Characterizing Staphylococcus Aureus Colonization During Eczema Disease Flares

The micro-evolution and micro-epidemiology of Staphylococcus aureus colonization during atopic eczema (AE) disease flares is poorly understood, according to a study published in the Journal of Investigative Dermatology,1 emphasizing the challenges involved in effectively eradicating S aureus colonization in patients with the condition. 

In the current study, a total of 9 children with moderate to severe AE were recruited through Ninewells Hospital in Dundee, Scotland, the United Kigdom. Skin swabs were obtained from 5 body sites, including 1 nostril, 2 areas of inflamed eczematous skin, and 2 separate areas of clinically unaffected skin. All of the swabs were colonized by S aureus at ≥1 sampled site. Of the 9 individuals with AE, 4 (44%) were nasally colonized in addition to having eczema-affected skin, and 7 (78%) were also colonized on clinically unaffected skin.

A total of 18 children who were nonatopic asymptomatic S aureus nasal carriers were chosen from the larger community control study population, from which skin swabs were obtained from a single nostril. All of the extranasal skin swabs taken from the controls were negative for S aureus.

Colonization by clonal S aureus populations was observed in both the patients with AE and in the controls, with all but 1 person containing colonies that belonged to a single sequence type. Phylogenetic analysis showed that AE disease flares were associated with the clonal expansion of the S aureus population, which took place over a period of weeks to months.

A significant difference in the genetic backgrounds of S aureus–colonizing patients with AE vs controls was reported (Fisher’s Exact test, P =.03). Assessment of intrahost genetic heterogeneity of the colonizing S aureus revealed evidence of within-host selection among the patients with AE, with “AE variants potentially selectively advantageous for intracellular persistence and treatment resistance,” the researchers wrote. The clonal populations observed in the AE group suggest that during disease flares, a clonal expansion occurs within the host.

The investigators concluded that these findings raise the question of whether lineage-specific features render S aureus isolates more adept at colonization of the vastly differing cutaneous environments of the nasal vs inflamed eczematous skin, thus highlighting an area in which future studies are warranted.

References

Harkins CP, Pettigrew KA, Oravcová K, et al. The micro-evolution and epidemiology of Staphylococcus aureus colonization during atopic eczema disease flare [published online September 23, 2017]. J Invest Dermatol. doi:10.1016/j.jid.2017.09.023