In Vitro Biofilm Formation of Commensal and PathogenicEscherichia coliStrains: Impact of Environmental and Genetic Factors

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Abstract
Our understanding ofEscherichia colibiofilm formation in vitro is based on studies of laboratory K-12 strains grown in standard media. However, pathogenicE. coliisolates differ substantially in their genetic repertoire fromE. coliK-12 and are subject to heterogeneous environmental conditions. In this study, in vitro biofilm formation of 331 nondomesticatedE. colistrains isolated from healthy (n= 105) and diarrhea-afflicted children (n= 68), bacteremia patients (n= 90), and male patients with urinary tract infections (n= 68) was monitored using a variety of growth conditions and compared to in vitro biofilm formation of prototypic pathogenic and laboratory strains. Our results revealed remarkable variation among the capacities of diverseE. coliisolates to form biofilms in vitro. Notably, we could not identify an association of increased biofilm formation in vitro with a specific strain collection that represented pathogenicE. colistrains. Instead, analysis of biofilm data revealed a significant dependence on growth medium composition (P< 0.05). Poor correlation between biofilm formation in the various media suggests that diverseE. coliisolates respond very differently to changing environmental conditions. The data demonstrate that prevalence and expression of three factors known to strongly promote biofilm formation inE. coliK-12 (F-like conjugative pili, aggregative adherence fimbriae, and curli) cannot adequately account for the increased biofilm formation of nondomesticatedE. coliisolates in vitro. This study highlights the complexity of genetic and environmental effectors of the biofilm phenotype within the speciesE. coli.