Nothing new under the Sun

 Sorry!  That was a click bait title.  However, as far as food poisoning goes, there really is very little that is new - the same old suspects keep turning up.

I've written about Clostridium botulinum before (and you can find those posts by searching the labels).  It has now caused food poisoning in Vietnam, this time in Minh Chay pate products, which have all been recalled.  The outbreak is reported in Food Safety News.  The article includes a photograph of the product, which is packed in screw capped jars and possibly cans.

The Department of Food Safety, Ministry of Health, inspected the premises and found 'sanitary issues' with cleaning and drainage.  The factory was instructed to cease production until the problems were fixed.

There is insufficient information in the article to make definitive pronouncements on the causes of the contamination, but some reasonable arguments can be made.  C. botulinum releases a toxin when it sporulates, and for this it must grow.  Since the bacterium is anaerobic, it requires the absence of oxygen.  It appears, therefore, that the pate was contaminated during manufacture, possibly from the unclean factory environment, and the organism then grew in the sealed containers.  The article doesn't state whether the product was hot-filled, or heat processed in the containers.  In the former scenario, the spores of C. botulinum could germinate and grow in the product, eventually leading to toxin production.  If the containers were heat processed after filling, it is possible that contaminated cooling water leaked into the containers through faulty seams or seals.

The toxin binds in the nerve synapses and prevents the secretion of acetyl choline, thus preventing nerve impulse transmission.  This usually causes respiratory paralysis, so patients need support to breathe.

Interestingly, if you search for 'Botulin toxin' on-line, the first five hits refer to Botox, the cosmetic treatment to reduce frown lines and crows' feet.  Food poisoning is mentioned almost as an afterthought.

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Clostridium botulinum vs Clostridium sporogenes

Over the last couple of weeks, I have been interviewed many times by radio, television and newspaper reporters on the issue of the Fonterra whey protein concentrate scare and the resulting recall of infant feeding formulae.

One question that has always cropped up is "Why did it take so long for the company and Ministry of Primary Industry to tell the public whether the contaminant was Clostridium botulinum or Clostridium sporogenes?"

I have never knowingly worked with C. botulinum.  It's a dangerous organism because it produces a neurotoxin and special precautions are necessary to work with it.  But when working with food samples and isolating anaerobes (microorganisms that grow in the absence of oxygen), there is always the possibility of unwittingly isolating and amplifying something dangerous.

However, some of my associates have worked with these bacteria.  They tell me that the two bacteria are very difficult to distinguish.  Indeed, Dr Heather Hendrickson, lecturer in evolutionary genetics, Massey University, has said that the two bacteria differ by only one gene.  So obviously, growing the bacteria in culture media and conducting biochemical testing will not allow them to be distinguished.  Very specific molecular techniques must be applied to show the difference and I am told that there are difficulties in carrying out this method.  ESR in New Zealand has the ability to conduct these analyses.

Just for interest, I searched for SEM images of the two bacteria and found the following on-line.  Both images are false colour, and show the impossibility of telling them apart by their appearance.  See the difference?

Clostridium in whey protein turns out not to be C. botulinum

The Ministry of Primary Industry today made a statement that tests on the Clostridium species isolated from Fonterra whey protein concentrate show that it is not C. botulinum.  The organism is C. sporogenes and poses no food poisoning threat.

This will be a huge relief to Fonterra, the New Zealand government and MPI, not to mention hundreds of parents of babies being fed on infant formula.  However, the damage to the company's reputation and the Pure New Zealand brand has been massive.  Even countries that did not receive any of the affected powder and formulae have banned the import of New Zealand dairy products.

Why has it taken so long to get a definitive answer and why did the company recall the product?

Tests of products that incorporated certain batches of whey protein concentrate showed growth of sulphite reducing clostridia, though the protein concentrate itself was within specification.  Further testing of the bacterial isolates suggested that they might be C. botulinum.  Because of the severity of the illness that this microorganism can cause, the company withdrew certain batches of whey protein concentrate from the market and advised its customers accordingly.

It is quite difficult to distinguish certain closely related types of bacteria, and this is the case with C. botulinum and C. sporogenes.  The bacteria have to be isolated in pure culture, various biochemical tests must be performed, DNA must be extracted and PCR reactions carried out with specific primers.  While this sounds easy, and appears to be very rapid if the CSI-type of TV programmes are to be believed, in practice it is very tricky and time consuming.  Extracting the DNA from the bacteria without its being degraded by DNAse enzymes is apparently difficult.  There are few laboratories in the world capable of carrying out the testing reliably.  (This is not a bacterium to be trifled with.  When I worked in England for a year at the Food Research Institute in Norwich, only vaccinated people were permitted to go into the botulinum laboratory because of the risk to workers of lethal intoxication).  The 'gold standard' test for toxigenic C. botulinum capable of causing the neuroparalysis is the mouse lethality test.  This must be performed very precisely, according to an internationally recognised approved procedure and involves specially bred mice of a particular age.  The various tests have now been completed, allowing the announcement from MPI today.

