Principles of an Environmental Monitoring Program for Listeria monocytogenes
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Contents
A. Developing an Environmental Sampling Program
a) Type of product and process/operation
b) Type of samples
c) Target organisms
d) Sampling locations and number of samples
e) Frequency of sampling
f) Sampling tools and techniques
g) Taking environmental samples
h) Analytical methods
i) Data Management
B. Actions in the Event of Listeria Detections
C. Additional Samples to be Taken
D. Enforcement Aspects
E. Particular Risk Points
F. Examples of Actions
G. Examples of Trending
A. Developing an Environmental Sampling Program
A generic environmental monitoring program is not possible for manufacturing environments, due to the variations in size, complexity and risk. A number of factors (a – i) should be considered when developing the sampling program to ensure the program’s effectiveness:
a) Type of product and process/operation
The need for and extent of the sampling program should be defined according to the characteristics of the RTE foods (supporting or not supporting growth), the type of processing (listericidal or not) and the likelihood of contamination or recontamination (exposed to the environment or not). In addition, consideration also needs to be given to elements such as the general hygiene status of the plant or the existing history of Lm in the environment. Environmental swabbing for Listeria in low-risk areas is required where product is decontaminated prior to being transferred to a high care area. This is to ensure that Listeria is prevented from building up in low risk and cross contaminating ingredients therefore ensuring the decontamination process remains effective.
b) Type of samples
Environmental samples consist of both food contact and non-food contact surface samples. Food contact surfaces, in particular those after the listericidal step and prior to packaging, have a higher probability of directly contaminating the product, while for non-food contact surfaces the likelihood will depend on the location and practices. When to take samples must be considered, either after cleaning, during production or at the end of production. Sampling after cleaning verifies the cleaning method or if repeated isolations are obtained, help identify the presence of a biofilm that will require removal. Sampling product after e.g., 2 hours of production or at the end of production may improve the chance of isolating Listeria as any organisms harbouring in crevices or undetected biofilms may be expelled and potentially cause widespread contamination. Any equipment or areas that are cleaned periodically should be sampled PRIOR to cleaning to validate the frequency of clean, as well as post cleaning to validate the efficacy. Raw materials may serve as a source of environmental contamination and may therefore be included in the monitoring program.
c) Target organisms
While this document addresses Lm, effective monitoring programs should also involve testing for Listeria spp; their presence is a good indicator of conditions supporting the potential presence of Lm. Where appropriate and shown to be valid, other indicator organisms may be used10.
d) Sampling locations and number of samples
The number of samples will vary with the complexity of the process and the food being produced. Locations should be considered a risk that are chilled, damp / wet, undisturbed e.g. difficult to clean or access or damaged and are in the proximity of food. Guidance on potential risk locations can be taken from Appendix 1, published literature, and based on process experience, expertise or in plant surveys. Sampling locations should be reviewed on a regular basis (minimum annually). Additional locations may need to be sampled depending on special situations such as major maintenance or construction or when new or modified equipment has been installed or when changes in working shift patterns are required.
e) Frequency of sampling
The frequency of environmental sampling would be based primarily on the factors outlined under subheading “Type of product and process/operation“. It should be based upon risk assessment and defined according to existing data on the presence of Listeria spp. and/or Lm in the environment of the operation under consideration. In the absence of such information sufficient suitable data should be generated to correctly define the appropriate frequency. These data should be collected over a sufficiently long period as to provide reliable information on the prevalence of Listeria spp. and/or Lm and the variations over time. The frequency of environmental sampling may need to be increased as a result of finding Listeria spp. and/or Lm in environmental samples. This will depend on the significance of the findings (e.g., Lm and a risk of direct contamination of the product). Frequency of sampling may be decreased if historical data demonstrates effective controls are in place. Routine sampling must be carried out according to a schedule, ensuring all production days and shifts are covered.
f) Sampling tools and techniques
It is important to adapt the type of sampling tools and techniques to the type of surfaces and sampling locations. For example, sponges (Fig 1) may be used for large flat surfaces, swabs (Fig 2 & Fig 3) may be more appropriate for cracks and crevices and areas that are hard to access, or scrapers (Fig 4) for biofilms / hard residues.
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Fig 2
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Fig 3
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Fig 4
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g) Taking environmental samples
All personal taking environmental samples must be appropriately trained.
Check swabs / sponges have been stored correctly and are within date.
Prior to taking samples hands must be washed and dried.
All swabs and sponges must be pre-moistened with either:
- Neutraliser effective against the cleaning chemical used e.g., sodium thiosulphate for chlorine, universal neutraliser for QACs or
- General buffered diluent e.g., peptone for sponges and swabs taken during or at the end of production
There are many other cleaning agents used e.g., peracetic acid – the effectiveness of any neutraliser used must be assessed in consultation with the testing laboratory.
