positive result microbiology

What to do when you get a positive result

positive result microbiology

What is a positive result?

A positive result is defined as any result that does not comply to specifications. This is usually with regards to the presence of pathogens (food poisoning bacteria), but can also relate to high counts of food spoilage bacteria which can affect the shelf-life of foods.

Microbiological Specifications

There are 3 possible specifications:

  1. Legal specifications that we need to comply to that would be country specific.
  2. There are also guideline specifications that are available from, for example Codex Alimentarius which have a comprehensive guide of all their microbiological specifications for food.
  3. There may be internal or client specific requirements.

Very often if you sell or manufacture food for various large corporations, they may have their own specifications that may or may not even be stricter than legal or guideline specifications. If that is the case, you usually have an agreement to comply to the specifications and then it is your obligation then to comply to those, in order to ensure that you are able to sell your food to your clients

Should there not be any legal specifications for a particular product, referring to Codex is always best practice. Clients may require certain standards to be met and can often be stricter that legal requirements.

Microbiological specifications should be separated into two areas:

1.Food Spoilage Microorganisms

  • These microorganisms are bacteria or yeast and moulds that are present in high numbers that cause foods to expire.

2. Food Poisoning (pathogenic) microorganisms

  • These cause people who consume food to fall ill or even die.

Food Spoilage Microorganisms

standard plate count
yeast and moulds
coliforms bacteria

The standard plate counts or total microbial activity, test for the total number of microorganisms in a product. You can also test specifically for yeasts and moulds.  Moulds are common food spoilage microorganism. Lactobacillus and lactic acid bacteria may also cause certain products to go off or even “blow” which is a problem especially for sauces as well as various other vacuum packed products.

These microorganisms may not necessarily cause food poisoning, but can cause food to:

  • Look off – slimy, mouldy and bad colour
  • Smell off – poor odours
  • Taste off – bad tastes

These microorganisms also produce gas and can cause the food to “blow”.

It is for these reasons that we don’t want to have out of specification results for the food spoilage microorganisms.

These microorganisms produce gas and cause food to bloat or blow. In order to maintain product quality , specifications are put into place to ensure the required shelf-life and quality of the product.

The lack of specifications can result in unnecessary costs in production by:

  • Poor perception of food by consumers.
  • Product recalls.
  • Loss of sales.
  • Lost trust by client and consumer

Food poisoning microorganisms

Listeria monocytogenes
food consulting services salmonella
Clostridium perfringens

These microorganisms are mostly bacteria such as

These are the germs that we cannot see , taste or smell and are therefore more difficult to identify as potential risks, as compared to the food spoilage microorganisms. We simply cannot know if these pathogens are present in the product unless it is specifically tested for. Hence the need for microbiological criteria.

With the presence of pathogens, some of the risks are different:

  • Economic losses due to:
    • Legal Action
    • Poor perception of food by consumers.
    • Product recalls.
    • Lost sales.
    • Lost trust.

Such an example is of the Listeriosis outbreak in 2018.

Finding a positive result in a product

positive result microbiology

Firstly we need to determine the extent of the contamination.

We do this by:

  • Examining any existing microbiological results.
  • Physically examine the foods
    • Have they blown
    • Is the product off
    • Showing any signs of spoilage
  • Test additional samples from the same batch to determine extent of problem.
  • Is the contamination sporadic or has it affected the entire batch?
  • Testing batches immediately before and after the affected batch. These would tell us if there is a trend that has developed or a ‘once off’ concern.

Contamination could be as a result of the presence of biofilms, as in the case of Listeria monocytogenes, which “hide” in biofilms and are only released sporadically and can vary from batch to batch.

There could also be a raw ingredient contaminant causing the concerns.

These tests and results help us identify the extent of the concern, as well as the appropriate action. These decisions can also have economic consequences if not correctly determined.

What must be done with the affected batch?

Before resolving the problems, we also need to know what to do with an affected product.

  • If there is a pathogen present and detected before distribution of food:
    • Don’t release food.
    • Destroy food correctly.

