AUTOFLUORESCENCE DETECTION OF ESCHERICHIA-COLI ON SILVER MEMBRANE FILTERS

This report describes the measurement of the limit of detection of the bacterium, Escherichia coli, on the surface of membrane filters employing autofluorescence. Investigation of detection of E. coli by this method was prompted by NASA's need for a method which could detect, principally, fecal coliforms in initially sterile storage water on-board the space station. This method was examined, with E. coli as a model, because it could be conducted rapidly with little or no need for disposables, large amounts of instrumentation, or constant human involvement. The autofluorescence of E. coli collected on the surface of silver membrane filters was quantitated by epifluorescence microscopy and related to a viable count of the bacteria. The fluorescence was excitated using a broad region of ultraviolet radiation from a mercury are lamp (approx. 250-400 nm) and examined in the wavelength region of 495 nm and higher through a long pass optical filter. From these measurements, the limit of detection of viable E. coli collected on the membrane filters was fewer than 550+/-32 viable bacteria or 170,000+/-10,000/ml in terms of solution concentration.