Effects of some extraneous factors on the bactericidal efficiency of ultraviolet radiation”

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Some extraneous factors affecting the bactericidal efficiency of UV light 254nm have been studied. The sensi¬tivities of various micro-organisms to UV radiation were found to vary considerably. Though non-lethal by Itself, UV light 350nm markedly Improved the antagonistic effect of an aqueous environment. containing various hydrogen ion concentrations - the higher the pH the greater the effect. On the other hand, the rather power¬ful Intrinsic antimicrobial effect of UV light 254nm completely masked any possible mutual enhancement of antimicrobial activity. An appreciable proportion of cells Injured from UV radiation could be revitalized when exposed Immediately to UV light 350nm but not to the dark; the effect was found to be more pronounced In more acidic Isotonic medium (pH 5.0) than In either neutral or alkaline environments. This observation could probably have Immense practical Importance In reversing cell damage due to UV radiation. Hypotonic and hypertonic solutions significantly enhanced the activities of both UV light 254nm and 350nm, but the extent of influence appeared to be for greater less self torelant E. coli than the more salt-tolerant staph. Aureus. Phenol and chlorocresol antagonized micro-organisms and better still in the presence of UV light 350nm; but phenol and to a lesser extent chlorocreso! significantly diminished the biocidal activities of UV radiation 254nm; the phenomenon was found to reflect the strong absorption of UV Iight 254nm by the phenolic compounds. Both compounds, In addition, abolished photoreactivatlon at 350nm of cells previously Injured by UV radiation. The non-Ionic surface active agent, polysorbate 80, Irrespective of whether the concentration was below or above that for micelle formation, reduced persistently the anti¬microbial efficiency of UV light 254nm. Thus the enhanced activity normally found with chemical antimicrobial agents In the presence of a surfactant below the CMC, that occurs as a result of reduced surface tension and Improved penetration of cells by chemical agents, could not be detected. Inactive at pH 5, chloroquine phosphate exhibited gradually Increasing antimicrobial activity, with Increasing relative alkalinity, that was further aggravated by UV light 350nm. At any specified pH, Increasing concentrations of the drug produced persistent reduction In the bactericidal efficiency of UV light 254nm, Though the drug did not completely abolish photoreactivation, It did nevertheless considerably reduce Its extent. Thus, although the physical sterilizing agent of UV radiation behaves, In the presence of some extraneous substances, as do chemical antimicrobial agents, they nevertheless vary considerably In most aspects; the overall response of one cannot therefore be superimposed on the other.
A thesis submitted in fulfilment of the requirements for the Degree of Master of Pharmacy of the University of Science and Technology, Kumasi, 1981