Previously successful decontaminations of equipment and likely niches

In Summary

L. monocytogenes can persist in a manufacturing environment, especially in specific niches.
The first table below lists specific niches in the environment and in equipment which may harbour L. monocytogenes, as well as treatments which controlled the risk.
The second table below lists an example environmental sampling programme which can be used to find any L. monocytogenes contamination.

Selection of environmental sampling sites likely to harbour L. monocytogenes

The table below is a non-exhaustive list of niches from a number of food processing plants that have been reported to contain L. monocytogenes. It is likely there are additional niches for L. monocytogenes that are not shown in the table. Also included in the table is a list of corrective actions that successfully removed the contamination. The table contents have been modified from a list originally assembled by Tompkin (2002). The information is provided so that plant operators can devise strategies to assess the contamination status of likely niches in their processing plants and previously effective decontamination strategies for equipment and environments.

Contaminated equipment	Contamination source	Successful corrective actions taken
Continuous brine chill chamber for product on racks with wheels	Doors made of rubber-coated fabric, large metal hinges extending the width of the door, and hollow bump guards at bottom of door	The doors were replaced with rigid cleanable plastic material; the large hinges and the bump guards were removed
Ammonia unit used to chill brine solution	Fibreglass insulation on ammonia line to brine chilling unit became saturated with brine that was splashing from chilling unit	The contaminated insulation was removed; the pipe and the area were cleaned and sanitised; the insulation was not replaced on the pipe close to the brine chiller
Brine chill exit	Hoses and spray nozzles at exit end of brine chill tunnel used to spray product	The hoses and the nozzles were replaced; daily cleaning and sanitation was initiated
Brine chill	Construction of brine chill tunnel had stainless steel framing with metal touching metal, causing an uncleanable hollow space at the point of contact	The framing was modified to facilitate cleaning and to prevent the material from getting into the space between the tunnel wall and the framing
Brine chill tunnel	Damaged rubber seals on stainless steel door at end of tunnel	The damaged seals were replaced; the cleaning procedures were tightened
Conveyor belt	Contaminated liquid was discovered within a hollow sprocket that had split open	The hollow sprocket was replaced with a solid sprocket
Conveyors (multiple events)	Hollow rollers	The rollers were replaced on detection; where possible, conveyors were replaced with sloping steel chutes to remove rollers and the danger of re-contamination
Conveyor between shrink tunnel and boxing	Worn conveyor made of rubber-coated fabric	A new belt was fitted
Collator and conveyor	Undetermined	The equipment was covered with a large tarpaulin and steam was injected at the bottom of the tarpaulin
1. Exit from spiral freezer 2. Spiral freezer	1. Wheel bearings for conveyor belt 2. Undetermined	1. The bearings were removed and replaced 2. The cleaning frequency was increased, and the equipment was allowed to defrost properly before commencement of cleaning
1. Between freezer and packing machine 2. Wire mesh conveyor between oven and freezer	1. Overhead conveyor 2. Hollow support rods for conveyor	The hollow rods were replaced with solid rods
Slicer	Worn hydraulic seals at base of slicer, oil with water and product residue	The slicer was stripped, cleaned, and sanitised; the parts were placed in the oven and moist heat was applied. Oil with sodium benzoate (an anti-listerial chemical) was used for lubrication
Slicer	Product detritus build-up inside safety cover on gear and drive belt; the material further contaminated conveyor belt below	The cover was changed so it could be removed for cleaning each night
Dicer (multiple events)	Undetermined	The entire dicer was moved into oven and heat was applied. Also, the dicer assembly was covered in tarp and steam was applied
1. Conveyor leading to packaging machine 2. Cooked product worktable	1. Fabric conveyor belt material 2. Handheld knives	1.The conveyor was replaced with a stainless-steel chute 2. The knives were cleaned and sanitised daily in automatic washer and were no longer stored in the employees lockers
Work table	Air duct used for blowing product storage bags open	The table was modified to make the duct accessible for nightly cleaning
Packaging machine	Crack in stainless steel covering on top edge of machine near product loading area	The area was cleaned, sanitised and the crack was welded shut
Packaging machine	Steel rods for pushing product into cartons	The rods were removed from the packer and cleaned/santised on a daily basis
Insulated concrete block wall	The insulation between fibreglass and concrete wall was contaminated by condensate from overhead pipes	All fibreglass/insulation was removed from the wall; the concrete wall was cleaned with an acid base cleaner, sanitized, and sealed. The overhead pipes were rerouted to be closer to the floor
Ingredients’ hoppers	Cinder blocks around an opening in the wall	The cinder blocks were sealed to prevent moisture from accumulating in the blocks
Refrigeration unit near ceiling of holding cooler	Condensate from refrigeration unit	The refrigeration unit was cleaned and sanitised

A typical programme for the collection of environmental swabbing in a fish processing plant

Below is a table of sample collection locations collated from a number of different sizes of fish processing and smoking plants in the UK. The table is provided because some of the larger processors have determined where the problem areas in their plants are and deliberately target these locations to ensure their plants don’t become colonised with persistent L. monocytogenes. Typically, the areas that are sampled repeat every few months in the majority of UK plants. In addition, to the sample collection sites listed below, fish processors may want to consider sample collections from areas in their plants that are frequently wet. L. monocytogenes tends to colonise places in food processing plants that are dry only occasionally. Advice on sample collections is available here.

