An examination of microorganisms and their antibiotic resistance patterns in rural, urban, and tidal water samples

To examine the quality of water sources in the Richmond, Virginia area with regard to fecal contamination, environmental samples as well as drinking water (from 12 rural sites, 3 urban sites, and 8 tidal sites) were screened using the Coliscan Easygel system. Fecal coliforms were found in four of the tidal samples and seven of the rural samples. No fecal coliforms were found in the urban tap water samples. The isolated fecal coliforms were screened via minimum inhibitory concentrations (MICs) for resistance to six common clinical antibiotics: ampicillin, cefuroxime, cephalothin, erythromycin, streptomycin, and tetracycline. Most of the rural fecal coliforms exhibited multiple resistance patterns, including very high MICs for cephalothin. Sensitive strains of Escherichia coli B and Staphylococcus aureus 9.144 were grown in membrane-filtered water from these same sites, along with appropriate growth media, for approximately ten days. Following incubation, MICs for the same six antibiotics were determined for these samples. Erythromycin resistance was induced in the S. aureus 9.144 strain following incubation in a tidal sample from the Piankatank River and in tap water from Hanover County. The MIC prior to incubation was 0.5μg/ml. Following incubation the MIC for the tidal sample was 500μg/ml and 125μg/ml for the tap water sample