A surface area of approx. 30x30cm is recommended where possible (templates should not be used as they can transfer contamination), however if this is not possible the trained personnel should swab areas in a consistent way for each location to enable results to be compared and trended. Swabs must be taken by swabbing or wiping the sponge over the surface vertically and horizontally, if a swab is being used it should be turned whilst wiping the surface (Fig 5). Sponges must be held through a sterile plastic bag or sterile disposable gloves.
Fig 5
Under certain circumstances it may be possible to composite (pool) certain samples without losing the required sensitivity. However, in the case of positive findings additional testing will be necessary to determine the exact location of the positive sample.
Carefully replace the swab / sponge back into the container provided without touching the sample or inside of the container.
After using a swab / sponge containing neutraliser, the sampling point should be recleaned or wiped using an alcohol wipe.
Samples must be stored at 5°C +/- 3°C[1] and ideally tested within 24 hours of the sample being taken. Label the samples with enough detail to enable trends to be monitored, e.g. date, time, exact location, pre/ post clean, during production etc.
The time of taking the sample, and the time of the analysis being carried out should be recorded.
h) Analytical methods
The analytical methods used to analyse environmental samples should be suitable for the detection of Lm and of other Listeria spp and based upon ISO 11290-1. Considering the characteristics of environmental samples, it is important to demonstrate that the methods are able to detect, with acceptable sensitivity, the target organisms. This should be documented appropriately. Best practice is for isolation of Listeria spp to be speciated and isolates of Lm held at the laboratory for a defined period of time by the FBO to allow further analysis and comparisons to be carried out.
Enumeration of Listeria is not usually required for environmental samples and results should be reported as cfu/swab.
i) Data management
The monitoring program should include a system to record the data and their evaluation, e.g. performing trend analyses. All species of Listeria must be recorded and trended, however the focus must be on Lm. A long-term (e.g., annual) review of the data is important to revise and adjust monitoring programs. It can also reveal low level, intermittent contamination that may otherwise go unnoticed. Results and trends must be assessed weekly, individual positive results require investigation, but more importantly trends must be identified quickly. Therefore, results must be recorded in a simple visual way to be able to recognise trends over a period of time (usually by week or month).
These could include:
- bar charts of percentage fails (not absolute numbers)
- graphs representing environmental performance against product results and even environmental swabbing for indicator organisms
- spreadsheets plotting product results against processes; equipment used, shift patterns, production days and times or
- factory mapping i.e. placing marks on the locations and dates where Listeria has been detected, (sometimes referred to a measle or bubble maps).
Factory mapping should only be used for stationary swab locations, and mapping should restart if actions have been taken to eliminate sources.
Trending should only be carried out for routinely sampled locations to enable comparisons to be made. Samples taken for investigation should be recorded and trended separately. When reviewing trends, i.e. locations where Listeria is consistently not detected over time should be reviewed as well as locations where Listeria has been detected. positive results. These can be replaced by an alternative location or a be sampled less frequently. If Listeria is expected but not detected, the exact sampling location or method of sampling should be reviewed.
B. Actions in the event of Listeria detections
The purpose of the monitoring program is to find Lm or other Listeria spp if present in the environment. Generally, manufacturers should expect to find them occasionally in the processing environment. There is no requirement to inform enforcement agencies but an appropriate action plan should be designed and established to adequately respond to Listeria detections. Investigations should initially confirm appropriate CCPs continue to be in place and monitoring data should be checked e.g. temperature monitoring, chemical concentrations followed by investigations into the hygiene procedures and controls. All data leading up to the positive result / trend should then be reviewed, rather than immediately collecting further samples without planning. This review will include microbiological results for finished product, component, raw material, hygiene (including ATP if used), including indicator organisms as well as any previous investigation sample results. Therefore, investigations can be planned and targeted to establish the contamination source or verify actions. Actions may include observing practices, auditing cleaning / production methods, dismantling equipment and taking swabs from inside, collecting component samples from different points of production. These results need to be received and reviewed before further action and samples are taken. The manufacturer should react to each positive result; however, the nature of the reaction will depend upon the level of contamination, likelihood of contaminating the products and their expected use. The plan should define the specific action to be taken and the rationale. This could range from no action (no risk of recontamination), to intensified cleaning, to source tracing (increased environmental testing), to review of hygienic practices and testing of product. Particular attention must be paid to any increasing trends, in which case a multi-disciplinary team is needed to develop and effective action plan which is routinely monitored and actions verified. Molecular methods to further type isolates held by the laboratory, may identify common sources of contamination. (Examples of actions are given here).
Both corrective and preventative actions must be considered.
All actions must be validated, monitored and verified.
