Validation criteria for nucleic acid amplification techniques for bacterial infections

Nucleic acid techniques (NATs), such as species-specific and universal polymerase chain reactions (PCRs), are finding ever wider use in the diagnosis of bacterial infection. However, although universal PCR assays, in particular, approach a type of modern Petri dish, they have a number of limitations which restrict their applicability. The sensitivity of universal PCR is lower than that of many species-specific PCRs, and the contamination of samples and PCR reagents with irrelevant DNA from various sources remains a problem. Thus, NATs in general and universal PCR assays in particular require careful validation to be of value for the diagnosis of infection. Validation includes sampling, DNA extraction/isolation, template amplification and visualisation of the results. Furthermore, it implies the establishment of measures of asepsis, the inclusion of positive and negative controls, techniques to optimise the release of DNA from bacterial cells, adequate repetition of the amplification reaction, and routine testing of reagent negative and inhibition controls. Finally, it entails the comparison of results obtained by NATs with those obtained by conventional microbiological methods and matching with clinical evidence of infection. Validation of NATs in clinical diagnosis remains an ongoing challenge. Because of these limitations, NATs can only serve as adjunct tools for the diagnosis of infection in selected cases; they cannot replace conventional culturing techniques.