Contamination of foodstuffs via the air is generally caused by viable airborne contaminants originating from biological sources (bioaerosols) (Lutgring, Linton, Zimmerman, Peugh, & Heber, 1997; Whyte, Collins, McGill, Monahan, & O'Mahony, 2001). Bioaerosols can be liquid or solid, or can be carried on another particle or suspended in a liquid droplet, and may comprise bacterial spores, cells, fungi, fungal spores, antigens, viruses, plant pollens, toxins, fecal material, or a combination of these (Cundith, Kerth, Jones, McCaskey, & Kuhlers, 2002; Rad-more, 1986; Whyte et al., 2001). When all these substances are distributed in the air, they can serve as a feasible route for food contamination and can ultimately affect the health of both food handlers and consumers (Lutgring et al., 1997). Information on the bioaerosol contamination of food-processing plants is, however, very limited, mainly because of lack of proper equipment, lack of expertise to perform bioaerosol surveys, fear of how the outcomes of such studies will affect various companies, or some combination of these factors. As a result, knowledge of the contribution of the airborne micro-biota to the contamination of food products remains limited.
Although indoor air environments are considered to be protective, they become contaminated with various particles that can be hazardous when concentrations exceed recommended maximum limits: 1,000 CFUs/[m.sup.3] for total number of bioaerosol particles, a limit set by the National Institute of Occupational Safety and Health and the American Conference of Governmental Industrial Hygienists (ACGIH), with the culturable count for total bacteria not to exceed 500 CFUs/[m.sup.3] (Cox & Wathes, 1995; Jensen & Schafer, 1998; Kalogerakis et al., 2005).
A number of authors have recognized poor ventilation systems as possible reservoirs that may distribute bioaerosols in meat-processing plants (Cundith et al., 2002; Whyte et al., 2001). In addition, employees may distribute contaminants through clothes, skin, hair, respiratory tract (coughing and sneezing), fecal matter, and poor hygiene (Chambers, 2001; Cundith et al., 2002; Lutgring et al., 1997). Food handlers are the primary sources of indoor bioaerosols in the food industry, according to Nel and co-authors (Nel, Lues, Buys, & Venter, 2004). Furthermore, airborne microorganisms may be of human origin from purulent discharges of an infected finger or eye; from abscesses, facial eruptions, or nasopharyngeal secretions; or from normal skin (Zadoks et al., 2002). Other sources that are indirectly related to bioaerosols are contaminants from waste handling and disposal, fungal or microbial growth niches in the building, and unsanitary practices, including improper maintenance and poor operating and sanitation. In addition, seasonal and weather-related factors such as geographical location are also known to influence bioaerosols within food-processing environments such as abattoirs (Chang, Chung, Huang, & Su, 2001; Cundith et al., 2002; Lutgring et al., 1997; Pastuszka, Kyaw Thaw Paw, Lis, Wlazlo, & Ulfig, 2000; Ren & Frank, 1992).
Some of the pathogenic bacteria most predominantly found in indoor bioaerosols are members of the Staphylococcus genus because of their ubiquitous nature (Wieser & Busse, 2000). This genus occurs naturally on the skin, as well as on the skin glands and mucous membranes of warm-blooded animals (Nagase et al., 2002a; Nagase et al., 2002b; Wieser & Busse, 2000). Staphylococcus aureus bacteria constitute about 10 percent of the nasal cavity bacteria of healthy humans and occur at levels between 0.01 and 0.1 CFUs/[m.sup.3] in the environment (Sheretz, Bassetti, & Bassetti-Wyss, 2001). Because of their ubiquitous occurrence in nature, staphylococci have been isolated from fresh water, meat, milk, cheese, soil, seawater, dust, and the air (Nel, Lues, Buys, & Venter, 2003; Wieser & Busse, 2000). Although extensive literature exists on the quality and safety of meat, milk, cheese and water, little information, as mentioned before, is available on the microbiological aspects of indoor air associated with red-meat abattoirs (Pastuszka et al., 2000).
The majority of the larger red-meat abattoirs have deboning rooms for the removal of retail cuts from the carcasses. During this stage the product undergoes extensive handling and exposure to surfaces and utensils (Nel et al., 2003). As a result, deboning rooms are prone to several factors that can contribute to the distribution of airborne staphylococci. These include 1) conveyer systems and cutting tables; 2) movement and actions of food handlers, especially through breathing, speaking, sneezing, or coughing; 3) water drains and splashing caused during high-pressure water washing of the floor; 4) the ventilation system; and 5) workers' hands or gloves (Ren & Frank, 1992).
The aim of the study reported here was to quantify the airborne staphylococci and total viable counts in the deboning rooms of selected South African red-meat abattoirs of various sizes and throughput rates. The staphylococci species found in the air are described in general and S. aureus coagulase types in particular were assessed in order to shed light on the airborne distribution of these microorganisms. The authors make suggestions about the role of the air environment as a vector of staphylococci contamination.
Materials and Methods
Bioaerosol samples were collected from four differently graded South African red-meat abattoirs (A, B, C, and D) in the Free State Province according to the old South African System (Van Zyl, 1998). Grade A, B, C, and D abattoirs comprise throughputs of >100, 51-100, 16-50 and 9-15 slaughter units, respectively, where one slaughter unit is equal to 1 bovine animal, 1 horse, 15 pigs, or 15 sheep. Grade E abattoirs, which comprise
During each sampling interval, samples were aseptically collected once an hour from various locations in the deboning room for a period of five hours. They were collected an hour after the beginning of the working shift, and sampling time was based on the busy hours of the morning, when only beef is processed. The majority of the abattoirs continue to process other meat species after the first six hours of the day Samples were collected with a single-stage microbial air sampler (SAS Super 90) (Chang et al., 2001; Clark, Rylander, & Larson, 1983; Cornier, Tremblay, Miriaux, Brochu, & Lovoie, 1990; Donham, Haglind, Perterson, Rylander, & Belin, 1989; Donham, Popendorf, Palmgren, & Larson, 1986; Haglind & Rylander, 1987; Heedrich, Brouwer, Biersteker, & Boleij, 1991; Thorne, Kiekhaefer, Whitten, & Donham, 1992). The air sampler was precalibrated at 28.3 liters per minute (L/min), and all removable components were pre-autoclaved and subsequently disinfected with 70 percent ethanol between sampling runs. The air sampler collects airborne microbes directly onto 55-mm rapid organism detection and counting (RODAC) plates through impaction (Theron, 2003). The collected samples were stored at low temperature during transportation to the laboratory.
For enumeration of total viable counts (TVCs), plate count agar (PCA, Anatech, South Africa) plates were incubated at 25[degrees]C for 72 hours (Vanderzant & Spittstoesser, 1992), while Baird-Parker agar (BPA, Anatech, South Africa) plates were incubated at 35[degrees]C for 48 hours for enumeration of presumptive Staphylococcus spp. (Nikanen & Aalto, 1978). Typical S. aureus colonies were confirmed with the rapid latex agglutination test (Slidex Staph Plus Test Kit, Bio Merieux, South Africa) (Griethuysen, Bes, Etienne, & Kluytmans, 2001).
Staphylococcal Species Identification
Staphylococcus spp. that the rapid latex agglutination test found not to be S. aureus were plated on blood agar and incubated for 18 to 24 hours at 35[degrees]C. These Staphylococcus species were identified with the API-Staph system (several S. aureus samples were also identified for further confirmation) (Nagase et al., 2002a; Nagase et al., 2002b) and APILAB software in accordance with the manufacturer's procedure...