Enzyme-linked immuno-strip biosensor to detect Escherichia coli O157:H7

A strip-based biosensor using the enzyme-linked immunosorbent assay technique was fabricated to detect Escherichia coli O157:H7. Two types of antibody specified to E. coli O157:H7 were used to form sandwich-binding complexes. To fabricate an immuno-strip, capture antibody (monoclonal antibody) was immobilized onto signal generation pad and polyclonal antibody conjugated with horseradish peroxidase (HRP) was utilized as detection antibody. Four different functional membranes have been used to fabricate immuno-chromatographic assay strip. A sample application pad was a glass fiber membrane pre-treated with polyvinyl alcohol. A conjugate release pad was fabricated using a glass membrane. A signal generation pad was made on nitrocellulose membrane. Finally, a cellulose membrane was used as an absorption pad. Under optimal conditions of analysis, a color signal in proportion to the E. coli O157:H7 concentration was measured using a detector. The measurement range was 1.8×10³–1.8×10⁸ CFU/mL.     

Influence of culture conditions on Escherichia coli O157:H7 biofilm formation by atomic force microscopy

Biofilms are complex microbial communities that are resistant against attacks by bacteriophages and removal by drugs and chemicals. In this study, biofilms of Escherichia coli O157:H7, a bacterial pathogen, were investigated using atomic force microscopy (AFM) in terms of the dynamic transition of morphology and surface properties of bacterial cells over the development of biofilms. The physical and topographical properties of biofilms are different, depending on nutrient availability. Compared to biofilms formed in a high nutrient medium, biofilms form faster and a higher number of bacterial cells were recovered on glass surface in a low nutrient medium. We demonstrate that AFM can obtain high-resolution images and the elastic information about biofilms. As E. coli biofilm becomes mature, the magnitude of the force between a tip and the surface of the biofilm gets stronger, suggesting that extracellular polymeric substances (EPSs), sticky components of biofilms, accumulate over the surface of cells upon the initial attachment of bacterial cells to surfaces.