The Shiga toxins ELISA Kit is an enzyme immunoassay for the simultaneous qualitative detection of Shiga toxin 1 (Stx1) and Shiga toxin 2 (Stx2) in a single test. It is intended for use with human fecal samples from patients with gastrointestinal symptoms to aid in the diagnosis of disease caused by Shiga Toxin producing Escherichia coli (STEC). It may be used directly with human fecal specimens, or broth or plate cultures derived from fecal specimens.
For the determination of intra-assay performance, 6 positive fecal specimens and 6 negative fecal specimens were analyzed. Each specimen was assayed in replicates of eight. All positives remained positive and all negatives remained negative.
The inter-assay precision of the Shiga toxins ELISA Kit was determined using 12 fecal specimens (six negative, two positive for Stx1, two positive for Stx2, and two positive for both Stx1 and Stx2). The samples were tested, twice a day over a 5-day period using 2 different kit lots. A positive and negative control was run on each day. All positives remained positive and all negatives remained negative.
The cutoff for the test for direct fecal specimens was established at concentrations of 0.28 ng/mL Stx1 and 0.23 ng/mL Stx2, and for broth cultures at concentrations of 0.18 ng/mL Stx1 and 0.30 ng/mL Stx2.
Shiga toxin producing Escherichia coli (STEC) were first described by O' Brien, et al. after discovering that E.coli culture supernatant, which was cytotoxic to HeLa and Vero cells, could be neutralized by rabbit anti-Shiga toxin antibodies (1). STEC cause foodborne and waterborne diarrheal disease worldwide which, if left undiagnosed, can progress to hemorrhagic colitis and/or hemolytic uremic syndrome (HUS) (2, 3). Since certain treatments and medications can increase the risk of HUS (4), prompt detection is necessary to prevent outbreaks and secondary transmission (5-9). STEC strain O157:H7 has historically been the focus of attention in the United States since first isolated from undercooked hamburgers (3, 10), causing an estimated 73,000 illnesses annually (11). However, STEC infections caused by non-O157 strains have become more prevalent in recent years, both in the United States as well as abroad (12-16, 29). O157:H7 infections are routinely diagnosed by culture of fecal samples on selective media (17, 18), but this methodology allows non-O157 STEC strains to go undetected. STEC produce either one or both Shiga toxins (Stx1 and/ or Stx2), both potent cytotoxins (19, 20). Isolates producing only Stx2 have been attributed to higher incidence rates of HUS (18, 21-23). Shiga toxins can be detected by tissue culture assay (24), but this method is both time consuming and labor intensive. By detecting the toxins, the SHIGA TOXIN CHEK test can detect STEC present in fecal samples or culture, regardless of the serotype or other virulence factors (25).