Friday, December 18, 2009

It’s not quite about food safety…

Recently I was asked by a reporter to test magazines found in doctors’ waiting rooms for presence of pathogens. She wanted to do a story about the risks of going to the GP. I wasn’t sure what to expect, but asked her to collect a range of magazines from various waiting rooms. She brought me ten glossy or super glossy magazines covering popular women’s and men’s titles.

Each magazine was opened randomly and two pieces of the right hand page were cut aseptically, using sterile scissors. Each piece was 100mm x 100mm; one piece was cut from the top right, the other from the bottom right. This was to increase the chance of sampling the area most handled by readers.

The pieces of paper were transferred to a sterile bag with sterile diluent and massaged thoroughly by hand and then for two minutes in a machine called a Stomacher. I transferred samples onto agar plates that would enable me to assess general microbial contamination, faecal bacteria and Staphylococcus.

After incubation, I examined the plates, looking for typical bacterial colonies. The levels of contamination on all media were low. The limit of detection in this analysis was 3.7 colony forming units/10 cm2. In the food industry, a count of less than about 100 cfu/cm2 is considered acceptable, though the count on food contact surfaces at the start of food processing should be close to zero. Thus, the analysis I used was sufficiently sensitive to indicate whether the magazines were microbiologically hazardous with respect to Staphylococcus and faecal bacteria.

Staphylococcus is typically found on the skin and can be transferred to food and there produce enterotoxin, which causes food poisoning when we eat the contaminated food. It is unlikely that the low levels of S. aureus detected in this work would lead to significant transfer between readers. No typical colonies of faecal coliforms were detected, suggesting that there were no, or very low numbers of faecal bacteria on the magazines and hence that the likelihood of faecal contamination of the pages was also low.

All of the samples were printed on glossy paper, which doesn’t absorb water, a fact I confirmed by measuring the water activity* of the samples. There was thus no opportunity for bacteria to grow on the pages and in fact, they may have died off reasonably quickly.

One thing I should point out is that it is not possible by any simple analysis to detect viruses, so the work done here doesn’t completely rule out contamination by viruses of upper respiratory tract or gastrointestinal tract origin. Some, such as the Norwalk virus that causes gastroenteritis, can survive on surfaces for long periods.

I conclude from this cursory examination that, with the possible exception of viruses, the pages of the magazines were relatively free of pathogens. Handling the magazines is therefore relatively hazard free. However, as always, it would be advisable to wash or sanitise hands before consuming foods, snacks or sweets after visiting the surgery.

Have a happy and safe Christmas, everyone. Make sure your Christmas fare and BBQs are safe.

* For a description of water activity see:

Wednesday, December 2, 2009

Raw milk and people with influence

It’s happened again! Bill Marler quotes a Washington State Department of Agriculture News Release, reporting that three recent Escherichia coli infections in Washington have been linked to drinking raw, unpasteurised milk. The Washington state departments of Health and Agriculture have put out new warnings about the risks of consuming unpasteurised milk and milk products.

All the patients involved have reported drinking raw milk from the same supplier. Though no E. coli have been found in the most recent batch of product tested, the Washington State Department of Agriculture did find in the dairy the same strain involved in one of the illnesses.
Bill Marler, Doug Powell and I have all written on many occasions about the hazards of consuming raw milk. Doug has emphasized that personal freedom is all very fine, but young children cannot exercise freedom of choice. They are often the ones made ill by bacteria carried in raw milk. If you think that we are a bit over the top on this issue, have a look at the You Tube clip of Barb Kowalcyk talking about her son, Kevin, who contracted haemorrhagic E. coli infection.

A few days ago, Tamati Coffey was shown on TVNZ’s “Breakfast” programme milking a cow and then drinking the milk. No real problem there. The show’s hosts, Pippa Wetzell and Paul Henry then discussed the merits of drinking raw milk. Typically, Paul reckoned he wouldn’t touch the stuff, but I was surprised when Pippa, who recently had a new baby, argued that drinking raw milk is good for you. Many people watch this programme every day and there must be a proportion of those who are mothers of young children. Judging by the daily feedback, viewers hang on every word the presenters utter. I have to admit that I too enjoy the quick repartee of Paul and Pippa, but her throwaway line could easily influence parents to feed raw milk products to their children, with potentially disastrous consequences.

