Persistent nasal carriage of Staphylococcus aureus is associated with deficient induction of human beta-defensin 3 after sterile wounding of healthy skin in vivo

Persistent nasal carriage of Staphylococcus aureus is the primary reservoir for this pathogen and a risk factor for infection. The nares of 12 to 30% of healthy individuals are persistently colonized with staphylococci. Elucidating the yet enigmatic determinants of this phenomenon is of major public health interest. We hypothesized that differences in the levels of antimicrobial peptides (AMPs) that are found in human skin and have pronounced antistaphylococcal activity may contribute to this phenomenon. We compared constitutive and induced mRNA levels of RNase 7 and human β-defensin 3 (HBD-3) in healthy and experimentally wounded gluteal skin of 60 volunteers after ascertaining their carrier status through repeated nasal cultures. We found that levels of HBD-3 expression in skin of persistent nasal carriers of S. aureus were lower: induced levels in carriers were 63% (95% confidence interval, 43 to 94%; P = 0.02) and constitutive levels were 76% (95% confidence interval, 52 to 110%; P = 0.14) of those found in noncarriers. No such associations were present for RNase 7. In conjunction with existing knowledge, these findings suggest that healthy individuals with deficient HBD-3 expression in keratinocytes are more prone to persistent nasal colonization with S. aureus.