Is Food less safe these days? Part 3

The final in this three part New Year soliloquy on food safety

You'll find the earlier parts in the panels below this one.

Communication: Globalisation has had another effect: within hours we know what has happened in other parts of the world. Multimedia cell phones allow people to send pictures and text; the Internet lets ordinary people put their thoughts in front of anyone who has a computer and of course the news media have worldwide coverage and transmit reports via satellite to every continent. The effect of all this is that we know almost immediately of large scale or unusual cases of food poisoning and food fraud as they occur throughout the world, thus increasing the perceived frequency of incidents.

Evolution: When I was an undergraduate microbiologist in the '60s, E. coli O157:H7 was unheard of. It was first identified as a human pathogen in 1982. Other new serotypes have also been recognized, usually as a result of an outbreak. It appears that evolution is continuing at a visible rate, at least in the microbial world. Dr Chris Bell and Alec Kyriakides† have expressed it beautifully: “Genetic promiscuity is facilitated by a range of genetic elements including plasmids, transposons, conjugative transposons and bacteriophages* . The ability to evolve through horizontal gene transfer and acquire ‘foreign’ DNA, has resulted in novel phenotypes and genotypes emerging”. This mix-and-match behaviour has resulted in the formation of diarrhoea-causing strains that possess previously unreported combinations of virulence factors. The study of DNA sequences in old lineages of E. coli has shown that these lines have acquired the same virulence factors in parallel. Natural selection has thus favoured an ordered acquisition of genes and a progressive build-up of molecular mechanisms that increase virulence (Reid et al., 2000. Nature, 406 64-7). Just this week in the journal Science, John Chen and Richard P Novick have reported that staphylococcal bacteriophage can transfer staphylococcal pathogenicity "islands", pieces of DNA containing superantigen genes and other transferable elements, to Listeria monocytogenes at the same high frequencies as they transfer within Staphylococcus aureus. See here

This might sound esoteric, but the practical result is that we will see more novel virulent bacteria that will in the future cause new food borne illnesses.



Obviously, the examples I have given above contain elements of more than one of the highlighted causes. Does this all add up to an answer to my original question? I think that we can draw some general conclusions.

• Modern food manufacturing processes may be technically more advanced than traditional food production
• These processes can be very reliable and make vast amounts of safe food at affordable prices
• When something does go wrong, the results may be catastrophic because of the scale of operations
• Human error and fraud are ever-present hazards to a safe food supply
• Our perception of the frequency of food poisoning or food fraud incidents may be influenced by the ease of international communication
• Microbial evolution means that we will never produce totally safe food

On balance, I think that our food is actually safer than it was 25 years ago.


†Bell, C. & Kyriakides, A. (2002) Pathogenic Escherichia coli. IN
Foodborne pathogens: Hazards, risk analysis and control. Blackburn, C. de W. & McClure, P.J. Woodhead Publishing, Cambridge, UK.

* Plasmid – a small circular independently replicating piece of DNA in bacteria; Plasmids often carry virulence factors, antibiotic resistance or toxin coding genes
Transposon - sequence of DNA that can move around to different positions within the genome of a single cell, possibly causing mutation
Conjugative transposon - integrated DNA elements that excise themselves to form a circular intermediate, which can transfer by conjugation to a recipient and integrate into the recipient's genome. Conjugative transposons have a broad host range and are probably as important as plasmids in the spread of antibiotic resistance genes in some genera of disease-causing bacteria (A A Salyers et al., (1995) Microbiol Rev. 59(4): 579–590).
Bacteriophage – a virus that infects bacteria and may ferry small sequences of bacterial DNA from one host cell to another. The DNA may integrate into the recipient’s genome and confer new characteristics, such as the ability to synthesise new enzymes.

Evolution in action

Over the last three weeks, a rare form of Escherichia coli has made an appearance in Germany.

E. coli is a normal inhabitant of the gut of man and animals and is found there in very large numbers.  They are mostly harmless and actually help us by producing vitamin K.  However, some strains are pathogenic and cause diarrhoea.

Individual strains are recognised by their antigenic signature. The antigens are found on the surface of the cells, on the flagella and in the capsule that surrounds the cells.  Thus one of the strains that hits the news quite frequently is referred to as O157:H7.

The strain now causing havoc in Europe is E. coli O104:H4.  This has rarely been seen as a cause of disease.  However, the current outbreak is shaping up to be one of the most dangerous ever seen.

Why has this happened?