Did Fonterra do the right thing in notifying its customers of the potentially hazardous product and recalling the protein concentrate?  In my opinion, they did.  Certainly, it has caused the company embarrassment and financial loss, but what of the other option - keeping quiet and hoping the problem would go away?  The death of even a single baby from botulism would have been far more damaging, and devastating for the parents.

Will things change in the future?  Only time will tell what regulatory changes may follow, and new testing requirements are imposed.  One thing is sure: occasionally, food manufacturers will make a mistake; equipment will malfunction, or a set of circumstances will come together that result in potentially unsafe food.  The entire food industry must strive to reduce the frequency of these incidents to an absolute minimum by close process control, based on appropriate and robust risk assessment and hazard control measures.

What is "sporulation"?

A friend asked me today "What is sporulation?"

There are essentially two genera of bacteria - Clostridium and Bacillus - that can produce very resistant stages called "spores" in response to unfavourable environmental conditions.  In contrast to the vegetative, or growing, cells, the spores are resistant to many environmental conditions, including heating and drying.  While the vegetative cells may be killed by heating to about 75C, the spores of C. botulinum can withstand boiling for more than four hours.

History gives us an example of how resistant spores can be:

In 1946, the British undertook some biological warfare experiments on Gruinard Island in the Inner Hebrides.  Small bombs containing anthrax spores (from Bacillus anthracis) were detonated near to groups of tethered sheep.  Within days, the animals were dying.  The government realised that the island would be hazardous to all mammals and quarantined the island indefinitely, occasionally testing the soil for viable anthrax spores.  On every testing occasion, the spores were shown to be viable.  This continued until a public campaign in 1981 forced the decontamination of the island.  This was achieved in 1986 by spraying 280 tonnes of formaldehyde solution onto the island and removing the most heavily contaminated topsoil.  The island was demonstrated to be safe and returned to its original owners.

It's important to note that soil normally contains some bacterial spores, including those of C. botulinum.  That means that raw vegetables and fruit carrying soil will often also be carrying spores.  Even milk drawn from healthy cows may initially be contaminated with soil organisms from their hides.  The normal pasteurisation process will kill the vegetative cells, but not the spores.

Clostridium botulinum causes problems for Fonterra

Fonterra, New Zealand's largest dairy manufacturer, last week issued a warning that Clostridium botulinum had been found in three batches of whey protein, (approximately 40 tonnes), which can be used to boost the protein content of many foods, including infant feeding formula.

The warning caused a New Zealand manufacturer of infant feeding formula to recall certain batches of product.  Fonterra Chief Executive, Theo Spierings also flew to China to discuss the issue with Chinese food safety authorities.

Apparently, the source of the bacteria has been traced to a dirty pipe in a processing factory.  If this is true, it's a serious lapse in process control and obviously should not have occurred.

The whey was made in May 2012 and it is unclear why the contamination has taken so long to come to light and why the company has been so slow to inform the government and the public.  The company became aware of the contamination in March, but it was not until Wednesday 31st July 2013 that tests confirmed the presence of the bacteria. 

There are some possible explanations for the delay: third parties may have tested the product at some point in their own manufacturing operations and found it;  the contamination levels may be very low, resulting in a requirement to test large amounts of product before the contaminants were found.  Certainly, once the bacteria had been isolated, using modern methods,it should not have taken long to confirm the identification.

It is not usual to test dairy products for the presence of Clostridium botulinum.  When bacteria occur in a product at very low level and very infrequently, testing is ineffective in assuring safety and the cost is prohibitive.  An Australian specification for whey protein concentrate does not mention Clostridia.

The concern about the presence of C. botulinum is real and justified.  The bacteria can produce a potent neurotoxin that causes paralysis and death.  There have been only a couple of cases in New Zealand in the last 35 years.  The toxin is released when the cells sporulate, so growth of the bacteria is necessary for toxin production.  Bacteria cannot grow at the low water activity conditions in whey protein powder, but spores could germinate and grow if infant formula containing the contaminated whey protein were made up and then held warm for some period.  The other very serious scenario is that infants fed the contaminated formula might then suffer botulism when the spores grow in the intestinal tract.

