What distinguishes highly pathogenic staphylococci from medium- and non-pathogenic?

Members of the genus Staphylococcus are widespread as commensals of humans and animals where they colonize the skin or mucous membranes. While this coexistence remains mostly untroubled, especially for the healthy host, the bacteria may pose a serious threat for the human or animal host when they get access to inner layers of the body through breaches in skin or membranes. Among the members of the genus a wide span exists in the ability to cope with the hostile conditions encountered in the bloodstream of the living host as a scarce supply of certain nutrients, attacks of the immune system, or anti-infective measures undertaken in the clinical field. In this respect, Staphylococcus aureus is by far the most versatile species of the genus. Its equipment with a huge repertoire of different virulence factors and additional supportive gene products that increase the capability to survive within the living host makes S. aureus the leading pathogen not only within the genus but also one of the most threatening microorganisms regarding hospitally and community-acquired infections. Compared with S. aureus, the other virulent species of the genus like S. epidermidis, S. lugdunensis, S. saprophyticus, and S. haemolyticus have a more limited arsenal of virulence factors resulting in a specialized spectrum of diseases and a generally lower degree of pathogenicity. Besides the highly and medium-pathogenic staphylococci, the genus comprises also species like S. carnosus, S. xylosus, and S. equorum that are generally inconspicuous regarding clinical occurrences. Some strains of this group are used in the food industry and can be graded as non-pathogenic. This review aims to work out the differences between the pathogenic properties of highly and medium-pathogenic staphylococcal species and to draw a comparison between the pathogenic species and the food-grade S. carnosus TM300.