Perhaps television presenters should be a bit more careful when it comes to expressing views on the safety of foods – they are not trained in food safety. As they said in the post-war years when I was a lad “Careless talk costs lives”. It’s just as true today.

Tuesday, October 20, 2009

New technology to double avocado shelf life: NZL FOODweek Online Main Features Page

New Zealand FOODweek Online published an article on high pressure processing (HPP) of avocado to extend shelf life. The link is shown below:

New technology to double avocado shelf life: NZL FOODweek Online Main Features Page

HPP has been used for some time, particularly in Japan for cold pasteurisation. In a future blog article, I will write about HPP and explain how it works and how it can be applied to foods.

Thursday, October 8, 2009

“The Law is an Ass” – with apologies to Mr. Dickens.

In the last week, the Far North District Council in New Zealand has enforced the law and required community members to desist from cooking pickles and jams and selling them through a Hospice Shop. Over the years, these wonderful people have raised around $5000 for the hospice funds each year.

It appears that the District Council received a complaint that the goods were being produced in private kitchens. Under the Food Hygiene Regulations, the council was then obliged to investigate. The regulations specify that production of foods for public consumption may be conducted in unregistered premises only on special occasions.

This situation crops up more than you might expect. About 25 years ago, when my children were small, our country school raised significant amounts of money by pizza drives. About three times a year, the Parents Association purchased commercially made pizza bases and assembled pizzas for sale. The council received a complaint from a commercial pizza parlour that this was unfair competition, since the school did not have a registered premises and therefore had lower costs. We were able to comply with the regulations by specifying the number of times a year our Occasional Food Premises would be used and by registering a relatively simple Food Safety Programme.

To give credit where it is due, the Far North DC and the New Zealand Food Safety Authority (NZFSA) are looking at ways the volunteer cooks can continue to produce their foods. Their home kitchens are not registered premises and it is not practical for the volunteers to set up a separate kitchen. I’m looking forward to seeing how the Authority gets around its own antiquated regulations.

However, what is the real risk? The products are essentially heated, acid foods – jams are made from acidic fruit and have a low water activity*, so the most likely microbial spoilage – if there were to be any – would be mould growth, which would be apparent to the consumer. Pickles are acidified foods and the low pH has the same effect, preventing the growth of pathogens. So the microbiological risk to consumers is low. Fruit cakes and similar baked goods are not hazardous either. Obviously, good hygiene in production and handling of all these foods is essential and potential contamination with cleaning chemicals etc. must be prevented.

What are the most hazardous foods on sale today? According to the Centre for Science in the Public Interest, these are leafy greens, with 363 outbreaks (13,568 reported cases of illness); eggs (11,163), tuna (2341), oysters (3409), potatoes (3659), cheese (2761), ice cream (2594), tomatoes (3292), sprouts (2022) and berries (3397). These are listed in order of outbreaks. Notice that jams, pickles and cakes don’t figure in the statistics.

Back in the Far North, everyone is looking to see this resolved soon, so that the volunteers can resume their work for the hospice. The Food Hygiene Regulations are due for replacement with a new Food Act that will shift the emphasis to risk assessment of food processing operations.

As the Assistant Director of NZFSA apparently said, “The law isn't based on common sense and we're looking to improve things."

* See the end of "Free Choice or Safety of the Population" for an explanation of water activity.

Thursday, August 20, 2009

A note on comments to this blog

Occasionally (sadly not very frequently) one of you readers posts a comment, often on a blog article I wrote months earlier. Your comments are moderated and appear under the relevant article.

Comments come to my private e-mail address for moderation and are anonymous, so I can reply only by posting another comment, which again appears under the relevant article.

If you have commented, please look at the article comments for my response. If you want me to reply directly, please use my e-mail address you see in the blog header.


Sunday, June 28, 2009

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.

Thursday, June 25, 2009

Do consumers understand “Use-by” and “Best-before” dates?

I think that many consumers don't understand these package marks.

I recently received a message from a very distressed reader. She'll recognise herself, but I'm sure she won't mind my writing this.

The reader had a 16-month-old son and had fed him a jar of organic apple, pear, blueberry and blackberry with vitamin C. The young man had eaten it all and was apparently bouncing around, as 16-month-olds tend to do. The jar and contents appeared normal, with a suitable vacuum in the headspace.

