Two distinct varieties of Giardia in a mixed infection from a single human patient.

Twenty-five in vitro cultures of Giardia duodenalis derived from a Brisbane patient were established to assess the genetic heterogeneity of a population. Each of the established lines carried a predominance of one of two distinct varieties of Giardia. The two varieties were heterogeneous by four unambiguous criteria that were representative of the whole genome. These included restriction enzyme polymorphisms, hybridization with the cloned rDNA repeat and with a gene encoding a cysteine-rich surface protein, electrophoretic karyotyping and DNA fingerprinting. Differences between parasites derived from this patient were greater than have been seen between all other established G. duodenalis in vitro cultures from both humans and animals. The cultures were heavily selected such that a single Giardia line carried a predominance of one genotype and was not representative of the entire original population.