Correlation of Twenty Virulence Genes of Staphylococcus aureus with Severity of Atopic Dermatitis in Children as Compared to Healthy Individuals

Abstract

Principles: Patients with atopic dermatitis (AD) have a higher susceptibility for colonization and infection with Staphylocccus aureus (S. aureus). S. aureus are capable of expressing a multitude of virulence factors including superantigens which may act to modulate the host immune response and affect the clinical course of infection. This study determines the genetic repertoire of S. aureus isolated from children with atopic dermatitis and compares it to healthy controls and to pathogenic S. aureus isolated from cutaneous skin infections. Methods: Bacterial cultures were obtained from 24 AD patients between 7 months and 18 years and 24 uninfected controls. PCR and DNA sequence analysis were used to determine microbial surface components recognizing adhesive matrix molecules (MSCRAMM) patterns, staphylococcus protein A, spa types, and the presence of the genes for 20 virulence factors, the gene for methicillin resistance, mecA. Virulence factor gene patterns from AD associated S. aureus were compared with gene patterns from control group isolates and with 72 S. aureus isolates previously characterized from infected skin lesions not associated with AD. Results: MRSA SCCmec type IVa made up approximately 8% of both AD and control isolates. There was no difference in the prevalence of any MSCRAMM or virulence factor gene pattern analyzed in AD isolates in comparison to the healthy control group except for a higher prevalence of chemostaxis inhibitory protein, chp, in control group. Isolates of AD patients compared to those of infected skin lesions were more likely to carry the gene for staphylococcal enterotoxin A, sea (p = 0.0327), which encodes for an enterotoxin known to act as superantigen. Prevalence of the genes encoding for exfoliative toxin A and B, eta and etb, were significantly associated with organisms isolated from non-AD infected lesions (eta: p = 0.0003, etb: p = 0.0001). No virulence factor gene was found to be specifically associated with severity of AD lesions. Conclusions: The genotypes of S. aureus strains colonizing AD patients do not differ significantly from the genotypes of strains colonizing healthy individuals. Isolates infecting patients without AD express significantly more eta and etb and therefore seem to be more virulent to overcome the intact skin barrier.