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.