Nine fecal-coliform-positive strains were isolated from pristine sites in a tropical rain forest. These sites included nonpolluted rivers and water from bromeliads (epiphytes) which were 30 ft (ca. 910 cm) above the ground. Phenotypically, all of these isolates were identified as Escherichia coli. Their DNA was isolated and purified, and the base composition (G + C content) was determined and compared with that of E. coli B (ATCC 11303). The DNA from the environmental isolates was also hybridized to radiolabeled DNA from E. coli B. Eight strains had a DNA base composition similar to that of E. coli B and gave more than 75% homology with E. coli B. One strain had a different DNA base composition and a relatively low percentage of homology with the reference strain. The finding of E. coli in pristine tropical waters suggests that this bacterium could be a natural inhabitant in these environments and is not a reliable indicator of recent human fecal contamination in tropical waters. The indicators that are currently used in the tropics to test the biological quality of water should be reevaluated
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