After the meal was over, the mother looked at the jar and found the “best before date was 29th July 2008!” (her exclamation mark). She went on: “I am very concerned that he could get Botulism from this - is there a way that I could get the remains of the food in the jar tested to make sure that he is not in any danger? Please, I am happy to pay for this and your time.

“I have spoken to a few people and they have all said that we will have to wait the 10 days to be on the safe side. Is there anything else I can do to protect my son? or help to prevent anything really nasty making him sick from this?”

This mother was obviously very frightened. Her concern was triggered by the best before date, which is an advisory to the consumer about quality. Chemical changes can occur slowly in cans or jars of food during storage. These changes may be accelerated if the food is exposed to sunlight or high temperatures. These changes may make the food less appetising, such as giving a "cardboardy" or flat, oxidized taste. The changes are not harmful. If the food is outside the Best Before date, it does not necessarily indicate that it is unsafe to eat, though that might be the case with something like ham or egg salad, which are much more perishable.

I didn’t have any further information on the product, but would expect that it would have been processed either as an acid food (pH less than 4.6) and pasteurised, perhaps hot-filled, or processed as a low acid food (pH above 4.6) and thus be given a 12D process (sterilised). In either case, Clostridium botulinum toxin would not be produced. Any changes occurring after the best before date would be quality deterioration only, not safety issues. There are several other points to come out of this discussion, but I'll cover them in a future posting.

Extrapolating from this, it is probable that consumers and perhaps retailers don’t fully understand the significance of “use-by” dates. I have certainly seen products in supermarket display cabinets with the original “use-by” date covered with a second label bearing a later date. The latter is illegal in New Zealand.*

And the boy? I had a message from his Mum today - this is the 11th day since he ate the food, which had actually been made in 2006. He didn't get sick and is now toddling around the home at high speed. Well, some food stories have happy endings!

* You can find an article "Date Marking - Standard 1.2.5" on the NZFSA website at

Saturday, May 23, 2009

Don’t read this if you have a weak stomach

The reason for the title will become apparent later on!

People who have an opportunity to influence the public have a duty to make sure they know what they are talking about and to think about the consequences of their comments.

Last week, popular TVNZ breakfast show host Paul Henry was talking about the state of cleanliness in public toilets. The breakfast show is a mixture of news, views and entertainment and Paul made a meal (if you’ll pardon the pun) of the issue, drawing out as much toilet humour as possible. Unfortunately, he also claimed that washing your hands in a public convenience would result in your hands being more contaminated than if you had not bothered.

This is hard to stomach. Certainly, taps and door handles may be contaminated, often with faecal bacteria and it may be that soap and soap dispensers are also contaminated. However, I find it difficult to accept that not washing hands is better than washing.

If you didn’t take the earlier warning, now is the time to quit reading.

If you have wiped your backside with toilet tissue, then the chances are that your fingers are contaminated with faecal bacteria and viruses. Way back when I started teaching food microbiology, I used to run an exercise with my students. They took various numbers of sheets of toilet tissue and placed them over a finger end, which they then gently wiped across a Petri dish of indicator bacteria. These, as it happens, were Escherichia coli, the bacteria always present in the gut. These bacteria have the ability to produce a green metallic sheen when they grow on an agar called Eosine Methylene Blue. Since they occur only in the gut, we should not normally expect to find them on our hands, except for the obvious reason. After the wiping phase of the experiment, the tissue was discarded and the same finger pressed onto the EMB agar, which was then incubated overnight. The students then washed their hands and dried them before making a further agar impression.

The students were usually horrified to discover that even when using 6 sheets of 2-ply toilet tissue, their finger impressions often grew bacterial colonies with a green metallic sheen. Now, not to put too fine a point on it, 6 sheets is an almost unmanageable wad of paper! Washing usually removed all the bacteria, but only if soap and warm water were used.

There are several messages here.
• No matter how much tissue you use, you can’t be sure that you won’t have faecal bacteria and viruses on your fingers.
• Washing your hands with soap and then drying them will remove most of the bacteria

Unfortunately, when you turn on the tap with contaminated hands, they will transfer bacteria and viruses to the tap. After you have washed, you recontaminate your hands when you turn the tap off. That’s why in hospitals and laboratories the taps have long handles that can be operated with wrists or forearms, or are operated by foot pedals or infra-red sensors. These days, many washroom taps have press buttons that allow the water to run for only 30 seconds or so and don’t need to be turned off.

