It’s not rocket science, but…..

How many times do we hear that expression? And anyway, who decided that rocket science should be the datum for the rest of us? The success rate in that field could be improved a lot!

I want to show that simple experiments can be valuable.

Food poisoning doesn’t seem to be going away, in spite of the many articles published, television advertorials and the plethora of antibacterial cleaning agents on the market. The current concern about fresh poultry being a source of Campylobacter in the kitchen has lead to dishcloths being suggested as potential vectors of cross contamination. We all know this already, but we continue use them. Can we make them safer? Should we move to paper towels (not always convenient and perhaps environmentally unfriendly) or should we take the more expensive approach using cloths but discarding them more often? Should we boil them or put them in the dishwasher?

Standard fabric cloths were used in the kitchen for a week in the normal way. The cloths were then cut up and Standard Plate Counts were performed on Plate Count Agar. The samples were then treated by one of the following: economy wash cycle with a mdium load of dishes in a dishwasher; microwaving for 20 seconds on high (1 Kw); washing in hot water containing dishwashing detergent, or treating with hypochlorite solution containing 200ppm free chlorine. The samples were then counted again. Four complete replicates were performed. The results are shown below as a graph of log(APC/g) vs treatment; the error bars represent one standard deviation.

We can take several important points from these results:
• Used for a week, dishcloths become “microbial zoos” and a major source of contamination in the kitchen when the cloth is used to wipe benches etc.
• Hot water washing has little effect on the population size
• Bleach reduces the count by a factor of only10, probably because it is rapidly inactivated by the organic materials
• Dishwashing reduces the count by about 100x
• Microwaving is apparently the best treatment, reducing the count by a factor of over 1000x but there is still a very large population present, which can be spread around the kitchen.

This was a simple experiment that shows us some very important facts about the safety of everyday items in our food preparation areas. It might not be totally original, but that doesn’t affect the interpretation.

Who was the non-rocket scientist who made these measurements? The experiment was planned and conducted by Elisabeth Bakker, an eleven year old schoolgirl in Palmerston North, New Zealand, who submitted her research for a science fair project.

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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For the second time of asking: "Should I eat the chicken?"

Over the last eight months we have heard a lot in New Zealand about the dangers of Campylobacter and poultry. Some of it has been well-informed and some has been blatant scaremongering that served only to confuse and frighten the consumers. The poultry industry was accused of producing New Zealand’s cheap and dirty food. Ad hoc solutions were advanced that would in all probability increase the cost of poultry in the market place without giving any guarantee that the rate of Campylobacter infection in the population would decrease.

The still small voice of reason is now being heard and concrete steps are being taken to understand and reduce the problem, which is not unique to New Zealand*. The New Zealand Food Safety Authority is studying possible control measures. Researchers at Massey University are examining isolates from the environment and from patients, building a comprehensive database on Campylobacter strains that can be used in epidemiological studies. The first version of the Poultry Industry Association of New Zealand Broiler Growing Biosecurity Manual has now been released. This is a comprehensive manual of approved procedures aimed at controlling infection and spread of Campylobacter in poultry flocks. When fully implemented, the procedures should greatly reduce the incidence of Campylobacter in poultry in the market place. The production of the manual is a creditable response of the PIANZ to the concerns expressed by scientists, politicians and the general public.

So does that mean that campylobacteriosis in New Zealand is under control? I don’t think so. I believe that it is highly unlikely that Campylobacter can be eradicated in poultry, at least in the short term. There are also other sources of the bacteria in our food supply and in the environment. Only a couple of weeks ago, a number of mountain bikers taking part in a contest became ill with campylobacteriosis. No food source could be identified as the source; infected surface water and mud, which had covered the competitors as they splashed through the puddles, was blamed as the source.

Distributors, wholesalers and retailers, together with the consumers themselves, must take some responsibility for the safety of food. Even though campylobacteriosis has been shown to be linked with consumption of undercooked barbecued chicken, I am not convinced that New Zealand’s high incidence of the disease can be attributed entirely to this cause. There are many routes of infection for the consumer. Leaking packages in display cabinets can contaminate other food purchases, the hands of customers and the handles of supermarket trolleys. Cross contamination in the restaurant or domestic kitchen via utensils and chopping boards may result in salads or other uncooked dishes becoming infected. The dose of bacteria required to initiate the illness in humans may be only a few dozen cells. This means that commercial and domestic food handlers must be properly educated in practical food hygiene and food safety. We can all contribute to the safety of our food.

Should we eat the chicken? You bet!

* Work conducted in Hong Kong by my team showed that between 50 and 60% of fresh chicken was contaminated with Campylobacter. This dropped to about 30% if the poultry had been frozen. These rates of contamination are entirely consistent with figures reported for other countries.

