Molecular characteristics of Staphylococcus aureus isolates colonizing human nares and skin

Staphylococcus aureus is an important opportunistic pathogen which can localize in human nares and skin. The bacteria carriage was deemed as a risk factor because it can cause endogenous S. aureus infection. However, epidemiological characteristics of these colonized strains have not yet been identified. Here, we isolated and analyzed all culturable bacteria from nasal and skin swabs of 526 healthy individuals with three different age groups. Obvious differences in culturable microbiomes either from different sites (the nares and skin) or from different age groups (children, young adults, and seniors) were observed. Remarkably, Staphylococcus was the predominant genus in both nares and skin, and coagulase-negative Staphylococci were the most abundant species in all groups. In addition, S. aureus can also be isolated from both nares or skin. Among them, we observed 52 co-localized S. aureus in both nares and skin simultaneously in 7 individuals. Further analyses of these S. aureus isolates revealed that the genotypes of S. aureus varied when isolated from a different or even from same organ per individual, while significantly different phenotypes including biofilm formation and hemolytic activity were also noted. Interestingly, we observed that human skin isolates were prone to adhere to skin epithelial cells as shown by both cell adhesion and mouse model. This suggests that bacteria evolved to adapt environments during colonization. In conclusion, S. aureus localized in different organs of the human body were not completely homogenous. The origin of S. aureus spread or endogenous infection was diverse.