Isolation of multiple antibiotic resistant Enterobacteriaceae from river water

Water samples from the Monocacy River in Frederick County, Maryland, yielded twenty-four isolates which were resistant to tetracycline (TeR, 25 micrograms/ml). Although these organisms were not initially cultured on a coliform-selective medium, twenty-two of the isolates were Gram-negative and carriers of antibiotic resistance to five or more antibiotics; erythromycin, methicillin, novobiocin, penicillin and tetracycline. Of the isolates 45% were biochemically identified as Providencia stuartii; one isolate which contained a 29.4 kilobase plasmid carried the determinant for tetracycline resistance.