C. Additional Samples to be Taken
In addition to the use of sponges and swabs used for environmental sampling, other samples must be taken to assess potential cross contamination. These include:
- Raw material samples on intake and in high care manufacturing areas
- Component samples within the manufacturing area or from equipment after processing. This can allow the detection of Listeria that is not removed during cleaning, harbouring within equipment and is released while the equipment is used. Component samples can also be used to detect any cross contamination from the surrounding environment and practices.
- Finished packed product, as this sample incorporates all raw materials, processes, equipment, handling, storage. Samples must be routinely tested either at point of manufacture (if growth of Listeria is not supported) or end of the shelf life (if growth is supported OR if this is unknown). This is to build data to demonstrate compliance with EU Regulation 2073/2005. Any positive results must be enumerated to demonstrate the criterion of 100cfu/g has not been exceeded.
- Hand swabbing (or gloves if worn) to monitor hand hygiene, especially in high care / high risk areas where product is handled.
- Condensate samples e.g., from evaporators, this will monitor any Listeria in the evaporators or any dead legs in the pipework or extraction hoods to identify moisture trap points. Work in progress samples (components awaiting assembly) from the production lines or in storage, to assess any potential cross contamination.
- Rinse water taken from pipework or CIP systems to assess the effectiveness of the cleaning and any potential harbourage points or dead leg
- Water, ice, compressed air samples, air samples at the high care /low risk interface.
- Product debris i.e. particles of food that may accumulate under belts, on scrapers and at transfer points
D. Enforcement Aspects
Testing of final packed product cannot guarantee food safety. Food safety can be demonstrated by HACCP plans supported by PRPs and all the records and data to demonstrate control. This includes validation data for critical processes and cleaning methods, monitoring records which includes microbiological results for environmental sampling, component (WIP) samples, and verification data for finished products e.g., monthly pathogen testing. In addition, food safety can be demonstrated by temperature records, traceability, staff training, raw material risk assessment etc. All data/records must be readily available in response to Competent Authority investigations or visits.
Demonstrating these data are regularly monitored trended and reviewed and any adverse results / trends are investigated and actioned in an appropriate timescale generates confidence that the HACCP plan is ensuring food safety.
E. Particular Risk Points
#EMaterialsMaterials
Raw materials, packaging, films
Conveyors (especially those that are linked or frayed), sealers, condenser and chiller units, blast freezers, spiral freezers, seals, hollow equipment (frames, shafts, rollers), flow wrap machines, condensation hoods, slicers, scales, filling and mixing equipment, bearings, valves, equipment used to transport food ingredient from one location to another especially wheels, containers, buttons, exposed screw heads, or poorly finished welds or damage on food contact equipment, injection equipment, motor housings, pumps. Hand utensils and storage. Equipment tipping machines which may allow drip from the undersides / wheels to contaminate food contact surfaces. Under equipment that is too close to the floor to allow thorough cleaning
Periodically cleaned / in frequently used equipment. Lubricating oil (should include listericidal agent)
Cleaning and maintenance equipment
Cleaning equipment (squeegees, floor cleaners, tray-wash, brushes, bin washers) engineering boxes, tools and materials.
#ManufEnvtManufacturing environment
Switches, plugs, storage areas especially for raw materials, ingredients and cleaned equipment, drains, wall floor junctions, cracks in floors and walls, door frames (especially if damaged), damaged pipes and hoses, electrical wires under / overhead machinery, lagging, pipework, air steam, condensation Waste, waste routes and waste hatches.
Exposed insulation and hidden sources of contamination, debris.
F. Examples of Actions
- Determine whether there been any changes to cleaning methods / practice
- Determine whether there been any changes to suppliers / products / ingredients
- Determine whether there been any changes to the manufacturing process
- Observe manufacturing practices – take appropriate samples
- Observe cleaning practices– dismantle and swab internal areas
- Review equipment / fabric condition – take swabs if necessary
- Redefine the depth of dismantle for routine cleans and periodic cleans
- Review cleaning method and practice
- Revalidate, verify and add monitoring of any revised cleaning method or practices
- Heat equipment parts (if possible) to >70°C. This can be carried out to immediately eliminate contamination, however this either needs to be added as a routine procedure and the frequency must be defined by routine monitoring or replaced by a thorough review of the routine hygiene procedure.
G. Examples of Trending
Keep trends simple and up to date
The following are examples of simple trends using made up data for demonstration purposes only. Plotting average results per month shows how increasing environmental detections has most likely caused contamination of product.
However, when the environmental data is plotted weekly, the increasing trend in the first 20 weeks can be identified earlier and the business can action and see the effects in a much timelier manner:
[1] Note: The EURL Lm shelf life document states 1-8°C during transit and 3°C + 2°C storage
Edited 8 August 2023