Improvements in the RT-PCR detection of enteric viruses in environmental samples

Current methods for the detection of nucleic acid from enteric viruses in environmental samples usually involve extensive concentration and purification of target viruses followed by RT-PCR amplification using two enzymes, reverse transcriptase and Taq polymerase. We have developed a modified method that improves RT-PCR assays by: (i) the use of an RT-PCR internal standard control RNA to identify potential false negative results caused by inhibition of RT-PCR enzymes; (ii) the use of rTth (Perkin-Elmer, Foster City, CA), a heat-stable enzyme that functions as both a reverse transcriptase and DNA polymerase in a single-tube, single-buffer, elevated-temperature reaction; and (iii) the use of thermolabile uracil N-glycosylase (HK-UNG) (Epicentre Technologies, Madison, WI) to prevent PCR product carryover contamination. The new method was compared to the traditional two-enzyme, RT-PCR method for detection of Norwalk virus (NV) and hepatitis A virus (HAV) in buffer, stool, clam and oyster samples. The new method was at least as sensitive in NV and HAV detection compared to the traditional two-enzyme method. The internal standard control successfully detected inhibitors to RT-PCR amplification. NV and HAV PCR products generated with dUTP replacing dTTP during amplification were seeded into subsequent samples to test the prevention of PCR product carryover contamination by HK-UNG. The new method successfully eliminated PCR product carryover contamination in contrast to the traditional two-enzyme method. These improvements to viral nucleic acid detection have the potential to improve sensitivity, specificity and confidence in RT-PCR results.