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CHLORINE DISINFECTION OF AEROMONAS
Johnson*, C H., E W. Rice*, AND L DeMaria*. CHLORINE DISINFECTION OF AEROMONAS. Presented at Water Quality Technology Conference, American Water Works Association, Salt Lake City, UT, 11/2/2000.
The bacterial genus Aeromonas is currently listed on the USEPA's Candidate Contaminant List (CCL). Resistance to chemical disinfection is an essential aspect regarding all microbial groups listed on the CCL. This study was designed to determine the inactivation kinetics of Aeromonas spp. for free available chlorine and monochloramine. Three species, Aeromonas caviae, A. hydrophila, and A. veronii, which are known to be associated with human infections, were studied in pure culture under oxidant demand-free conditions. Free chlorine experiments were conducted at pH 7 and 8 at 5 and 22C. Experiments using preformed monochloramine were conducted at both temperature at pH 8. Three media were evaluated for their ability to recover chlorine-stressed organisms (nutrient agar, ampicillin dextrose agar and Ryan agar). Experiments using free chlorine indicated that the Aeromonas spp. were readily inactivated under all conditions studied. The organisms were inactivated by more than five-orders of magnitude within a one minute exposure to free chlorine at both temperatures. Inactivation kinetics were similar for other bacterial organisms, with greater inactivation occurring at lower pH values and at higher temperatures. For free chlorine there was no observable difference in recovery of chlorine-stressed organisms on the three bacteriological media. Two wells and one cistern containing Aeromonas spp. (approximately 10(3) CFU/100 ml) have been located in recent survey. Water from these wells and cistern will also be used in disinfection experiments to determine inactivation rates for indegenous occurring Aeromonas spp. in natural waters. These data suggests that Aeromonas spp. do not exhibit any unique resistance to these commonly used disinfectants.