Contaminations occurring in fungal PCR assays

Successful in vitro amplification of fungal DNA in clinical specimens has b een reported recently. In a collaboration among five European centers, the frequency and risk of contamination due to airborne spore inoculation or ca rryover contamination in fungal PCR were analyzed. The identities of all co ntaminants were specified by cycle sequencing and GenBank analysis. Twelve of 150 PCR assays that together included over 2,800 samples were found to b e contaminated (3.3% of the negative controls were contaminated during the DNA extraction, and 4.7%, of the PCR mixtures were contaminated during the amplification process). Contaminants were specified as Aspergillus fumigatu s, Saccharomyces cerevisiae, and Acremonium spp, Further analysis showed th at commercially available products like zymolyase powder or 10x PCR buffer may contain fungal DNA. In conclusion, the risk of contamination is not hig her in fungal PCR assays than in other diagnostic PCR-based assays if gener al precautions are taken.