So what can you do?
• Turn the tap on with your wrist
• Wash your hands thoroughly with soap (sing “Happy birthday" to yourself twice to ensure you wash for long enough)
• Thoroughly dry your hands on a paper towel and then use it to turn the tap off
• If the washroom has blower hand dryers, be careful not to touch the machine (if it has an on button, push it with your knuckle)

Watch a microbiologist in a washroom. When I go in there, I do all the above and then open the door with the crook of my little finger. It’s not foolproof, but a lot better than not washing. If you are still paranoid, buy a small spray bottle of hand sanitizer and carry it in your bag for use after you have left the washroom and before you eat.

I hope you read this far, Paul.

Wednesday, May 20, 2009

Can legislation control Salmonella?

Obviously, some very intelligent people think so. Unfortunately many of them misunderstand the control of food safety.

Food safety legislation is similar to the laws governing road traffic. There are lots of requirements for the design and maintenance of vehicles and prescribed behaviours for their operation. Maximum speeds for each piece of road are set by traffic authorities and advised by signs on the roads. If you exceed the speed limit, you might get away with it most of the time, but speed cameras may catch you. Then you get a ticket and a fine. That’s just money and perhaps demerit points on your licence. Do the speed signs and threat of punishment make us better or more responsible drivers?

Suppose we have an accident and injure or kill another motorist or pedestrian. If we are shown to be at fault, perhaps because of ignoring the speed limit, does the fact that we receive a stiff fine make it any better for the injured party or their family? No way.

The recent outbreak of salmonellosis in the US, carried in peanuts, was almost certainly the result of the flouting of many food safety regulations – the factory was dirty and infested and in-process peanuts were not protected from recontamination. Yet the factory had been inspected and the overall level of food safety was pronounced “superior”. It must be pointed out that the inspector was given only one day to inspect a factory processing several million pounds of peanuts each month and was not an expert in this type of operation. A federal investigation team later discovered that company testing records showed that Salmonella had been found in its products on at least 12 occasions since June 2007. Those products were apparently retested until negative results were obtained and then released to the market.

At least nine people have died from salmonellosis associated with the peanut products and 22,500 were sickened. The existing legislation clearly did not protect them. Some products containing the affected peanuts are apparently still on retail outlet shelves.

In a radio and television address to the American people on 14th March*, President Obama offered his “top ten” ideas for improving food safety. He noted that only about 5% of the 150,000 food production premises were inspected last year, so one billion dollars would be invested in the FDA to increase its ability to inspect premises. Penalties for selling unsafe food would be increased. Unfortunately, he then went on to state that only government can ensure that foods are safe to eat. Wrong, Mr. President!

Food safety is a partnership of trust between government, food producers and suppliers and the consumer. Sure, regulations are required and must be enforced, but no inspection force can guarantee the production and supply of safe food; the manufacturers must be committed to doing so on every day of the year, whether the inspector is due or not.


Tuesday, April 14, 2009

Black-balled peas

If Talleys of New Zealand have been correctly reported, it seems to me that they have placed the wrong priority on their response to the complaint by Humphrey Elton about his finding Black Nightshade berries in a pack of frozen peas last August. A number of other contaminated packs of peas and beans have turned up since then, the latest being frozen peas and corn last week. One complainant has claimed that almost half of the peas were actually Black Nightshade. If that really is the case, then there is a serious problem in the factory or on the farms.

According to Mr. Elton, Talleys informed him that this is a common agricultural weed and nothing to worry about. He received a cheque for five dollars as compensation.

The New Zealand Food Safety Authority has noted that the berries are “mildly toxic and should be avoided; the contamination is a food quality issue”. It seems that it has been an issue for at least 8 months, but for some reason has only recently hit the headlines.

The fact is, Mr Elton and other consumers bought frozen vegetables. They did not expect to receive anything else in the pack. Being told that the berries are nothing to worry about is akin to complaining to the waiter about a fly in the soup and then being told not to let other diners hear - it’s extra protein and a bonus.