It may possible to treat the food in order ensure it is safe for consumption or could be reworked. A cost/benefit analysis would need to be made. Other criteria may include affected quality and what is the probability of the eradication of positive result with rework would be.

  • If there is a pathogen present and detected after distribution of food:
    • Recall the food immediately.
    • Destroy the food correctly

How did the contamination happen?

What caused the positive result?

1.Failure to identify a critical control points.

It is important to analyse the food process and that  a Critical Control Point (CCP) is correctly identified. If a CCP was unintentionally left out it would have a direct effect on the quality of the product due to the growth of  microorganisms, which can cause problems.

We would need to have a relook at the CCP’s to ensure they have been correctly identified. This needs to be done for each critical control point. The results of these findings may suggest a relook at the entire production process.

2. Failure of an identifiable critical control point.

It is possible to have an identified critical control point fail. Should this failure not be picked up for whatever reason and only identified after an  investigation, and was found to have failed, and resulted in microbial growth.

It could be the reason why the product now has a positive result.

3. Unhygienic practices/ incorrect handling of the food after the CCP

The critical control point is there to reduce the bacteria levels. Meaning to eliminate the bacteria altogether after the critical control point. It is still important to make sure the food is hygienically handled.

If we implement a critical control point, it reduces the bacteria to correct levels, but then we do something after that, to re-contaminate, we are going to get positive results.

If a product goes through a cooking process, the correct time or correct temperature, and it comes out of that cooking process, the bacteria have been reduced to the correct level, if we then have another process such as the cooling process which is not controlled properly, it may re-contaminate the product.

4. Ineffective cleaning and sanitising

Possibly the most common concern, is ineffective cleaning and sanitising.  We often find that factories have put in great effort to have good record systems and checks, but forget to have the basics of cleaning and sanitising in place. This means having the correct chemicals and the correct procedures.

The incorrect chemical types and problematic chemical manufacturers, which are not registered with the National Regulator for compulsory specification can cause microbial growth.

  • It is important to review your cleaning programme
  • Engage regularly with the chemical supplier
  • Understand that the right chemical support is needed
  • Have the correct cleaning and sanitising applications
  • Chemicals are correctly diluted.

Once the chemicals have been correctly diluted and applied, we should receive the desired results of reducing the bacterial counts in the factory.

5. Poor understanding of CIP or clean in place systems.

Very often, factories such as sauce manufacturers will have a cooking pot where they cook the sauce which then gets distributed via pipe work. They feel that if they are now heating up some water with a detergent solution and flushing through the pipes that is a Clean In Place (CIP) system.

That is not a CIP system, a true CIP system is a system where you have sufficient pressure, sufficient temperature and the correct chemicals that are pumped around the system to eliminate the product and to also clean and sanitise and eliminate biofilms.

If you are using normal pumps and systems to remove the detergents and sanitisers through the food factory, that is not a dedicated CIP system.  It is important to understand whether you have a true CIP system or whether you are just utilizing your normal pumps and systems.  If you don’t have a true CIP system you are going to have to dismantle your plant and clean and sanitise the entire system.

positive result microbiology

6. Poor cleaning and sanitising

Poor cleaning and sanitising will result in biofilm growth, which consists of slimes, bacteria and other microorganisms that build up in pipes and various sections of the factory where the food is flowing through.  As these build up they start to break off and can get into the food and eventually into the products which are going to cause positive results.

Intermittent and erratic microbiological problems are usually an indication of biofilm build-up in the factory. If you test your product and it is not the entire batch that has been affected and only affected a certain percentage of the product, the biofilms are breaking off into the food and entering the product causing them to blow or to have a positive pathogen result.

Poor cleaning and sanitising and/or lack of a CIP is one of the main issues in terms of positive results. Getting back to basics, understanding cleaning and sanitising and putting an effective system in place is one of the most common problems and an easy solution to fix.

7. Poor design of plant and equipment

We often find dead ends that are building up biofilm and bacteria within the system where food is stagnating for either too long or as a result of poor welding or poor joints. It’s important to make sure that the entire food process, whatever equipment that is being used is correctly designed.

