VALIDITY OF FLUOROCHROME-STAINED BACTERIA AS TRACERS OF SHORT-TERM MICROBIAL TRANSPORT THROUGH POROUS-MEDIA

The effect of fluorochromes on interactions between bacteria and porou s media is of concern when such stains are used to tag bacteria for us e in transport studies. Column experiments were carried out to test th e effect of 4', 6-diamino-2-phenylindole (DAPI) and 3,6-bis[dimethylam ino]acridinium chloride (acridine orange) on short-term transport of t wo bacterial species through aluminum hydroxide-coated sand. The bacte rial species were Escherichia coli, an indicator of fecal pollution, a nd Acinetobacter sp. (ATCC 31012), a strain originally isolated from b each tar. The superficial flow rate through the l-m long columns was t ypical of rapid sand filters (1.9 mm s(-1)). DAPI did not significantl y affect the transport of either E. coli or Acinetobacter sp. (P < 0.0 5). 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 tagg ing bacteria in short-term transport studies. (C) 1998 Elsevier Scienc e B.V.