Autoflurosecence detection of Escherichia coli on silver membrane filters

Abstract

This report describes the measurement of the limit of detection of the bacterium, Escherichia coli, on the surface of membrane filters employing autofluoresence. Investigation of detection of E. coli by this method was prompted by NASA's need for a method which could detect, principally, fecal coliforms is initially sterile storage water-on-board the conducted rapidly with little or not need for disposables, large amounts of instrumentation, constant human involvement. The autofluorescence of E. Coli collected on the surface of silver membrane filters was quantitated by epifluoresencence microscopy and related to a viable count of the bacteria. The fluorescence was excitated using a board region of ultraviolet radiation from a mercury arc 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.