title: Evaluation of parameters affecting quantitative detection of Escherichia coli O157 in enriched water samples using immunomagnetic electrochemiluminescence.
abstract: We report here the use of immunomagnetic (IM) electrochemiluminescence (ECL) for quantitative detection of Esherichia coli O157:H7 in water samples following enrichment in minimal lactose broth (MLB). IM beads prepared in-house with four commercial anti-O157 monoclonal antibodies were compared for efficiency of cell capture. IM-ECL responses for E. coli O157:H7 (strain SEA13B88) were similar for all four commercial anti-O157 LPS monoclonal antibodies. The ECL signal was linearly correlated with E. coli O157:H7 cell concentration, indicating a constant ECL response per cell. Twenty-two strains of E. coli O157:H7 or O157:NM gave comparable ECL signals using IM beads prepared in-house. To assess the potential for interference from background bacteria in MLB-enriched water samples, 10(4) cells of E. coli O157:H7 (strain SEA13B88) were added to enriched samples prior to analysis. There was considerable variability in recovery of E. coli O157:H7 cells; net ECL signals ranged from 1% to 100% of expected values (i.e., percent inhibition from 0% to 99%). Cultures of Klebsiella pneumoniae, Klebsiella oxytoca, and Enterobacter cloacae, subsequently isolated from MLB-enriched water samples via IM separation (IMS), were observed to interfere with the binding of E. coli O157:H7 cells to IM beads. Recoveries of 10(4) E. coli O157:H7 cells were </=10% in the presence of ca. 10(8) K. pneumoniae, K. oxytoca, or E. cloacae cells. None of these strains gave a positive IM-ECL signal. Although competitive binding decreased sensitivity, there still was a linear correlation between ECL signal and higher E. coli O157:H7 cell concentrations. These studies indicate that IM-ECL in conjunction with MLB enrichment is capable of quantitatively detecting as few as 10(3) to 10(5) E. coli O157:H7 cells ml(-1), depending on percent recoveries, in enriched samples that contain ca. 10(9) total lactose-fermenting bacteria ml(-1). Assuming comparable growth rates for E. coli O157:H7 and other lactose-fermenting bacteria in MLB, it may be possible to detect as few as one E. coli O157:H7 in 100 ml of raw water containing as many as 10(4) to 10(6) lactose-fermenting bacteria (i.e., total coliforms).
authors: Environmental Microbial Safety Laboratory, U.S. Department of Agriculture, ARS Bldg. 173, BARC-East, 10300 Baltimore Avenue, Beltsville, MD 20705-2350, USA. sheltond@ba.ars.usda.gov
authors: Daniel R
authors: DR
authors: Shelton
authors: Jo Ann S
authors: JA
authors: Van Kessel
authors: Marian R
authors: MR
authors: Wachtel
authors: Kenneth T
authors: KT
authors: Belt
authors: Jeffrey S
authors: JS
authors: Karns
mesh_terms: D019453:Escherichia coli O157 / Q000302:isolation & purification*; D018189:Immunomagnetic Separation / Q000379:methods*; D008163:Luminescent Measurements; D014871:Water Microbiology