This story is not over yet and Safe Food will monitor the developments.

Bacteria in canned food

Looking through the search terms that produced hits on Safe Food this month, I came across "Listeria in canned food".

Is canned food hazardous from the point of view of Listeria?  In my opinion, the answer is "No" with just one small caveat:  "unless the food has been grossly underprocessed, or post- processing contamination has occurred".

Canned foods are divided into two main categories: Low Acid (LACF) and Acid Canned foods (ACF).  The dividing line is pH 4.6, low acid foods having a pH greater than this, and acid food having a pH lower than 4.6.

The significance of this pH value is that Clostridium botulinum can grow at pH above 4.6. 
C. botulinum is able to form very heat resistant spores and can grow in the anaerobic conditions in canned food.  Since C. botulinum also produces a lethal toxin, it is essential to destroy the spores.  So we heat the food in the cans to temperatures above boiling point (in fact we heat to the equivalent of 121.1C for 2.52 minutes and this is called a 12D process).  Properly processed LACF is safe.

When we look at acid foods, we find that C. botulinum is incapable of growth under these acid conditions and so no toxin can be produced.  Since we don't need to deliver a 12D process, we can heat for a shorter time or at lower temperature.  This has the advantage that the food is changed less and it costs less to deliver the process.  Depending on the food and the degree of acidity, we really need only destroy vegetative (i.e. non-sporulating) pathogens and spoilage microorganisms.  This will then destroy Listeria.

What about my conditional clause above?  If the food canner doesn't properly control the process, it might be possible for cans to be underprocessed.  This might occur if the steam supply to the retort (pressure cooker) is lacking or turned off too soon.  Another possibility is that cans might by-pass the retort altogether.

Post-processing contamination could occur if the cooling water is contaminated.  The can seals are not 100% watertight while they are still hot, so using contaminated water may allow a few bacteria to enter the can during cooling.  This resulted in a typhoid outbreak in Aberdeen in 1964, when people consumed imported Argentinian canned  corned beef that was cooled in untreated, sewage-contaminated river water.

Damage to the can seams caused by rough handling can also allow contamination, as there is a partial vacuum in the can.  Momentary opening of the seam caused by a blow can permit bacteria to be drawn into the can.

In summary, providing cans are properly processed and handled with reasonable care, LACF are essentially sterile, so all bacteria, including Listeria will have been killed; ACF are pasteurised and this process will also kill Listeria.

Can I build a business around Mum's secret recipe?

I am often asked this question.

On the face of it, this is a simple question.  Mum has for years made a special dish or sauce and the whole family enjoys it.  Perhaps it is a traditional dish made back in "the old country" and an enterprising emigrant wants to make it commercially in the adopted country.  All that is necessary is to scale up production, right?

In some cases, this might be so.  However, there may be hidden pitfalls.

Perhaps the most important difference between Mum's cooking and a commercial operation is the timing - Mum cooked the dish or sauce and served it straight from the kitchen, whereas commercial manufacture involves packaging, storage, transport, retail display and purchase.  The shelf life must also leave time for the consumer to store it at home before consumption.

How about putting the sauce into a glass jar or a plastic pouch?  This introduces a new variable not present in the original.  This is exactly the scenario presented to me recently and I want answers to some additional questions before I'll agree that the product is safe.

For example: what is the pH of the product - acid or low acid?  This is not just about flavour.  If Mum poured a low acid sauce over your food and you ate it straight away, there was no problem.  But if we now wish to sell it in an hermetically sealed container, it may support the growth of Clostridium botulinum.  Even if the raw materials are heated during preparation, spores will have survived and can germinate and grow, producing botulin toxin during storage.  There may be no apparent change in the product, but it could be lethal.  In the case of a low acid product, a full 12D process must be applied and this process must be filed with the regulatory authority, must be followed for every batch and under the control of a registered person and full records kept.  Special equipment, capable of heating the product to well over 100C is needed to deliver a 12D process.

What about stability?  Will the sauce separate during storage and transport?  It may need a stabiliser to be added to prevent separation and thus ensure that it looks good to the consumer.  It's not a safety issue, but dissatisfied customers are unlikely to be repeat purchasers.

What shelf life should we put on the label?  Properly conducted storage trials are essential. For that matter, what are the requirements for labelling?  You can't just put a picture of the product onto the label and call it "Mum's special pasta sauce"; in most jurisdictions, there are very specific requirements, including name and address of the manufacturer and a list of ingredients, possibly with warnings about potential allergens like peanuts.  These requirements extend to specifying the size of type required for the nutritional information label.

