Airborne bacteria and mold in slaughterhouse facilities

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Contamination of meat products by microorganisms such as airborne bacteria and mold is a major economic problem in the meat industry. In the past it was thought that food products were contaminated when they came in contact with contaminated surfaces, but now it is known that additional product contamination occurs from contact with airborne bacteria.

There are several pathways in which pathogenic airborne bacteria and spoilage organisms can be introduced to products. It is known that contamination can occur at various points during the slaughter process, cold storage, and processing of meat animals.

One potential source of contamination that is often overlooked is air. Air is a potential source of contamination by pathogenic and spoilage organisms in meat processing plants and should be considered a processing critical control point.

Unsanitary environmental conditions in food processing plants can occur due to suspended bacterial particles in the air. These biological particles are microscopic, with a diameter of 0.5 to 50 μm and are suspended in the air as an aerosol. Airborne contaminants are also known as bioaerosols and include bacteria, fungi, viruses and pollen. These may be present in the air as solid (dust) or as liquid (condensation and water).

An aerosol is a two-phase system of gaseous phase (air) and particulate matter (dust, pathogens), thus making an important bacterial vehicle. Pathogenic bacteria attach to dust particles and condensation, and travel around the processing facility. This contaminated air comes in contact with food products, containers, equipment and other food contact surfaces during processing.

It is impossible to keep airborne bacteria, yeast and mold in food processing areas at a zero level. Some of the major sources of contamination in food processing facilities are wastewater, rinse water and spilled product that become aerosolized. Airborne bacteria, yeast and mold are generated in processing facilities by heating, ventilation and air conditioning systems (HVAC).

These systems contribute airborne microorganisms under normal operation because they provide fertile areas for growth due to moisture. Worker activity, equipment operation, sink and floor drains, and high pressure spraying are also major sources of bioaerosols. Worker activity, talking, sneezing and coughing create dust particles and air disturbances creating airborne microorganisms. The workers’ contribution of airborne bacteria depends on their health, condition of clothing, hygiene and location in processing facility.

Equipment operation contributes to variations in microorganism levels. Airborne bacteria also increase with the use of conveyor systems which cause bacterial aerosols that adhere to conveyor surfaces. Barriers like walls and doors are used to separate clean and unclean areas. Sink and floor drains can harbor microorganisms because they are humid and contain nutrients from wastewater which provide a fertile growth environment.

Flooding of drains causes microorganisms on the surface to become aerosolized and air disperses them, causing increased levels of aerosolized bacteria in the food processing facility. High pressure spraying also causes an increased level of aerosolized bacteria after spraying.

Intense husbandry practices and long term residence of cattle in feedlots and pens provide great opportunity for microorganisms to affix to hoofs and hides. Animals entering a slaughter facility have a vast population of aerobic microorganisms on their hide, hooves and inside their intestinal tract, while the internal surface of carcasses is generally considered to be sterile.

It is generally agreed that the majority of microorganisms on a dressed red meat carcass are directly transferred from the contaminated hide and ruptured gastrointestinal tract. Bacterial transfer to the carcass also occurs by aerosols, dust generation, workers hands, and the contact of the hide with the exposed tissue. The majority of carcass contamination occurs during slaughtering and dressing procedures.

Research regarding airborne bacteria contamination levels in meat processing facilities indicates airborne microbes are a potential source of microbiological contamination in various meat products.

The majority of the Gram negative airborne bacteria usually isolated during slaughtering are from the Enterobacteriaceae and Pseudomonadaceae family. Most of the Gram positive airborne bacteria isolated during slaughtering are Staphylococcus, Microbacterium, Bacillus and Micrococcus species.

The potentially pathogenic microorganisms usually found in the air sampling areas and on the carcasses are Escherichia coli, Salmonella spp., Shigella spp., Staphylococcus spp. and Bacillus spp. and the spoilage microorganisms are Moraxella spp., Pseudomonas spp., Acinetobacter spp., Brochothrix spp. and Micrococcus spp. According to the research, the isolation of various organisms, including Staphylococcus, Escherichia, and Salmonella species, from both air samples and carcass swabs during slaughtering supports the theory that bioaerosols transport bacteria and contribute to the contamination of pork and beef carcasses.

