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Plan properly for microbiological testing

Plan properly for microbiological testing

A properly designed microbiological testing plan is vital for small businesses if they are to achieve their objectives and avoid wasting time and money, writes Roy Betts

Food producers frequently need to do microbiological testing. Some producers will have a good knowledge of what to do in these situations, for others it will be challenging journey into the unknown. Here we try to shed some light onto the process of getting foods tested for microorganisms, hopefully making that journey a little less fearful for the uninitiated. The first thing to make clear is that testing will never  assure safety. You can never ‘test’ a food safe. Safety is designed and manufactured into foods, and this involves the correct use of risk assessment and risk management procedures. The classic risk management procedure is correct implementation of HACCP and testing plays a role as a HACCP verification activity.

As a testing laboratory we will often get requests from producers to test their products for ‘full micro’. This term has no meaning and would tend to suggest that the requester has no real understanding of what they need, what the significance of the tests are and more importantly, what they will do with the results. On occasion, even producers who have long standing sampling and testing plans may find that they have not revisited their plans for many years and may be doing unnecessary testing, or worse not testing for something that they really need to. So, what are the steps when thinking of undertaking microbiological testing?

1. Define the need

The first requirement is to understand the need: ‘why do I want to test? This may be driven by legislation, or customer specifications, or simply that the producer has identified a requirement to do a particular test. There must be a reason why a test is required, and this must be understood. It may be for safety reasons: testing for a pathogen to verify the HACCP plan is working, or for the presence of a viable microorganism in a sterile food. It may be for quality reasons: testing for a spoilage organism that would reduce shelf life, or it could be to check hygiene in production by looking for ‘hygiene indicators’. Never set out to test a food until you know the objective of why you are testing.

2. Determine the goal

Before you start to test, you must know what you will do with the results. When you get a test result you will have information that you did not have before, and you must know how you will use that information. If you test for a pathogen, never assume that every test will be negative. What will you do when you get a positive pathogen result? What action will you take. You need to determine and document this before you start testing. Similarly, if the test is for a spoilage organism or hygiene indicator organism, you will need to have set ‘accept/reject’ criteria and maybe also an ‘action level’, but the question is what action will you take. Again, this must be determined and documented before you start to test.

3. Establish the criteria

It is usual for companies that undertake microbiological testing to set out their ‘microbiological criteria’. These are important statements that document several key points about the microbiological testing that you do. Some of the items that must be included in any microbiological criterion are listed here:

a) The test item: is this a product at the start of its shelf life; an end of life sample; a work in progress sample; an ingredient; an environmental sample from a particular point in production. Basically, what are you going to test.

b) What are you going to test for: This may be a single organism, or a whole range of organisms and groups. This part of the criterion may be driven by legislation, customer specification, a need for HACCP verification or simply a perceived risk, but the decision must be based around the Step 1 noted above: you must know why you are testing

c) How are you going to test it: what test method do you want to use? It is possible that the test method will be defined in legislation, or in a supplier specification, but it is up to you to decide how the test will be conducted and what method will be used. If you don’t feel that you have the right knowledge and expertise to do this, it may be worth calling in a reputable consultant to help.

d) Sampling: how many samples are you going to test, and how often? This is an important consideration as it can have major cost implications. Again, you may be driven to a particular testing frequency by legislative or customer requirements, but it’s important to understand why you are testing at the frequency you choose and the implications of testing too frequently, or infrequently. Frequent testing may give a greater confidence that HACCP is working well but could be costly. However infrequent testing could be more costly. Take an example of monthly testing for a pathogen, you’ve been getting negative results, then you suddenly obtain a positive- you need to recall. But does this mean you have to recall all production over the month as you have no data to prove the pathogen was absent since the last negative test. If you were testing daily, then your consideration may only be recalling a day’s production. This is only a hypothetical situation but shows how carefully you must consider test frequency when setting a microbiological criterion.

e) ‘Accept/reject’ criteria: You now know what you are going to test, how you are going to test it and how often, but the next question is, what will you do with the results? What does acceptable look like and why? What does unacceptable look like and why? If an unacceptable result occurs, what action are you going to take? Depending on the test you’ve done, actions may range from doing a production line audit and some extra cleaning and testing right through to informing the authorities and doing a full public recall. The action you take will depend on the type of test you’ve done and in some cases the level of organism detected, but you must document your intended actions in the criteria you set.

