RESUMEN
Extremely limited knowledge exists on the occurrence of protozoan pathogens in surface and waste water in the developing world. The article addresses one of the major reasons for this: prohibitively costly immunomagnetic separation (IMS) and commercial DNA extraction kits are required for the pathogen detection. As the presence of inhibitory substances critically impedes the polymerase chain reaction (PCR)-based detection of Cryptosporidium and Giardia in environmental samples, several direct DNA extraction methods based on the combination of physico-chemical means were evaluated in terms of reducing the impact of PCR inhibitors present in (oo)cyst-spiked water concentrates. Modifications that included the use of guanidine thiocyanate as a lysis agent and a sonication step were found to be more efficient in extracting DNA from (oo)cysts, while treatment with Chelex 100 chelating resin at post-lysis proved to be effective in the removal of the PCR inhibitors rather than the inclusion of the PCR facilitators during thermocycling. Direct DNA extraction protocol at a substantially reduced cost is proposed for the use in the PCR-based detection/quantification of the pathogens.