Week	Sampling locations
1	Packing feed conveyor x6, Raw fish skinning machines x3, Cooker/hot smoker door handles and seals x5 on the refrigeration side of the oven, Cold smoker door handles and seals x5 on the high care side of the unit, Blast chiller entry door handles and seals x10 on the side of the ovens (which may exhaust hot, moist air) Blast chill floor x10, Drains in high care area, especially if located near slicing equipment.
2	Pack line weighing balances x8, Cooker/hot smoker door handles and seals x5 on the refrigeration side of the oven, Cold smoker door handles and seals x5 on the high care side of the unit, Final product chiller door seals x10, Drains in post cook/smoke work room x4, Blast chiller exit door handles and seals x10, Blast chiller drains x5.
3	Main packing exit conveyor, concentrating on rollers and belts x6, Rejected product packing exit conveyor, concentrating on rollers and belts x6, Kiln/oven door handles x10, Final product chill door handles, Ceiling condensation squeegee for area between chillers and smokers/cookers, Drain in area between chillers and smoker/cookers, Drains in post cook/smoke work room x4.
4	Slicer on/off switches and controls x6, Packing line control panel x6, Kiln/oven door handles x10, Randomly selected fish transport racks, concentrate on the wheels, x10, Ceiling squeegee for area between chillers and cookers, Staff changing area floor, Random areas of high risk area floor x10. Drains in post cook/smoke work room x4, Blast chiller floors x10.
5	Knife blades (x6) as a pooled sample, Ingredient hoppers and shelving in ingredients store x10, Kiln/oven door handles x10, Final product chill door handles, Ceiling squeegee for area between chillers and cookers, High risk area floor dry detritus squeegee, Blast chiller floors x10, Drains in raw product chiller, especially if melting ice leaks onto floors x5, Random areas of the dry ingredient store floor x5.
6	Packing feed conveyor x6, Product racks in packing area x6, Cleaner’s anti cut gloves as a pooled sample, Blast chiller exit handles and door seals x10, High risk area brushes and squeegees x5, A new pair of randomly selected disposable gloves from a glove’s dispenser x5.
7	Drain gully in front of cooker high-risk exit at smokers/cookers x5, Random areas of the dry ingredient store floor x5, Blast chiller entrance handles and seals x5, Random boot soles in high-risk area entrance x10 Hosepipe nozzles x5 Automatic boot washing equipment x5.
8	Blast chiller exit handles x10, Blast chiller exit seals x10, High risk area brushes and squeegees x5, Blast chiller floors x10, Drain gully in front of cooker high-risk exit at cookers x5.
9	Blast chiller evaporator coils pooled x5, Product temperature probes x5, On/off switches on temperature probes x5, Kiln/oven door handles x10, Kiln/oven door seals x10, High risk area drains at random points x10, A used pair of randomly selected disposable gloves from a glove’s dispenser x5.

Simmonds and Wiedmann (2018) consulted 16 experts in the USA and assembled a list of 77 locations that should be sampled as a strategy to detect potential plant residency by L. monocytogenes and to verify the effectiveness of cleaning and sanitation. The sample locations were subdivided into one of four zones. Zone one was food contract surfaces. The list extended across a range of food processing facilities and so were not specific for fish processing plants. However, there were 73 sites which were applicable to seafood in total. The paper outputs are available without charge as supplementary information in the form of an excel spreadsheet from the publication homepage. There were around 30 food contact surfaces that were applicable to seafood. These locations and additional material be authored that reinforces the importance of process environment sampling (it is a legal requirement under 2073/2005).

Fish processing plants are under a near continuous assault from L. monocytogenes and it is likely once testing begins that there will be a positive isolation. You can find advice on how to sample your plant environment for L. monocytogenes on these pages. How to effect decontamination is described on these pages – chemical and heat decontamination of equipment. In addition, a positive isolation of L. monocytogenes from a plant environment may be grounds for a review of processing practices by a FBO.

References

Tomkin, R. B. (2002). Control of L. monocytogenes in the food-processing environment. J. Food Prot. 65, 709-725

Simmons, C.K. and Wiedmann, M. (2018) Identification and classification of sampling sites for pathogen environmental monitoring programs for Listeria monocytogenes: Results from an expert elicitation. Food Microbiol. 75, 2-17.