Fungal β-1,3-Glucan Increases Ofloxacin Tolerance of Escherichia coli in a Polymicrobial E. coli/Candida albicans Biofilm

Abstract

ABSTRACTIn the past, biofilm-related research has focused mainly on axenic biofilms. However, in nature, biofilms are often composed of multiple species, and the resulting polymicrobial interactions influence industrially and clinically relevant outcomes such as performance and drug resistance. In this study, we show thatEscherichia colidoes not affectCandida albicanstolerance to amphotericin or caspofungin in anE. coli/C. albicansbiofilm. In contrast, ofloxacin tolerance ofE. coliis significantly increased in a polymicrobialE. coli/C. albicansbiofilm compared to its tolerance in an axenicE. colibiofilm. The increased ofloxacin tolerance ofE. coliis mainly biofilm specific, as ofloxacin tolerance ofE. coliis less pronounced in polymicrobialE. coli/C. albicansplanktonic cultures. Moreover, we found that ofloxacin tolerance ofE. colidecreased significantly whenE. coli/C. albicansbiofilms were treated with matrix-degrading enzymes such as the β-1,3-glucan-degrading enzyme lyticase. In line with a role for β-1,3-glucan in mediating ofloxacin tolerance ofE. coliin a biofilm, we found that ofloxacin tolerance ofE. coliincreased even more inE. coli/C. albicansbiofilms consisting of a high-β-1,3-glucan-producingC. albicansmutant. In addition, exogenous addition of laminarin, a polysaccharide composed mainly of poly-β-1,3-glucan, to anE. colibiofilm also resulted in increased ofloxacin tolerance. All these data indicate that β-1,3-glucan fromC. albicansincreases ofloxacin tolerance ofE. coliin anE. coli/C. albicansbiofilm.