Novel method for studying the public health significance of macroinvertebrates occurring in potable water.

An experimental procedure was developed to study the association of selected bacteria and macroinvertebrates and their response to free available chlorine disinfection. The organisms selected for study were Escherichia coli ( LacZ545 ), Enterobacter cloacae (ATCC 23355), and the amphipod Hyalella azteca . E. coli was shown to bind tightly (1.6 X 10(4) CFU per amphipod ) to this macroinvertebrate and to resist repeated attempts to wash it off. E. cloacae was shown to bind much less tightly (1.4 X 10(3) CFU per amphipod ) to H. azteca and was less resistant to removal by washing. The extent of association is a function of macroinvertebrate size (surface area), but the procedure produces repeatable results usable for controlled experimentation. This method, together with the dual bacterial identification criteria (morphology and antibiotic resistance), was used to study the response of unassociated and associated E. coli and E. cloacae to disinfection with free available chlorine at 1.0 mg/liter. Unassociated E. coli populations decreased to less than 1% of their zero time controls within 1 min of contact time, whereas more than 2% of the associated E. coli populations remained viable after 60 min of contact at 1.0 mg of free available chlorine per liter. Unassociated E. cloacae populations decreased to less than 1% of their zero time controls within 1 min of contact time, whereas ca. 15% of the associated E. cloacae populations remained viable after 60 min of contact at 1.0 mg of free available chlorine per liter.(ABSTRACT TRUNCATED AT 250 WORDS)