Bacterial infections and pathogenic situations: The case of .

Traditionally, researchers have viewed different species and strains of bacteria as pathogens or as commensals. Different bacterial species and strains may be placed on a spectrum of pathogenicity or virulence, with highly pathogenic bacteria at one end, and minimally pathogenic bacteria at the other. It has also been recognized that a species or strain of bacteria can behave sometimes as a pathogen, and at other times as a commensal. Consequently, researchers have proposed that a spectrum of less pathogenic to more pathogenic bacteriological be produced, in contrast to the spectrum of less pathogenic to more pathogenic bacteriological . I propose that a third spectrum of pathogenicity should be developed: a spectrum of . This is illustrated using the example of . Some researchers consider to be a commensal that might be used to eradicate the dangerous pathogen from a patient's nose, whereas other researchers consider to be a dangerous pathogen in its own right. Inoculating into the nose of a patient might be understood as inoculating them with a dangerous pathogen. However, thinking in terms of pathogenic situations, this same intervention could be understood as reducing the pathogenicity of the situation. As knowledge of the situations in which is dangerous is incomplete, this review of concepts of pathogenicity should not be used to justify challenge experiments, but rather to illustrate a different way of thinking about pathogenicity.