Cross-institute evaluations of inhibitor-resistant PCR reagents for direct testing of aerosol and blood samples containing biological warfare agent DNA.

Rapid pathogen detection is crucial for the timely introduction of therapeutics. Two groups (one in the United Kingdom and one in the United States) independently evaluated inhibitor-resistant PCR reagents for the direct testing of substrates. In the United Kingdom, a multiplexed Bacillus anthracis (target) and Bacillus subtilis (internal-control) PCR was used to evaluate 4 reagents against 5 PCR inhibitors and down-selected the TaqMan Fast Virus 1-Step master mix (Life Technologies Inc.). In the United States, four real-time PCR assays (targeting B. anthracis, Brucella melitensis, Venezuelan equine encephalitis virus [VEEV], and Orthopoxvirus spp.) were used to evaluate 5 reagents (plus the Fast Virus master mix) against buffer, blood, and soil samples and down-selected the KAPA Blood Direct master mix (KAPA Biosystems Inc.) with added Platinum Taq (Life Technologies). The down-selected reagents underwent further testing. In the United Kingdom experiments, both reagents were tested against seven contrived aerosol collector samples containing B. anthracis Ames DNA and B. subtilis spores from a commercial formulation (BioBall). In PCR assays with reaction mixtures containing 40% crude sample, an airfield-collected sample induced inhibition of the B. subtilis PCR with the KAPA reagent and complete failure of both PCRs with the Fast Virus reagent. However, both reagents allowed successful PCR for all other samples-which inhibited PCRs with a non-inhibitor-resistant reagent. In the United States, a cross-assay limit-of-detection (LoD) study in blood was conducted. The KAPA Blood Direct reagent allowed the detection of agent DNA (by four PCRs) at higher concentrations of blood in the reaction mixture (2.5%) than the Fast Virus reagent (0.5%), although LoDs differed between assays and reagent combinations. Across both groups, the KAPA Blood Direct reagent was determined to be the optimal reagent for inhibition relief in PCR.