Acid-treated Staphylococcus aureus induces acute silkworm hemolymph melanization

Area of Science:

• Microbiology
• Immunology
• Dermatology

Background:

• The skin microbiome is crucial for skin health; its disruption causes inflammatory skin diseases.
• Staphylococcus aureus and Cutibacterium acnes are skin pathogens that activate innate immunity.
• Silkworms serve as invertebrate models for studying innate immune responses, indicated by melanization.

Purpose of the Study:

• To investigate the interaction between S. aureus and C. acnes in activating innate immunity.
• To determine if C. acnes enhances the immune-activating properties of S. aureus.
• To explore the role of acidification in S. aureus-induced immune activation in silkworms.

Main Methods:

• Utilized silkworm hemolymph melanization assay to measure innate immune activation.
• Treated autoclaved-killed S. aureus (S. aureus [AC]) with C. acnes culture supernatant.
• Exposed S. aureus [AC] to organic acids (propionic, acetic, lactic) and hydrochloric acid.
• Investigated the effect of protease treatment on acid-treated S. aureus-induced melanization.

Main Results:

• C. acnes culture supernatant, which lowers pH, increased S. aureus [AC]-induced silkworm melanization.
• Acid treatment (propionic, acetic, lactic, hydrochloric acid) significantly enhanced S. aureus [AC]'s melanization activity.
• Protease treatment of acid-activated S. aureus [AC] reduced its melanization-inducing capacity.

Conclusions:

• Acid treatment of S. aureus induces innate immune activation in silkworms.
• S. aureus proteins appear to play a role in mediating this acid-induced innate immunity.
• This study highlights a potential interaction mechanism between S. aureus and C. acnes in skin immunity.