Development of a rapid screening method for the detection of pathogenic Escherichia coli using a combination of Colilert^® Quanti-Trays/2000 and PCR

The use of culture based methods for the detection of Escherichia coli (E. coli) only gives information on the occurrence of E. coli and not pathogenicity of the organisms detected. To detect the both indicator and diarrhoeagenic E. coli (DEC) a method was developed using the Colilert^® Quanti-Tray/2000 system and polymerase chain reaction (PCR). A total of 619 samples were collected from springs (33), boreholes (24), taps (5), rivers (36), streams (8), domestic storage containers (253), raw sewage (1), final effluents (5), stool (149), soil (5) and toilet seat swab (100) samples from various provinces in South Africa. E. coli was enumerated using the Colilert^® Quanti-Tray's/2000 and DNA extracted from E. coli positive wells and used as template for a multiplex-PCR targeting genes specific to entero-pathogenic- (EPEC), entero-haemorrhagic- (EHEC), entero-invasive- (EIEC), entero-toxigenic (ETEC) and entero-aggregative E. coli (EAEC). The internal control was detected in 99% of positive E. coli samples. EAEC was detected in 17%, EIEC in 4%, ETEC in 11%, EHEC in 9% and EPEC in 21% of the E. coli positive samples. It is shown that this method can be used for the detection of DEC from a wide range of samples enriched with Colilert^® Quanti-Tray's/2000.