Validity of fluorochrome-stained bacteria as tracers of short-term microbial transport through porous media

The effect of fluorochromes on interactions between bacteria and porous media is of concern when such stains are used to tag bacteria for use in transport studies. Column experiments were carried out to test the effect of 4′, 6-diamino-2-phenylindole (DAPI) and 3,6-bis[dimethylamino]acridinium chloride (acridine orange) on short-term transport of two bacterial species through aluminum hydroxide-coated sand. The bacterial species were Escherichia coli, an indicator of fecal pollution, and Acinetobacter sp. (ATCC 31012), a strain originally isolated from beach tar. The superficial flow rate through the 1-m long columns was typical of rapid sand filters (1.9 mm s−1). DAPI did not significantly affect the transport of either E. coli or Acinetobacter sp. (P<0.05). Acridine orange significantly increased retention of E. coli, but did not have a significant effect on transport of Acinetobacter sp. (P<0.05). These results suggest that DAPI is a good candidate for tagging bacteria in short-term transport studies.