P3-09 Prediction of Escherichia coli O157 Load Using Immunomagnetic Separation and Regression Analysis

Wednesday, July 31, 2013
Exhibit Hall (Charlotte Convention Center)
Alexandra Calle, Texas Tech University, Lubbock, TX
Mindy M. Brashears, Texas Tech University, Lubbock, TX
Guy H. Loneragan, Texas Tech University, Lubbock, TX
Introduction: Immunomagnetic separation (IMS) is commonly used for detection and isolation of Escherichia coli O157. Positives samples that are to be enumerated undergo additional steps that include enrichment and plating on selective media, which can be expensive and time consuming.

Purpose: The purpose of this study was to investigate the use of a regression formula to predict the E. coli O157 concentration of a sample following IMS.  

Methods: A five-strain cocktail of E. coli O157 was freshly prepared by incubating each individual strain in tryptic soy broth for 18 to 24 h at 37°C, combining equal amounts of the grown cultures, and preparing serial dilutions to achieve final culture concentrations of ca. 1, 2, and 3, log CFU/ml.  IMS was performed using an automated bead retriever and recovered cells were plated on tryptic soy agar and incubated for 20 to 24 h at 37°C; obtained colonies where confirmed with latex agglutination.  A regression analysis was applied to estimate the relationship between the initial bacterial concentration and the colonies obtained after IMS.

Results: A relationship (P < 0.01) was detected between initial culture concentration (log CFU/ml as the response variable) and cells recovered after IMS (log CFU/ml from washed IMS beads). In other words, concentration of E. coli O157 recovered from IMS beads may be used to predict concentration of E. coli O157 in sample (given the simple matrix included in the study described herein).  Estimates of the model intercept and slope values were 1.4049 and 0.7170, respectively.

Significance: This method can serve as an alternative to quantification of E. coli O157 as a semi-quantitative measurement to predict high shedding animals and can be considered as a cost and time efficient option. Results also can also be used to estimate the capture efficiency of the magnetic beads binding to E. coli O157 cells.