Development and evaluation of enzyme-linked immunosorbent assays for detection of shiga-like toxin I and shiga-like toxin II

Abstract

Shiga-like toxin (SLT)-producing Escherichia coli has been associated with a spectrum of human illnesses, including hemorrhagic colitis and hemolytic uremic syndrome. It produces at least two antigenically distinct toxins designated SLT-I and SLT-II, which have been implicated in disease. Currently available toxin assays, however, are not suitable for most clinical or public health laboratories. In this study, we have developed two sandwich enzyme-linked immunosorbent assays (ELISAs) based on toxin-specific murine monoclonal capture antibodies and rabbit polyclonal second antibodies which are specific for SLT-I and SLT-II. The SLT-I ELISA detected 200 pg of purified SLT-I, and the SLT-II ELISA detected 75 pg of purified SLT-II. The types of SLT produced by 166 human and 54 animal isolates of E. coli that produced moderate to high levels of toxin were determined by the ELISA, and results were confirmed by cytotoxin neutralization assays. With the exception of results from three strains, the tests agreed on the types of toxin present. DNA probe assays of 86 of 87 isolates also agreed with the ELISA and neutralization results. Although the SLT-II ELISA was specific for the SLT-II variant produced by porcine edema strains, most of the isolates examined produced levels of toxin (less than 50 50% cytotoxic doses [CD50] per ml) below the detection limit of the test. The ELISAs were not sufficiently sensitive to consistently detect low levels of toxin (less than 50 CD50 per ml) found in fecal extracts. On the basis of these findings, both ELISAs appeared to detect significant levels of SLT-I ( > 100 CD50 per ml) and SLT-II ( > 50 CD50 per ml) in E. coli culture extracts and should be useful diagnostic tools in many microbiology laboratories.