The influence of experimental conditions on the antimicrobial activity of thiomersal has been studied in this work. Of these, factors such as temperature, pH, composition of test solution and age of test culture were demonstrated to have a marked effect on the activity of this organic mercurial, and served to emphasise the need for standardisation of methods for determining the efficiency of preservatives. Photochemically degraded solutions of thiomersal were demonstrated to have an increased antimicrobial activity. This is especially evident with Ps. aeruginosa, where with increased photodegradation, a concomitant increase in activity was obtained, when solutions were prepared in isotonic Sorensen's phosphate buffer, pH 7.0. Subsequently, EDTA was included in formulations to determine if the enhanced activity observed was related to chelateable ions. This was indeed shown to be the case, as in the presence of EDTA, a reduction in antimicrobial activity was observed, although in all cases, degraded solutions were still more effective than their undegraded counterpart. An HPLC system was developed to study the composition of degraded solutions. This gave good separation of thiomersal from its degradation products and was not affected by the presence of EDTA in a formulation. The numbers of degradation products obtained made it impossible to attempt to relate a particular product or variation in peak height with observable enhanced antimicrobial activity. Chromatograms of test solutions revealed that no breakdown of undegraded thiomersal could be detected after microbial challenge experiments. When degraded solutions from microbial challenge experiments were chromatographed, however, it became evident that the micro-organisms had degraded these further, possibly in the search for suitable carbon sources.
|Date of Award||1982|