4. Confident testing

After understanding the need for testing and the treatment of results, you can now start to think about getting testing done. Some food producers will have their own on-site laboratories, others will use contract laboratories to do the work. Whichever you use, you must have confidence that the laboratory will deliver a high-quality service that is consistent with your requirements.

If you have your own on-site laboratory, how do you know that it is using the most appropriate methods or handling the samples in the correct way? Basically, how do you know you have confidence in its results. You can achieve this in several ways: employing previously trained microbiologists with a proven track record; sending your staff on appropriate training courses; ensuring your laboratory takes part in proficiency testing for all the test methods it operates; ultimately and perhaps the target for all testing laboratories would be accreditation. Accreditation offers the best assurance that a laboratory is operating to a high standard of quality, that staff are trained, methods are appropriate, equipment serviced and calibrated and quality assurance systems in place.

If you are going to use a contract testing laboratory, you will be looking for one that is accredited by the national accreditation body within the country that it is sited (e.g., UKAS in the UK and INAB in Ireland), but you must also ensure that the methods it will use on your tests are appropriate. Check that the methods are included within the scope of that laboratory’s accreditation. Do the methods they use fulfil the requirements that you will have detailed in section 3(c).

A good example may be that a laboratory is accredited and has a method for Listeria detection within its accreditation scope, however you are testing to a legal requirement that states the use of one very specific method for Listeria detection. It’s up to you to ensure that the specific method noted in legislation is used, or your test result may well be unacceptable for its intended use.

When using contract laboratories, you also must check how the samples will be transported and delivered to that laboratory. Remember that microorganisms are living, and it is unlikely that they will remain at static numbers in your sample for long periods of time, they will either grow to higher levels or die off. You must ensure that the way the sample is handled from the point it is taken in your factory, to the point the microbiological test is initiated, allows the absolute minimum change in microbial number. This may require chilled storage and rapid transport to the laboratory, and an assurance from the laboratory that they will test the sample immediately on arrival or use chilled storage for the minimum time before testing commences.

Finally, you must also agree how results will be transmitted from contract laboratory to you. You will undoubtably want to have any result that is above your ‘accept/reject’ criteria (3e) reported to you with all haste, as you may have major actions to take.

Final thoughts

Setting out to do microbiological tests on foods may initially sound easy, but it is not. It is not unusual to see food producers waste enormous sums of money on testing approaches that are poorly designed, and give inappropriate, unwanted, or unacceptable results. Spending time on planning a good testing approach, asking ‘why am I doing this?’, ‘what will the results show me?’ and ‘what am I going to do with any out of specification results that I obtain?’, will be time very well spent. Once you have spent that time, then document all those factors and reasons. It will be important in the future to fully understand why you made the decisions that you did, documentation is the only way to do this. You may find that talking to an expert that can help you design the testing regime and the criteria that best fit your needs, will be of benefit to you. Finally keep in close contact with your testing laboratory, they are your partner in doing this work, you will rely on their competency to get correct results.

Remember, testing does not make a food safe, that is the job of a well-constructed and implemented HACCP system, but a properly designed microbiological testing plan will complement this and give confidence that the system is operating as expected.


About Roy Betts

Roy Betts is a Fellow at Campden BRI, an independent international food consultancy and research organisation. His role is to ensure that the industry maintains a full awareness of all microbiological concerns and to help companies respond to and manage microbiological issues relevant to them and their products.


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