Aims

The principal aims of this chapter are:

• to describe the various categories of bacterial exotoxins and their cellular effects

• to provide examples of toxins from each category and their role in pathogenesis

• to emphasise that exotoxins may have subtle effects at low concentrations that do not cause target cell death

• to describe the role that exotoxins have played in the dissection of eukaryotic signalling pathways

• to highlight some therapeutic uses of exotoxins

Introduction

Bacterial exotoxins are a diverse collection of proteins responsible for many of the symptoms caused by pathogens during infection. Exotoxins are actively exported by bacteria or else are released on cell lysis. Some toxins can kill cells outright by a number of different means. Others interfere with fundamental cellular activities to the ultimate benefit of the bacterium.

A number of bacteria produce a barrage of toxic activities, some of which may appear at first glance to be ‘blunt instruments’. These include toxins that degrade host cell membrane components, and the channel-forming toxins that punch holes in target cell membranes. Closer inspection of some of these toxins, however, reveals an underlying degree of sophistication in function that may result, for example, in interference with host immune defence mechanisms. Other toxins are perhaps more analogous to the stiletto dagger, being exquisitely specific in their target selection. This is perhaps best exemplified by the clostridial neurotoxins.