The main thing we want to avoid is any kind of dead spots or dead ends in the system because if the product is able to stand for a certain time, the bacteria then have the opportunity to grow to high levels which are going to cause a positive result.

The design of the plant will often have welding spots which are very rough.  Remember bacteria in the system need to cling to or find a place or a home in the system. The rougher the weld the rougher the surface and the easier the bacteria can then adhere and ultimately grow and cause positive results.

So it’s a good idea to have a look at your entire system, make sure that the actual surfaces and equipment that is being used is correctly designed to try and prevent the growth of the bacteria.

8. Poor design of the production processes.

Observing processes in the factory in its entirety, we often find an entire system where there is no person handling the food, except for machinery. So, no human is handling the food except after the CCP’s, where there is a brief handling of the food. When you have people introduced into the system, there is an opportunity for risk. The system should have been designed to eliminate people completely from the system, so that the food never touches anyone’s hands or is not carried or handled by anybody.

There are concerns that are very unique to a food production plant and as a result needs to be designed as efficiently as possible, which also identifies possible areas where contamination could be coming into the system. It might be a drain flowing in the incorrect manner from a low risk to a high risk where it should be from a high risk to a low risk area. This is because you don’t want bacteria coming from the low risk area with high numbers of bacteria to a high risk area with low numbers of bacteria.

9. Poor maintenance of equipment and plant

This is often the area that cannot easily be improved in food factories, due to budgets and CAPEX allowances that need to be considered. However, if the factory is not well maintained:

  • Cracks
  • Nooks and crannies
  • Broken equipment
  • High-level cracks where the product falls out of.

It is going to make it very difficult to have a clean and effective factory. We need to ensure that the maintenance programme is up to date.

10. Poor staff hygiene

Another area could be poor staff hygiene, and very often it’s the staff themselves bringing bacteria into the facility. Ensuring good personal hygiene and regular hand washing regimes is critical in preventing bacteria from entering the factory.

11. Supplier/ ingredient problems

A supplier could be causing problems or providing raw materials which have contaminated and making it difficult to eliminate contamination and ultimately to provide a safe final product. Is often the main causes of positive results.

How to resolve positive results

positive result microbiology

We need to examine the entire food production process, from receipt of raw materials to the delivery of the final product. And try and determine if there any problems in the system.

Use the knowledge of main causes of positive results to identify the problem(s). Go through the entire food production process:

  • Identify CCP’s
  • Are the CCP’s passing?
  • Does the factory us the correct chemicals?
  • Are staff managed correctly?
    • Are they washing their hands effectively?
  • Is the plant well maintained?

Run through these possible causes in  in a systematic way and make sure that all the basics have been covered.

If there are still ongoing concerns, it may be a good idea to call in an external consultant with a fresh pair of eyes and ideas.  Very often working in the same environment day after day, year after year, can cause factory blindness, where you see something that is a problem, yet you become used to that problem and that problem has now become the norm and is difficult to see.

What can be done at each point

Once we have identified the potential problem areas, additional microbiological testing may be required to determine if these areas are indeed problematic.

Failure of a CCP

  • We can test foods before and after the CCP to determine if bacterial numbers/ pathogens are adequately reduced or eliminated.

CCP not identified

  • Once identified, implement and test before and after new the CCP. Ensure adequate bacterial reduction!

Poor handling after a CCP

  • Test foods immediately after CCP, then after the poor/ unhygienic practice.
    • For example, we have a cooking process in production, as foods come out of that cooking process, make sure they have been cooked at the correct temperature and time and take them straight off the line, test them and see what the bacterial numbers are and compare that with the final packaged product.
    • If we have got a  big variance in bacterial numbers/pathogens, we know that somewhere along the line after the CCP is a concern, up until packaging. We can now focus in that area.

