Is MRSA a type of bacterial infection?

MRSA: A Bacterial Infection Overview

MRSA (Methicillin-Resistant Staphylococcus aureus) is a type of bacterial infection caused by a strain of Staphylococcus aureus that has developed resistance to many antibiotics. 1

What is MRSA?

• MRSA is a specific strain of Staphylococcus aureus bacteria that has acquired resistance to methicillin and other beta-lactam antibiotics through the acquisition of the mecA gene 1
• This resistance is mediated by the production of PBP2a (penicillin-binding protein 2a), which has significantly lower affinity for beta-lactam antibiotics 1
• MRSA emerged from methicillin-susceptible S. aureus (MSSA) after acquiring the SCCmec genetic element that contains the mecA gene 2

Types of MRSA

• Healthcare-Associated MRSA (HA-MRSA):

  • Initially the predominant form of MRSA 1
  • Associated with healthcare settings and patients with healthcare risk factors 1
  • Often carries SCCmec types I, II, III, VI, and VIII 1

• Community-Acquired MRSA (CA-MRSA):

  • Emerged in the mid-1990s among previously healthy individuals without healthcare risk factors 1
  • Generally more susceptible to non-beta-lactam antibiotics than HA-MRSA 1
  • Often carries SCCmec type IV and frequently produces Panton-Valentine leukocidin (PVL) toxin 1
  • In the US, USA300 is the predominant CA-MRSA clone, while Europe has greater diversity of CA-MRSA clones 3

Clinical Manifestations of MRSA

• Skin and Soft Tissue Infections (SSTIs):

  • Most common presentation of MRSA, particularly CA-MRSA 1
  • Range from simple abscesses to more severe infections like necrotizing fasciitis 1

• Invasive Infections:

  • Bacteremia (blood infection) occurs in approximately 75% of invasive MRSA cases 1
  • Can lead to infective endocarditis, pneumonia, bone and joint infections 1
  • Severe manifestations include septic thrombophlebitis, necrotizing pneumonia, and toxic shock syndrome 1

• Other Manifestations:

  • Osteomyelitis (bone infection) 1
  • Central nervous system infections 1
  • Sepsis and septic shock 1

Epidemiology and Transmission

• MRSA has become increasingly prevalent worldwide since its first clinical isolation in 1961 1
• The epidemiology has become complex with co-mingling of CA-MRSA and HA-MRSA strains in both community and healthcare settings 1
• MRSA can be transmitted through:
  • Direct person-to-person contact 1
  • Contact with contaminated surfaces 1
  • Close living quarters (military barracks, athletic facilities, correctional facilities) 1
  • Animal contact (particularly in livestock workers) 3

Treatment Approaches

For Skin and Soft Tissue Infections:

• Incision and drainage is the primary treatment for purulent SSTIs 1
• For outpatients with purulent cellulitis, empirical therapy for CA-MRSA is recommended pending culture results 1
• Oral antibiotic options include:
  • Clindamycin 1
  • Trimethoprim-sulfamethoxazole (TMP-SMX) 1
  • Tetracyclines (doxycycline or minocycline) 1
  • Linezolid 1

For Invasive MRSA Infections:

• For bacteremia:

  • Vancomycin or daptomycin 6 mg/kg/dose IV once daily for at least 2 weeks for uncomplicated bacteremia 1
  • 4-6 weeks of therapy for complicated bacteremia 1
  • Some experts recommend higher daptomycin dosages (8-10 mg/kg/dose) 1

• For MRSA pneumonia:

  • Vancomycin is recommended as first-line therapy 4
  • Linezolid is an alternative option with equivalent efficacy 4

• For osteomyelitis:

  • Surgical debridement combined with antibiotic therapy 1
  • Parenteral options include vancomycin and daptomycin 1
  • Duration of therapy is typically 8 weeks minimum 1

Prevention Strategies

• Personal hygiene measures:

  • Regular handwashing with soap and water or alcohol-based hand sanitizers 1
  • Keeping wounds covered with clean, dry bandages 1
  • Avoiding sharing personal items that contact skin 1

• Environmental cleaning:

  • Focus on high-touch surfaces 1
  • Use appropriate cleaners according to label instructions 1

• Decolonization strategies for recurrent infections:

  • Nasal decolonization with mupirocin 1
  • Topical body decolonization with chlorhexidine or dilute bleach baths 1

Clinical Significance and Impact

• MRSA remains a significant clinical threat with high morbidity and mortality despite recent declines in some regions 5
• The economic impact of MRSA infections is substantial due to prolonged hospitalizations and complex treatment regimens 1
• Successful treatment often requires multidisciplinary approaches, including infectious disease consultation and source control 5

MRSA continues to evolve, with emerging resistance to additional antibiotics creating ongoing challenges for clinical management and public health 1. Understanding its nature as a bacterial pathogen is essential for appropriate diagnosis, treatment, and prevention strategies.