Effects of pretreatments on detection of E. coli O157

Escherichia coli (E. coli) O157:H7 was detected by using a surface plasmon resonance (SPR) biosensor and two antibodies with different characters. The lower limit of detection of E. coli 0157:H7 samples after pretreatments was determined by SPR. Seven pretreatment methods for preparing E. coli 0157:H7 samples for SPR detection; beads disruption, sonication, and heat shock, osmotic shock, lysozyme, alkali, and boiling treatments were compared for SPR signal with untreated cells as a control. In the case of the antibody raised against intracellular substance, β-D-galactosidase (β-gal), was used for the detection, the lower limit of detection was 4.9x10⁵ CFU/ml for both sonicated and alkali treated samples. The lower limit of detection was 8.3x10⁶ CFU/ml for beads disrupted samples, and 8.2x10⁸ CFU/ml for both lysozyme treated and untreated samples. In contrast, significant SPR signal was not obtained for heat shocked, osmotic shocked and boiled samples even at 8.2xl0⁸ CFU/ml. Sonication pretreatment improved the lower limit of detection for E. coli 0157:H7 by three orders of magnitude compared with that of untreated sample when anti-β-gal antibody was used for detection by SPR biosensor. In the case of antibody raised against lipopolysaccharide (LPS), the cell surface substance, was used, sonicated E. coli 0157:H7 sample was detected by SPR at 1.3xl0⁵ CFU/ml. The lower limit of detection was 1.1x10⁵ CFU/ml for heat shocked, lysozyme treated, alkali treated, boiled and untreated samples, and 7.7x10' CFU/ml for beads disrupted samples, respectively. After the osmotic shock treatment, E. coli O157:H7 was not detected by SPR even at 2.1x10⁸ CFU/ml. These results show that sonication was the most effective pretreatment method for the detection of E. coli O157:H7 by SPR using both antibodies recognizing intracellular β-gal, and cell surface LPS.