Emily Edens

Project title: Distribution and Characterization of the Methicillin-Resistant Staphylococcus aureus in Three Seattle Area Beaches

Degree: MS | Program: Environmental Health (EH) | Project type: Thesis/Dissertation
Completed in: 2011 | Faculty advisor: Marilyn C. Roberts


Staphylococcus spp. are halotolerant, gram-positive cocci bacteria that are ubiquitous in the environment. Many Staphylococcus spp. are innocuous residents of the normal skin flora of healthy individuals. However some species, such as Staphylococcus aureus, are opportunistic pathogens and can cause illness if inoculated into a skin wound S. aureus can cause disease by the production of extracellular enzymes and toxins, for example hemolysins, sugar antigens, coagulase, hyaluronidase, penicillinase, and leukocidins, potentially causing localized infections, necrotizing fasciitis, necrotizing pneumonia, systemic disease, and even death. Methicillin-resistant S. aureus [MRSA], a drug-resistant variant first isolated in 1961 in the United Kingdom, was initially resistant to all b-lactam antibiotics, such as methicillin and penicillin that are broad-spectrum antibiotics commonly used for treatment against Gram-positive infections. However, MRSA has gradually become multi-drug resistant over time due to the pervasive use of antibiotics in healthcare and agriculture. MRSA has been historically associated with immunocompromised populations in a hospital setting and referred to as hospital-acquired MRSA [HA-MRSA].

S. aureus and MRSA frequently colonizes the skin and nasal mucosa, and has also recently been found to colonize the throat. S. aureus nasal colonization rate in healthy adults in North America as well as in Europe and the Middle East has been documented between 25-35.7%, with approximately 1.5% of this population colonized with MRSA. It has been suggested that over the past decade S. aureus colonization in the US has been declining, while colonization with MRSA has increased. Although colonization does not always result in illness, carriers of MRSA are at a 4-fold increase in risk of infection as compared to being colonized with methicillin-susceptible Staphylococcus aureus (MSSA).