Classification of subgroups of Giardia lamblia based upon ribosomal RNA gene sequence using the polymerase chain reaction.

A sensitive and specific polymerase chain reaction-based assay has been developed to detect and analyze polymorphism in the Giardia lamblia 18S ribosomal RNA gene. Efficient amplification required the inclusion of cosolvents (glycerol and dimethyl sulfoxide) in the reaction. Following the optimization of conditions for amplification and subsequent hybridization of amplified product with radiolabeled oligonucleotide probe, a detection limit of less than one organism's worth of DNA was achieved. Thirty-five different G. lamblia strains obtained from various human and animal host types and geographic locations were analyzed by this method. The strains could be divided into 3 groups on the basis of defined nucleotide substitutions within the 183-bp amplified DNA fragment of the 18S ribosomal RNA gene. The groupings based upon the 18S ribosomal RNA gene sequence correlated with groupings previously assigned based upon patterns of surface antigens and restriction enzyme analysis. Analysis of the G. lamblia 18S ribosomal RNA gene sequences present in fecal specimens obtained from giardiasis patients revealed the presence of the different sequence types in these specimens. Some specimens contained more than one sequence type. The identification of subgroups of G. lamblia may facilitate studies of virulence, infectivity, and the epidemiology of giardia infection.