Staphylococcus Strains in Atopic Dermatitis in Children: Toxins Production and Resistance Properties

Abstract

Staphylococcus spp. skin colonization is involved in the pathogenesis of atopic dermatitis (AD). While coagulase-positive Staphylococcus aureus strains are known to worsen symptoms, the role of coagulase-negative staphylococci (CoNS) remains controversial. Further research is needed to clarify the pathogenicity of CoNS in AD patients. A study involving 329 children with AD (mean age: 4.89 years) assessed the frequency of staphylococcal colonization on affected skin, along with the toxin-producing properties and antibiotic resistance of isolated strains. Mild AD: Predominantly colonized by CoNS (especially S. epidermidis). Moderate/Severe AD: Showed a significant increase in S. aureus colonization. CoNS (including S. epidermidis) could produce enterotoxins (A, B, C) and toxic shock syndrome toxin-1 (TSST-1), though less frequently than S. aureus strains. In severe AD, the number of toxin-producing CoNS strains (especially enterotoxin A producers) was higher than in mild AD, and the number of non-toxin-producing strains was lower. CoNS exhibited higher resistance rates than S. aureus. Methicillin-resistant S. epidermidis (MRSE): 23.4%. Methicillin-resistant S. aureus (MRSA): 1.27%. CoNS may contribute to AD pathogenesis through toxin production (exacerbating inflammation) and antibiotic resistance (limiting treatment options). Severe AD may involve a synergistic effect between S. aureus and toxin-producing CoNS.

Keywords: Staphylococcus aureus; Staphylococcus epidermidis; antibiotic resistance; atopic dermatitis; children; enterotoxins; toxic shock syndrome toxin-1.

Figure 1

Toxin-producing properties of Staphylococcus spp. SEA was detected at similar frequencies in undiluted bacterial filtrates among all staphylococci. In the 1:10 dilution, SEA was detected at similar frequencies in S. aureus and S. epidermidis strains, and less frequently among other CoNS species (p < 0.05). In the 1:50 dilution, SEA was detected more frequently in S. aureus strains compared to CoNS, including S. epidermidis (p < 0.05). SEB was detected at similar frequencies in undiluted filtrates. In the 1:10 dilution, it was detected more frequently in S. aureus strains compared to CoNS, including S. epidermidis (p < 0.001). SEC was detected more frequently in S. aureus filtrates compared to S. epidermidis filtrates (p < 0.01). TSST-1 was detected at similar frequencies in undiluted filtrates and in the 1:10 dilution of both S. aureus and S. epidermidis. However, other CoNS strains exhibited significantly lower TSST-1 detection rates (in both undiluted and 1:10 filtrates) compared to S. aureus (p < 0.01).

Figure 2

Staphylococcus spp. toxins production and AD severity: (a) CoNS strains (including S. epidermidis): toxin-producing properties were studied in 51 strains (mild AD—13, moderate AD—18, severe AD—20). In mild AD, CoNS produced SEA less often compared to severe AD group (p < 0.05). The number of non-toxin-producing strains was significantly higher among mild AD compared to severe AD (p < 0.05). (b) S. aureus strains: toxin-producing properties were studied in 32 strains (mild AD—5, moderate AD—6, severe AD—21). The strains had pronounced toxic properties, regardless of the severity of the disease.

Figure 3

Staphylococcus spp. antibiotic susceptibility in descending order for S. aureus. S. aureus demonstrated absolute sensitivity to vancomycin, linezolid, and later-generation fluoroquinolones (levofloxacin and moxifloxacin), with a low MRSA prevalence of 1.27% as determined by oxacillin resistance. S. epidermidis showed significantly more resistant properties to most antibiotics, including β-lactams, macrolides, cephalosporins, tetracyclines, aminoglycosides, lincosamides, and fluoroquinolones (p < 0.05). The incidence of MRSE was 28.4%.