The effect of formalin fixation on the polymerase chain reaction characterization of Entamoeba histolytica

Formalin fixation is the most common storage, transportation and preservati on method for stool samples. However, fixation dramatically reduces our abi lity to extract from stool samples DNA that is a suitable template for poly merase chain reaction (PCR)-based diagnostic tests. In this study we evalua ted the effects of formalin concentration and of the time stored in fixativ e on the success of PCR amplification. We found that the deleterious effect s of formalin are both time and concentration dependent and may result from fragmentation of fixed DNA during its purification.