How do you find a needle in a haystack?
Currently, effort and money are being invested by the Dutch government to take another step in food safety. Raw milk sale will be released on 1 January 2025, but that comes at a price: STEC (Shiga toxin-producing E.coli) and other zoonoses must always be absent. But how do you find STEC and is every finding relevant? Finding STEC is mostly searching for a needle in a haystack. In the laboratory, highly sensitive methods are used to find the enemy. STEC is an example, how the world of microbes (bacteria, viruses and fungi) is in a constant turn-over, changing, mutating. Replacing a generation of humans takes 20-30 years, bacteria take less than a day. Changes in this microbial world therefore happen at lightning speed. During the exchange of genetic material, mutations occur, giving the bacteria new properties. Because of our acquaintance with the Corona virus, by now everyone is familiar with the ‘new variants’ (such as delta or omikron) that kept flooding us and alternating over time. It was cause for new fear, new containment measures.
Shiga toxine producing E.coli
The nasty thing about STEC is that it produces toxins, which are released in the gut. The stx-genes are responsible for the toxins. However, the bacterium must also contain an attachment gene for the gut, because only if the bacterium ‘sticks’ in the small intestine, it can release enough toxins to the organism. If not, the bacteria will be defecated without harm. Even more is needed, namely a sensitive organism, like a young child. Because strangely enough, the same bacterium does not make any damage in the intestine of a cow (as well as most adult humans).
It is now known which combination of genetic traits are ‘necessary’ for a replication of this undesirable bacterium to enter the human gut. In the laboratory, detection tests have been developed that can indicate whether a particular combination of genetic traits is present in a milk or cheese sample. And that is really looking for a needle in a haystack. It is therefore important to increase the catch rate, you must make ‘more pins’ for the sensitive equipment to find something. In the PCR run, genes are searched and multiplied. If you want to do it well, you need to culture living bacteria that carry the unwanted genetic traits. And that requires a lot of lab work, experience and knowledge.
The PCR test is thus used to find very low concentrations of harmful bacteria. This is done because STEC bacteria can cause problems for certain groups of people even at very low concentrations: from diarrhoea to kidney failure and even death.
Better safe than sorry
The European government has quite a dilemma. Its task is to monitor the food safety of the population, and it faces the dilemma that the bacterial world does not stand still. On top of that, we are all not getting healthier, our resistance is probably decreasing, we are getting older and eating unhealthily. While originally the STEC bacterium was linked to ruminant products (milk, meat), it was a ‘total surprise’ that over 10 years ago mainly women (in the age of 20-40) died from a new STEC variant. A new STEC bacterium was found to have spread in fresh salad, probably through a human source of infection. Nothing to do with cows, milk, cow shit and cheese. What you see after such events (outbreak with mortality) is a tightening of the rules, under the guise that this ‘must never happen again’. Meanwhile, across Europe, all STEC-accredited laboratories use the same test to catch STEC in food. Milk products are thereby pushed into the ‘suspected’ category for which applies, that one enforces differently here than in foods that theoretically pose fewer problems.
Searching for STEC in the lab
After 25 grams of (finely ground) cheese or milk is incubated in a buffer medium for 24 hours to multiply bacteria, the PCR test is unleashed on the mixture to detect stx-1 and/or stx-2 genes. If so, your cheese is already labelled as ‘suspected presence of STEC, or ‘STEC suspect’. If you want to get it right as a government or control institution, you have to do more, namely you have to demonstrate, that you are dealing a) with live cultureable STEC-bearing E.coli bacteria, and b) that there are also combinations of genetic traits in the same bacteria, such as the attachment gene eae plus stx1 or stx2 variants. In some European countries additional testing for so-called serotypes is done, a kind of ‘blood group testing’, where the naming O157H7 shows up or other combination of O and H traits. This serotyping is more often replaced by genetic determination of the stx genes, which can be done more easily. How do you act now as a government? The initial screening for STEC is the same everywhere, namely the PCR test for stx genes. Whether you then do further, deeper research to detect whether this STEC is dangerous due to its combination of genetic traits, is not done the same everywhere. Sometimes it stops already with the observation, that stx genes have been found and the product is ‘therefore suspect’.
Coincidence or real problem?
From previous research among German Vorzugsmilch (Berge and Baars, 2019), it is striking, that when STEC is found positive in milk, it is almost impossible to find STEC again in new milk samples. The researchers indicate that one reason for this is that STEC is not homogeneously distributed in milk or cheese and advocate taking larger sample quantities, such as 5 x 25 g of product. Others advocate detecting STEC in places where it can concentrate, such as the paper milk filter, where all cow’s milk has flowed past. No one eats a milk filter and there are still many actions on a farm to further hygienic practices so that E.coli and STEC do not end up in the milk. Almost never do you hear or read, that the test method used might lead to a false-positive result too quickly. Then it depends on your risk assessment whether you sound the alarm, block a farm, or dare to watch it.
When it comes to cheese sampled at an age of 14 days, you can keep the batch of cheese separate until you know more. This is because STEC always disappears from a maturing, ageing cheese, however, depending on its age. This is different with the consumption of raw milk, which is usually been done, before you even get the first lab result. Which does not alter the fact that, as a dairy farmer, you should have additional milk samples tested to prove that you are STEC-free.
STEC is an E.coli bacterium, an intestinal or faecal bacterium found in the intestines of ruminants. E.coli is part of the Enterobacteriaceae family. To find STEC, your sample also have to contain E.coli, and therefor as a farmer, you have to prevent contamination and smearing of cow dung, clean the teats and udders properly, every time. STEC and E.coli are largely a hygiene problem, which can be solved by cleanliness, hygiene, regularity and habits on a farm.
Does the Loch Ness monster exist or not?
Regular news resurfaces and the question remains, what is swimming around in that huge Scottish lake and whether you can prove it. The monster is a needle in a haystack that is hard to find. What methods can you use to find such a sample and, moreover, will you then know whether it is dangerous? Bacteria in a lake of milk are like the Loch Ness monster, rather monsters. We don’t know when and if and to whom they are dangerous now. If you can already find them with very sophisticated methods, we still don’t know anything about the quantities, the concentrations in the lake of milk, nor do we often know whether the sample carries the right combination of scary, nasty properties. As a regulator, it is then easiest to ban any suspicious bacteria you find in a foodstuff: better safe than sorry. For livestock farmers and cheesemakers, this usually means a very uncertain time, with moodiness and fear surrounding your product. After all, every STEC finding must be reported to the control organisation, the government demands of laboratories; big brother is watching you. Consumers cannot properly assess the danger and turn away from the product. Farmer cheese makers stop producing raw milk cheese as they must live off the sale of their product. In the end, the range of flavours and cheeses narrows, and everything goes through the unitisation of heating, pasteurisation of cheese milk. In doing so, a culture is lost.
