Differentiation of distribution systems, source water, and clinical coliforms by DNA analysis.

During a 2-week period, Enterobacter cloacae was isolated from throughout the water distribution system in New Haven County, Connecticut. There was no forewarning of this event and no apparent reasons for it. Several epidemiologic and public health questions required rapid answers. Were these E. cloacae isolates the result of treatment failure and breakthrough or was regrowth occurring within the system? Did the E. cloacae isolates represent a health threat and were they causing infection? Pulsed-field gel electrophoresis utilizing whole-cell DNA digestion with restriction endonuclease SpeI permitted the rapid generation of specific information to answer these questions. Gel bands were stained with ethidium bromide and photographed with UV illumination. Homogeneity among isolates was confirmed by repeat digestion with XbaI. From each of the water distribution isolates, a single pattern of restriction endonuclease fragments was generated, indicating that only one clone of E. cloacae was in the distribution system. There was no homogeneity between source and distribution water E. cloacae isolates. Moreover, E. cloacae clinical isolates from patients from New Haven area hospitals showed no identity with E. cloacae isolated from the distribution system. Therefore, pulsed-field gel electrophoresis DNA analysis demonstrated that the E. cloacae from the distribution system was the result of a regrowth bloom within the system and not the result of treatment failure and that this clone was not causing a public health risk.