Expert: Dana Krempels, Ph.D. - 2/21/2011

Question
Dear expert,

Scientists realized that flies have bacteriophage germs on their surface (they even extract them from flies to create antibiotics:
http://abc.gov.au/science/articles/2002/10/01/689400.htm ),

but when flies catch and transport pathogen and then touch your food,
why can't their anti-bacteria germs prevent you from being infected?


                                          Sincerely

Answer
Dear Ed,

Well, I've never thought about this before.  But here's my best "educated guess."  It's just a hypothesis that would need to be tested, scientifically.  :)  (This could be a cool lab project!)

The bacteriophages on the surface of the fly are there to protect the fly.  They don't move in any appreciable numbers when the fly lands on food or other surface, and because the fly is their natural host, these bacteriophages are not likely able to reproduce on the surface of the food or anything else, even if they did end up there.

Potential pathogens, however, often have no such constraints.  While the bacteriophage viruses sit and languish on the food (if any have even been transferred), even a single surviving bacterial pathogen on the food can begin to reproduce immediately.  It may simply be a question of numbers and opportunity.

Hope that helps.

Dana