Antibacterial and Antibiofilm Activity of Aspergillus-Derived Gliotoxin Against Streptococcus pneumoniae and Staphylococcus aureus: Interaction with Conventional Antibiotics

Antimicrobial resistance and the formation of biofilms in Gram-positive pathogens such as Streptococcus pneumoniae and Staphylococcus aureus are making the treatment of infections increasingly difficult. This study systematically evaluates the effect of gliotoxin (GT), an antimicrobial metabolite produced by Aspergillus fumigatus, on bacterial growth and biofilm formation, as well as its activity in combination with antibiotics. Three strains of S. pneumoniae and two strains of S. aureus (one methicillin-susceptible and one methicillin-resistant) were analysed. Planktonic growth was examined, and biofilm prevention assays were conducted by assessing biomass via crystal violet staining and viable cell counts. In addition, the combined effect of GT with cefotaxime and vancomycin was evaluated. GT inhibited planktonic growth and significantly reduced the biomass and viability of biofilms in a concentration-dependent manner. Moreover, its combination with conventional antibiotics (cefotaxime or vancomycin) showed strong synergy, drastically decreasing bacterial survival. These findings highlight the potent antibacterial and anti-biofilm activity of GT and its ability to enhance antibiotic efficacy, providing insight into fungal–bacterial interactions and suggesting potential therapeutic applications.