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The competitive interactions of genetically distinct isolates of Giardia duodenalis with different growth rates were studied in vitro. Electrophoretic analysis of mixed cultures showed that competition between 2 cloned isolates occurs under normal in vitro culture conditions, with faster-growing isolates outcompeting those with slower growth rates. The addition of sublethal concentrations of metronidazole to clonal mixtures in vitro prevented the competitive exclusion, which was seen in normal culture. This apparently occurred because the drug reduced the growth rate of the faster-growing but not the slower-growing clone.

The competitive interactions of genetically distinct isolates of Giardia duodenalis with different growth rates were studied in vitro. Electrophoretic analysis of mixed cultures showed that competition between 2 cloned isolates occurs under normal in vitro culture conditions, with faster-growing isolates outcompeting those with slower growth rates. The addition of sublethal concentrations of metronidazole to clonal mixtures in vitro prevented the competitive exclusion, which was seen in normal culture. This apparently occurred because the drug reduced the growth rate of the faster-growing but not the slower-growing clone.

Using a novel method for cloning Giardia duodenalis from cultures and fecal samples, 47 clones from 7 isolates were established in vitro. Average colony-forming efficiency in established cultures was 43.2% compared to 11.2% when cloning directly from excystation. The highest success rate of cloning was found with the Portland (P1, ATCC No. 30888) isolate, with a colony-forming efficiency of 92.7%. Cloned and parent populations were compared over a range of 13 enzymes using starch gel electrophoresis. No genetic difference was found between any of the clones and the parent isolates.

Using a novel method for cloning Giardia duodenalis from cultures and fecal samples, 47 clones from 7 isolates were established in vitro. Average colony-forming efficiency in established cultures was 43.2% compared to 11.2% when cloning directly from excystation. The highest success rate of cloning was found with the Portland (P1, ATCC No. 30888) isolate, with a colony-forming efficiency of 92.7%. Cloned and parent populations were compared over a range of 13 enzymes using starch gel electrophoresis. No genetic difference was found between any of the clones and the parent isolates.