Quantitative PCR Profiling of Escherichia coli in Livestock Feces Reveals Increased Population Resilience Relative to Culturable Counts under Temperature Extremes

Abstract

The relationship between culturable counts (CFU) and quantitative PCR (qPCR) cell equivalent counts ofEscherichia coliin dairy feces exposed to different environmental conditions and temperature extremes was investigated. Fecal samples were collected in summer and winter from dairy cowpats held under two treatments: field-exposed versus polytunnel-protected. A significant correlation in quantifiedE. coliwas recorded between the qPCR and culture-based methods (r= 0.82). Evaluation of the persistence profiles ofE. coliover time revealed no significant difference in theE. colinumbers determined as either CFU or gene copies during the summer for the field-exposed cowpats, whereas significantly higher counts were observed by qPCR for the polytunnel-protected cowpats, which were exposed to higher ambient temperatures. In winter, the qPCR returned significantly higher counts ofE. colifor the field-exposed cowpats, thus representing a reversal of the findings from the summer sampling campaign. Results from this study suggest that with increasing time post-defecation and with the onset of challenging environmental conditions, such as extremes in temperature, culture-based counts begin to underestimate the true resilience of viableE. colipopulations in livestock feces. This is important not only in the long term as the Earth changes in response to climate-change drivers but also in the short term during spells of extremely cold or hot weather.