Antibacterial Activities of Stationary Phase Culture Filtrates of Aspergillus fumigates

Our previous studies performed for the development of polymicrobial biofilm showed that simultaneous coculturing of Aspergillus fumigatus conidia or sporelings with Pseudomonas aeruginosa resulted in the killing of A. fumigatus cells whereas hyphae older than 12h were recalcitrant to the bacterial fungicidal activity. Since A. fumigatus produces an array of antimicrobial molecules, we examined the antibacterial activity of A. fumigatus culture filtrates on bacterial growth to examine the possible role of such small molecules minimizing the fungicidal activity of P. aeruginosa by spectrophotometric and colony forming unit assays. Culture filtrates collected from 48h stationary phase cultures inhibited the growth of P. aeruginosa and S. aureus, but not that of Candida albicans. Colony forming unit assay of culture filtrate-treated P. aeruginosa cells showed that the effect was bacteriostatic. Culture filtrate incubated in a boiling water bath for 15min retained its antibacterial activity compared to that of the unboiled culture filtrate. These results show that stationary phase liquid cultures of A. fumigatus produce a heat stable bacteriostatic compound(s) in liquid culture that is released into the growth medium inhibits the growth of P. aeruginosa.