Bacteria and Diseases of Unknown Cause

In recent years, many diseases for which the cause was unknown have been shown to be due to bacteria. These include Legionnaire disease (Legionella species) [1], cat scratch disease (Rochalimaea species) [2], the hemolytic-uremic syndrome (Escherichia coli strains, such as O157:H7, producing Shiga-like toxins) [3], peptic ulcer disease (Helicobacter pylori) [4], and a form of chronic arthritis resembling rheumatoid arthritis (Borrelia burgdorferi) [5], among others. Physicians had thought that these disorders were caused by autoimmune phenomena (the hemolytic-uremic syndrome, for example), metabolic processes (peptic ulceration), or viruses [cat scratch disease], and it is instructive to consider why recognition of bacterial causation was delayed. The reasons may be classified as follows: 1) fastidious growth characteristics of the causative bacteria; 2) absence of defined bacterial properties; 3) low bacterial concentrations; 4) uncommon sequelae of common infections; and 5) the power of dogma.

Pathogenic bacteria often cannot be readily cultured on artificial media because of adaptation to in vivo niches and because they may be overgrown by more rapidly dividing organisms. Thus, not surprisingly, the etiologic agent for many commonly occurring clinical infections, including pneumonia, acute diarrhea, and vaginitis, is recognized in only a few cases. With Legionnaire disease, it was the recognition of an epidemic of severe pneumonia that led to extraordinary clinical and laboratory studies done to identify an agent [1]. We now know that sporadic Legionnaire disease commonly occurs, but such cases continue to be underdiagnosed because …