That's a question that none of us can answer yet, but the information on this strain is growing rapidly.  It can produce a very damaging toxin, called Shigatoxin.  The bacterium causes bloody diarrhoea, which is bad enough in itself.  But bacteria producing this toxin can also go on to produce Haemolytic Uraemic Syndrome, normally affecting around 2 to 10% of patients, who are often very young or immunocompromised.  However, O104:H4 appears to be very virulent and around 30% of patients, who were not in the high risk group, have developed this life-threatening syndrome.  So far, 18 people have died.

The fact is, bacteria evolve very rapidly.  We see one strain develop resistance to an antibiotic and soon other strains become resistant too.  This happens because bacteria can  exchange genetic information by a number of different mechanisms.  The rate of mutation might be very small, perhaps one in 10 million replications produces a mutant and most of these mutations are probably lethal.  However, a single cell can potentially produce a population of around 17 million cells in 8 hours.  That allows for a lot of mutations.  If even one of these mutants has some advantage over the rest of the population, or at least no disadvantage, the mutation will spread through the population.

This might surprise you, but bacteria also suffer from virus infections.  These viruses, or bacteriophages, invade the cells and cause them to make more virus particles before bursting open to restart the infection cycle.  Occasionally, the new virus particles contain a bit of bacterial DNA and transfer it to the next host.  Sometimes, whole genes can be transferred.

It appears that O104:H4 has not only the Shigatoxin gene, almost certainly transferred by bacteriophage, but has also picked up some other virulence factors.  This is why it is so dangerous - the toxin is very damaging to human cells, particularly in the kidney, and the bacterium appears very capable of initiating infection.

I believe we are seeing evolution in action.  A normally benign bacterium has become a killer.

Is Food less safe these days? Part 2

You'll find Part 1 in the panel below this.

Globalization: The globalized food supply means that raw materials may be processed outside of our own country and the foods transported to our local suppliers for distribution. The opportunities for poor process control and contamination are again significant. Many countries rely heavily on imports of food. The development of Chinese industry means that these imports are often sourced from China, though not exclusively. The Chinese government is moving to improve control over food manufacture, but faces an uphill battle in such a large country with so many diverse regulatory authorities.

Greed: The huge demand for food is a temptation for some unscrupulous manufacturers to try to make a fast buck by adulterating food or passing off poor quality materials. The prime example in our time is the use of melamine to increase the apparent protein content of milk and pet food. See here However, food fraud has been going on literally for centuries.

Adulteration of food is usually done with inferior materials to increase the bulk of the real item and thus increase profits. In 1820, a German scientist Frederick Accum published his book “A Treatise on Adulterations of Food and Culinary Poisons”. He described sloe leaves added to tea, lozenges made from pipe clay, custards poisoned with laurel leaves, floor sweepings mixed into pepper and copper used to colour pickles green.

In 1857 Arthur Hill Hassal, an English physician and microscopist, wrote a book “Adulterations Detected, or Plain Instructions for the Discovery of Frauds in Food and Medicine”. He noted that “Adulteration prevails in nearly all articles which it is worth while to adulterate, whether it is food, drink or drugs”. Watering of milk or of “cream ice” was a popular activity, but clay and dust were used to bulk up many foods. These days, companies have analytical techniques to detect adulteration of food, but this works only if the company is not involved in the fraud. Government organizations like the New Zealand Food Safety Authority and the US Food and Drug Administration cannot guarantee the safety of foods by end product testing. See here The best that can be achieved is management of food safety through risk management programmes.

The following new book offers interesting reading: Wilson B (2008). “Swindled: the dark history of food fraud, from poisoned candy to counterfeit coffee”. London: John Murray Publishers.

In the final, Part 3: click here:  Communication and Evolution

E. coli strikes again

Five people in the United States have died since March and approximately 200 are sick as a result of an Escherichia coli infection apparently acquired from romaine lettuces grown in the Yuma region of Arizona.  However, the authorities have been unable to pinpoint the source of the contamination.

Though E. coli are found in the gut of man and animals, only certain strains cause serious illness.  These strains have assembled many genes that enable them to attach to the cells lining the intestine and produce very damaging toxins called Shigatoxins.  This is an example of the continuous evolution of bacteria.  Many of these new strains are the result of bacteriophage infection transferring genes between bacteria or possibly by direct transfer between strains.

Various posts responding to news reports of the outbreak have suggested washing the lettuces as a means of preventing illness.  Unfortunately, washing, even in chlorinated water, will not guarantee removal of the bacteria, as they can attach to the lettuce or even localise in the stomata of the leaves.  I obtained the following image from https://www.inverse.com/article/28938-e-coli-detection-lettuce-feces.

You can see bacteria within the stoma; it is clear that they would be very difficult to wash out.