Not least is the requirement for the product to be manufactured in a suitable premises.  These premises must be inspected and it is unlikely that the home kitchen can be approved for even minor commercial production.

In New Zealand, food manufacturers must have a suitable food safety programme in place.  New legislation will require this programme to be based on an assessment of risk posed by the product and process, and the programme must be documented and detailed records kept, so that premises and process can be audited.

There are many wonderful products on the market today that had their origins in Mum's kitchen in some part of the world.  To avoid tears, the budding entrepreneur should seek the advice of a professional food technologist before putting the product on the market.

Poor quality of reporting

I have just read a couple of articles in a national newspaper.  These report on the recall of bagged salads because of possible Listeria contamination and the death from avian botulism of wild birds in Auckland.

Listeria monocytogenes is a bacterium that causes a rare, but serious disease in humans.  (See Listeria hysteria).  The first article includes an information box, in which the symptoms are described as "a mild viral infection".  Bacteria are not viruses and the two entities are as different as lobsters and soft cheese!

The second article describes the increase in numbers of wild birds dying because the very warm water temperatures (up to 26C) have allowed rapid proliferation of Clostridium botulinum, which produces a neuroparalytic toxin.  The information box in this article claims that "the toxin thrives in still, shallow, warm water".  The toxin does not "grow or increase in bulk", though the bacterial cells that produce it may do.

Neither of these errors is likely to result in injury if the reader follows the advice in the articles, but it is just plain, sloppy reporting.  Google lists 1.16 million articles on L. monocytogenes and 541,000 on C. botulinum, so there is no excuse for the reporters' not having done a bit of background reading.  We all make mistakes in our writing, but if we set out to educate, then we really ought to check the simple details. 

I stand ready to get hammered if this blog contains stupid errors!

Avian botulism is caused by Type C toxin, which does not affect humans.

Follow-up on canned food production.

In the last posting, I was writing about canned foods and the consequences of their going out of their “best before” date.

I was confident that the young man in question was not at risk. Here’s why (sorry for the lecture).

Canned foods have been made commercially in significant amounts since about 1874, when Schriver invented the closed kettle – a device that allowed processing at temperatures above that of boiling water. Before that, commercial production was carried out, but the products sometimes spoiled. (We tend to forget that up until 1860 it was not known that bacteria cause food spoilage. The spoilage was almost certainly the result of failing to deliver a harsh enough heat process to destroy bacterial spores. Some spores can survive more than 4 hours in boiling water).

In all that time, manufacturers have developed reliable processes by experience. Scientists have been able to explain why the heat treatments work and thus design new processes with confidence. In the case of low acid canned foods (LACF) we have to rely totally on the process. We cannot test for safety.

You might ask “Why would it be difficult?” The problem is that we demand a high level of security i.e. we set the acceptable risk of food poisoning from LACF as around 1 in a billion (I mean a million million) i.e. only one can in a billion would contain a viable spore. There is no testing regime that could detect the presence of viable spores even ten times that limit.

The LACF process is designed, using a combination of knowledge of the type of microorganisms likely to be found in the food (and able to grow under those conditions) and the measured death rate of these bacteria, to calculate a process that will guarantee to destroy them. In the case of LACF, we are interested in a process that will destroy the heat resistant spores of Clostridium botulinum, leaving only one survivor in a billion. We call this a "12D" or 12 decimal reduction process. (See also the previous posting).

So when my reader contacted me and asked me to test the food for her, I knew that it was pretty much pointless. If the food had been processed properly and the seal remained unbroken, then she could rely on the food being safe for her son.

Botulism is back

Botulism is back in the news. The US Food and Drug Administration has announced that a canning company in Michigan is recalling certain lots of canned beans. The reason given was that these particular batches of product were not adequately heated during the processing.

As I wrote in “Deadly Poison in the Kitchen” on 5th September last year, the testing of canned foods for Clostridium botulinum is impractical. No sampling plan could detect the very low level of faulty cans that we accept. We are therefore totally reliant on the correct delivery of the thermal process by the manufacturer. Not surprisingly, the regulations covering the processing of Low Acid Canned Foods* are tight and specific.

The cans must be heated in a pressurized vessel called a retort at temperatures greater than 100C (the temperature of boiling water) because the C. botulinum spores are very heat resistant. They can survive for longer than 4 hours in boiling water. Full records must be made of the process, using special controllers and monitoring instruments. The retort operator must sign these records as soon as the cooking process is completed and they must be inspected and signed off by a responsible member of Management within 24 hours.