There are various methods for the detection of viable airborne bacteria and other microorganisms. The quantitative determination of airborne microorganisms is possible by sedimentation, impaction on solid surfaces, impingement in liquids, filtration, centrifugation, electrostatic precipitation and thermal precipitation.

Swabbing of equipment is typically used to determine the sanitation level of food processing plants. This method does not always provide an effective enumeration of airborne contaminants.

Air sampling is more effective because it collects aerosols settled on equipment and food contact surfaces. Through air sampling, food processing facilities can identify airborne contamination due to air contact with food products. Ideally, an air sampler would be able to collect all of the viable microorganisms per unit volume of air, but this is not possible because not all airborne cells can be physically separated from the air without killing them during sampling.

The majority of air samplers used in the food industry use impaction as the method for collecting bioaerosols. Impaction methods use the inertia of particles to separate them from the air currents. Impactors collect airborne microorganisms onto an agar surface or an adhesive coated surface with the use of a vacuum. An impactor consists of an air jet that is directed over the impaction surface causing the particle to collide and stick to the surface.

There are two types of impactors: slit (i.e. STA) or sieve (i.e. Andersen sampler) samplers. A slit sampler is cylindrical in shape and has a tapered slit tube that creates a jet stream when an air samples is pulled by a vacuum. The air sample is collected onto an agar plate which is rotating on a turn table to create an even distribution of particles. A slit sampler requires a vacuum to draw a constant flow rate of usually 28.3 liters per minute.

Sieve samplers function by drawing air (i.e. 28.3 l/min) through a metal plate with many small holes. Air particles impact on the agar surface which is a few millimeters below the metal sieve.

Impaction methods obtain higher recovery rates than other air sampling methods and are used when bioaerosol levels are expected to be low. This method results in a low sampling stress and after collection no further manipulation is needed because particles are on agar plates. Impactors possess relatively high sampling efficiencies, are rugged and simple to operate.

As per the research studies, it is important to control contaminants in the air of slaughtering facilities. Airborne contaminants cause human illness due to ingestion of contaminated foods and also reduce product shelf life resulting in an economic loss. According to the Food and Drug Administration (FDA), the food industry must reduce product contamination by reducing airborne microorganisms.

If you are considering testing for the airborne bacteria or mould in your slaughterhouse facility, contacting Mold & Bacteria Consulting Laboratories would be a good choice. Our analysts are trained on air sampling methods and detection of airborne bacteria and moulds. You can call our Ontario, Mississauga office at 905-290-9101 or the British Columbia, Burnaby office at 604-435-6555 and see how we can help.



G.H.C.Sutton. 2004. Enumeration of Total Airborne Bacteria, Yeast and Mold Contaminants and Identification of Escherichia coli O157:H7, Listeria Spp., Salmonella Spp., and Staphylococcus Spp. in a Beef and Pork Slaughter Facility. University of Florida: 1-141.

M.Dobeic, E.Kenda, J.Mičunovič, I.Zdovc. 2011. Airborne Listeria spp. in the Red Meat Processing Industry, Czech J.Food Sci., 29 (4): 441-447.

C.J.Cundith, C.R.Kerth, W.R.Jones, T.A.McCaskey, D.L.Kuhlers. 2002. Air-cleaning Systems Effectiveness for Control of Airborne Microbes in a Meat-processing Plant. Food Microbiology and Safety: 1-5.

T.M.Rahkio, H.J.Korkeala. 1997. Airborne Bacteria and Carcass Contamination in Slaughterhouses. J. Food Prot. 60 (1): 38-42.

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Dr Jackson Kung'u
Dr. Jackson Kung’u is a Microbiologist who has specialized in the field of mycology (the study of moulds and yeasts). He is a member of the Mycological Society of America. He graduated from the University of Kent at Canterbury, UK, with a Masters degree in Fungal Technology and a PhD in Microbiology. He has published several research papers in international scientific journals. Jackson has analyzed thousands of mould samples from across Canada. He also regularly teaches a course on how to recognize mould, perform effective sampling and interpret laboratory results. Jackson provides how-to advice on mould and bacteria issues. Get more information about indoor mould and bacteria at
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