Wednesday, December 31, 2014

Raw cookie dough and Salmonella

A recent post on FaceBook caused me some concern, amusement and despair.  The argument centred on whether you can get salmonellosis from eating raw cookie dough.  Comments ranged from serious through flippant to borderline insane.

What concerned me was the level of ignorance on basic food safety and the authoritative, but incorrect, advice given.  For example, one writer said that there was no problem with cookie dough containing raw egg, because Salmonella is found only on the outside of the shell; washing the outside of the egg would remove faecal material, rendering the eggs safe.  Both of these comments are wrong.

The egg shell is not an hermetic seal; if eggs are washed and then they cool, moisture can be drawn into the egg and bacteria on the outside may also pass through.  There is a defence mechanism in the egg white.  Lysozyme is an enzyme that can attack the cell wall of Gram positive bacteria.  Unfortunately, Salmonellae are Gram negative, so may survive.  In addition, the hen may be infected with Salmonella, so the egg may be contaminated even before the shell is formed.

Laying flocks in New Zealand are unlikely to be infected with Salmonella because of the biosecurity measures employed on New Zealand poultry farms.  The situation may be different in other countries.

Commercial cookie dough may be made with pasteurised egg, in which case any Salmonellae will have been destroyed.  But unpasteurised eggs may contain Salmonella.

Statements that athletes drink raw egg drinks for breakfast and suffer no consequences are without scientific support.  Arguments that real mayonnaise is made with raw egg are also misleading, as mayonnaise also contains vinegar, which not only loosens the emulsion, but also reduces the pH.

Most of us at some time in our lives have scraped the mixing bowl with no ill effects.  The infecting dose for Salmonella varies with the strain, and we may have been exposed to only low numbers of bacteria.   However, to eat large quantities of raw cookie dough is playing Russian roulette.

My two favourite comments from the many posts:

"I know that if you put Nutella on salmon, you get Salmonella"

"I've eaten it twice, and died both times"

Wednesday, December 24, 2014

Fungi for Christmas!

The image below is my Christmas card to you all.  I didn't create it - the image has been doing the rounds on a science website, but it is truly a microbiologist's Christmas card.

For those who are interested, the Petri dish was seeded with the following:
Top: Talaromyces stipitatus; Tree: Aspergillus nidulans; Ornaments: Penicillium marneffei; Trunk: Aspergillus terreus
Not all of these are likely to be found in food -  T. stipitatus was isolated from rotting wood and can produce some interesting enzymes that may have application in the agri-food industries, P. maneffei can cause human disease, mainly in HIV patients.  A. nidulans was probably one of the first fungi I studied as a microbiology undergraduate, and has been very important in the study of recombination, DNA repair and experimental evolution.

Tuesday, December 23, 2014

Happy and safe Christmas to you all

For us in New Zealand, Christmas Day is only 12 hours away.  It is summer and we will be having BBQs and parties outside.

Don't forget - if you are cooking outside on a fire or a BBQ, steak requires only to be cooked on the outside, as the inside of meat from a healthy animal is essentially sterile.  If the steaks are thick, make sure that the edges are also cooked.  However, meat patties have been made by blending together minced meat and possibly egg as a binder.  The inside of the patty is not sterile and so the patties must be cooked through properly.  Use a meat thermometer to be sure that the inside has reached at least 75C.  You can't judge whether the meat is cooked just by its colour.

I prefer not to cook chicken on the BBQ because it is difficult to ensure even heating.  However, if the BBQ has a hood, it is essentially the same as an indoor oven.  Ensure that the chook is cooked properly, again using a meat thermometer.  I also prefer not to put stuffing into the body cavity - it slows down the cooking process and it's difficult to determine when it's done.  Cook the seasoning separately.

Round our place, there are very rarely any leftovers.  However, make sure that food doesn't stay in the sun any longer than necessary.  Ham that has been handled may well be contaminated with Staphylococcus.  If eaten straight away, this is no problem, but if left at room temperature, the bacteria may grow, since all their competitors have been killed in the preparation process, leaving them free to grow in the salty favourable conditions.

Remember that several food borne pathogens can grow, albeit slowly, in the refrigerator, so use leftovers within a day or so.

Recent changes in legislation in New Zealand mean that driving after more than one alcoholic drink risks being charged with driving under the influence of alcohol.  Better to have a designated driver, or stay off the turps!

