Antimicrobial Agents and Chemotherapy vol:59 issue:6 pages:3052-3058
In the past, biofilm-related research has mainly focused 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 that Escherichia coli does not affect Candida albicans tolerance to amphotericin or caspofungin in an E. coli / C. albicans biofilm. In contrast, ofloxacin-tolerance of E. coli is significantly increased in a polymicrobial E. coli / C. albicans biofilm as compared to an axenic E. coli biofilm. The increased ofloxacin-tolerance of E. coli is mainly biofilm-specific as ofloxacin-tolerance of E. coli is less pronounced in polymicrobial E. coli / C. albicans planktonic cultures. Moreover, we found that ofloxacin-tolerance of E. coli decreased significantly when E. coli / C. albicans biofilms were treated with matrix-degrading enzymes such as the -1,3-glucan-degrading enzyme lyticase. In line with a role for -1,3-glucan in mediating ofloxacin-tolerance of E. coli in a biofilm, we found that ofloxacin-tolerance of E. coli increased even more in E. coli / C. albicans biofilms consisting of a high -1,3-glucan-producing C. albicans mutant. In addition, exogenous addition of laminarin, a polysaccharide mainly composed of poly-β-1,3-glucan, to an E. coli biofilm also resulted in increased ofloxacin-tolerance. All these data indicate that -1,3-glucan from C. albicans increases ofloxacin-tolerance of E. coli in an E. coli / C. albicans biofilm.