| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
PROCESSING, PRODUCTS, AND FOOD SAFETY |
Unit for Applied Food Science and Bio-Technology, School for Agriculture and Environmental Sciences, Central University of Technology, Free State, Bloemfontein 9300, South Africa
1 Corresponding author: mtheron{at}cut.ac.za
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
|---|
Key Words: bioaerosol • chicken slaughtering • South Africa
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
|---|
Bioaerosols implicated in respiratory-associated hazards have received much attention, but the potential of food-associated microorganisms and foodborne pathogens in bioaerosols to cause food spoilage or food-associated infections needs to be elucidated. Airborne microorganisms have been indicated to cause allergic reactions, irritation of the eyes and upper respiratory tract, respiratory infections, and other symptoms such as fatigue, especially in individuals working in the offloading, receiving, and defeathering areas (Savilahti et al., 2000; Chang et al., 2001; Huang et al., 2002). This study was undertaken to determine the levels and distribution of airborne microorganisms in various processing areas in a high-throughput chicken abattoir during processing, to concomitantly monitor various environmental factors in the different areas over a specific period, and to evaluate their influence on the microbial population associated with the bioaerosols.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
|---|
Air samples were collected from a high-throughput chicken abattoir (±32,000 birds slaughtered per day) situated in the industrial area of Kroonstad in the Free State province, South Africa. This facility employs approximately 400 workers and operates 16 h per day. Operations carried out at this plant include the receiving and killing of birds, scalding, defeathering, evisceration, head and feet removal, spin-chilling and air-chilling of carcasses, whole bird packaging, and portion packaging of the final product (Figure 1
).
|
Samples were collected in duplicate at monthly intervals over a 4-mo period (August to November) from 6 processing areas, which included receiving-killing, de-feathering, evisceration, air-chilling, packaging, and dispatch (Figure 1
). Bioaerosol samples were collected by impaction on agar plates using a SAS Super 90 air sampler (PBI Int., Milan, Italy) that collects airborne microorganisms onto 55-mm Rodac plates [Merck (Pty.) Ltd., Modderfontein, South Africa]. The air sampler was pre-calibrated and adjusted to a flow rate of 28 L/min. All removable parts of the air sampler were sterilized by autoclaving before sampling and sterilized between samples with 70% ethanol.
Isolation of Microorganisms
Samples were analyzed for the presence of S. aureus, coliforms, E. coli, P. aeruginosa, L. monocytogenes, B. cereus, Salmonella spp., and fungi.
Enumeration of S. aureus was done on Baird Parker Agar (Biolab Diagnostics, Merck, Wadeville, South Africa) after 48 h of incubation at 36°C. Typical S. aureus colonies were recognized as gray-black and shiny, with clear zones surrounding the colonies.
Violet red bile MUG agar (Biolab Diagnostics) was used to isolate E. coli and other coliforms (International Standards Organization, 1993). Inoculated plates were incubated at 37°C for 24 h; E. coli colonies were detected as dark red and coliforms as small pink colonies.
Cetrimide Agar (Biolab Diagnostics) with added glycerol was used for culturing and enumerating P. aeruginosa. After 48 h of incubation at 25°C, typical yellowish P. aeruginosa colonies were identified.
Enumeration of L. monocytogenes was performed on Listeria selective agar [Merck (Pty.) Ltd.], and plates were incubated at 37°C for 48 h. Listeria monocytogenes colonies were recognized as greenish-gray with a black core and halo.
Bacillus cereus selective agar (Scharlau Chemie SA, Barcelona, Spain) was used for culturing and enumeration of B. cereus. Agar plates were incubated at 30°C for 18 to 24 h and examined for typical B. cereus colonies, recognized as large (±5mm in diameter) turquoise-peacock blue colonies and small zones of egg yolk precipitate.
Brilliant green agar [Merck (Pty.) Ltd.] plates were inoculated for culturing and enumerating Salmonella spp. and incubated at 42°C for 48 h. Salmonella colonies are typically reddish-pink opaque and surrounded by brilliant red zones.