To all my readers, I wish a happy Christmas and an enjoyable New Year.

Wednesday, December 17, 2014

Comment on potential hazards of raw milk consumption.

I was recently asked for comment on the tragic death of a youngster in Australia, apparently caused by consumption of raw milk.  I was given only 200 words to get the message across.  Rather than go over all of the arguments again, I have reproduced my comments below:

The recent tragic death of a 3-year old infant and serious illness of four other children in Australia is  yet another example of the risks associated with consumption of raw milk.

Proponents of the consumption of raw milk claim that this is a natural food and has been consumed for hundreds if not thousands of years.  That is true, but ignores the fact that many diseases can be transmitted from animals to humans in the milk.

The hazards of consuming raw milk have been known for a long time. In Ontario around 1900, over 10% of all childhood tuberculosis was thought to be caused by unpasteurised milk. The rate of tuberculosis infection and many other milk-borne diseases in children fell dramatically after enactment of a law in 1938 requiring milk to be pasteurised; this was hailed as a major achievement.

The fact is that between 1998 and 2005, a total of 45 outbreaks resulting in more than 1,000 illnesses, 104 hospitalisations and two deaths due to raw milk or soft raw milk cheese were reported to the US Centres for Disease Control and Prevention. 

There is some evidence that consumption of raw milk early in life can reduce the incidence of allergies.  Bacteria in the raw milk may transiently colonise the intestine, resulting in stimulation of the immune system through infection.  

In addition, when milk is digested, a variety of beneficial ‘bioactive peptides’ are released.  However, it should be noted that pasteurisation does not adversely affect the release of these peptides.

I have said this before and say it again:  Adults who decide for whatever reason to consume raw milk should consider the potential hazards and make an informed decision.  Children, who have no choice in the matter, should not be fed raw milk or soft raw milk cheeses.

The situation is a little different for hard cheeses, such as Parmesan, in which the conditions, or the process, are inhibitory to most pathogens.  Food Standards Australia and New Zealand has made the following determinations:

Extra hard raw milk cheeses pose a low to negligible risk to public health and safety as survival and growth of Campylobactyer jejuni/coli, enterohaemorrhagic Escherichia coli (EHEC), Salmonella spp., Staphylococcus aureus and Listeria monocytogenes is very unlikely.
The selected Swiss-type raw milk cheeses were all assessed as posing a low to negligible risk to public health and safety for the general population as survival and growth of C. jejuni/coli, E. coli (EHEC), Salmonella spp. and S. aureus is very unlikely. 

Note:  The FSANZ document is comprehensive and readers should consult the report for more detail. See:

Thursday, November 13, 2014

The wonder fat?

This press release came to me via the NZIFST FaceBook Group of the same name.  See

The bad oil on coconut oil.pdf

The original article was released by a marketing, PR and communications consultancy consultancy, AMG.

Like many snake oil adverts, this release contains some grains of truth.  However, it also make many unsubstantiated health claims, which is illegal in New Zealand.
I'm not going to comment on the release; suffice it to say that I shall not be buying any of the product.  Have a look and decide for yourself whether this is the sort of oil that you want to use for cooking and treating your family.

Wednesday, October 8, 2014

Food poisoning with a difference

The usual symptoms of food poisoning are vomiting, with or without diarrhoea, and sometimes fever.  Abdominal pain is also a frequent accompaniment.  Yersinia pseudotuberculosis doesn't fit this mould.

Since the beginning of September 2014, there has been a total of 124 confirmed cases and 18 suspected cases of Y. pseudotuberculosis in New Zealand.  I was asked by the Science Media Centre (NZ) to comment on this outbreak, and to provide a general overview of the bacterium, how it is transmitted in the food chain, and what the potential sources of the current outbreak.

Yersinia is a genus containing 11 species of Gram negative rod-shaped bacteria (the Gram stain is a relatively simple microscopy technique used by microbiologists to divide bacteria into convenient groups for study).  Three species of Yersinia cause illness in humans,  the most infamous member being Yersinia pestis, which caused the Black Death. 

The other two human pathogens are Yersinia enterocolitica and Yersinia pseudotuberculosis, the latter being much less commonly seen in infections.

The natural hosts of Y. pseudotuberculosis are rodents and sometimes other mammals.  Infection of humans normally occurs through consumption of foods contaminated with faeces or urine.  The outbreak currently occurring in New Zealand appears to be associated with bagged lettuce and raw carrots.  The full cause of the infections is still being investigated by Ministry of Primary Industry workers.