Coliforms and Faecal Contamination

I recently read a newspaper article about the potential contamination of ground water from failing septic tanks. Sanitarians had found septic tank systems close to a restaurant that might be feeding human faecal matter to the ground water. However, wells in the surrounding area, both up and downstream of the potentially contaminated site tested negative for Escherichia coli. The significance of this finding is that the sanitarians could not demonstrate that the wells were in fact contaminated by human faeces or the outflow from the septic tanks.

Escherichia coli is a bacterium found in the intestines of man and animals, but it doesn’t grow in water and doesn’t grow well in the environment. So if it is found in water, the implication is that the water has been contaminated with faecal material. Some strains of E. coli, such as O157:H7, cause serious disease, though most do not. The micro-organism is used as a Faecal Indicator. The importance of finding any E. coli in water or food is that other enteric pathogens, such as Salmonella or Norovirus, might be present.

The article went on to say that 28% of the wells tested did contain “coliforms” and this indicated that the water system was at risk of more serious contamination. This is probably correct, because a properly constructed well should draw water from deep in the ground; such water has often been in the ground for hundreds of years and has been filtered through the soil and should have a low bacterial count. Though the article was correct, it may have caused some confusion in the mind of the reader.

The finding of coliforms in water is not necessarily indicative of danger. The coliform group is defined by the tests* that we use, i.e. “coliform” is not a species, it simply says that these organisms give us a positive result in the tests we apply. This means that some bacteria are included in the group that have no faecal connotation at all. These bacteria may be found in plant material that has never come in contact with faeces of man or animals and the bacteria may even be transmitted in the seeds of the plants. So if we find coliforms in the water or in food, it is not a cause for immediate panic. Obviously, if we find large numbers present, we should look to find out why. The well may be affected by inward leakage of surface water; fresh salad vegetables may have these micro-organisms present at low numbers on their tissues, but high numbers suggest poor kitchen hygiene or temperature abuse.

If we wish to demonstrate that contamination by faeces has occurred, we need to do further tests on the bacteria to see if they are actually E. coli. The tests involve different culture media, different incubation temperatures and biochemical tests.

*The tests that we use to detect coliforms vary somewhat between countries. The tests are based on the ability of coliforms to grow in the gut, so they must be able to grow in the presence of bile salts. Bile salts are secreted into the intestine to aid in digestion of fats; they are natural detergents. So some media formulations include bile salts, while others employ synthetic detergents. The media also contain lactose as a carbon and energy source for the bacteria and the tests are incubated at the optimum temperature for the growth of the target organisms. So the coliform group is defined by their ability to produce a positive result:
Acid and gas production in 24 to 48 hours from lactose at 37C in the presence of bile salts.

If we wish to demonstrate that Escherichia coli is present, then we may subculture into a similar medium containing selective agents (which prevent other similar micro-organisms from growing) and raise the temperature to 44.5C and again look for gas production. At the same time we may look for the ability of the micro-organisms to convert tryptophan to indole; produce sufficient acid to change the colour of methyl red pH indicator; produce acetoin from glucose and grow on citrate as the sole carbon and energy source. This series of tests is known as the IMViC tests. E. coli normally gives a "++--" profile. Finally, we may grow the culture on Eosin Methylene Blue agar and look for the formation of a metallic green sheen. If all these tests give the correct result, we can be pretty sure that E. coli is present and faecal contamination has occurred.

Free Choice or Safety of the Population?

Governments and regulators are always in a difficult position. Do they allow total freedom of choice, or does their responsibility to the population require them to make restrictive decisions based on the greater good of the people? The government then performs a balancing act, running the risk of being labelled as Big Brother (or at least Nanny Government) or as being irresponsible. For example, should we all be allowed to use any chemical we can obtain to relieve the monotony of our daily lives, or should there be regulations to control the use of mind-altering substances and thus protect us from ourselves? If we allow unfettered use of any substance and thus maintain personal freedom, how do we protect the innocent - those who are too young or too poorly educated to know that these materials may be harmful?

Most people would probably come down on the side of some restrictions for the use of drugs, though some would argue for freedom of choice. The same applies to the sale and consumption of raw milk and raw milk products.

I have discussed raw milk before in this blog. I might have left it at that, but the New Zealand Government, in the form of the New Zealand Food Safety Authority has now called for submissions on a proposal to permit direct imports of Roquefort, a soft raw milk cheese made in France, and extra hard Parmesan-style raw milk cheeses Grana Padano, Pamigiano Reggiano, Romano, Asiago and Montasio. An extensive programme of risk assessment has already been undertaken and the Authority is now consulting with industry groups.