Potato dextrose agar (Biolab Diagnostics) plates, acidified with tartaric acid to pH 3.5, were inoculated for culturing and enumeration of fungi and incubated at 25°C for 5 d. Yellowish-white colonies were identified as yeasts, whereas mold growth was recognized by its mycelial appearance.
Control Strains
Bacterial strains included as controls were S. aureus ATCC 25923, E. coli ATCC 25922, P. aeruginosa ATCC 27853, L. monocytogenes ATCC 19117, B. cereus ATCC 14579, and Salmonella enteritidis ATCC 13076.
Environmental Parameters
Temperature, RH, wind velocity, and airborne particulates were evaluated from August to November (winter to spring), and the readings were done in triplicate at a height of 1.5 m above the floor (Venter et al., 2004). Direct reading instruments used for monitoring were as follows: 1) area heat stress monitor (QUESTemp°15; Quest Technologies Inc., Oconomowac, WI) to measure temperature as well as RH, 2) airflow anemometer (Airflow Instrumentation LCA 6000 VT; High Wycombe, Buckinghamsire, UK) for measuring wind velocity, and 3) handheld aerosol monitor (1005/1060; PPM Enterprises Inc., Knoxville, KY) for determining airborne particulates (Venter et al., 2004).
Statistical Processing
Data were represented as the means of samples collected during the 4 sampling months at 3 different points in each area. Box plots were constructed to show the 25th and 75th percentiles as well as the means. For normally distributed data, general ANOVA and correlations were used to measure significant differences among means of the environmental factors and bioaerosols. The data consisted of 4 observations (August to November) with duplicate samples. Stepwise regression was used in determining the significance of the independent variables (environmental factors) in various regression models. The t-statistics indicated the independent variable to be significant if the related P-value < 0.05. A statistical program, STATISTICA Base (version 7.1, StatSoft Inc., Tulsa, OK), was used to calculate r- and P-values.
|
RESULTS AND DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
|---|
, panels A to H). There was a definite decline in the numbers from the receiving-killing area downstream toward the dispatch area, whereas the air-chilling area had the lowest microbial counts. The high prevalence of airborne microorganisms in the receiving-killing area is attributed to the flapping of wings and the excessive movements of the birds (Lutgring et al., 1997).
|
, panel A), except in the air-chilling area, where average counts were 3.9 x 101 cfu/m3. Due to its clump-like structure, S. aureus is able to readily adhere to surfaces (Lutgring et al., 1997; Plaatjies, 2004), and in previous studies, the microbiota from the receiving area were described as consisting of mainly Staphylococcus spp. (Holt et al., 1994; Ellerbroek, 1997).
Airborne fungi counts of up to 1.3 x 104 and 1.2 x 104 cfu/m3 were detected in the receiving-killing and defeathering areas (Figure 2, panel B). Fungal spores are very small, relatively resistant to drying, and are readily aerosolized. Although clear correlations between the presence of airborne fungi and their effect on human health have not unambiguously been identified in epidemiological studies, indoor fungi is regarded as a potential health hazard (Bornehag et al., 2001; Burge, 2001).
The highest total coliform counts were found in the defeathering area (average 1.6 x 103 cfu/m3; Figure 2, panel C), whereas E. coli predominated in air samples from the packaging area (average count 1.5 x 103 cfu/m3; Figure 2, panel D). Geornaras et al. (1996) also reported on the dominance of E. coli in a similar processing plant, comprising 95.6 and 93.7% of the isolates from the de-feathering and packaging areas, respectively. Escherichia coli is exclusively a large-intestine organism and is used in gauging the level of processing or postprocessing contamination by fecal sources (Levinson and Jawetz, 1994), whereas the other members of the coliforms are found in the environment also and are more commonly used as indicators for assessing microbial proliferation in foods (Department of Health, 2000). The relatively high prevalence of E. coli in the air of the receiving-killing and the defeathering areas could have resulted from fecal particulates spreading by the flapping of wings. Fecal contamination is often caused when the lower intestinal tract is ruptured during processing, resulting in the release of contaminating fecal material and the consequent high counts of E. coli in the postprocessing areas. However, if handled in the correct manner, birds should have a minimum of waste material in their digestive tracts (Summer, 2004).
