Environmental and Finished Dairy Product Sampling Monitoring for Listeria monocytogenes
1.6 Inspection Procedures for Environmental Sampling

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1.6.1 Preparation for Environmental Sampling

The environmental sampling frequency is stated in the microbiological sampling guidelines under sampling plan D222 (Environmental sampling for cheese processing establishments).

Prior to conducting an environmental inspection, provide the establishment with at least 24 hours notice to ensure that a packaging line is in operation and that the establishment can make arrangements for breaks during production for swabbing. This will also enable industry to schedule any changes in product distribution plans (e.g. voluntarily holding the product affected by the sampling). Inspectors should verify that the best before date stated on the environmental kits has not been exceeded. Expired kits should not be used. It is also important to place gel packs from the kit into the freezer at least 24 hours before the sampling is going to be conducted.

1.6.2 Selection of Food Contact Surface Sample Sites

Food contact surfaces (FCS) are anywhere an exposed surface or object has direct contact with the unpackaged RTE product. For environmental sampling, select sites in the final packaging area which are exposed to both the environment and the product or where there is a higher probability of RTE product contamination and the greatest potential to affect the safety of the final product. Suggested food contact surface sites in the final packaging area are:

  • Slicers, dicers, shredders, etc.
  • Carts/racks
  • Cheese molds
  • Blades of slicers
  • Packaging tables, conveyor belts
  • Scales
  • Cutting tables
  • Utensils (knives, trays)
  • Packaging equipment (vacuum packaging, etc.), packaging material
  • Employee gloves/hands, aprons. Note that it is recommended to randomly swab at least two employees if these sites are selected.

Select one (1) specific packaging line. Give priority to the packaging line most at risk, i.e. those packaging the highest risk cheeses in category 1, and to shredding, slicing and dicing operations where the risk of post-processing contamination is higher. Ideally 10 FCS sites should be selected (minimum of 5 FCS) in the packaging area. The number of sampling sites will vary according to the complexity of processing system or packaging line. Prior to starting sampling, survey the packaging line to determine sites to be sampled, and document them on the LSTS submission form. A 900 cm2 (30 x 30 cm or equivalent) surface should be swabbed whenever possible. Surfaces are to be swabbed after the start of the operations (i.e. 2-3 hrs into processing is recommended).

In cheese processing establishments the highest risk cheeses would include:

  • Soft mold ripened cheese lines (e.g. Brie, Camembert, Blue, Gorgonzola);
  • Soft and semi soft fresh cheeses (e.g. Feta, Havarti, Queso Fresco, Queso Blanco);
  • Paneer, Ricotta, Mozzarella;
  • Washed rind cheeses (e.g. St. Paulin, Oka, Tomme).

1.6.3 Environmental Sampling Techniques

Aseptic sampling must be used for all samples taken for microbiological purposes. It is a technique which uses sterile containers and equipment to prevent the introduction of any contamination from outside sources into either the product or sample taken.

When samples are taken under these conditions, it is assumed that the results of the analysis indicate the actual conditions under which the product was manufactured or handled. Cross-contamination caused by the person taking samples is avoided, if proper procedures are followed. If Lm is found in the sample, then it can be indicative that it was introduced during the manufacturing process and not by the sampler.

Environmental sampling kits are supplied by the operational centre. Ten pre-moistened swabs for sampling food contact surfaces are provided with each kit. Upon receipt of the kits and before taking samples, review the instructions on sanitary sampling techniques and the content list supplied with the kits. Report any problems with the sampling kits immediately to the Area Program Specialist. Avoid contaminating the materials from the sampling kit, the samples, the equipment or the product being sampled. If resources permit, it is recommended that the swabbing process be completed by two inspectors.

Use the following sampling techniques when taking the swabs:

  1. Label the Twirl-ties sample bags and record information about the sampling sites. Use a waterproof soft felt pen for labelling all bags and ensure that while writing you do not puncture the plastic bag.
  2. Thoroughly wash and dry hands.
  3. Open the package containing the pre-moistened sterile swab, put on sterile gloves and take sterile swab out.
  4. Rub the swab firmly and thoroughly over the surface to be sampled, without lifting the swab, swab the surface area up and down until the whole target surface is covered (see Figure A), then turnover the swab and swab the surface area from right to left until the whole target surface is covered (see Figure B)
    This image displays the swabbing using an up and down motion
    Figure A: Up and down motion
    This image displays the swabbing using a right to left motion
    Figure B: Right to left motion

    Note that for surfaces which are difficult to swab because of their contour (i.e. conveyor belts), it may not be possible to swab a defined area using the mentioned procedure. In this case, swab the area to be sampled using the same described technique (Up and down/ left to right) and then turn over the swab once again and swab the surface area in a diagonal pattern. This allows the sampling of every plane of the surface that will likely come into contact with the food (see Figure C)

    This image displays the swabbing using an up and down/right to left and diagonal motions
    Figure C: Swabbing of irregular surfaces - Up and down/right to left and diagonal motions.
  5. Release the swab into the appropriately labelled Whirlpak® sample bag. Do not let the swab touch the outside of the bag.
  6. Seal the bag, making sure not to contaminate the sample.
  7. Place the bag in the Styrofoam box.
  8. Sanitize the sample site using a 70% ethanol spray solution following environmental swabbing (note that some establishments might want to perform their own FCS sanitation after CFIA swabbing)
  9. Change gloves for the next sampling site and complete swabbing all selected sites.
  10. Once all samples have been taken, place the freezer pak at the bottom of the Styrofoam box. Use newsprint or similar material to prevent direct contact between the pak and the samples.
  11. Place the sample in the middle and use fillers to prevent shifting of the samples during shipping. Add another freezer pak on top.
  12. Include a complete LSTS submission form inside an empty Whirlpak® bag. Seal and label the box.
  13. Send to the laboratory indicated in the sampling guidelines within 1 working day.

Note that sampling under this plan is linked to sampling under D221, Listeria monocytogenes in cheese. When taking a sample under D222 take a finished and packaged cheese sample (consisting of 5 sub samples-at least 200 g) from the selected packaging line and if possible, around the same time the line was swabbed under D222. It is recommended that industry hold all finished product lots produced on the sampled packaging line between full sanitation cycles. A full sanitation cycle means cleaned and sanitized (i.e. clean-up to clean-up). Any distributed products produced between these sanitation cycles are subject to a recall if finished product results are unsatisfactory.

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