SURVIVAL OF LEGIONELLA-PNEUMOPHILA IN THE AQUATIC ENVIRONMENT

Survival of Legionella pneumophila SG 1 in seawater and river water was assessed using plate counts on buffered charcoal yeast extract agar amended with alpha-ketoglutarate (BCYE-alpha) and [H-3]thymidine-labeling. The [H-3]thymidine-labeling method for assessing survival of L. pneumophila in aquatic environments was compared with viable counts, direct fluorescent microscopy (DFA), and acridine orange direct counts (AODC). Protozoa were isolated from the samples employed in the study and identified by characteristic trophozite and cyst morphology. Selective filtration employing 2.0-mu-m Nuclepore filters was used to determine the effect of grazing on survival of L. pneumophila in seawater and river water. Legionella viability as measured by plate counts (CFU/ml), declined to a greater extent than cell lysis, assessed by thymidine, DFA, and AODC counts, suggesting that L. pneumophila survives in aquatic habitats to a greater extent than revealed through culturable counts.