In the processing flow, the highest counts of presumptive Salmonella spp. were detected in the first 3 areas (averages 5.5 x 103, 3.3 x 103, and 3.8 x 103 cfu/m3). In the last 2 areas downstream (packaging and dispatch), average counts of 2.3 x 103 cfu/m3 and 5.6 x 102 cfu/m3 were recorded, whereas the counts found in the air-chilling area were 1.2 x 101 cfu/m3 (Figure 2, panel H). Apart from false positive counts of Salmonella in the receiving-killing area reported by Gallo et al. (1988), Salmonella has seldom been isolated from any of these areas (Lutgring et al., 1997). High prevalence of P. aeruginosa was detected in the receiving-killing area (1.9 x 103 cfu/m3; Figure 2, panel E) and could have been introduced upon the arrival of the birds at the processing plant. Airborne P. aeruginosa was also found in the evisceration and the packaging areas, with counts ranging from 1.5 x 102 to 3.3 x 102 cfu/m3 (Figure 3, panel E). Pseudomonas spp. are often found along with other gram-negative bacilli in poultry meat and has been called one of the most notorious bacteria to cause spoilage of refrigerated foods, originating predominantly from water or soil on equipment (Geornaras et al., 1996; Ellerbroek, 1997; Buys et al., 2000).
|
, panel F). Although Listeria spp. are psychrotrophic and proliferation is not inhibited by normal refrigeration (Rammel, 2003), L. monocytogenes counts were lowest in the air-chilling area. This organism is nonspore-forming, notably resistant to pH fluctuations, high salt concentrations, and desiccation, and the majority of the more than 22 species identified are found in food-processing plants (Ryser and Marth, 1991; Miller, 1992). Bacillus cereus counts in the air samples of the receiving-killing and the defeathering areas were relatively high (1.8 x 104 and 8.04 x 103 cfu/m3, respectively), which again could be attributed to wing flapping (Figure 2, panel G). Bacillus cereus is a common airborne and dustborne contaminant that readily multiplies in meat products. The production of spores enable these organisms to withstand unfavorable conditions such as low temperatures or heat and may improve the chances of B. cereus to be present in high numbers (Stevenson and Segner, 1992; Whyte et al., 2001). In a study done by Nel et al. (2003), B. cereus levels were reported to rapidly increase when a product was exposed to poor handling and processing procedures. The most common airborne Bacillus spp. were, for many years, dismissed as harmless contaminants with weak to nonexistent pathogenicity. However, infections are increasingly reported, and because the spores are abundant in the environment and usual methods of disinfection and antisepsis are powerless in controlling them, these organisms are becoming a serious health risk (Talaro and Talaro, 1999). Microorganisms detected in the indoor air of processing plants are frequently found to be derived from humans but may also emanate from intramural sources or enter from the outside environment. High concentrations of microorganisms may reflect on insufficient ventilation in relation to the number of persons and activities involved (Verhoeff et al., 1992; Otten and Burge, 1999). This is often the result of ventilation systems that are not properly maintained and that generate excessive condensation and moisture (Law et al., 2001; Lee et al., 2002; Guo et al., 2004). The importance of the airflow pattern in food processing plants can be overlooked, and ventilation systems are sometimes designed without taking into consideration the settling of particles (Holmberg and Chen, 2003). In a room with a low air exchange rate, microbial concentrations have been reported to be twice as high as in rooms with higher exchange rates (Barlett et al., 1999). Buildings such as the poultry slaughtering facility should, therefore, be designed to achieve proper air distribution and to control the dispersal of particles and microbes (Goodman, 1999).
The overall RH in area 1 (receiving-killing) reached an average of 71% (Figure 3, panel A), which could have been influenced by rainy conditions prevailing during the second sampling interval. The evisceration (77%) and packaging (64%) areas had the highest mean RH. Multiple processes carried out in the relatively small evisceration area, which included the final washing of carcasses and the weighing and packaging of livers, feet, and heads, could contribute to elevated RH. It is preferred that RH not exceed 100%, which would elevate condensation processes and cause high levels of discomfort (Wang et al., 2001; Cappella, 2004; Williams, 2004). The South African Bureau of Standards (2001) also stated that the RH should be controlled to protect food quality. Although the majority of microorganisms survive better in an environment with high RH, B. cereus appears to prefer a dry environment, because RH and B. cereus counts in the receiving-killing area indicated a strong negative relationship (r = –0.9838; P-value = 0.016). Relative humidity also had a negative effect on the dispersal of airborne Bacillus spores. The presence of P. aeruginosa, on the other hand, showed an increase associated with an increase in RH (r = 0.9687; P = 0.031).
