Aurantiogliocladin inhibits biofilm formation at subtoxic concentrations

Abstract

Infections where pathogens are organized in biofilms are difficult to treat due to increased antibiotic resistances in biofilms. To overcome this limitation new approaches are needed to control biofilms. One way is to screen natural products from organisms living in a wet environment. The rational is that these organisms are preferentially threatened by biofilm formation and may have developed strategies to control pathogens in these biofilms. In a screen of fungal isolates obtained from the Harz mountains in Germany several strains have been found producing compounds for the inhibition of biofilms. One of these strains has been identified as Clonostachys candelabrumproducing aurantiogliocladin. Biological tests showed aurantiogliocladin as a weak antibiotic which was active against Staphylococcus epidermidisbut not S. aureus. Aurantiogliocladin could also inhibit biofilm formation of several of the tested bacterial strains. This inhibition, however, was never complete but biofilm inhibition activity was also found at concentrations below the minimal inhibitory concentrations, e. g. Bacillus cereuswith a MIC of 128 μg mL–1showed at 32 μg mL–1still 37% biofilm inhibition. In agreement with this finding was the observation that aurantiogliocladin was bacteriostatic for the tested bacteria but not bactericidal. Because several closely related toluquinones with different antibiotic activities have been reported from various fungi screening of a chemical library of toluquinones is suggested for the improvement of biofilm inhibition activities.

Keywords

• biofilm
• fungi
• <em>Clonostachys candelabrum</em>
• biofilm inhibition
• minimal inhibitory concentration
• <em>Staphylococcus epidermidis</em>
• quorum-quenching activity