Isolation of Staphylococcus aureus and Antibiotic-Resistant Staphylococcus aureus from Residential Indoor Bioaerosols

The introduction of antimicrobial agents to treat human disease was one of the most significant public health accomplishments of the 20th century. Although many factors (e.g., improvements in sanitation, nutrition, and standard of living) worked in concert with antibiotic therapy to control and limit infectious disease transmission, antibiotic therapy was unique in that it not only allowed for the prevention but also for the curing and control of certain diseases (Barker 1999; Cohen 1992). Although the introduction and successful development of this therapeutic class of agents represents a significant medical achievement, this success has also led to complacency within both greater society and the scientific community with regard to the development of bacterial resistance (Neu 1992). That micro-organisms possess the ability to develop resistance to antibiotics was recognized soon after the introduction of antimicrobial therapy, when resistant bacteria were initially identified in the 1930s (Smith and Coast 2002; Virk and Steckelberg 2000). Reoccurring episodes of infection with multiple resistant organisms have affected hospitals since the early 1950s when penicillin-resistant staphylococci initially emerged (Cohen 1992). In spite of the increased understanding of the factors contributing to the development of resistance over the last 60 years, the extent of this problem has not decreased with time and is currently among the strongest global threats to the treatment of infectious disease (Conly 2002). The degree to which this problem has progressed is demonstrated by the fact that resistance has developed against all available classes of antibiotics (Rao 1998; Virk and Steckelberg 2000). As a result of the significant difficulties associated with the accurate measurement of airborne bacteria, little data exist on the concentration of bacteria in indoor air in comparison to other airborne contaminants [Institute of Medicine Committee on Damp Indoor Spaces and Health (IOM) 2004]. Although there are significant difficulties in measuring airborne concentrations of most bioaerosols, the health effects associated with exposure to aerosolized bacteria have received less research attention than those associated with exposure to other organic dusts, such as molds and animal allergens. Also, many bacteria have traditionally been thought of as infectious organisms, with disease resulting only from transmission via large droplets over short distances or through contact with contaminated surfaces (Roy and Milton 2004). Roy and Milton (2004) suggested that this paradigm be questioned and that there is a need for improved understanding of aerosol-acquired disease. This need is made more urgent by the increasing environmental burden of antibiotic-resistant bacteria. Multidrug-resistant Staphylococcus aureus is an example of a bacterium for which the role of exposure to aerosolized organisms in disease transmission should be more closely evaluated. An international survey of infections due to Staphylococcus species resulted in the finding that S. aureus was the most prevalent cause of hospital- and community-acquired bloodstream, skin and soft tissue, and lower respiratory infection (Diekema et al. 2001). In the hospital setting, the most common mode of transmission of resistant S. aureus is close contact with infected persons or with health-care workers with contaminated hands or clothing (Cooper et al. 2004). Recent evidence suggests, however, that airborne dispersal and transmission may also be important (Beggs 2003; Cooper et al. 2004; Roberts et al. 2006), and case studies implicating airborne transmission in the hospital setting have been published in the literature (Cotterill et al. 1996; Wagenvoort et al. 1993). Although drug-resistant S. aureus has historically been a significant problem only in hospitals, the urgent need for further study of the ambient airborne concentrations and the role of airborne transmission of this organism in non-hospital environments is demonstrated by the increasing prevalence of methicillin-resistant S. aureus (MRSA) infections in the community (Chambers 2001). Most alarming about this trend is that infection has been observed among individuals with and without known risk factors (Gorak et al. 1999). The primary objective of this study was to determine the levels of respirable S. aureus, including antibiotic-resistant and multidrug-resistant S. aureus (those resistant to at least two classes of antibiotics) found within the bio-aerosols of residential homes. We hypothesized that S. aureus, including antibiotic-resistant and multidrug-resistant S. aureus, were present in the bioaerosols of the average home.