Cheilitis in an atopic dermatitis patient associated with co-infection of Staphylococcus pseudintermedius and Staphylococcus aureus.

Background: Atopic dermatitis (AD) is an inflammatory skin condition distinguished by an activated Th2 immune response. The local skin microbial dysbiosis is a contributing factor to the development of AD. The pathogenic coagulase-positive Staphylococcus aureus is the primary species responsible for the progression of AD. Even though Staphylococcus pseudintermedius is an animal-origin pathogen, it is increasingly becoming a source of concern in human diseases. As another coagulase-positive Staphylococci, it is crucial to pay more attention to S. pseudintermedius isolated from the lesion site.

Results: In our investigation, we presented a case of cheilitis in a patient with atopic dermatitis (AD). We utilized culture and next-generation genomic sequencing (NGS) to identify the bacteria present on the skin swabs taken from the lip sites both prior to and following treatment. Our findings indicated that the predominant bacteria colonizing the lesion site of AD were S. pseudintermedius and S. aureus, both of which were eradicated after treatment. The Multi-locus sequence typing (MLST) of S. pseudintermedius and S. aureus demonstrated coordinated antibiotic susceptibility, with ST2384 and ST22 being the respective types. Although the skin abscess area resulting from S. pseudintermedius infection was significantly smaller than that caused by S. aureus in mice, the expression of cytokines interleukin-4 (IL-4) and interleukin-5 (IL-5) were significantly higher in the S. pseudintermedius-infected mice.

Conclusions: The S. pseudintermedius strain isolated from the lesion site of the AD patient exhibited a higher expression of IL-4 and IL-5 when colonized on mouse skin, as compared to S. aureus. This observation confirms that S. pseudintermedius can effectively induce the Th2 response in vivo. Our findings suggest that animal-origin S. pseudintermedius may play a role in the development of AD when colonized on the skin, emphasizing the importance of taking preventive measures when in contact with animals.