INTRODUCTION

A vast number of microbial aggregates fall into this ‘catch-all’ name – biofilm. Whether this unifying term does a great service or the opposite to a core branch of microbiology is open to some doubt – for biofilm is found in almost every environment graced with surfaces, sufficient nutrient and some water. A gentle digital examination of the waste outlet of the average kitchen sink will reveal a certain sliminess which embraces the quintessential soul of a biofilm! That ‘dirt’ which can block car windscreen washer jets is from the same stable. It does not seem necessary to list all possible examples of such structures. They range from growth on the leads of cardiac pacemakers, through biofilm attached to the inner surfaces of water distribution pipes, to the epilithon of rocks in streams and accumulated plaque on the surface of teeth.

There are almost as many definitions of biofilm as there are scientists working in the field or types of the structure itself. Any reasonable definition needs to incorporate the idea of a surface or interface on or at which microbes proliferate; it should also invoke the unifying effect of extracellular polymers which can envelop and probably protect the microbial colonies forming. It might also embrace a sense of community with the implication of emergent properties.

It is worth trying to classify a number of microbial systems that seem to be related to biofilm since they share many of its properties. In fact, members of the whole family of microbial aggregates have more in common than separates them (Table 1).