Not all Staphylococcus aureus strains are equally pathogenic

Abstract

Extract: Members of the bacterial species Staphylococcus aureus are considered important human pathogens by all microbiologists and infectious disease specialists. A significant number of humans are persistently colonized in the nose with S. aureus strains, and long term colonization, up to years, has been observed. For 80% of all severe staphylococcal infections, the source seems to be endogenous, so ecological balance during colonization seems to be a key concept. During lifetime, many of the colonized individuals may suffer from mild infections, usually limited to the skin. The occasional furuncle is not a life-threatening disease, neither is impetigo or eczema (related to S. aureus carriage). However, once a person becomes severely ill and hospitalized, the opportunities for the Staphylococcus to manifest itself as a dangerous and invasive threat to human life are greater. It has been demonstrated recently that bacteremia (bacteria entered the blood circulation) caused by S. aureus is more frequent among nasal carriers than among non-carriers. The risk for the staphylococcal carriers increases threefold. In contrast, the risk of dying from an S. aureus bacteremic period is significantly higher in non-carriers. So carriage predisposes individuals to the development of infections but the sequels of these infections are less severe than in the case of infection in a non-carrier.