Susceptibility of clinical Staphylococcus aureus isolates to innate defense antimicrobial peptides

Differential induction of innate defense antimicrobial peptides in primary nasal epithelial cells upon stimulation with inflammatory cytokines, Th17 cytokines or bacterial conditioned medium from Staphylococcus aureus isolates

To date it is incompletely understood why half of the human population is intrinsically resistant to Staphylococcus aureus colonization whereas the other half is intermittently or permanently colonized. Nasal colonization represents the primary niche for S. aureus. We therefore investigated whether primary nasal epithelial cells (HNEC) express antimicrobial peptides (AMPs) upon stimulation by inflammatory cytokines or bacterial conditioned medium (BCM) of different colonizing and invasive staphylococci. Stimulation with classical cytokines (IL-1β, TNF-α, IFN-γ) potently induced hBD-3 and RNase7 in HNEC. Th17 cytokines (IL-17A, IL-17F, IL-22) yielded comparably weak hBD-3 and RNase7 induction and no synergistic effects with classical cytokines. BCM of S. aureus and Staphylococcus epidermidis isolates moderately induced hBD3 and RNase7 mRNA expression without significant differences when comparing colonizing vs. invasive isolates. Our results indicate that HNEC contribute to the innate defense by secretion of an AMP-containing chemical defense shield along the nasal mucosa i.e. within the primary colonization niche of S. aureus. Further studies are needed to investigate whether a deficient AMP expression in the nasal mucosa may be related to different S. aureus carrier states. AMPs or AMP-inducing agents may be promising candidates for future topical decolonization regimens that aim to prevent invasive S. aureus infections.

Staphylococcus aureus Colonization: Modulation of Host Immune Response and Impact on Human Vaccine Design

In apparent contrast to its invasive potential Staphylococcus aureus colonizes the anterior nares of 20–80% of the human population. The relationship between host and microbe appears particularly individualized and colonization status seems somehow predetermined. After decolonization, persistent carriers often become re-colonized with their prior S. aureus strain, whereas non-carriers resist experimental colonization. Efforts to identify factors facilitating colonization have thus far largely focused on the microorganism rather than on the human host. The host responds to S. aureus nasal colonization via local expression of anti-microbial peptides, lipids, and cytokines. Interplay with the co-existing microbiota also influences colonization and immune regulation. Transient or persistent S. aureus colonization induces specific systemic immune responses. Humoral responses are the most studied of these and little is known of cellular responses induced by colonization. Intriguingly, colonized patients who develop bacteremia may have a lower S. aureus-attributable mortality than their non-colonized counterparts. This could imply a staphylococcal-specific immune “priming” or immunomodulation occurring as a consequence of colonization and impacting on the outcome of infection. This has yet to be fully explored. An effective vaccine remains elusive. Anti-S. aureus vaccine strategies may need to drive both humoral and cellular immune responses to confer efficient protection. Understanding the influence of colonization on adaptive response is essential to intelligent vaccine design, and may determine the efficacy of vaccine-mediated immunity. Clinical trials should consider colonization status and the resulting impact of this on individual patient responses. We urgently need an increased appreciation of colonization and its modulation of host immunity.

Impaired β-defensin expression in human skin links DEFB1 promoter polymorphisms with persistent Staphylococcus aureus nasal carriage

BACKGROUND

Genetically determined variation in the expression of innate defense molecules may explain differences in the propensity to be colonized with Staphylococcus aureus.

METHODS

We determined S. aureus nasal carriage in 603 volunteers; analyzed polymorphisms in the DEFB1 promoter at positions -52 G>A (rs1799946), -44 C>G (rs1800972), and -20 G>A (rs11362); and measured the content of human β-defensin 1 (hBD-1) and hBD-3 messenger RNA (mRNA) in 192 samples of healthy and experimentally wounded human skin.

RESULTS

Compared with GGG at the positions -52/-44/-20, the ACG haplotype was more common among persistent S. aureus nasal carriers (odds ratio, 1.93; 95% confidence interval [CI], 1.2-3.1; P = .006) and was associated with reduced expression of hBD-1 (GGG>ACG>GCA; P < .001) and hBD-3 (GGG>GCA>ACG; P = .04) in skin when measured 72 hours after wounding. Furthermore, a 50% decrease in hBD-1 and hBD-3 mRNA expression in wounded skin increased the odds of persistent carriage by 1.45 (95% CI, .93-2.26; P = .1) and 1.48 (95% CI, 1.01-2.17; P = .04), respectively. Adjustment for known risk factors of persistent S. aureus carriage did not substantially change the associations of both DEFB1 haplotypes and β-defensin expression with S. aureus colonization.

CONCLUSIONS

DEFB1 polymorphisms may promote persistent S. aureus colonization by altering β-defensin expression in keratinocytes of human skin.

Activity of short lipopeptides and conventional antimicrobials against planktonic cells and biofilms formed by clinical strains of Staphylococcus aureus

Background: The therapy for staphylococcal skin diseases is facing several difficulties caused by the growth of biofilms and development of resistant strains. Short synthetic lipopeptides designed on the basis of antimicrobial peptide structure seem to provide an alternative to conventional therapy. The purpose of this study was to synthesize a group of lipopeptides and evaluate their antistaphylococcal activity against biofilms formed by clinical strains of Staphylococcus aureus. Results: The compounds exhibited a strong antibiofilm activity against all the isolates. The maturity of the biofilms has shown a well-defined influence on antimicrobial activity of conventional antimicrobials. Discussion: Results showed that the lipopeptides were promising agents as the time of the culture did not greatly affect their activity.