24 MRSA Yamaki Flashcards
What are the two commonly divided classifications of MRSA?
Hospital Acquired (HA) vs. Community Acquired (CA)
What is the most common burden of MRSA disease in the US?
Bacteremia
What is the definition of HA-MRSA?
MRSA being identified after 48 hours of admission to a hospital or does not meet criteria for CA-MRSA. Skilled nursing facility (SNF) transfer. Ventilator associated pneumoniae (VAP). Catheter associated infections (PVC/CVC)
What is the epidemiology of HA-MRSA?
Emerged shortly after methicillin introduction. Initially majority of all MRSA infection were nosocomial (until CA-MRSA emerged)
What are the at risk groups for HA-MRSA?
Hospitalized patients. Patients w/ intravenous catheters, prosthetic devices. Surgical wounds. On ventilators
What is the definition of CA-MRSA?
Persons have no significant medical history in past year (hospitalization, admission to nursing home/skilled nursing home or hospice, dialysis, surgery)
What are the at risk groups for CA-MRSA?
Correctional fascilities. Military. Close contacts in families. Athletic teams. MSM. Daycares. Native Americans, Pacific Islanders
What cassettes do HA-MRSA bacteria have?
SCCmec I, II, III (larger, can carry more resistant genes)
What cassettes do CA-MRSA bacteria have?
SCCmec IV, V (smaller, less resistant genes)
What are the genetic characteristics of CA-MRSA?
Methicillin resistance conferred by mecA gene (SCCmec types IV and V, rarely multi-drug resistant). ACME. Accessory gene regulator (agr) type I or III
What is ACME?
Arginine Catabolic Mobile Element. Found in USA300 strains of CA-MRSA only. Enables use of arginine as an energy source. Depletion of Arginine –> Decrease in NO production. ACME gene deletion –> less virulence
What is “Pathogenicity”?
The capability of a pathogen to cause disease
What is “Virulence”?
The degree in ability of a pathogen to cause disease
What does Protein A (pathogenicity factor) do?
Evades immune system by binding to Fc portion of IgG antibodies
What does FnbA/FnbB (pathogenicity factor) do?
Fibronectin binding proteins. Recognize and bind to sites containing fibronectin
What does Coagulase (pathogenicity factor) do?
Converts fibrinogen to fibrin –> clotting. May protect bacteria from immune system recognition and elimination
What does ClfA/ClfB (pathogenicity factor) do?
Clumping factor. Membrane bound coagulase
What are the virulence factors associated with MRSA?
a-Hemolysin. Panton-Valentine Leukocidin (PVL). Phenol-Soluble Modulins (PSMs). Toxic Shock Syndrome Toxin (TSST-1)
What is a-Hemolysin (Hla)?
Heptameric pore forming toxin produced by nearly all S. aureus strains. Lysis of RBCs –> Fe. Up-regulated in CA-MRSA. Studies demonstrated it may play a role in pneumonia. Demonstrated protection with vaccine directed against Hla. Never give someone with an infection iron
What is Panton-Valentine Leukocidin (PVL)?
Bi-component pore forming toxin encoded by prophage, targets PMNs. Common in CA-MRSA strains, rare in HA-MRSA. Significant association with invasive skin infections. Linked to necrotizing pneumonia. High concentrations cause lysis of PMNs, low concentrations cause apoptosis of mitochondria
What is Phenol-Solubule Modulins (PSMs)?
Two groups alpha and Beta. Four types a-PSMs (pore forming in PMNs) and two B-PSMs (biofilm). Up-regulated peptides in CA-MRSA vs. HA-MRSA
What treatment is used for MRSA in severe, invasive infection?
IV therapy. Vancomycin remains as 1st line empiric treatment (alternative agents need to be considered based on site of infection, MIC, development of nephrotoxicity). Step down to oral therapy once patient stable, tolerating POs
What are the antibiotics used for treatment of MRSA?
Vancomycin (trough 15-20). Daptomycin (6mg/kg IV Q24h). Linezolid (600mg IV Q12h). Synercid (7.5mg/kg IV Q8h). All of these can be used with AGs or Rifampin for synergy
What are some cautions with Vancomycin use?
Acute Kidney Injury