Direct amplification of DNA from clinical specimens, such as blood and faeces, by polymerase chain reaction (PCR) is most often hindered by endogenous inhibitory substances, including haemoglobin and bile acids. We tested whether Ampdirects' A (Shimadzu), a novel reagent cocktail that has been shown to suppress the inhibitors in blood, is also useful for faecal samples, and found that the vero toxin genes (VTl and VT2) of Escherichia coli 0157 could be efficiently amplified from the supernatant of boiled faeces by PCR in the presence of this cocktail without prior extraction of DNA. We compared the efficiency of amplification with and without the cocktail, using the supernatant of boiled normal faeces supplemented with E. coli 0157. PCR without the cocktail failed to amplify the vero toxin genes from the supernatant diluted < 6400-fold or containing >0•02% (final concentration) of boiled faeces. By contrast, PCR with Ampdirect A amplified the toxin genes in the mixture containing as much boiled faeces as 0•5% and as few E. coli as 4 to 8 colony-forming units (CFU). The minimum limit for E. coli 0157 detection by this method was estimated to be about 10 4 CFU!g faeces. The results obtained by this direct method agreed well with those obtained by the indirect method using DNA preextracted from patients' faeces (the detection limit being 10 3 CFU!g faeces).
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