Who do I test for?

So you are asking yourself, what on earth is she talking about, who is she talking about?

Well, I am referring to the microscopic, living cells, bacterial or fungal....the microorganisms with both a name and a surname, that you need to select to test for in your sample/s. That is why I would not say “what should I test for?”, but “who?”!

Microorganisms are named using a term referred to as Binomial nomenclature. It is a two name system (name and surname), but in microbiological jargon.

1. Genus; and 2. species (greek or latin origin), that describes some characteristic of organism. For example: 

Bacillus subtilus
Bacillus: a small rod subtilus: slender

Escherichia coli
Escherichia: after discoverer, Prof. Escherich coli: of the colon

Staphylococcus aureus
Staphylococcus: Staphyle, a bunch of grapes coccus, berry aureus: L. adj. aureus, golden

Now that you know why a microorganism is called what it is, this may assist you in determining and understanding why
certain tests are performed on different food products. 

Here are some general guidelines on how to select who to test for?

  • Food products are all exposed to three types of microorganisms: natural flora, flora responsible for spoilageand pathogens. Natural flora and spoilage flora may be categorised as the similar flora. Natural flora are microorganisms that are a part of the food makeup and may be responsible for the characteristics of the product e.g. Lactic acid bacteria & gherkins, yoghurt production; and yeast in block of Baker’ Yeast. However, these microorganisms can also result in spoilage of the product and influence the product’s shelf-life when they multiply to numbers that exceed the specification of the product.

    Pathogens are the group of organisms that may result in the product causing disease and/or death in the person consuming the product. They include gram negative species from the Enterobacteriaceae group like E.coli and Salmonella. Gram positive pathogens are also well-known contaminants and include Bacillus cereus, Listeria monocytogenes, Clostridium spp. and Staphylococcus aureus.

    Pathogens are generally not inherent to the product, as GMP and HACCP ensure that the food is safe to consume. However, should the product not be manufactured according to such guidelines or poor hygiene practice causing post-manufacture contamination, these microorganisms shall contaminate your product. By using these two/three types of microorganisms as a base of who to test for in your food: Spoilage bacteria and pathogens, you can’t go too wrong.


  • Spoilage microorganisms: these microorganisms are generally covered in the following range of tests and depend on the type of product you are testing. They generally result in product spoilage and are considered as good competition for the pathogens. If the spoilage microorganisms are high in number, they will out-compete an invasion by pathogens for their territory. Such tests include: 

o Total Aerobic Count/Total Viable Count/Aerobic Plate Count
o Lactic Acid Bacteria Count (not applicable to fermented products)
o Yeast Count
o Mould Count

You may consider the spoilage of your product by microorganisms a financial loss to your company, but how do you compensate for someone’s death? Spoilage microorganisms are definitely preferred over their nemeses, the pathogens. One must just consider that some products may contain inherently high numbers of natural or spoilage flora, and may not undergo any further processing that would significantly reduce the microbial load, making the above testing necessary. Examples of such products may include fresh vegetable grown in or on the ground (carrots, lettuce, spinach). Reasons for such high load may be attributed to the plants root systems that draw vital nutrients, water and microorganisms into the root (carrot) and leaf (lettuce and spinach). The microorganisms thus form part of the internal make-up of the product, which cannot be treated without destroying the product itself.

  • Pathogens: these microorganisms may vary from product to product and factory to factory. However, one common factor that may cause contamination of your product by such microorganism is the human factor.

    o Human factor: products that are handled at any point of your process and where there is no post-human processing that could eliminate such contamination, should be tested for the following:

- Escherichia coli (E.coli) (poor hygiene practices such as handwashing)
- Staphylococcus aureus (S.aureus) (nasal infections or boils)

  • Other factors that need to be considered as sources of contamination include:

o Water: Do you use treated water or water from a borehole, dam or river? Water may be a common contaminant of pathogens including E.coli, Salmonella and Vibrio spp. Your factory water and source thereof, need to be tested too. According to SANS 24, Total Plate Count, Faecal Coliform Count and E.coli Count are minimal testing requirements for any of your water samples.
o Raw materials: Are pathogens being transported into your factory by raw materials such as raw meats (fish, chicken, red) or spices? If such materials are not kept separate and treated before use in your process, they shall serve as reservoirs of pathogenic contamination. And such contamination into your factory may be fuelled when good manufacturing practices and hygiene practices are not met.

Now you know you need to test for two major groups of microorganisms (spoilage and pathogens) - so who in the pathogen groups do you test for?

A general rule is to test final products for these tests related to pathogens (if applicable):

1. Coliform Count (collection name and count for colon derived gram negative bacteria), and specifically E.coli.
One may also test for the larger group of bacteria that combine coliforms with all the other gram negative enteric bacteria – Enterobacteriaceae Count. This is a more general test that would indicate the presence of any enteric microorganisms and family related pathogens. As a general test it does not specify which Enterobacteriaceae have been detected and may include E.coli spp., Salmonella, Shigella and many more.

2. S.aureus Count (should human contact have taken place at any point in the process).

3. Salmonella spp. Detection

4. Bacillus cereus Count (should the product be of carbohydrate/starch origin or contain such e.g. rice, pasta)

5. Listeria monocytogenes Count/Detection (should the product require storage at 4°C or lower). This bacterium is able
to grow at such low temperatures and generally inhabit cold storage units.

6. Clostridium spp. (C.botulinum and/or C.perfringens) (should the product give rise to anaerobic growth conditions in the product, and/or undergo a process by which the microorganism can convert to it spore form). These bacteria are strict anaerobes (survive only in the absence of oxygen) and under adverse conditions undergo metamorphosis from vegetative form to a protective and highly resistant, spore form which enables survival for a long time in products until favourable growth conditions arise. Canned products and ready-to-heat-and-eat products provide favourable conditions for C.botulinum and C.perfringens, respectively.

7. Other pathogens to be considered are Vibrio spp. (fish and related products), Campylobacter spp. (poultry and related products), Pseudomonas spp. (poultry and related products), E.coli O157 spp. (raw meat, fresh produce and related products.

Combinations of the above pathogen tests, depending on the product and its source, should enable you to check who should not be in your product. One just needs to clarify the difference between tests that count the number of microorganisms in the product and tests that detect the microorganisms in your product. Counts, as the name implies, enumerates the microorganisms in the product and generally applies to microorganisms that are allowed to be present at a predetermined and acceptable level in the product e.g. Bacillus cereus: 100 cfu/g. This method of testing would involve plate counting of the number of viable Bacillus cereus in the product. This also enables risk assessment of the product as one can determine whether the count is a cause for concern (80 cfu/g) or not (<10 cfu/g). One must remember, however, that counting methods are limited to counts of 10 cfu/g/ml or more, so if one has a result of <10 cfu/g/ml it does not mean that Bacillus cereus were absent from the product, it just refers to the detection limit of the method used i.e. 10 cfu or more.

By following your product process from farm to fork and applying the above guidelines, you shall know what and who to test for. You are asking do I carry out all testing on all products each time I test...well there is enough argument there for another article! I trust you are on your way to confidently selecting your tests...

Remember small steps and you will MAKE SENSE OUT OF MICRO....




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