Many scientific sources agree - the processing environment can be a primary source of L. monocytogenes. The ability of the organism to survive low temperatures means that even in chilled environments, any Listeria present will carry on multiplying. Low numbers of cells in inaccessible places provide a hidden reservoir that can continually cause recontamination after cleaning has been carried out. Another of the features of Listeria is that it is better able to withstand drying than many bacteria. Again this means it can persist in low moisture environments, so it can survive after being transferred by aerosols or in dust and re-contaminate the environment. Together these properties explain why it can become persistent in factories.
While product testing is important, the focus in a manufacturer should be to prevent contamination and this is where maintenance plays a significant role through the hygienic design and construction of the plant. Hygienically designed, correctly installed and operated equipment should reduce the number of harbourage sites or niches while preventative maintenance of surfaces will minimise cracks and exposed rough areas that could provide growth areas.
Listeria is quite versatile in using different types of nutrients. In nature it grows equally well on decaying plant matter or in an animal gut. In the food factory, therefore, lots of different types of food residues can provide the appropriate nutrients for growth. This feature means that it can often be found colonising food production equipment, such as chopping blades and vacuum packing equipment and it can also colonise chillers and refrigeration units. Even food grade lubricants can allow the survival and even growth of microorganisms, including Listeria.
The food safety team should ensure that all potential hazards that could impact on food safety are identified and controlled. During the identification of hazards, the potential contamination from lubricants, greases and other maintenance related chemicals in the processing environment should be addressed. The control measure in most cases would be to replace unsuitable chemicals with suitable food grade lubricants.
For confidence that lubricants used are in fact suitable to use in a food facility, an internationally recognized classification system should be consulted. Lubricants manufactured for use in a food facility are classified as H1, H2 and H3 types. The classification is based on where they are used and the potential for direct food contacts. H1 lubricants are often referred to as “above the line” lubricants—used on equipment or mechanical components where there is the possibility they may drip onto the food production line below and cause incidental contact. They comply with food regulations because they are physiologically inert, tasteless and odorless. They are suitable for incidental, technically unavoidable contact with a food product up to 10ppm.
H1 lubricants may be safely used for handling, canning, bottling, blending, chilling, cooking, cutting, slicing and peeling on machinery components such as pumps, mixers, gearboxes, chain drives and conveyor belts.
H2 and H3 lubes, on the other hand, are often referred to as “below the line,” where there is little or no chance of the lubricant being sprayed or splashed onto the food line above.
Selecting the correct lubricant is essential in removing the chemical hazard but could introduce the potential for a biological hazard – Listeria monocytogenes.
Synthetic and mineral oil based lubricants used in the food industry have been shown to allow for the survival and growth of Listeria monocytogenes. In a 2007 study on the Finnish food industry it was shown that lubricants used in maintaining the equipment may act as contamination vehicles of L. monocytogenes. Water-based chain conveyor lubricants are also susceptible to microbial contamination, including environmental pathogens such as L. monocytogenes. The survival of microbes in lubricants has been reported to be enhanced when the lubricants are contaminated with organic material and water. In a 2012 study, the survival of three L. monocytogenes strains in eight H1 lubricants, seven greases and one oil, applicable for food-processing machinery. None of the native lubricants contained Listeria spp. above the detection limit of 103 cfu/g. In artificially contaminated lubricants, the viable counts of different L. monocytogenes strains decreased by more than 99.9% within 7 days, and the reduction rates were found to dependent on the composition of the respective lubricant as well as on the L. monocytogenes strain.
The FAO and many industry guidelines advise that lubricants should be preserved. The addition of antimicrobial substances such as glutaraldehyde, sodium benzoate or isothiazoline has been reported to inhibit the growth of microbes. When selecting the correct lubricant ensure these are appropriately preserved to ensure these will be listericidal.
So, make sure you ask ALL the right questions when selecting your lubricants to effectively control chemical AND and ensure maintenance team members are trained on biological hazards and the importance of cleaning drip trays and taking all measures possible to preventing cross contamination of lubricants.
Lubricants can be contaminated with water, organic material, residues of other lubricants, physical or chemical substances causing oxidation and other chemical reactions, particles from corrosion (Anon., 2003), or with micro-organisms. Contamination in lubricants can lead to contamination of food products e.g. through leakage from bearings, dripping from open lubrication points e.g. chains, leakage from oil circulation systems or from corroded joints of oil-filled heat exchange systems or contact between oil-coated machine surfaces (Anon., 2003).
The microbes must often tolerate anaerobic conditions and low water activity in lubricants. L. monocytogenes is capable of withstanding the above mentioned conditions (Buchanan et al., 1989; Lou and Yousef, 1999). It has been shown to survive in butter, which was the vehicle in a Finnish L. monocytogenes epidemic in 1998-1999 (Lyytikainen et al., 2000). Rossmoore (1988) reported findings of L. monocytogenes in dairy conveyer lubricants. Use of lubricants in conveyers has also caused hygiene problems in breweries (Heinzel, 1988). Acinetobacter sp., Algaligenes sp., Pseudomonas sp. and sulphate reducing bacteria have been isolated from lubricants (Ortiz et al., 1990; Hamilton, 1991). Petitdemange et al. (1995) observed clear differences between strains of Clostridium butyricum in their ability to survive and grow in industrial glycerol.
Excerpt from dissertation thesis - Kaarina Aarnisalo
Kaarina Aarnisalo, Laura Raaska, Gun Wirtanen, Survival and growth of Listeria monocytogenes in lubricants used in the food industry, Food Control, Volume 18, Issue 9, 2007
Guidelines for controlling Listeria monocytogenes in small to medium packing and fresh cut operations http://anrcatalog.ucanr.edu/pdf/8015.pdf, accessed Feb 2018
FSIS Compliance Guideline: Controlling Listeria monocytogenes in Post-lethality Exposed Ready-to-Eat Meat and Poultry Products, Jan 2014 https://www.fsis.usda.gov/wps/wcm/connect/d3373299-50e6-47d6-a577-e74a1e549fde/Controlling-Lm-RTE-Guideline.pdf?MOD=AJPERES