Published: 18 August 2014

Are you playing barbecue roulette?

With many of us looking forward to eating al fresco this coming Bank Holiday weekend, an experiment by microbiologist Dr Simon Park reveals why it’s important to keep flies away from your food.

Picnics in the park and barbecues in the garden are British summertime staples. But as well as longer days and warmer evenings, summer sees a spike in food poisoning rates.

“When meat is burnt on the outside but still uncooked in the centre, the bacteria that can cause food poisoning aren’t killed,” said Dr Park. “So it’s perhaps no surprise that the incidence of illness causes by Campylobacter, an organism found on chicken products and the most common form of food poisoning in the UK, correlates strongly with increases in hot weather and the use of barbecues.”

Flies are another unwelcome accompaniment to eating outdoors, but, aside from being irritating, what impact do they really have when they buzz about the barbecue or picnic?

To find out, Dr Park temporarily trapped three blue bottle flies in a plastic Petri dish filled with solid bacterial growth media and allowed them to walk over the surface for 10 minutes.

After a day or so, the bacteria tracks left by the flies grew into visible points or colonies showing the grim effect tiny fly footprints could have on picnic or barbecue food - see pictures of the fly footprints on the right-hand side of this page.

“The blue bottle fly seems to be equally at home feeding on rotting bodies, faeces or our carefully prepared food. This, and other habits, make it an unparalleled vector for transmitting disease,” said Dr Park. “If a blue bottle has recently fed on faeces it may carry as many as six million bacteria on its feet.”

So what’s the best way to prevent food poisoning or stop flies from adding their own accompaniment to your summer meals?

  • Make sure that frozen meat is thoroughly defrosted before cooking
  • Check that meat is properly cooked and that any juices run clear before serving
  • Ensure food stays covered to keep flies away
  • During hot weather, keep food such as salad and sandwiches cool to prevent food poisoning bacteria from multiplying
  • Make sure fridges are working correctly, with a temperature low enough to prevent the growth of food poisoning bacteria

Learn more about our programmes in the field of Biosciences and Medicine and research in the Faculty of Health and Medical Sciences.


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