Udo Reischl

Institute of Medical Microbiology and Hygiene, University of Regensburg, Franz-Josef-Strauß-Allee 11, 93053 Regensburg, Germany

Received 06/18/96; Accepted 07/19/96; On-line 08/01/96

Improvements in antibiotic and antiviral therapy for specific microorganims will require development of increasingly more accurate method of diagnosis. Nucleic acid-based technology has the potential to become one of the most powerful tools in clinical microbiology since it essentially circumvents the necessity for the microorganism to be isolated in pure culture prior to its definitive identification.

PCR or other methods for the direct detection of pathogens can be used in conjunction with more traditional techniques and is likely that it will not completely replace microscopy, culture or antibody assays in the near future. Although amplification methods were established for an increasing number of infectious agents, conventional culture techniques for most bacterial pathogens are often just as sensitive, rapid, and inexpensive; they also allow detection of multiple microorganisms in a single procedure.

For infectious diseases, modern serological techniques, more and more based on recombinant antigens, are being proven to be specific, rapid and less labor intensive. The decision to use a nucleic acid-based method is likely to be dictated by the sensitivity and specificity of the respective in vitro nucleic acid amplification procedure as compared to the low-cost, time-proven conventional method, and the clinical need for definitive results.

Above all, PCR may prove very useful in clinical situations where conventional methods turned out to be either too insensitive (e.g., during the asymptomatic stage of HIV infection), too slow (e.g., mycobacterial culture) or too cumbersome to be used on a large scale (e.g., virus isolation). Another important application of PCR is to monitor the emergence of mutations in the genome, for instance, the selection of resistant variants during antiviral/antibiotic therapy.

This can be achieved by identifying specific mutations directly by PCR or by determining the nucleotide sequence of a DNA fragment generated by PCR. The recently developed RT-PCR will allow sophisticated evaluation techniques for the evaluation of the effectiveness of antibiotic therapy and the molecular regulation of disease by the selective amplification of messenger RNA.

A number of unsettled questions, including the true clinical significance of PCR results and the associated costs, have delayed the wide adoption of these methods. However, in the face of the current problems in laboratory diagnosis of infectious diseases, it is apparent that the continued use of older and slower methods of detection is unacceptable. Especially in the case of severe infections, the diagnostic capabilities of molecular biology-based techniques will have major positive impact on health care costs, as well as on the associated morbidity and mortality. If, for example, generation of a report that a given patient is infected with an antibiotic-resistant pathogen, can help the physician to better tailor therapy to that person's needs. Undoubtedly, the next few years will show which of the competing methods, all embodying their individual strengths and weaknesses in terms of sensitivity, ease of use, costs and reliability, will prove successful in the clinical laboratory practice.