Average temperatures in the receiving-killing and de-feathering areas were below 18°C, and in the packaging and dispatch areas, they were below 21 and 22°C (Figure 3, panel B). The evisceration area had an average temperature of 23°C and the air-chiller 4°C throughout the 4-mo sampling intervals. According to poultry regulation, meat should be subjected to uninterrupted chilling to reduce the core temperature of chilled meat to 4°C within 12 h, and meat that is being frozen may not be removed from the freezer before a core temperature of –12°C has been reached (Republic of South Africa, 2000). In addition to the microorganisms being inhibited at low temperatures, their adhesion to surfaces is also influenced by temperature (Czechowski, 1990; Pompermayer and Gaylarde, 2000). By employing the statistical program STATISTICA Base (StatSoft Inc.), a positive correlation (r = 0.9738; P = 0.026) was observed between the temperature and S. aureus counts in the receiving-killing area and between fungi counts and temperature in the evisceration area (r = 0.9761; P = 0.024).
An important function of airflow or wind velocity is to ensure proper mixing of the temperature and humidity throughout the processing environment (Godish, 1995; Goodman, 1999). The wind velocity in the receiving-killing area reached an average of 3.7 m/s (Figure 3, panel C), which could have resulted from an enhancing effect by the air from the outside environment. Elevated wind speed could then result in the dispersal of airborne particles (Holmberg and Chen, 2003). Because low air exchange affects humidity that could lead to high dust concentrations, the air supply to processing areas with a high prevalence of contaminants should be filtered to at least 2 µm (Goodman, 1999; South African Bureau of Standards, 2001). The majority of airborne microorganisms observed in this study correlated with the airflow in the receiving-killing area, and airflow also contributed to the dispersal of B. cereus spores. In the defeathering area, however, a negative correlation was found with B. cereus counts. This was also evident with P. aeruginosa found in the packaging areas.
The highest concentrations of airborne particulates were measured in the receiving-killing and defeathering areas (3.76 and 3.83 mg/m3; Figure 3, panel D). The high levels of particulates in the receiving-killing area could again be associated with wing flapping, whereas the high concentrations in the defeathering area could be caused by the absence of a physical segregation between the receiving-killing and defeathering area. More variation was demonstrated over time with the airborne particulates than with the other 3 parameters. A strong correlation was found between airborne particulates and the presence of Salmonella spp. in the receiving-killing area (r = 0.9439; P = 0.056). Because Salmonella has rarely been isolated from other processing areas than receiving-killing, it is suggested that this organism could have been introduced into the facility via dust spread by the birds (Mitchell, 2000). Airborne particulates were also the only environmental factor to have a significant influence on the dispersal of coliforms (r = 0.9869; P-value = 0.013) or Salmonella spp. (r = 0.9867; P = 0.014) in the air-chilling area.
The RH and airborne particulates demonstrated significant influence on the presence of microorganisms. With B. cereus as a selected independent variable, the RH in the receiving-killing area showed significance at P = 0.0167 and the airborne particulates at P = 0.0032. The values for P. aeruginosa (P = 0.0016) and B. cereus (P = 0.0633) in the receiving-killing area were significantly different when airflow was used as a parameter estimate. The presence of S. aureus, fungi, and coliforms in the defeathering area could not be correlated with the environmental factors monitored. In the packaging area, S. aureus, fungi, coliforms, L. monocytogenes, B. cereus, and Salmonella spp. showed no linear relationship with any of the environmental factors, whereas airflow in the packaging area with general ANOVA showed a linear relationship between P. aeruginosa and airflow in the same area (P = 0.0077). Staphylococcus aureus and coliforms in the dispatch area showed no significant difference, because no variables met the 0.5 significance level in this area of the abattoir. Correlations between environmental factors and bioaerosol composition have previously been demonstrated by Venter et al. (2004) in chicken egg production plants, and the implications of parameters such as RH, temperature, wind velocity, and airborne particulates and the relationship with the airborne microbial loads require further investigations.
