Abstract
Over the last decade community-acquired methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a major cause of disease in the general population with no health care exposure or known classical risk factors for MRSA infections. The potential community reservoirs have not been well defined though certain strains such as ST398 and USA300 have been well studied in some settings. MRSA has been isolated from recreational beaches, high-touch surfaces in homes, universities, and other community environmental surfaces. However, in most cases the strains were not characterized to determine if they are related to community-acquired or hospital-acquired clinical strains. We compared 55 environmental MRSA from 805 samples including sand, fresh, and marine water samples from local marine and fresh water recreational beaches (n = 296), high touch surfaces on the University of Washington campus (n = 294), surfaces in UW undergraduate housing (n = 85), and the local community (n = 130). Eleven USA300, representing 20% of the isolates, were found on the UW campus surfaces, student housing surfaces, and on the community surfaces but not in the recreational beach samples from the Northwest USA. Similarly, the predominant animal ST133 was found in the recreational beach samples but not in the high touch surface samples. All USA300 isolates were multi-drug resistant carrying two to six different antibiotic resistance genes coding for kanamycin, macrolides and/or macrolides-lincosamides-streptogramin B, and tetracycline, with the majority (72%) carrying four to six different antibiotic resistance genes. A surprising 98% of the 55 MRSA isolates were resistant to other classes of antibiotics and most likely represent reservoirs for these genes in the environment.
Highlights
Staphylococcus aureus is part of the normal flora and can be found in the anterior nares as well as on the skin, axilla, perineum, and pharynx
Ten (3.4%) out of 294 university surface samples were methicillin-resistant Staphylococcus aureus (MRSA) positive, while nine (3.1%) were methicillin-susceptible S. aureus (MSSA). This compares to an earlier study which found no MRSA from 70 high touch surfaces in a large urban US university, though samples from keyboards, telephone mouthpieces, and an elevator button were positive for S. aureus (Brooke et al, 2009)
It is unlikely that the level of resistance found in the environmental MRSA isolates is unique to the Seattle, WA area or to the selected environmental surfaces examined
Summary
Staphylococcus aureus is part of the normal flora and can be found in the anterior nares as well as on the skin, axilla, perineum, and pharynx. MRSA strains are S. aureus that have a mecA gene which codes for a unique penicillin-binding protein that has decreased affinity for β-lactams. This protein allows for cell growth in the presence of penicillins and other β-lactam antibiotics, which are the antibiotics of choice for staphylococcal skin and soft tissue infections (Eady and Cove, 2003; Grundmann et al, 2006). In North America, most CA-MRSA disease is due to a single strain, USA300, which produces a number of toxins and has the ability to cause skin and soft tissue infections in otherwise healthy individuals and appears to be more robust on fomites (Desai et al, 2011).
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