised individuals 6
  • Patients undergoing cardiac surgery (prosthetic valve endocarditis) 1

Distinguishing Features from Other Staphylococci

• Unlike S. aureus, MRCoNS are coagulase-negative (unable to produce free coagulase) 4
• MRCoNS are normal inhabitants of human skin and mucous membranes but can become opportunistic pathogens 4, 7
• MRCoNS typically form biofilms on implanted medical devices, making them difficult to eradicate 8
• Most MRCoNS exhibit extensive antimicrobial resistance profiles beyond just methicillin resistance 6

Diagnostic Challenges

• The main diagnostic challenge is distinguishing true infection from contamination 3
• Multiple positive blood cultures from different sites strongly suggest true infection rather than contamination 3
• A single positive blood culture with negative concurrent cultures likely represents contamination 3
• S. lugdunensis should be specifically identified among CoNS due to its higher virulence 3

Treatment Considerations

• For confirmed MRCoNS infections, vancomycin is typically the first-line therapy 1
• Alternative agents for MRCoNS infections include:
  • Linezolid, which has activity against methicillin-resistant staphylococci including CoNS 9
  • Tedizolid, which has been shown to be active against methicillin-resistant S. epidermidis 2
  • Daptomycin for bloodstream infections 1
• For uncomplicated catheter-related bloodstream infections, treatment for 5-7 days is recommended if the catheter is removed 3
• For more serious infections like endocarditis, longer treatment courses (4-6 weeks) are typically required 1

Prevention Strategies

• Proper hand hygiene before and after patient contact is essential to prevent transmission of MRCoNS 1
• Use of appropriate infection control measures during insertion and maintenance of intravascular catheters 1
• Daily cleaning of frequently touched surfaces in healthcare settings with EPA-approved disinfectants 1
• Judicious use of antimicrobial agents to prevent further development of resistance 1

Special Considerations

• S. lugdunensis, despite being a CoNS, should be managed more aggressively (similar to S. aureus) due to its higher virulence and ability to cause endocarditis 1, 3
• Catheter removal is generally recommended for MRCoNS bloodstream infections, especially with short-term catheters 3
• For long-term catheters with uncomplicated MRCoNS infection, salvage therapy with systemic antibiotics plus antibiotic lock therapy may be considered 1