Degree Name

Master of Science (MS)

Semester of Degree Completion

1985

Thesis Director

William A. Weiler

Abstract

Researchers over the years have been trying to improve recovery techniques for fecal coliform bacteria. Improved techniques would provide better estimates of the number of fecal coliform bacteria as well as better estimates of fecal contamination with potential pathogenicity of food and water.

Stressed, but viable, fecal coliform bacteria if placed under the appropiate conditions, can recover, thus presenting the possibility of inadequate disinfection. Chlorine sanitization, as done in potable and wastewater treatment, is one such method of stressing bacteria.

Techniques of recovery were studied using presumably unstressed and chlorine stressed samples. Phase one of this study was the comparison of the standard mFC broth medium method and the two-layer agar medium method. The two-layer method utilized a base medium of mFC agar overlayed with a top layer of lactose agar. This method provided a pre-enrichment (recovery) medium (lactose agar) and a preincubation of 2 hr at 35 ± 0.5C before being transferred to the selective temperature (44.5 ± 0.2C) characteristic for fecal coliform bacteria enumeration. The procedure provided increased recovery compared to that of the standard mFC method.

Phase two of this study compared a two-"layer" broth method with the two-layer agar method. The two-"layer" broth method used the same concept of pre-enrichment medium and pre-incubation time and temperature. It allowed the membranes to be first placed on a pad saturated with lactose broth and incubated at 35 ± 0.5C for 2 hr before being aseptically transferred to a pad saturated with mFC broth and incubated at the elevated temperature (44.5 ± 0.2C) for 22 hr. The two-"layer" broth technique, although easier to do in the laboratory than the two-layer agar method, apparently did not recover fecal coliforms as well as the latter method.

Phase three of this study compared Standard Methods buffered phosphate diluent and rinse fluid to buffered 0.1% peptone diluent and rinse fluid. The buffered 0.1% peptone fluids consisted of Standard Methods buffered phosphate fluid with 0.1% peptone. On both the unstressed and stressed samples the buffered peptone fluids recovered as well as the Standard Methods buffered phosphate diluent and rinse fluids but not any better.

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