The symptoms of Y. pseudotuberculosis infection include fever and right-sided abdominal pain, which makes diagnosis difficult, since these symptoms are also seen in appendicitis.  The patient may have diarrhoea, but this is often absent.  Less frequently, long-lasting joint pain may occur.  Symptoms take 5 to 10 days to develop, so it is often difficult for the patient to remember what foods they had eaten that might have transmitted the infection.

Y. pseudotuberculosis is very well adapted to infecting humans.  The bacterial cells have a number of virulence factors, most encoded on a small transmissible piece of DNA called a plasmid.  The virulence factors enable the bacterial cells to adhere strongly to intestinal cells, and to evade the host’s normal defence mechanisms, while other proteins enable the bacteria to invade host cells.

The best way to avoid infection is probably to throw away bagged pre-prepared lettuce or shredded carrots that have been in your refrigerator for a while, and to prepare these items fresh as required.  Since Yersinia species are not heat resistant, they can be killed by normal cooking.  Be careful to maintain good kitchen hygiene, and avoid cross contamination of cooked foods from raw foods of any kind.

Saturday, September 27, 2014

Don't put Cleaning Chemicals in Food Containers!

It's happened again! According to Doug Powell's Barfblog Daily, a woman was poisoned and nearly died after drinking iced tea containing cleaning chemicals at a suburban Salt Lake City restaurant.

Apparently, a worker at the restaurant put cleaning lye (probably sodium hydroxide) into a sugar bag. A second worker put the material into an iced tea dispenser. The restaurant chain claims that this is the first time in 73 years that this has happened.

Indeed, if the restaurant chain is using any kind of food safety programme, this should never have happened, and as Doug says, "It has never happened before" is no defence. One of the basic principles of Good Catering Practice and HACCP is not to put non-food materials into food containers, and to store cleaning chemicals away from food.

There are many incidences of accidental poisoning occurring because of mis-identification of chemicals. All could have been avoided by using proper containers and labelling them clearly with the contents.

Of course, this principle doesn't just apply to restaurants - it is just as important at home. Ayesha tells me that the kitchen is her preserve, and she knows what is in the glass jars in the pantry. On some occasions when I have had to fend for myself, deciding on the identity of the white powders in the identical unlabelled glass jars has taxed my scientific abilities! Icing sugar and cornflower are subtly different, and custard powder is slightly yellow with a vanilla odour. Salt and castor sugar look the same but taste different. These are trivial examples, but in the high pressure of a restaurant kitchen, unlabelled materials, or worse, mislabelled materials are unlikely to be identified and will find their way into foods, sometimes with serious consequences.

Wednesday, August 6, 2014

Vomiting and Diarrhoea doesn't necessarily mean food poisoning.

If someone reported that they had vomiting and diarrhoea, I would normally suggest that they had contracted food poisoning.  Further questions about recent meals, travel history, etc. would help to clarify the situation.

However, with the current Ebola virus outbreak in West Africa - Sierra Leone, Guinea and Nigeria - and two Americans apparently infected, together with a reported potential case in Sydney, the possibility of a world wide epidemic is not far fetched.  

Ebola viral disease is not new - it first appeared in 1972, just after I qualified as a microbiologist, in the Sudan and Democratic Republic of Congo.  There was then and still is no licenced vaccine and the fatality rate can be as high as 90%.  

Ebola is not transmitted by food.  The reservoir appears to be wild animals and there are documented cases of transmission of the virus to humans through handling or contact with bodily fluids of infected chimpanzees, gorillas, fruit bats, monkeys, forest antelope and porcupines found ill or dead or in the rainforest (WHO, 2014).  Transmission is then human to human, again by contact with bodily fluids through broken skin or mucous membranes.  Contact with environments contaminated with fluids from infected individuals can also result in transmission.