Cleaning problems

  • Dismantle parts of the plant not often cleaned, or not part of a true CIP system.
  • Examine and swab these parts.
  • Often areas may be visually contaminated with biofilm build up.
  • Pay special attention to flexible hoses.
  • Dismantle your entire food production system as far as possible.
  • The CIP has to be designed by a professional expert company that can ensure that  the right temperature and pressure with the addition of the correct chemicals are in place. Otherwise you will not have effective cleaning.
  • Long pipes that has many turns in it and no way to dismantle that pipe.
    • We have been into factories where we have actually asked them to angle grind or cut off the actual pipe. We then have a look inside the pipe and in the pipe we see the actual biofilm build up.
  • Flexible hoses
    • Most equipment would be stainless steel, but here and there are packing machines there are flexible type hoses usually made out of rubber or a similar compound. These are very high risk.
    • These are not replaced often enough and the rubber starts to perish.
    • Small cracks start to form and bacteria can then adhere to these areas more easily than the stainless steel.
    • These then have the opportunity to grow into biofilms.

Often ,the last portion of the packaging machine is not involved in the loop of the CIP, is not going to be part of the true CIP system.  These nozzles and pipes must be dismantled regularly and then cleaned and sanitised manually. scrubbed down and soaked in a proper sanitiser.

By examining all of the parts of the plant we will often find visible contamination.  Swabs can be taken of the visible contamination for confirmation however, the contamination may not be visible, where swabbing is also recommended.

Poor plant design

  • Look for parts of the plant that are rough, hard to reach areas, rough joints, or areas which could harbour bacteria.
  • These rough welds or rough parts of the system that are difficult to get to  or difficult to.  It’s going to be easy for bacteria to hide and grow.
  • We need to  make sure that the entire plant is as smooth as possible, in order to prevent the bacteria from adhering and growing in these sections.
  • Any rough wells, rough joins, poorly maintained parts of the plant, swab these sections and then do the testing.

Poor plant maintenance

  • Look for damaged areas in the plant , these may be cracked tiles.
  • We have swabbed cracks in the tiles, deep floor grouting, cracks in the walls and found pathogens hiding in these areas.
  • Floors are especially of concern, because they are wet and moist and often have dirt build up that creates the perfect environment for bacteria to grow in.
  • Damaged conveyors, damaged pipes, seals, where ever there are taps and valves, are areas where seals can perish and become damaged and support bacterial growth.

Staff hygiene

Observe staff in the factory rather than just taking hand swabs. Spending anywhere up to an hour possibly even more depending on your processes and just watching staff. See what they are doing

  • Are they dropping something onto the floor and picking it up?
  • Are they scratching part of their body?
  • What are they actually doing?
  • Are they washing their hands properly? Observe their hand washing procedure,
  • Are they scrubbing their boots properly?

You may have the correct processes and procedures in place when it comes to staff hygiene, but what are the staff actually doing?  The only way to find out what they are doing is to observe them.

In terms of swabbing, we would recommend taking random hand swabs.  If you are looking for pathogens, you can swab staff members while they are busy working, swab boot washers and brushes.  Meaning that the equipment that the staff are using to clean themselves with, may also be a problem.

We have found Listeria contamination  in boot washing machines before, because they were not subjected to a cleaning and sanitising process.

  • Check all of your PPE.
  • Check the systems involved with cleaning of your staff.
  • Observe your staff, see what they are doing.

Raw materials

If your raw materials are suspected, testing the raw materials will be necessary. Raw material in a process which does not make use of heat as a CCP, such as salads are obviously very important.

If you have a heat based CCP that does eliminate or reduce bacteria, usually heat, then you  have that CCP to rely on. However, if you are making food that is not being heat treated you don’t have heat as a weapon against the bacteria.

Its vital to food safety  to make sure that you are buying raw materials of a high standard because whatever you put into that salad or that sandwich is ultimately what is going to go out.  Because you don’t have the opportunity to kill the bacteria.  We would recommend that suppliers of  raw materials to your business have a food safety system in place and that they are also able to provide their own microbiological tests or evidence of their own microbiological tests.

And that you engage with them to understand what they are doing and what systems should they have in place. Random testing of products will also give you comfort that the foods are of the correct quality. If you have got a positive result, testing specific batches of raw materials that are used in the product will also help to either prove or to eliminate your raw materials as part of the problem.

positive result microbiology

Once we have been through the entire process, had a look at everything from

  • Receipt of raw materials.
  • Right through to the distribution of the final product and everything in between.
  • Checked your staff hygiene.
  • Cleaning and sanitising
  • PPE
  • No CCP failures
  • No problems with the equipment
  • We have now identified our problem.

