ARS | Publication request: Comparison of Molecular Methods and Traditional Plate Counting for Detecting Campylobacter Jejuni and Escherichia Coli from Environmental Samples

Submitted to: American Society for Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: April 10, 2008
Publication Date: June 2, 2008
Citation: Rothrock Jr, M.J., Cook, K.L., Bolster, C.H., Sorrell, J. 2008. Comparison of Molecular Methods and Traditional Plate Counting for Detecting Campylobacter Jejuni and Escherichia Coli from Environmental Samples. American Society for Microbiology Annual Meeting.

Technical Abstract: The accurate detection of pathogenic bacteria from environmental samples is vital from both agricultural and human health perspectives. The goal of this study was to compare the detection of Campylobacter jejuni and Escherichia coli from environmental samples using quantitative real-time PCR (QRT-PCR) and traditional plate count methodologies. According to dilution studies, the efficiency of both QRT-PCR assays was found to be high for pure and mixed culture samples (0.90 for C. jejuni and 0.97 for E. coli) and the limit of detections were similar (>103 cells/ml). In both assays, the minimum difference between dilutions that was accurately detected was a 0.5 log decrease. For E. coli, less than 10% difference was observed between cell concentrations as determined by the QRT-PCR assay and Eosin-Methylene Blue Agar (EMB) plate counts, whereas nearly 1 log lower concentrations were found using Campylobacter-Selective Agar (CSA) as compared to the QRT-PCR assay for C. jejuni. When testing water that has passed through a sand column, C. jejuni concentrations using QRT-PCR were found to be 2 logs higher than the CSA plate counts, while less than 0.5 log difference was observed for the E. coli concentrations using QRT-PCR or EMB plate counts. This indicates that transport through sand either is lethal to, or increases the concentration of viable, but non-culturable C. jejuni cells, but has minimal effects on E. coli cells. In soils and manure samples, background concentrations of C. jejuni were below our detection limit, although the limit of sensitivity in soils/manure (105 cells/g) was 2 logs higher than in water samples. Surprisingly 40% of the poultry litter samples tested (n = 12) exhibited relatively high concentrations (>107 cells/g) of C. jejuni. Natural E. coli concentrations were found to be high in both soils and manure samples (8x104 and 3 - 8x107 cells/g, respectively). These results suggest that E. coli concentrations from environmental samples are similar between culture-based and molecular methods, whereas C. jejuni concentrations are typically greater than 1 log higher using molecular assays.