In conclusion, the elevated counts of airborne microorganisms observed in the receiving-killing and the de-feathering areas emphasize the importance of controlling the microbial levels before processing, in addition to the control measures implemented in the processing facility. Opposed to well-documented hazards of bioaerosols containing respiratory-associated microorganisms, the presence of food-associated microorganisms and foodborne pathogens in bioaerosols requires further in-depth studies, concerning their potential role in food spoilage and food-associated infections. In a poultry-slaughtering facility, pathogens that are known to become airborne should be reduced to minimal levels to limit the carryover from areas known to generate high counts to downstream areas where the product is exposed to air and surface contamination. Poultry products are prone to microbial contamination, and the focus should not only be on surface cleaning and disinfecting of utensils, but also on reducing or eliminating microbial air contamination, and adaptations should take the climate and other environmental characteristics of the region into consideration while addressing the hygiene requirements. Suggestions made on the findings in this study may contribute to improved practices during raw poultry processing.
Received for publication April 25, 2006. Accepted for publication July 18, 2006.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
|---|
Bennet, R. W., and G. A. Lancette. 1995. Staphylococcus aureus. Pages 1–5 in Bacteriological Analytical Manual. 8th ed. CFSAN, College Park, MD.
Borch, E., and P. Arinder. 2002. Bacteriological safety issues in red meat and ready-to-eat meat products, as well as control measures. Meat Sci. 62:381–390.
Bornehag, C. G., G. Blomquist, F. Gyntelberg, B. Jarvholm, P. Malmberg, L. Nordvall, A. Nielson, G. Pershagen, and J. Sundrell. 2001. Dampness in buildings and health. Nordic interdisciplinary review of the scientific evidence on association between exposure to "dampness" in buildings and health effects. Indoor Air 11:72–86.[Web of Science][Medline]
Burge, H. A. 2001. Fungi: Toxic killers or unavoidable nuisances? Ann. Allergy Asthma Immunol. 87:52–56.
Buys, E. M., G. L. Nortjé, P. J. Jooste, and A. Von Holy. 2000. Bacterial population associated with bulk-packaged beef supplemented with dietary vitamin E. Int. J. Food Microbiol. 56:239–244.[Web of Science][Medline]
Cappella, C. 2004. Subject: What is the best humidity for indoors? http://www.usdatoday.com Accessed Oct. 2004.
Chang, C. W., H. Chung, C. F. Huang, and J. H. J. Su. 2001. Exposure of workers to airborne microorganisms in open-air swine houses. Appl. Environ. Microbiol. 67:155–161.
Czechowski, M. H. 1990. Gasket and stainless steel surfaces sanitation: Environmental factors affecting bacterial attachment. Austr. J. Chem. 15:38–39.
Department of Health. 2000. Role and Responsibility of the Public Health Sector in South Africa Regarding Food Safety Control. Dept. Health, Pretoria, South Africa.
Donnelly, C. W. 1994. Listeria monocytogenes. Pages 215–252 in Foodborne Diseases Handbook. Volume 1. Y. H. Hui, J. R. Gorham, K. D. Murrel, and D. O. Cliver, ed. Marcel Dekker Inc., New York, NY.
Eisel, W. G., R. H. Lintion, and P. M. Muriana. 1997. A survey of microbial levels for incoming raw beef, environmental sources, and ground beef in a red meat processing plant. Food Microbiol. 14:273–282.
Ellerbroek, L. 1997. Airborne microflora in poultry slaughtering establishments. Food Microbiol. 14:527–531.
Forsythe, S. J. 2000. The Microbiology of Safe Food. Blackwell Sci. Ltd., Oxford, UK.
Gallo, L., R. E. Schmitt, and W. Schmidt-Lorenz. 1988. Microbial spoilage of refrigerated fresh broilers. Lebensm. Wiss. und Technol. 21:216–223.