This development may lead some members of the community to believe that Big Brother has been wrong all along and is now backing down. Extra hard cheeses have a low water activity* of about 0.693 that prevents the growth of most bacteria. Soft cheeses, such as Brie, Camembert and Roquefort have much higher water activities and thus may permit the growth of pathogens such as Listeria monocytogenes (see post To Pasteurize or not? - 10th December 2006). The truth is that cheeses made from raw milk are not as safe as those made with pasteurized milk.

European Community (EC) legislation sets microbiological, food safety and process hygiene criteria that reduce the risks in consumption of raw milk cheeses. NZFSA has recommended that if these products are to be directly imported and ultimately manufactured in New Zealand, additional risk mitigation measures should be introduced:

• 100% verification of certificates attesting that the relevant EC standards have been met

• continuing monitoring of products to check for E. coli levels, which can indicate unsafe manufacturing conditions leading to faecal contamination of the cheese.

It is expected that leaflets, posters and point of sale brochures will be required to educate the consumers on the risks of eating cheeses made from unpasteurized milk and that labelling of the products will be mandatory. Yet another acronym has been added to our lexicon: YOPI - Young, Old, Pregnant or Immunocompromised. This group of the population should not consume raw milk products.

*Water activity is a measure of the ability of water to take part in biological and chemical reactions. It is measured as a ratio of the partial vapour pressure of the food to that of pure water. That sounds complicated, (it's not) but it results in a scale of water activity running from 0 to 1. Generally speaking, the lower the water activity, the harder it is for micro-organisms to grow. Water activity in foods can be controlled by salts and sugars. So we can formulate food to have a particular water activity and thus preserve the food.

Yet more on unpasteurized milk

This post was updated on 30th April, 2007.

In the previous post I mentioned the potential for contraction or spread of disease that could result from the consumption of raw milk or products made from unpasteurized milk. In that case the consumers may have contracted salmonellosis from the milk.

This week the Grey Bruce Health Unit in Ontario, Canada, issued a press statement, warning pregnant women to avoid consumption of raw milk and unpasteurized dairy products. The warning was issued to help prevent listeriosis infection in newborn babies. The original release can be found at:
http://www.publichealthgreybruce.on.ca/HOME/NewsEvents/2007/Mar/2006Mar14_Infant-Listeriosis.htm

Non-pregnant humans are highly resistant to the infection, though if they do become infected, the symptoms can be very serious, including meningitis and sepsis (invasion of the blood or tissues by bacteria or their toxins). Pregnant women may contract Listeriosis, but show no serious symptoms beyond mild influenza-like signs. Their foetus, however, may be infected, resulting in abortion or stillbirth. If the infant is infected during delivery, symptoms of meningitis begin 1 to 4 weeks later.

The Grey Bruce Health Unit news release stated that it had received a laboratory-confirmed report of an infant who contracted the disease. The most likely source of infection was said to be the mother’s consumption of raw milk cheese.

The release went on to say that pregnant women are at a 17 times higher risk than the general population of contracting the disease.

My personal and professional opinion is that any perceived benefits of drinking raw milk are far outweighed by the risks, both to the individual and to others in the same household. This is supported by scientific evidence: In the last decade the Center for Disease Control and Prevention has documented more than a thousand cases of food-borne illness and two deaths, all caused by unpasteurized dairy products. I have advised my pregnant daughter-in-law to avoid raw milk and raw milk products.

More on unpasteurized milk

The arguments about the desirability or otherwise of drinking unpasteurized milk continue. It seems that its proponents will hear nothing said against the practice; many scientists and doctors provide comment, often supported by case studies, that suggest that there are significant and serious risks associated with drinking unpasteurized milk.

The following report was posted recently on the Food Safety Network mailing list on behalf of Doug Powell of Kansas State University:
Begins
http://www.wdbj7.com/Global/story.asp?S=6170552&nav=S6aK
WDBJ7 News
HARRISBURG, Pa. -- The Pennsylvania Health Department is, according to this story, warning consumers not to drink raw milk from a York County dairy farm after confirming that two people who drank it last month were sickened by salmonella.Health Secretary Calvin Johnson was cited as saying the state Agriculture Department has also obtained three samples from Stump Acres Dairy in New Salem that tested positive for salmonella.
Ends

Of course, the facts that two consumers of the product contracted salmonellosis and that samples taken from the dairy tested positive do not prove that the unpasteurized milk was the source, though detection of the same serotype in patients and the milk would be very strong evidence. However, the correlation between raw milk consumption and illness is hard to ignore.

There are sometimes suggestions that the pasteurization process is too severe. The process was originally designed to eliminate Salmonella, but was later modified to be slightly more rigorous to ensure that Coxiella burnetti (a rickettsia-like organism which is the cause of Q-fever - a febrile disease of man and which sometimes has serious sequellae), was eliminated. There is currently some investigation of the time/temperature relationships in milk pasteurization to see if there is a possibility of making the process less severe.