I don’t know the details of the investigation, other than the information provided in the FDA announcement (http://www.fda.gov/oc/po/firmrecalls/newera01_08.html). However, it does appear that the procedures mentioned above were not followed. The FDA announcement, quoting the company, stated that the recall was made “because a records review identified the possibility that a small number of cans from each lot may not have been adequately cooked”. These cans should not have entered the distribution network until after the processing records had been inspected.

For the benefit of anyone who has concerns about the hazards of handling foods thought to be contaminated with the toxin (botulin) I have quoted the FDA release verbatim below:

“Any food that may be contaminated should be disposed of carefully. Even tiny amounts of toxins ingested, inhaled, or absorbed through the eye or a break in the skin can cause serious illness. Skin contact should be avoided as much as possible, and the hands should be washed immediately after handling the food. Customers who have the product or any foods made with these products should throw them away immediately. Double bag the cans in plastic bags that are tightly closed, then place in a trash receptacle for non-recyclable trash outside of the home. Restaurants and institutions are encouraged to assure that such products are only placed in locked receptacles which are not accessible to the public. Additional instructions for safe disposal can be found at www.cdc.gov/botulism/botulism_faq.htm. Anyone with questions can call FDA at 1-888-SAFEFOOD”.


* A Low Acid Canned Food (LACF) is defined as a food packed in an hermetically sealed container, whose finished equilibrium pH is greater than 4.6 This includes, but is not limited to foods like canned beans, peas, carrots, corn etc. It is not safe to try to make these products at home and industrial production must be conducted in approved premises, using processes approved by thermal processing experts and filed with the authority (in the US this will be either FDA or USDA; in New Zealand it is NZFSA).

Deadly Poison in the Kitchen - updated

February 29, 1984, was an unusual day for New Zealand – it was leap year and the date when the country’s first ever cases of human botulism were confirmed.

Botulism is quite rare in the developed world, (fewer than 200 cases of all forms of botulism are reported each year in the United States) but not a new disease. Emperor Leo VI of Byzantium forbade the eating of blood sausages because the link between their consumption and the disease was recognized. However, it was not until 1895 that it was understood that the disease is caused by the growth of bacteria in the food. Clostridium botulinum can produce one of the most deadly toxins known to man. The toxin is so potent that the lethal dose for humans is approximately 1 μg/Kg body weight.

In the last year there have been several cases of intoxication by foods containing botulin toxin reported around the world – a man in Ireland became ill after eating food sent to him from Poland; bottled carrot juice caused several cases in apparently related incidents; canned chili, stew, hash and other foods were withdrawn from sale after an outbreak, but several days after the recall, the products were still on sale in stores.

In all these cases, the basic rules of food production and distribution had been ignored, or someone had failed to take proper care of the food. The isolated Irish case was probably the result of unsterile food being packaged in an airtight container, resulting in growth of the strict anaerobe C. botulinum and hence production of toxin. In the other cases, the foods were commercially manufactured. The carrot juice may have been pasteurised, but this will not destroy spores of C. botulinum, so the product required refrigeration; the canned products were all low acid foods and should have received a 12D* thermal process, which is sufficient to kill spores and sterilize the product. If this had not been properly delivered, or there had been post-process contamination, spores could have survived and germinated. As for the product remaining on the shelves after the recall, the only comment I can make is that the recall process was flawed, someone was grossly negligent or totally unscrupulous.

One final point: testing of canned foods for C. botulinum is impractical. No sampling plan could detect the one in 10^12 (a 1 followed by 12 zeros) faulty cans, so we are totally reliant on the correct delivery of the thermal process. The fact that the only case we have seen in New Zealand was caused by home-preserved food shows that our canning industry is getting it right.

* A 12D process is one designed to reduce the population by a factor of 10^12. In the case of low acid canned foods, such as canned meats or vegetables, this heating process is based on killing the spores of Clostridium botulinum.

Since I wrote this article, residents of Florida have been advised to throw out products manufactured by Gourmet de Lyon. This company produces food products from a kitchen in a Delray Beach restaurant that has no permit to produce or sell canned products or those sold in jars. It would be fair to say that many of the C. botulinum cases seen in developed countries are caused by consumption of low acid canned foods produced by unlicenced manufacturers or home-canned goods sold illegally. The problem stems from the inability of such producers to control the process sufficiently accurately to ensure the destruction of the C. botulinum spores, which are highly resistant to heat.

For more information on the Florida case, see Bill Marler's website:
http://www.foodpoisonblog.com/2007/12/articles/
food-poisoning-watch/florida-botulism-risk-from-canned-products/index.html

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