Detection and quantification of Escherichia coli O157 : H7 in environmental samples by real-time PCR

Aims: To apply the real-time Polymerase chain reaction (PCR) method to detect and quantify Escherichia coli O157:H7 in soil, manure, faeces and dairy waste washwater. Methods and Results: Soil samples were spiked with E. coli O157:H7 and subjected to a single enrichment step prior to multiplex PCR. Other environmental samples suspected of harbouring E.coli O157:H7 were also analysed. The sensitivity of the primers was confirmed with DNA from E.coli O157:H7 strain 3081 spiked into soil by multiplex PCR assay. A linear relationship was measured between the fluorescence threshold cycle (C (T) ) value and colony counts (CFU ml(-1) ) in spiked soil and other environmental samples. The detection limit for E.coli O157:H7 in the real-time PCR assay was 3.5 x 10(3) CFU ml(-1) in pure culture and 2.6 x 10(4) CFU g(-1) in the environmental samples. Use of a 16-h enrichment step for spiked samples enabled detection of <10 CFU g(-1) soil. E. coli colony counts as determined by the real-time PCR assay, were in the range of 2.0 x 10(2) to 6.0 x 10(5) CFU PCR-1 in manure, faeces and waste washwater. Conclusions: The real-time PCR-based assay enabled sensitive and rapid quantification of E. coli O157:H7 in soil and other environmental samples. Significance and Impact of the Study: The ability to quantitatively determine cell counts of E.coli O157:H7 in large numbers of environmental samples, represents considerable advancement in the area of pathogen quantification for risk assessment and transport studies.