Geornaras, I., A. E. de Jesus, E. van Zyl, and A. Von Holy. 1995. Microbiological survey of a South African poultry processing plant. J. Basic Microbiol. 35:73–82.[Web of Science][Medline]
Geornaras, I., A. E. de Jesus, E. van Zyl, and A. Von Holy. 1996. Bacterial populations associated with poultry processing in a South African abattoir. Food Microbiol. 13:457–465.
Godish, T. 1995. Sick buildings: Definition, Diagnosis, and Mitigation. Lewis Publishers, Boca Raton, FL.
Goodman, J. 1999. Relationship between humidity and body feelings of cold and warmth. http://www.madsci.org Accessed October 2004.
Guo, H., S. C. Lee, and L. Y. Chan. 2004. Indoor air quality investigation at air-conditioned and non-air-conditioned markets in Hong Kong. Sci. Total Environ. 323:87–98.[Medline]
Holmberg, S., and Q. Chen. 2003. Air flow and particle control with different ventilation systems in a classroom. Indoor Air 13:200–204.[Web of Science][Medline]
Holt, J. G., N. R. Kriel, P. H. A. Sneath, J. T. Staley, and S. T. Williams. 1994. Bergey’s Manual of Determinative Bacteriology. 9th ed. Williams and Wilkins, Baltimore, MD.
Huang, C., C. Lee, F. Li, Y. Ma, and H. Su. 2002. The seasonal distribution of bioaerosols in municipal landfill sites: A 3-year study. Atmos. Environ. 36:4385–4395.
International Standards Organization. 1993. ISO 7402. General Guidance for the Enumeration of Enterobacteriaceae without Resuscitation-MPN Technique and Colony-Count Technique. 2nd ed. Int. Stand. Org., Geneva, Switzerland.
Law, A. K. Y., C. K. Chau, and G. Y. S. Chan. 2001. Characteristics of bioaerosol profile in office buildings in Hong Kong. Build. Environ. 36:527–541.
Lee, S. C., H. Guo, W. M. Li, and L. Y. Chan. 2002. Inter-comparison of air pollutant concentrations in different indoor environments in Hong Kong. Atmosph. Environ. 36:1929–1940.
Levinson, W. E., and E. Jawetz. 1994. Medical Microbiology and Immunology. 3rd edition. Prentice-Hall Int. Inc., Englewood Cliffs, NJ.
Lutgring, K. R., R. H. Linton, N. J. Zimmerman, M. Peugh, and A. J. Heber. 1997. Distribution and quantification of bioaerosols in poultry-slaughtering plants. J. Food Prot. 60:804–810.
Miller, A. J. 1992. Combined water activity and solute effects on growth and survival of Listeria monocytogenes. J. Food Prot. 55:414–418.
Mitchell, B. 2000. Zapping airborne Salmonella and dust. Agric. Res. Mag. 48:20–21.
Nel, S., J. F. R. Lues, E. Buys, and P. Venter. 2003. Bacterial populations associated with meat from the deboning room of a high throughput red meat abattoir. Meat Sci. 66:667–674.
Otten, J. A., and H. A. Burge. 1999. Bacteria. Pages 18-1 to 18–10 in Bioaerosols, assessment and control. Am. Conf. Gov. Ind. Hyg., Cincinnati, OH. ACGIH, Cincinnati, OH.
Plaatjies, Z. 2004. The occurrence of Staphylococcus species in the deboning room of a high throughput abattoir. MS thesis. Cent. Univ. Technol., Free State, Bloemfontein, South Africa.
Pompermayer, D. M. C., and C. C. Gaylarde. 2000. The influence of temperature on the adhesion of mixed cultures of Staphylococcus aureus and Escherichia coli to polypropylene. Food Microbiol. 17:361–365.
Raj, A. B., L. J. Wilkins, M. O’Callaghan, and A. J. Phillips. 2001. Effect of electrical stun/kill method, interval between killing and neck cutting and blood vessels cut on blood loss and meat quality in broilers. Br. Poult. Sci. 42:51–56.[Web of Science][Medline]
Rammel, J. M. 2003. Subject: New food safety measures to control your facility’s environment. http://www.iafa/ways-fresh.com/listeria.html Accessed Aug. 2003.
