Introduction

Abstract

The ability to sense and respond to the signals deriving from either the environment or other living organisms, is one of most important features of life. Pathogenic bacteria, like all living organisms, have developed efficient systems to scout the surroundings and adapt their life according to the signals that they can sense. The signals sensed by bacteria can be divided into three main categories: those deriving from the environment, those deriving from other organisms and those deriving from other bacteria (population signals). The signals perceived from the environment can be of physical or chemical nature, such as temperature, osmolarity, pH, light, CO₂, ammonia, oxygen, metals, nutrients, etc. The signals deriving from other living organisms may be either diffusable molecules such as chemoattractants, or signals that derive from direct contact with the organism. The signals deriving from other bacteria are usually diffusable molecules produced by the bacteria themselves which accumulate in the medium and increase in concentration with the bacterial cell density. This book contains nine chapters describing the regulatory systems of bacterial virulence that have been best characterized at the molecular level. The chapters go from the ironmediated regulation of diphtheria toxin production that is the oldest report of environmental regulation of virulence, described by Pappenheimer and Johnson in 1936,¹ to the most recent reports on autocrine regulation of virulence expression in Staphylococcus aureus and Pseudomonas aeruginosa. In the following pages, we would like to give a general overview of the different systems, in an attempt to point out the mechanisms that are common to most bacteria. A summary of signals perceived by bacteria is shown in Figure I.1.