A 116-year story of bacterial protein toxins (1888–2004): from “diphtheritic poison” to molecular toxinology

The concept that pathogenic bacteria might elicit their harmful effects in humans and animals by means of poisons elaborated by these microorganisms in the infected host is almost as old as the notion of pathogenic bacteria itself (William Edward van Heyningen 1950, 1970). The heuristic impact of the concept of bacterial poisons was considerable after the discovery of bacteria and their relation to disease. It was undoubtedly influenced by the knowledge that other biological organisms do produce poisons such as animal venoms and plant alkaloids. Indeed, the idea that the harm caused by infectious disease might be due to microbial poisons was entertained long ago even before the germ theory of disease was established. Both endotoxins and exotoxins were foreseen in 1713 by Vallisnieri, who suggested on one page of his Riposta that the “little worms of the most atrocious pests are of themselves of a poisonous nature” (van Heyningen, 1955). The first attempts to demonstrate experimentally the production of bacterial poisons were undertaken by Edwin Klebs (1834–1913) for staphylococci, Robert Koch (1843–1910) for Vibrio cholereae, and Friedrich Loeffler (1852–1915) for diphtheria bacillus, respectively. These attempts failed for methodological reasons that are now understandable. Klebs (1872) suggested that chemical substances named “sepsins” were responsible for the lesions caused by staphylococci, but no evidence for the existence of such substances was found. The first experimental demonstrations of staphylococcal toxin(s) were reported later by von Leber (1888), De Christmas (1888), van de Velde (1894), and other microbiologists by the early 1900s (see Arbuthnott, 1970). As concerns cholera, Koch (1884) expressed the view that the disease was a toxicosis, since the causative organism proliferated in the gut without appearing to invade or damage this organ or any of the neighboring tissues. Parenteral injection of V. cholereae filtrates did not produce any toxic effects in experimental animals, and the idea of an extracellular poison was abandoned. However, 75 years later, Koch's hypothesis was confirmed when two Indian researchers, De (1959) and Dutta et al. (1959) working independently of one another, showed that cell-free preparations from V. cholerae caused relevant symptomatology in animal models (adult rabbit ligated loop and infant rabbit, respectively). In 1969, the putative toxin was purified and biochemically characterized by C H A P T E R