This outbreak was originally thought to be caused by bagged and chopped lettuce, but inmates in a prison in Alaska also became ill after eating whole head lettuce.  In view of these facts, it is unfortunate that consumer advocates are urging the FDA to introduce new rules to speed up investigation of such outbreaks.  It is hard to see how new rules would influence the investigations, given that it has so far been impossible to tie the contamination to a single farm, processor or distributor.

The one fairly sure conclusion is that the lettuces have become contaminated with faeces, since this E. coli is not a natural inhabitant of the environment.

Is food less safe these days? Part 1

Over the Christmas period I have done a lot of eating and drinking and being merry. I’ve also done a lot of thinking about food safety. In the last year we seem to have read almost daily of Listeria being found in deli meat, that babies have been poisoned by formula milk, children have been hospitalized with failing kidneys resulting from Escherichia coli O157:H7 infection, that melamine has turned up in yet another food product, or that an established company has closed its doors because of massive losses resulting from a food recall. Is our food less safe these days?

I don’t think that there is a simple answer, but I do have some suggestions. In this three-part posting I’ll share them with you.

I think that the whole thing can be analysed under a few subheadings.

Food Preparation: Some of my Christmas celebrations have involved large functions where caterers have served meals to hundreds of partygoers. These meals could not have been produced on the premises, so the food must have been pre-prepared and transported to the venue in insulated containers or perhaps reheated before serving. Other celebrations have been more modest, catered by the “bring a plate” approach. We have had barbecues, where foods were cooked outside on gas or charcoal burners. All of these scenarios have at least one thing in common – the foods were prepared by others for us, perhaps in non-ideal conditions, or were not eaten immediately after preparation. The opportunities for contamination of the food, incomplete cooking and growth of bacteria were numerous.

Centralization: The economies of scale lead to evolution of very large manufacturing operations with huge distribution networks. Smaller companies are squeezed out of the market. If something goes wrong in this supply chain, the impact can be widespread. In 2000, Staphylococcus aureus bacteria built up in raw milk that was unable to be cooled for several hours after fat separation in Snow Brand's Taiki factory. Ultimately, at least 14,700 people, mostly in western Japan, were affected by food poisoning after consuming milk or related products made by the company. Topps Meat Company, a US company specializing in manufacture of frozen ground beef, recalled 21.7 million pounds of ground beef, bringing the total recalls in the US between April and October 2007 to over 30 million pounds of red meat, mostly hamburger. The reason was that there had been a number of cases of Escherichia coli O157:H7 infection tied to its products. There was evidence of an inability to identify unique batches of product and this probably contributed to the size of the recall. The USDA also cited the company for “inadequate process controls in the non-ground meat production line”.

Ignorance may play a part. Last Easter in New Zealand, 22 people were poisoned, some seriously, when they consumed comb honey which had been made by bees that collected honeydew from tutu plants (Coriaria arborea) infested by vine hoppers. The upshot was that the honey contained large amounts of the toxin tutin, which is found in the sap of the tutu plant. In April last year, I wrote that this was not a new problem. See here Indeed, F.S. Fastier, Roslyn Emeritus Professor of Pharmacology at University of Otago, wrote last week that he was present at a meeting of interested parties in Wellington in 1964, where the issue was debated. Beekeepers have known how to manage this hazard for a long time, but a small beekeeping operator last year apparently failed to take account of the fact that there were tutu bushes in flower in the bees’ foraging area and continued to sell the comb honey. The resulting poisonings have led to the New Zealand Food Safety Authority introducing legislation to limit the amount of tutin that may be present in honey offered for sale. See here
This has not pleased everyone – some think the regulations don’t go far enough, some in the industry consider them to be unnecessary. However, NZFSA could not stand by and do nothing without risking the health of the population and the future of the lucrative New Zealand honey industry. The regulations will be reviewed at the end of the 2009 season.


In Part 2: click here:  Globalization and Greed

Fungi for Christmas!

The image below is my Christmas card to you all.  I didn't create it - the image has been doing the rounds on a science website, but it is truly a microbiologist's Christmas card.

For those who are interested, the Petri dish was seeded with the following:

Top: Talaromyces stipitatus; Tree: Aspergillus nidulans; Ornaments: Penicillium marneffei; Trunk: Aspergillus terreus

Not all of these are likely to be found in food -  T. stipitatus was isolated from rotting wood and can produce some interesting enzymes that may have application in the agri-food industries, P. maneffei can cause human disease, mainly in HIV patients.  A. nidulans was probably one of the first fungi I studied as a microbiology undergraduate, and has been very important in the study of recombination, DNA repair and experimental evolution.