In a world where consumers are highly aware of food safety and quality, I would have expected a more pro-active response from the company. They could have told the complainants that they were very sorry about the contamination and that they were investigating the occurrence and should not have offered such a miserly compensation. If the problem has been known since last year, they should have been doing something about it long ago. What a difference this would have made to the public perception of the company. The downside is that Paul Henry (TVone Breakfast host) would have been robbed of an opportunity to clown around, testing frozen peas by hitting them with a mallet on the Breakfast table.

How could the contamination have occurred? The most likely causes are excessive growth of Black Nightshade in the fields as a result of favourable weather conditions and failure to control this growth by suitable spraying. When the peas are harvested, a harvesting machine cuts the whole pea vine and separates the peas from the other parts of the plant. The harvester cannot differentiate peas from nightshade berries. Sorting and separation in the processing plant was obviously ineffective.

Saturday, March 28, 2009

The temperature's rising (but why?)

I was recently asked to explain some of my comments on detection of faecal coliforms. <See Coliforms and Faecal Contamination Wednesday, July 18, 2007>

I have extracted the essentials of the questions below:

“Since the coliforms when tested… are grown at optimum growth temperature of 37C, why would you need to raise the faecal coliform test temperature to 44.5C to show thermotolerant E. coli are present? Why would food safety people be looking for thermotolerant bacteria in food rather than bacteria that grow at normal temperatures?”

In my article, I provided some background information on "faecal indicator microorganisms", which we use to show that a food or water sample may have been contaminated with faeces. These tests originated in the early days of public health services and safety of public water supply. The coliforms are easier to detect and enumerate than are Salmonella or Shigella or faecal viruses. (Salmonella and Shigella are not coliforms). The reason for incubating at 44.5C to demonstrate the presence of Escherichia coli dates from 1904 when Eijkman suggested it as a means of separating the "B. coli" originating in the faeces of warm blooded animals from the strains characteristic of cold blooded animals and thus providing us with a means to detect faecal contamination of water supplies by warm blooded animals, including humans.

So the answer to the first question is “we are not particularly interested in thermotolerant coliforms; rather we want to show that the water supply may have been contaminated by human wastes and hence potentially contains faecal pathogens”.

Having said that, of course there are other areas of food microbiology where we are very interested in the presence of thermotolerant or thermophilic bacteria. If we pasteurize milk with plate heat exchangers (the standard method) we may find that the cooling stages become colonized by thermotolerant streptococci, which may cause spoilage. In the case of canned foods, we find that some sporeforming bacteria can survive even a very rigorous thermal process. These bacteria are of no public health significance, but they may cause spoilage if the cans are held at high temperatures (greater than about 40C) as might be found in storage facilities in very hot countries or in a restaurant kitchen.

Saturday, March 14, 2009

Tha’s gorra eat a peck o’ muck afore tha dies.

For those readers not lucky enough to have been born in Yorkshire, northern England, an approximate translation of this old expression is “You will eat a barrel-full of dirt during your lifetime”.

What brought that on? According to Abby Alford, writing in the Western Mail (1), there may have been some scientific basis to the saying. Bangor University lecturer, Dr Prysor Williams, believes that an obsession with cleanliness reduces contact with dirt and thus with harmful bacteria. Our immune systems become weakened, leaving us susceptible to infection. Unfortunately, the evidence for this view is somewhat lacking, though Dr. Williams is not the only one to have argued this.

Stuart Levy, Director of the Center of Adaptation Genetics and Drug Resistance at Tufts University, provided substantial evidence that the substitution of anti-bacterial agents for good old soap and water increases the ability of bacteria to develop resistance. A few bacterial cells containing genes that confer resistance to the antibiotics can protect neighbouring sensitive cells, rendering the antibacterial agent ineffective. Levy’s group tested the ability of Escherichia coli to mutate to become resistant to triclosan, which inhibits an enzyme involved in fatty acid biosynthesis and thus interferes with membrane biosynthesis. The work was published in the prestigious journal Nature.

In a carefully constructed randomized, double-blind trial, Elaine Larson and her co-workers have also shown that using antibacterial home cleaning and hand-washing products has no significant effect on the incidence of infectious disease symptoms (2).

The take-home message is that while cleanliness may be next to godliness, we do not live in a sterile environment. If we try too hard to protect ourselves and our children from microorganisms, we don’t give our immune systems the chance to develop resistance to bacterial pathogens.


(2) Annals of Internal Medicine, 2 March 2004, Volume 140 • Number 5 321

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