Friday, December 17, 2010

Why do people buy insurance?

Do you sometimes think "Why do I keep paying insurance premiums for my car, boat, house, personal liability, camera etc?  I hardly ever make a claim".  In all the years I have been paying premiums, I have only once made a claim on my car insurance, and that was when one of the local semi-evolved simians stole it and drove it into a ditch.  Would you consider not insuring your house?  Would you be able to continue with business as usual if your offices burned down?  The chances of making a claim and getting some of the premiums back are quite small.

The probable reason we continue to pay is that it gives us peace of mind, knowing that if we do smash the car into a BMW or Rolls Royce, we won't be bankrupted by the repair bills for the other car.  We can drive, secure in the knowledge that we have that one covered.

Pasteurisation of milk is insurance and free.  A mild heat treatment kills all the pathogens that might have got into the milk during milking and transport, leaving the nutritional value essentially unchanged.  Why would you even consider drinking raw milk or eating raw cheese, knowing that there is a small chance that it could result in illness that would change your life or that of your family for ever?    There has been plenty written about the dangers of Escherichia coli O157:H7 and other STECs, so I'm not going to go over it again here.  (See other posts on E. coli by clicking the E. coli label at the RHS of this blog).

Please, this Christmas season, if you really want to eat and drink raw milk products, you can make an informed choice.  But don't give these products to children - they don't have that choice and a dose of E. coli O157:H7 can lead to HUS, which will probably ruin the rest of their lives.

Thursday, December 16, 2010

Microbial tongue twisters

Today Bill Marler published a link to a clip of Larry King making an ass of himself while introducing a segment on Escherichia coli.

Perhaps it's a good thing he used the abbreviation E. coli

That set me thinking.  Does the general public find the names of bacteria so difficult to pronounce that they put all thoughts of them to the back of their minds?  Or do they regard all bacteria as "germs"?

The difficulty is that there are literally thousands of different bacteria, so microbiologists have to give them names that mean something and so that they can be grouped for study.  Sometimes the genus is named after its discoverer, or in honour of a famous microbiologist.  Salmonella was named after D.E. Salmon, an American bacteriologist; Bacillus is named from the Latin noun meaning "a small rod", while Acetobacter is so named because it oxydises ethanol to acetic acid (vinegar).

When microbiology students start out, they often have difficulty in remembering, or even pronouncing, names like Vibrio parahaemolyticus and Pediococcus pentosaceus.  Small wonder that the rest of the population has problems.

In fact, in terms of food poisoning, Joe Sixpack doesn't need to know these names.  Basically, if you mistreat food by contaminating it, or by holding it at temperatures that permit growth, there is a possibility that numbers of pathogenic bacteria will increase to what is termed an "infecting dose" or that toxins will be secreted into the food.  The latter cause food poisoning when ingested.  So what is our favourite bloke going to do to keep himself and his family safe?

Easy - clean, cook, cover and chill.  This little mnemonic includes it all: Clean-handle all foods with clean hands and utensils; Cook frozen foods after proper defrosting and use a thermometer to ensure that poultry or meat patties are properly heated through.  If foods are to be reheated, ensure that the temperature reaches at least 75C right through to the centre; Cover cooked foods during cooling and place in the refrigerator within 30 minutes; Chill foods to 4C and hold at that temperature until served (remember that some bacteria grow readily at refrigerator temperatures, so even chilled food will not remain safe forever) or hold above 60C.  You can find more extensive guidelines for these important concepts on the MAF website in New Zealand, or the FDA sites in America.

In the Southern Hemisphere, we are at the start of the barbecuing season.  It's important to be really careful - never put cooked meat on the same plate as raw meat and pre-cook chicken legs etc. making sure that patties are heated right through.

I was once at a company barbecue, standing in line to collect my meal.  I heard someone behind me whisper "See what he takes, he's a microbiologist".  I didn't need to name the bacteria that might have survived on my meats, choosing only steak and thoroughly cooked burger patties.

Saturday, December 11, 2010

Make those bacteria do the 100m hurdles

When I was a kid (last century) at Grammar School in the UK, taking part in athletic activities was compulsory.  One event that sticks in my mind is the 100m hurdles.  It's important to get a rhythm going and take the same number of steps between the landing and takeoff for each hurdle.  This seemed to go well for the first two or three hurdles, but it often became apparent that I was progressively falling short of my takeoff point for the later hurdles.  Eventually, I either stumbled or had to take a couple of extra steps.

This principle is applied to modern food preservation.  "Hurdle Technology" is a term coined by Lothar Leistner in about 1985.  The concept is simple.   Set up a series of "fences" and force bacteria to jump over them; if they don't fall at the first one, a later fence may trip them.  In food, the fences are low levels of preservatives, modified atmospheres, special packaging, low temperatures, acid pH and so on.  Some bacteria will be able to grow at refrigerator temperatures, but not in acid, or without oxygen etc.

There is a tendency among consumers to regard food processing as something sinister thought up by food technologists and done by manufacturers; fresh food is somehow better.  In fact, by use of multiple hurdles, food can be kept for longer and the amounts of preservatives in the food are reduced without compromising safety.