Republic of South Africa. 2000. Meat Safety Act (Act 40 of 2000). Gov. Printer, Dept. Health, Pretoria, South Africa.
Rylander, R., V. Hsieh, and C. Courteheuse. 1994. The first case of sick building syndrome in Switzerland. Indoor Environ. 3:159–162.
Ryser, E. T., and E. H. Marth. 1991. Listeria, Listeriosis and Food Safety. Marcel Dekker Inc., New York, NY.
Savilahti, R., J. Uitti, P. Laippala, T. Husman, and P. Roti. 2000. Respiratory morbidity among children following renovation of a water-damaged school. Arch. Environ. Health 55:405–410.[Web of Science][Medline]
Shale, K. 2004. The prevalence of meat-borne and airborne staphylococci in deboning areas of low and high-throughput red meat abattoirs. PhD Thesis. Cent. Univ. Technol., Free State, Bloemfontein, South Africa.
South African Bur. Stand. 1049/SABS 049. 2001. Code of Practice: Food Hygiene Management. 3rd edition. South African Bur. Stand., Pretoria, South Africa.
Stevenson, K. E., and W. P. Segner. 1992. Mesophilic aerobic sporeformers. Pages 265–274 in Compendium of Methods for the Microbiological Examination of Foods. 3rd ed. C. Vanderzant and D. F. Splittstoesser, ed. APHA, Washington, DC.
Summer, J. 2004. Faecal contamination during processing. Poult. Sci. 66:62–67.
Talaro, K. P., and A. Talaro. 1999. Pages 564–569 in Foundations in Microbiology. 3rd ed. McGraw-Hill, New York, NY.
Thaler, A. M. 1999. The United States perspective towards poultry slaughter. Poult. Sci. 78:298–301.
Turcsan, Z., L. Vargal, J. Szigeti, I. Csurak, and M. Szalai. 2003. Effects of electrical stunning frequency and voltage combinations on the presence of engorged blood vessels in goose liver. Poult. Sci. 82:1816–1819.
Venter, P., J. F. R. Lues, and H. Theron. 2004. Quantification of bioaerosols in automated chicken egg production plants. Poult. Sci. 83:1226–1231.
Verhoeff, A. P., J. H. van Wiljnen, B. Brunekreef, P. Fischer, E. S. van Reenen-Hoekstra, and R. A. Samson. 1992. Presence of viable mould propagules in indoor air in relation to house damp and outdoor air. Allergy 47:83–91.[Web of Science][Medline]
Wang, Z., T. Reponen, S. A. Grinshpun, R. L. Górny, and K. Willeke. 2001. Effect of sampling time and air humidity on the bioefficiency of filter samplers for bioaerosol collection. J. Aerosol Sci. 32:661–674.
Whyte, R. T. 2002. Occupational exposure of poultry stockmen in current barn systems for egg production in the United Kingdom. Br. Poult. Sci. 43:364–373.[Web of Science][Medline]
Whyte, P., J. D. Collins, K. McGill, C. Monahan, and H. O’Mahony. 2001. Distribution and prevalence of airborne microorganisms in three commercial poultry processing plants. J. Food Prot. 64:388–391.[Web of Science][Medline]
Williams, J. 2004. Subject: Understanding humidity. http://www.usatoday.com Accessed Oct. 2004.
This article has been cited by other articles:
|
|
 |
|
  K. Fallschissel, P. Kampfer, and U. Jackel Direct Detection of Salmonella Cells in the Air of Livestock Stables by Real-Time PCR Ann. Hyg., August 12, 2009; (2009) mep060v1. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 V. Lopez, S. Ortiz, A. Corujo, P. Lopez, D. Poza, J. Navas, R. Moreno, and J. V. Martinez-Suarez Different Contamination Patterns of Lineage I and II Strains of Listeria monocytogenes in a Spanish Broiler Abattoir Poult. Sci., September 1, 2008; 87(9): 1874 - 1882. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
