Video: Eric Johnson, Professor of Bacteriology, University of Wisconsin-Madison, USA

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Interview transcript: Eric Johnson, Professor of Bacteriology, University of Wisconsin-Madison, USA (13 August, 2013)

I’m Eric Johnson a professor at University of Wisconsin, Madison. I became interested in clostridium Botulinum when I was studying at MIT in Harvard where I worked on clostridia, and then I went to University of Wisconsin in the mid 1980’s.

I have worked on clostridium Botulinum for nearly thirty years; I am an expert in the field. My laboratory and my research studies fundamental as well as basic aspects of the organism, the pathogen and its potent neurotoxins.

University of Wisconsin has a rich history of studying clostridium Botulinum mostly from a food botulism perspective.

Clostridium Botulinum is a spore-forming organism and spores are highly resistant forms of the organism that are spread worldwide. And traditionally the spores have been known to cause food poisoning where they get into the food and they’ll produce toxin, and the toxin they produce is the most poisonous substance known and people traditionally have consumed that and come down with foodborne botulism.

Infant botulism was discovered in the mid 1970’s by which the spores get into a baby’s intestine under one year old and the spores are able to germinate and produce toxin in the intestine and cause botulism in the child. It’s extraordinarily rare. In the United States about 70% of the cases occur which is 70-100 per year and so worldwide there are probably less than 150 cases of hospitalized infant botulism.

Clostridium Botulinum spores are prevalent in every region of the world so most people are exposed likely on a daily basis including infants actually dust and things other than food are probably the most common route of spore ingestion.

There’s four main types of clostridium Botulinum around the world. The third type comprising of a certain group of toxins are found in New Zealand and those do not cause human botulism they cause botulism in animals primarily and birds.

In New Zealand I know of only one case of botulism since botulism was discovered in the 1970’s.

Clostridium Botulinum is present in the environment, as I mentioned, and many foods do become contaminated with the spores. Most of these foods are vegetables and associated foods that contact the soil. The number of spores in infant formula is either non-existent or extraordinarily few and so the likelihood of getting infant botulism from infant formula is extremely rare in fact there are no cases known of babies developing botulism from infant formula.

The spores have been found in formula. It is rare. Many surveys have been done and most of the surveys show that clostridium Botulinum is not in infant formula however it is possible that the spores are there but they’re at such low concentrations because milk has, it’s been estimated, one spore per litre and so the levels of spores are extremely low and the number of spores in a food correlates with the likelihood of coming down with the illness.

The number of spores to cause botulism is not known, but based on honey studies it is thought to be as low as perhaps ten spores on ingestion up to much more – a hundred spores or more.

So in infant formula the number of spores generally are much lower than the dose required to lead to disease.

When a children becomes ill, typically it does not defecate for several days. It is constipated, but that is not a definitive symptom. The definitive symptom invariably involves your cranial nerves that [innovate] your eyes, and so blurred vision and maybe symptosis or sagging of the face and also a general malaise and weakness of the child: its suck, its cry are weakened compared to what you see as your normal, healthy child. And these children should be brought to a doctor, preferably a neurologist, and also their serum and their fecal matter should be examined for the presence of Botulinum toxin ‘cause that would provide a definitive diagnosis.

The treatment is very careful nursing care where most of the children who enter hospital do not have difficulty breathing. They’re there for a period of a few weeks. Some develop severe infant botulism where the toxin will descend and cause paralysis of your respiratory ability and in those cases the children will be put on a respirator. There’s been very few children, you can count them on your both hands, that have actually succumbed or died from infant botulism. So with proper nursing care they will survive. The toxin does not enter into your brain, your CNS, and so it is not known to have any permanent damage.

Now there were two infant botulism cases which I was involved with and one of the scientists who handles children with botulism, he tested formula that was being fed to those infants that had botulism and clostridium Botulinum spores were not found in the infant formula. And so as I’ve mentioned in the past, environmental sources are the normal route of infection and so the testing that is done strongly indicates that the environment, as opposed to the food, is the source of the spores.