According to staff at the Mayo Clinic, signs and symptoms typically begin abruptly within five to 10 days of infection with Ebola or Marburg virus. Early signs and symptoms include:
Severe headache
Joint and muscle aches

Of course, some other diseases including influenza can produce similar symptoms. However, in the case of Ebola viral disease, symptoms become increasingly severe and may include:
Nausea and vomiting
Diarrhea (may be bloody)
Red eyes
Raised rash
Chest pain and cough
Stomach pain
Severe weight loss
Bleeding, usually from the eyes, and bruising (people near death may bleed from other orifices, such as ears, nose and rectum)
Internal bleeding

There is no need to panic if you or family members have vomiting and diarrhoea, but the application of sensible precautions can help to limit the spread of the virus or any other causative agent.  Air travel is a very rapid way for infections to spread around the world.  If you have been in Central or West Africa within the last few days and start to show the early symptoms listed above, you should immediately contact a doctor and, to be fair to your fellow man, avoid air travel.  If you have been on an aircraft where someone had vomiting and diarrhoea, it might also be a good idea to consult a doctor, even thought the cause is most likely food poisoning.

As with all cases of vomiting and diarrhoea, take great care with personal hygiene and ensure that those people looking after you do the same.  The chances are that you don't have Ebola, but this outbreak looks to be the most widespread so far. 

WHO (2014)  Fact sheet N°103. Updated April 2014.Retrieved from:

Wednesday, March 12, 2014

Unsafe Hospital Food? There is a greater concern

A couple of days ago, I came across a reference to a report that claimed 85% of raw chicken delivered to the University Hospital in Geneva tested positive for strains of Escherichia coli resistant to extended-spectrum beta lactam antibiotics. These antibiotics belong to the penicillin family. The original study was published in  Infection Control and Hospital Epidemiology, the journal of the Society for Healthcare Epidemiology of America.  (Unfortunately, when I tried it, the link was broken).
Apparently, there were workers in the hospital kitchen who tested positive to carriage of the ESBL E. coli, however, the frequency was no greater than in the general population.

The finding of the high rate of contamination with ESBL resistant bacteria in the raw chickens is a concern, not because patients were at risk, but because it indicates that the poultry flocks had probably been exposed to antibiotics that are still used in therapy.  Proper procedures in the kitchens should ensure that the contaminating bacteria are destroyed and that cross contamination from raw meat to cooked or fresh foods is controlled.

The use of antibiotics in animal husbandry is leading to increased incidence of antibiotic resistant bacteria.  See my previous posts on antibiotics:    
et seq.

When I gave my inaugural lecture as Professor of Food Microbiology, I reviewed the developments in microbiology that led to the discovery and development of penicillin.  Before the advent of this antibiotic, a simple scratch with a rose thorn could be a death sentence if the scratch became infected.  It would be a catastrophe if we returned to those days because we had squandered our slim advantage over the pathogenic bacteria for short term financial gains by the animal rearing industries.

Sunday, March 2, 2014

To flush or not to flush ...

This post was originally published on 7th February, 2011.  I accidentally deleted it while trying to answer a question from a reader.  Here it is again.

No, this one isn't about faecal bacteria, at least not directly.

Our major TV news broadcaster was guilty over the weekend of a dreadful beat-up on the use of gas mixtures to extend the shelf life of fresh meat.  Under the banner of "How safe is your meat?", the channel made a big deal of the use of gas mixtures containing carbon dioxide to inhibit bacteria on the meat.  They implied that suppliers were trying to pass off old meat as "fresh" and that the process was used to make the meat look redder and thus deceive the consumer into thinking that the meat was fresher.  A further implication of the banner was that gas flushed meat is unsafe.  Must have been a slow news day.

Meat technologists and microbiologists have known for many years that gas mixtures containing carbon dioxide inhibit bacteria, such asPseudomonaswhich are responsible for the development of slime and odours on meat stored under refrigerated conditions.  The gas also inhibits many pathogens, which may potentially cause disease.  

Consumers interviewed in supermarkets said that the meat should be labeled to indicate that it had been gas flushed.  Of course, one supermarket chain said they would do this if customers wanted it, while another tried to take the high ground and claim that they would never gas flush meat.

This is all playing on the ignorance of many consumers about food technology and food safety.  Certainly the meat keeps longer when gas flushed. Why does meat normally have such a short shelf life?  Because some bacteria can grow under refrigeration conditions and turn the meat slimy or produce odours that consumers find objectionable.

Should we ignore and reject the many years of research on food preservation?  Should we perhaps go back to taking meat home wrapped in paper and cooking it the same day?  That's "natural".  Should we reject vacuum packaging - it's not natural, but in fact works in a very similar way to gas flushing.  Consumers have demanded longer shelf life in all sorts of foods - meat, strawberries, smoked mussels, cakes and pastries.  In response, food technologists have developed ways to deliver such foods and these techniques involve preservative chemicals, vacuum packaging, pasteurisation and gas flushing (modified atmospheres).  If we are prepared to go back to foods with a shelf life of just a few days, we can reject gas flushing and other technologies.

