SPATIAL AND TEMPORAL VARIABILITY OF ANTIBIOTIC-RESISTANCE IN FRESH-WATER BACTERIAL ASSEMBLAGES

Spatial and temporal variability in antibiotic resistance was examined in bacterial assemblages from streams and ponds on the US Department of Energy's Savannah River Site (SRS) in South Carolina. Sites sampled have been impacted to varying degrees by contamination with organic c ompounds, heavy metals, and radioactive materials because of productio n of nuclear materials on the site. Antibiotic resistance in the cultu rable portion of the;bacterial assemblage was determined from colony f ormation on media containing antibiotics. Eight antibiotics, chloramph enicol, cycloserine, kanamycin, neomycin, novobiocin, rifampicin, stre ptomycin, and tetracycline, were used at concentrations of 50 and 200 mu g ml(-1). Statistically significant differences in frequency of ant ibiotic resistance were observed among sites and among dates at a sing le site. Bacterial densities (total and culturable), dissolved organic carbon (DOC) concentration, and human impact also varied among sites but bore no overall relationship to resistance frequency. SRS operatio ns did not have a detectable impact on antibiotic resistance.