2.3. E. coli enumeration on a chromogenic culture
medium
A 1 mL sample of river water was diluted with 24 mL Ringer’s
solution and filtered as described above. The disc filter was placed onto a Chromocult TBX Agar (Merck, Darmstadt,
Germany) plate and incubated for 18 h at 37 C. Green colonies
(E. coli) were counted; each sample was filtered and plated in
triplicates. Initially, the sample dilution was varied to establish
optimum conditions for reliable colony counting.