If consumers are really concerned about gas flushing, they can recognise flushed packs by the fact that the film is sealed to the tray, or in some cases, such as gas flushed bakery goods, the package looks like a pillow.

Me?  Well, I'll happily buy carbon dioxide flushed meat - it keeps longer and in some cases looks better.

Saturday, February 22, 2014

Survival in Antarctica

I hesitate to write this blog article in case someone misinterprets it.  So... DO NOT TRY THIS AT HOME!

I recently spent three weeks in the Taylor Dry Valley in Antarctica.  Conditions are relatively harsh, though we had excellent extreme cold weather gear, warm tents and double layer sleeping bags.  Approximately 19 scientists and several visitors, who stayed for a couple of days, shared a Polar Haven working tent - insulated wooden floor and heated by a diesel stove, with electrical power provided by a generator.  Conditions in the tent were quite crowded; we ate our meals in there, operated scientific instruments, and analysed data.

What does this have to do with food safety?

There is no opportunity to bathe or even wash hands and only the most primitive sanitation facilities are available.  Baby wipes are the main means of keeping clean.  Nineteen individuals cooked for each other and ate together.  We ate all meals with our own cutlery and plastic food bowls and all drinks were contained in thermally insulated cups. Washing up consisted of a wipe with a paper towel or a non-scented baby wipe.  Because of the extremely dry conditions, we attempted to drink 4 litres of water every day, and all water came from Spaulding Lake, which is fed from the glaciers.  (Incidentally, the water tastes wonderful!)  Everyone carried their own 1 litre drink bottle.

Nobody contracted food poisoning.  I had both a personal and a professional interest in this!

This feat was the result of a combination of extreme personal hygiene care, the environmental conditions, and our diet.

In our Antarctic Skills Training programme, the importance of personal hygiene was emphasised - the Taylor Valley is very isolated and not a place to get sick.  Besides the use of baby wipes, tubes or pump dispensers of hand sanitiser were available everywhere and most team members carried their own supply too.

All our food, other than the dehydrated material, was stored outside in insulated boxes in the shade.  The mean ambient temperature was around 0C, so no opportunity for bacterial multiplication.

Our meals were either hot - bacon, pasta, meat stew, risotto, hashbrowns (lots), curry etc. -  or preserved in some way, such as dried and canned - cereals, canned fruit, milk powder, biscuits, soups, chocolate, muesli bars, peanut butter, jam, hard cheese, English muffins etc.  Most meals therefore were cooked in the outside camp kitchen and eaten immediately.  There were never any leftovers or reheating, so again no opportunity for bacteria to multiply or produce toxin.

I don't recommend that anyone should eat or prepare food for others without washing their hands, but this experience does show that with the proper precautions, it is possible, even in primitive conditions, to maintain food safety.

Odd Spot:  Perhaps the highlight of our 3-week deployment in Taylor Valley came the day after we ran out of meat.  Two of the helicopter pilots secretly organised to bring 4 or 5 large pizzas on one of the resupply missions.  They were heroes!

Wednesday, January 8, 2014

Norovirus in a confined space

I am currently down at Scott Base, Antarctica, heading out into the field tomorrow for two to three weeks' scientific work.

The base is on high alert, but not because of weather or acts of terrorism etc.  The concern this time is the outbreak of norovirus at McMurdo Station, which is only just over the hill from here and is normally visited regularly by both scientists and service personnel.

We are taking extreme precautions; the Thursday night American Night has been cancelled and visitors are strongly discouraged if not completely barred.  There are hand sanitiser pumps throughout the base and it is a requirement to sanitise hands before entering the mess.  Communal food items, such as loaves of bread are not to be handled with bare hands, because the virus can easily be transmitted on surfaces.  The bathrooms and toilets are being regularly sanitised and there too, there are warning signs that hands must be washed with soap and water and hand sanitiser is freely available.

It is to be hoped that the virus doesn't make it over to Scott Base - there are several projects kicking off now, and many more scientific teams will be arriving shortly, to the extent that some teams are being asked to reschedule their time at Scott Base to free up bunk room space.  An outbreak here could be catastrophic for the scientific programme, not to mention the misery for the victims.