Quantitative biofilm assay using a microtiter plate to screen for enteroaggregative Escherichia coli

The gold standard for identification of Enteroaggregative Escherichia coli (EAEC) remains the HEp-2 cell adherence test, which is time-consuming and requires specialized facilities. We evaluated the usefulness of a quantitative biofilm assay to screen for EAEC from a total of 1,042 E. coli strains from children with diarrhea. Bacteria were incubated overnight in high-glucose Dulbecco's modified Eagle's medium using a polystyrene microtiter plate. The plate was stained with crystal violet after washing, and the biofilm was quantified using an enzyme-linked immunosorbent assay plate reader. The aggR gene was evaluated by a polymerase chain reaction. Forty-eight (77.4%) of 62 strains with an optical density at 570 nm (OD₅₇₀) > 0.2 were identified as EAEC by the HEp-2 adherence test, while no EAEC was found in strains with an OD₅₇₀ ≤ 0.2. Twenty-one aggR+ and 27 aggR- EAEC strains could be screened by an OD₅₇₀ > 0.2 using this assay. Although confirmation by a HEp-2 cell adherence test is needed, this biofilm assay is convenient and useful in screening for EAEC.