title: Improving the Enrichment and Plating Methods for Rapid Detection of Non-O157 Shiga Toxin-Producing Escherichia coli in Dairy Compost.
abstract: A culture method to detect non-O157 Shiga toxin-producing Escherichia coli (STEC) was optimized in this study. The finished dairy compost with 30% moisture content was inoculated with a cocktail of six non-O157 STEC serovars at initial concentrations of 1 to 100 CFU/g. Afterward, non-O157 STEC cells in the inoculated dairy compost were enriched by four methods, followed by plating onto cefixime-tellurite sorbitol MacConkey agar supplemented with 5 mg/liter novobiocin (CTNSMAC) and modified Rainbow agar containing 5 mg/liter novobiocin, 0.05 mg/liter cefixime trihydrate, and 0.15 mg/liter potassium tellurite (mRBA). Immunomagnetic bead separation (IMS) was used to compare the cell concentration of individual non-O157 STEC serotypes after enrichment. There was no significant difference (P > 0.05) between CTN-SMAC and mRBA for non-O157 STEC enumeration. The single-step selective enrichment recovered ca. 0.54 log CFU/g more cells (ca. 0.41 log CFU/g for compost-adapted cells) (P < 0.05) compared with the two-step enrichment. Furthermore, the duration of the process to detect non-O157 STEC from dairy compost by selective enrichment, followed by IMS, was optimized. Among six non-O157 STEC serotypes, serotypes O111, O45, and O145 reached the highest cell density after enrichment in dairy compost, and the cell populations reached 7.3, 7.4, and 7.8 log CFU/g within 16 h of incubation, respectively. In contrast, without an enrichment step, the IMS detection limit of individual non-O157 STEC serovars ranged from 3.15 to 4.15 log CFU/g in dairy compost. These results demonstrate that low levels of non-O157 STEC can be detected within 2 days from dairy compost by using a culture method with an optimized enrichment procedure followed by IMS.
authors.affiliation: Department of Food, Nutrition, and Packaging Sciences, Clemson University, Clemson, South Carolina 29634, USA.
authors.forename: Hongye
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Biological Sciences, Clemson University, Clemson, South Carolina 29634, USA.
authors.forename: Zhao
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Department of Food, Nutrition, and Packaging Sciences, Clemson University, Clemson, South Carolina 29634, USA. xiuping@clemson.edu.
authors.forename: Xiuping
authors.initials: X
authors.lastname: Jiang
mesh_terms: D003470:Culture Media / Q000737:chemistry; D018189:Immunomagnetic Separation; D057230:Limit of Detection; D008372:Manure / Q000382:microbiology*; D054323:Shiga-Toxigenic Escherichia coli / Q000302:isolation & purification*; D012988:Soil Microbiology
chemical_list: D003470:Culture Media; D008372:Manure