How to Prevent a positive result in the future

So once we know what the cause of the positive result was, we need to ensure that it never happens again.

Failure of a CCP

Look at why the CCP failed and  ensure this is eliminated going forward.

If it was Failure of equipment, you may need to have another type of equipment or a better supplier of that equipment. If it’s a thermometer that hasn’t worked correctly you made need to calibrate your equipment more regularly, you may need to thermometer verifications more regularly.

Why did the CCP fail and put something in place to ensure that it doesn’t fail again in the future.

Has the CCP been correctly identified?

  • Implement the new CCP and ensure it is monitored.
  • It is important to understand why was the CCP missed in the first place.
  • It may be the way that are you reviewing or having a look at your processes but whatever the reason is, again try to find what that is.
  • Is it a lack of education, is it a lack of understanding of what a CCP actually is, find out what that is and again make sure that it doesn’t happen again in the future.

Poor handling after CCP

  • Ensure the foods are handled with the utmost care after the CCP to prevent contamination.
  • Try and understand why was this problem not picked up in the first place.
  • Your initial analysis of your system, why wasn’t that problem picked up in the first place.

If you can understand why the problem was not detected  in the first place, whatever those problems may be, we are ultimately going to be able to understand the what, how and why’s and prevent them from happening in the future.

Cleaning problem

A reputable chemical supplier, one that preferably has their own ISO standards in place and products registered with the NRCS, is your first port of call.  Make sure that you are getting the right advice and the right service from the chemical suppliers.

They are ultimately the companies that are making the chemicals that have made chemicals for a specific reason, for a specific cleaning or sanitising within a specific environment and they are the ones that need to be guiding you in terms of what products you need.

You will need a detergent to remove the dirt, and then you will need a sanitiser to kill the bacteria afterwards. These are your two most essential chemicals.

  • But what types of detergent?
  • What types of sanitisers will be best supplied within your facility?

Its going to be something that your chemical suppliers will be able to help you with.

If it’s a cleaning problem, implementing a true CIP.

We would recommend calling in a professional company that deals with the design and implementation of CIP’s and make sure that all areas of the plant that are not part of the true CIP are dismantled, scrubbed and sanitised on a regular basis. These sections of the plant are critical. If you are not getting to them, either with the CIP or regular dismantling and cleaning.  It is almost guaranteed that over time you are going to have a biofilm build up in those sections, which will cause problems down the line.

This is absolutely critical and we have seen this in so many cases, anything from water bottling plants, through to sauce plants through to meat processing.  It is extremely important to make sure that you are accessing all of your areas of your plant, either via a true CIP or properly dismantling, cleaning and sanitising.

Poor plant design

  • You may have to redesign or eliminate the poorly designed part of the plant.
  • By way of example, a plant many years ago had trolleys where the food was placed on to and the bottom of the trolley had a standard metal mesh. The mesh is extremely difficult to properly clean because there are so many little nooks and crannies and it turned out that this was one of the areas where the bacteria was breeding.  Just by taking the mesh out and putting in a smooth stainless steel surface at the bottom of the trolley, that part of the problem was eliminated.
  • Ensure that the plant is properly designed to be smooth and smooth as possible wherever the food makes contact.
  • Any dead ends must be eliminated from the system.
  • We don’t want anywhere where the food, water or any kind of liquid or solid can accumulate and spend extended periods of time, because the bacteria are going to grow.

Plant maintenance

Plant maintenance is defined as any damaged areas of the plant especially cracks and damaged sections which could allow the bacteria to grow.

Poorly maintained parts of the plant that come into direct contact with the food are the most critical, yet even if you have chipped or cracked tiles where bacteria are growing and surviving they are going to be picked up by the foods and people and spread throughout the plant.

