A profile of antibiotic resistant bacteria in the James River

Spatial and temporal variability in the antibiotic resistance of bacterial assemblages in the lower portion of the James River was examined. The antibiotic resistance of culturable coliforms was compared to the resistance in the microbial community. Antibiotic resistance was determined via colony formation on media containing antibiotics. The antibiotics ampicillin, chloramphenicol, streptomycin and tetracycline were used at concentrations ranging from 10 to 500 ug/ml. Statistically significant differences in the mean number of antibiotic resistant isolates were observed among both sample sites and dates. The sampling site at river mile 99 just below Richmond showed both increased antibiotic resistance and bacterial density making this site a possible public health risk. It is possible that increased salinity in the lower portion of the river resulted in a significant decrease in bacterial density and antibiotic resistance. The percentage of antibiotic resistant coliform bacteria was significantly greater than those isolates representing the microbial community as a whole, except when tested against streptomycin at 10 ug/ml