Disruption of Aspergillus fumigatus biofilm by Streptococcus pneumoniae: Mycelial fragmentation by hydrogen peroxide.

Biofilm is a complex structure consisting of microorganisms such as bacteria, fungi and an extracellular matrix (ECM). Biofilms are involved in most microbial infections and show persistent resistance to antibiotic treatment and immune response. Both Aspergillus fumigatus and Streptococcus pneumoniae are colonizers that can form biofilms in the respiratory tract. These pathogens have been simultaneously isolated from the same patient, but their interaction is poorly understood. We observed morphological changes in single- and mixed-species biofilms prepared for confocal laser scanning microscopy and scanning electron microscopy (SEM). Pneumococci suppressed the development of a fungal biofilm, and it even disrupted a preformed fungal biofilm. When a preformed fungal biofilm was treated with pneumococci, the mycelial network was fragmented, and only bacteria could develop. SEM revealed that the fragmented mycelium was further disrupted into fine filaments as treatment time progressed, and that the ECM of the preformed fungal biofilm had disappeared. The pneumococcal culture supernatant contained mycelial fragmentation activity that was heat-sensitive. The culture supernatant of a mutant pneumococcal strain deficient in pneumolysin (Δply) also exhibited the mycelial fragmentation activity. Enolase and lactate oxidase, which are involved in glycolysis and hydrogen peroxide production, were identified in the culture supernatant of the Δply mutant. Neither the wild type nor the mutant strain could fragment the mycelium in the presence of catalase. These data suggest that hydrogen peroxide could fragment the mycelium and would terminate the co-existence of A. fumigatus and S. pneumoniae in biofilm.