Date of Award


Document Type

Doctoral Thesis

Degree Name

Doctor of Philosophy


Biological and Pharmaceutical Science

First Advisor

Dr Mary Concannon


The biological activity of oxytetracycline-hydrochloride was investigated using the indirect conductivity method which is based on the measurement of metabolically generated CO2. A number of laboratory strains and a fresh natural inoculum were exposed to oxytetracycline in the presence and absence of 12% sterile sediment. Results comparing sediment and sediment free systems for all test cultures revealed elevated minimum inhibitory concenrations (MIC) of the agent in the presence of sediment; percentage bioactivity results ranged between 0.50 and 2.07%. pH differences betw'een sediment and sediment-free systems were found not to effect MIC results, and the use of different buffers resulted in significant variations. Methods are outlined for the determination of the minimum effect concentration (MF.C) of oxytetracycline-hydrochloride, defined as the minimum concentration of agent required to exert a detectable effect on metabolic CO2 production. It is proposed that the use of the MEC as an alternative to MIC measurements has the potential to produce data of greater environmental relevance and lower limits of detection. MEC results were obtained as low as 15 fold below the corresponding MIC result. The occurence of persistence mechanisms of resistance and multiple low level resistance to oxytetracycline was investigated incorporating conductance techniques. Efforts were made to design a protocol which would eliminate CO2 production by background bacteria in sediment samples, using solvents and freeze thaw methodology, without success. An indirect conductance method is described for the determination of the stability of oxytetracycline hydrochloride over time in sediments.

Access Level


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Biology Commons