Fly touched your food? Think twice before tucking in

Study says insects carry more dangerous bacteria than we thought … and city picnics are best avoided

MOST picnickers would brush away flies and think nothing of bugs briefly landing on their sandwiches.

But a new study suggests the insects carry far more dangerous bacteria than previously thought, meaning those sandwiches are best avoided.

Researchers at Penn State Eberly College of Science in the US found that common houseflies carry salmonella,

E. coli and bacteria that can lead to stomach ulcers and deadly sepsis. The researchers say flies may have been overlooked by public health officials as a source of disease outbreaks.

Flies in urban areas were found to carry more bacteria than the countryside, leading scientists to suggest avoiding city parks for a picnic.

“People had some notion that there were pathogens that were carried by flies but had no idea of the extent to which this is true and the extent to which they are transferred,” said Dr Donald Bryant, a professor of Biotechnology at Penn State University.

“We believe this may show a mechanism for pathogen transmission that has been overlooked by public health officials. It will make you think twice about eating that potato salad that’s been sitting out at your next picnic.”

DNA sequencing techniques were used to study the collection of microbes found in and on the bodies of the housefly (Musca domestica) and the blowfly (Chrysomya megacephala).

The housefly, which is ubiquitous around the world, was found to harbour 351 types of bacteria. The blowfly, which is found in warmer climates, carried 316. A large number of these bacteria were carried by both types of fly. Scientists found 15 instances of the human pathogen Helicobacter pylori – which causes ulcers in the human gut – on Brazilian blowflies. Flies probably pick up the bacteria from faeces and decaying organic matter that they use to nurture young, the study indicated.

The team also investigated the microbes on individual fly body parts. Dr Stephan Schuster, a research director at Nanyang Technological University, Singapore, found that the legs transferred most of the microbial organisms from one surface to another, suggesting even a brief step onto food could leave behind bacteria.

“The legs and wings show the highest microbial diversity in the fly body, suggesting that bacteria use the flies as airborne shuttles,” said Dr Schuster.

However, the researchers believe flies could have their uses – acting as early warning systems for disease or even living drones sent into tight spaces to search for microbes.

“The flies could be intentionally released as autonomous bionic drones and, upon being recaptured, inform about any biotic material they have encountered,” said Dr Schuster.

The research was published in the journal Scientific Reports.