There are no foods to my knowledge that are routinely tested. It requires considerable time and there would be so many non-existent or negative results that in my view it would not be practical to test foods for the presence of spores of clostridium Botulinum.

You test for clostridium Botulinum by its route of intoxication which involves absorption into the blood and then trafficking to the nerve, binding to a receptor, internalization into the nerve and cleavage of a [substrain]. That takes quite a long period, so the only test that will follow all those steps of intoxication currently is the mouse bioassay which is very expensive, uses a number of animals but it’s a very sensitive assay. There are other assays being developed including one in my lab where you use neuronal cells to test for the toxin but right now that is the only definitive test.

The mouse bioassay involves isolating the spores from a food, growing them in a culture medium for the bacterium, for clostridium Botulinum, taking that culture medium and injecting mice intraperitoneally and then observing them for typical signs of botulism and eventually death. However that is not conclusive of botulism unless you add antibodies specifically to the toxin to neutralize it and if the mice then survive, that is the definitive diagnosis of botulism.

Clostridium Botulinum is a very poor competitor with other organisms in foods and the intestine and so that is the reason that only very young children can get it because the competitive organisms are not present in their intestinal tract.

To identify the strains of clostridium Botulinum there are seven main serotypes. Only three of those cause botulism those three serotypes are not found in New Zealand. However to identify the serotype of the of the seven, you would inject a mouse and then you would neutralize with serotype-specific antibodies. So in other words if there is botulism in an individual and you use antibodies to Type A, when injected the mouse will survive it will no longer die from that.

There are other methods that have been used but they are not definitive such as heating an extract that has been lethal to a mouse, and this is in fact what was done in this case, to this point, but that is not definitive for a diagnosis of botulism because there are many heat [liable] substances in foods.

The testing method of sulfite reduction on ager is a general test that identifies organisms that reduce sulfur to a component that is readily detectable on ager plates. It is produced by a large variety of organisms and it is not specific to clostridium Botulinum. So it can indicate high levels of different organisms that can cause mainly spoilage in food.

In my candid opinion the sulfite reduction rest for organisms in milk powder or other foods is valuable for testing for potential spoilage but is not valuable for pathogens especially toxigenic clostridia such as clostridium Botulinum.

The diagnosis for botulism is detecting the toxin. It’s the toxin that is solely responsible for the disease. It is not the organism, unlike other diseases like salmonellosis or other pediatric diseases and so detection of the toxin is the only definitive proof and at this time that has not been accomplished.

I think Fonterra have been careful and have taken the right steps in trying to reassure the public, especially I guess parents of infants that the disease is extraordinarily rare and that if symptoms are observed and fortunately they have not been, to my knowledge in any cases, then they will be treated with proper medical care.

In order to move forward in view of this presumptive incident I feel that there should be assurance within a plant – a dairy plant – that spores of Botulinum are extremely rare. However I do not feel based on epidemiology and the methods required that routine testing will be of value in diagnosis of potential foods that could cause botulism.

I admire Fonterra for being proactive in this incident without having evidence that the sulfite-reducing organisms that were detected were clostridium Botulinum, as I’ve mentioned that’s a general test that tests a number of different clostridia. However this was complimented by a mouse bioassay where the mice were injected and one of the several injected did have a fatality. But antibodies were not available at the time so that test could have detected many lethal substances in food in which in my own laboratory we find are extremely common. So in essence, the proactive of Fonterra bringing this to the community and the general public and dairy organizations is appropriate.

At this time there is no conclusive proof of the tests and reports that have been disseminated that botulism is an issue in this incident and that is being tested now by a laboratory that I know very well – the Centre for Disease Control – and they will have a definitive test, but at this time it should not be concluded that botulism is associated with this incident.

Very simply it’s extraordinarily rare and has been virtually non-existent in the dairy industry.