Photoactivated Gallium Porphyrin Reduces Colonization on the Skin and Suppresses Its Ability to Produce Enterotoxin C and TSST-1.

is a key pathogen in atopic dermatitis (AD) pathogenicity. Over half of AD patients are carriers of . Clinical isolates derived from AD patients produce various staphylococcal enterotoxins, such as staphylococcal enterotoxin C or toxic shock syndrome toxin. The production of these virulence factors is correlated with more severe AD. In this study, we propose cationic heme-mimetic gallium porphyrin (GaCHP), a novel gallium metalloporphyrin, as an anti-staphylococcal agent that functions through dual mechanisms: a light-dependent mechanism (antimicrobial photodynamic inactivation, aPDI) and a light-independent mechanism (suppressing iron metabolism). GaCHP has two additive quaternary ammonium groups that increase its water solubility. Furthermore, GaCHP is an efficient generator of singlet oxygen and can be recognized by heme-target systems such as Isd, which improves the intracellular accumulation of this compound. GaCHP activated with green light effectively reduced the survival of clinical isolates derived from AD patients (>5 log CFU/mL) and affected their enterotoxin gene expression. Additionally, there was a decrease in the biological functionality of studied toxins regarding their superantigenicity. In aPDI conditions, there was no pronounced toxicity in HaCaT keratinocytes with both normal and suppressed filaggrin gene expression, which occurs in ∼50% of AD patients. Additionally, no mutagenic activity was observed. Green light-activated gallium metalloporphyrins may be a promising chemotherapeutic to reduce colonization on the skin of AD patients.