Staff hygiene

  • Training is also important. Make sure that staff are trained and remind them until it becomes a habit.
  • Don’t think you have trained the staff, told them what to do once and they are going to remember that forever going forward.  It doesn’t happen that way.
  • You have to watch what your staff are doing, don’t walk through your plant with a blinker on or just walk through your plant.
  • Make sure your eyes are open to what’s going on all the time.  Watch your staff, see what they are doing and if there is something that you identify that is a problem,  call them out and correct them until it becomes a habit.

Raw materials

  • Sign on raw materials from companies that have a proper food safety management system in place and that can also supply their own certificate of analysis for their food.
  • You need to be confident that your suppliers are providing you with the correct quality and safe food.

Implementing a monitoring system

positive result microbiology

A monitoring or microbiological system in your plant is going to be there and it is going to be designed to try and detect if there are any problems.  So the programme must be designed to find potential problems and not just try to give good results.

Very often we see microbiological environmental swabbing programmes or testing programmes that are designed to try and show that the foods don’t have any problems. Rather than trying to uncover problems.

There is a fundamental difference. 

When trying to uncover a problem in the factory, we really need to go and look for it. If you have pathogens hiding in your factory you really need to try and find them. You cannot just pay lip service to environmental monitoring.

If you have Salmonella or Listeria hiding in your factory you need to be going and looking in those hard to reach areas, nooks and crannies, swabbing and trying to find out where it is.

You cannot just be swabbing clean surfaces and easy to reach areas, taking 10 swabs and saying they all came back negative, that “I don’t have a problem in my factory”. Because those problems may be in the hard to reach areas where you are not looking.  The monitoring systems need to be  designed to try and detect the problems.

Because if you don’t know that you have got them you are not going to be able to fix them. Testing for pathogens is different for testing to prove cleaning efficacy. When you trying to prove cleaning efficacy you are going to clean down the areas that you want to swab.

Once its cleaned, you are going to take a swab of the certain area, usually a 10cm x 10cm. You would then usually do a total bacterial count possibly even yeasts and moulds sometimes even an E. coli count to prove that your cleaning and sanitising has worked.

When we are looking for pathogens, we don’t have to limit ourselves to a 10 x 10 cm area.

We want to try and find what is going on. Don’t swab a small 10×10 cm area of the drain, swab as much of the drain as possible. Take the trap out of the drain, swab as deep down as you can, remember we are trying to detect the pathogen, we are not trying to determine counts per square centimetre.

We really want to find is there pathogens hiding in that drain or if you have got particular machine that you are worried about.   Try and swab as much of the area in question as possible to try and detect this pathogen.

You may also want to swab during production because remember if you have a production line especially after a CCP, if you are looking for pathogens, swab during production.

Don’t be scared to do that because during the production process there shouldn’t be those pathogens present anyway. We are not going to do total bacterial counts because general bacteria from the product may be resulting in these high counts.

The detection method is far more sensitive

But when we can’t  find pathogens, make sure you have a different mind-set to try to find them.  When trying to find pathogens, make sure that you use detection methods in the laboratories.  So when you send your tests off to the lab, when you are looking for pathogens such as Salmonella, or Listeria use the detection method.

The detection method is far more sensitive than the enumeration method and can detect pathogens at very low levels in swabs or in the foods.

We often find factories that have got an environmental monitoring system or they have got a food testing system in place and its coming back with a negative result all the time, we have a look at what types of tests are being done and it may be an enumeration method that is not sensitive enough to pick up low levels of the pathogen.

It is very important to use a detection method and implement an effective food testing programme.

You don’t need to test every single product that comes out of your factory, because you won’t have anything to sell. But according to the risk of the product and your factory, get an effective food testing programme together where you are testing some of your raw materials, testing in process foods, testing final products, and doing environmental swabs.

Remember, proving efficacy  versus trying to look for pathogens, testing your water, taking hand swabs.

This is going to give you information over time as to what is going on in your factory.  And it will also be an early warning system to provide you with information that there are potentially problems occurring in your factory.

Lastly,  use a SANAS accredited laboratory for all your microbiology tests.  A SANAS accredited laboratory will ensure that the correct methods are being used and that you have accurate results that are being explained to you.

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