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Atrazine solutions (0.1, 1, 10 and 100 microg/L) inoculated with Escherichia coli and Enterococcus faecalis under natural conditions significantly increased (p < or = 0.05) the population levels of both test bacteria; it indicates the ability of bacterial cells to degrade atrazine and to use the original compound or its degradation products as nutrient(s). In some cases, alterations in the morphology of the colonies were also observed on selective solid media. Biochemical differentiation was also found and, on the other hand, a loss of culturability was recorded; this suggests that bacteria have entered in a viable but nonculturable state. A re-appearance of the colonies occurred after inoculation on tryptone-soy agar with atrazine.

In order to investigate the effects of the herbicide trifluralin on the indicator bacteria Escherichia coli and Enterococcus faecalis, these bacteria were inoculated into four different concentrations of trifluralin (0.1, 1, 10 and 100&ThickSpace;µg/L). The bacterial growth was monitored turbidimetrically, followed by membrane filtration where membranes were placed on selective media agar. A non-typical morphology of colonies together with loss of culturability was recorded in all cases. Furthermore, differentiation in the strains’ biochemical profiles was noted. E. coli was identified as Hafnia alvei and Ent. faecalis as Enterococcus faecium or Enterococcus avium . The current study suggests that the use of these two indicator bacteria in routine microbiological analysis of water might be questioned since trifluralin diluted to contaminated water has the potential to promote their growth and change their morphological and biochemical characteristics. [ABSTRACT FROM AUTHOR]