Sensitive detection of Escherichia coli O157:H7 based on cascade signal amplification in ELISA

In this study, cascade signal amplification in ELISA involving double-antibody sandwich ELISA and indirectly competitive ELISA was established to sensitively detect Escherichia coli O157:H7. In the double-antibody sandwich ELISA, a complex was formed comprising anti-E. coli O157:H7 polyclonal antibody, E. coli O157:H7, biotinylated anti-E. coli O157:H7 monoclonal antibody, streptavidin, and biotinylated beta-lactamase. Penicillin solution was then added into the ELISA well and hydrolyzed by beta-lactamase. Afterward, the penicillin solution was transferred to indirectly competitive ELISA. The concentration of penicillin can be sensitively detected in indirectly competitive ELISA. In the cascade signal amplification system, increasing the amount of added E. coli O157:H7 resulted in more beta-lactamase and less penicillin. The detection sensitivity of E. coli O157:H7, which was 20 cfu/mL with the cascade signal amplification in ELISA, was 1,000-fold higher than that of traditional ELISA. Furthermore, the novel method can be used to detect E. coli O157:H7 in milk (2 cfu/g). Therefore, this new signaling strategy will facilitate analyses of highly sensitive foodborne pathogens.