[chris (OP)]

This question came in from Malcolm yesterday by email:

As humans, we are told to regularly wash our hands, even sometimes with anti-bacterial soaps or gels. When it comes to eating fruit or vegetables, we are advised to merely rinse them under a tap before eating. Do fruit and vegetables have fewer and different bacteria on them to what we have on our hands?

What do you think?

[chris (OP)]

Just like a human, the skin of fruits and vegetables are covered in micro-organisms. This is where the yeasts come from that turn grapes into wine. But the difference between the flesh of a fruit and the flesh of an animal are sufficient that the forms of microbes that tend to live on fruits are (in a healthy person) non-pathogenic; that is, they cannot cause disease.

But, the important exception to this is when fruits and vegetables have been "fertilised" using sewage, which is a widespread practice in many countries. Sewage is rich in minerals and micronutrients, like phosphorus, meaning that it can make a valuable contribution to soil fertility. But, as we all know, by definition sewage is rich in the types of bacteria that are carried by - and can infect - humans. These can include coliforms (E. coli), salmonellae, campylobacter and so on.

Many of these bugs can survive for extended periods of time in the environment, on the surfaces of - and within the flesh of - fruits and vegetables that come into contact with them. This is thought to be the origin of the E. coli O104 outbreak in Europe in 2011.

So the best guidance is always to "peel it, boil it or leave it" when dealing with fruits and vegetables that you've not grown yourself and to assume that this sort of contamination may have occurred.

In other words, it's not the bugs that the fruit itself will attract but what bugs - to say nothing of pesticides and fungicides - the farmer may have added too.