Monday, January 19, 2009

Peanut butter with that little bit extra

Over the last couple of weeks, Peanut Corp. of America has recalled 21 lots of peanut butter manufactured in its Blakely plant in Georgia. The product has been linked (by molecular biology techniques) with clusters of Salmonella infections in schools, long-term care facilities, hospitals and other institutions. Genetically indistinguishable strains have been isolated from the product and from patients. 470 people in 43 states have been confirmed as being infected with genetically indistinguishable strains of Salmonella Typhimurium and 90 have been hospitalized. Unfortunately, at least six deaths have been attributed to this outbreak.

The FDA has taken the extraordinary step of urging consumers to postpone eating any commercially prepared or manufactured products containing peanut butter and institutionally served peanut butter (because the implicated peanut butter is supplied only in bulk) until further information becomes available as to which products may be affected. Clearly, this will have far-reaching effects and we are already seeing voluntary recalls of various products in Tennessee, Indiana and New York.

How could this situation have arisen? This is not the first time that peanut butter has been linked with Salmonella infection. The New Zealand Food Safety Authority classes peanut butter as a prescribed (high risk) food because it is produced from peanuts, which have been found to contain mycotoxins (including aflatoxin), mould and insects. So the potential hazards are known. We need to go back and look at the process of peanut butter manufacture for a possible explanation of the current outbreak. The following description is something of a simplification:

Peanuts are actually groundnuts – the flower wilts and bends over, penetrating the ground. The peanut forms under the ground. Harvesting, cleaning and pre-preparation is an involved process, but the most important process is drying to a moisture content that prevents mould growth. The peanuts are shelled, roasted at around 175C and then cooled quickly to 30C. Any Salmonella present on the peanuts is by now destroyed. The peanuts are finely ground and sweetener, salt, oil if necessary and emulsifier are mixed in. The mix is hot filled at around 38C. A further pasteurization step in the jars in a hot water shower may be used here, but not always.

Now we can see where the problem may have arisen. Roasting and blanching are the only lethal process steps in the manufacture of peanut butter. Any contaminating microorganisms entering after these steps may survive in the finished product. Where could Salmonella come from? We don’t know about the Blakely plant yet, but birds often carry Salmonella, so strict control of birds and insects is required. Discharge of fines onto the roof of the factory may attract birds, which defecate on the roof. If the building is not well maintained, rain can wash the contaminating bacteria into the plant. A leaky roof and sprinkler system was the cause of an outbreak in February 2007 at the ConAgra Foods Inc. plant in Sylvester, Georgia. In that case, the Salmonella were thought to have come from raw peanuts or peanut dust. Equipment may harbour Salmonella in seals and hard-to-clean parts. Personnel may also carry Salmonella into the plant, either in their intestines or on footwear, so again, careful supervision of employee hygiene practices and use of red line areas in the post blanching operations is the way to control contamination.

It will be interesting to see what the FDA comes up with in the current investigation. When it’s all finished, this blog will carry a further article.

Thursday, January 1, 2009

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.

: 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.

Is Food less safe these days? Part 2

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

: 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