The Killing of Bacterial Spores in Fluids by Agitation with Small Inert Particles

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Abstract
Bacterial spores (several aerobic spp.) and vegetative bacteria (Escherichia coli) are progressively destroyed when their fluid suspensions are long and vigorously agitated with finely-divided abrasives. Spores so treated die at a rate which corresponds with the unimolecular law for chemical reactions. The cumulative result of abrasion and repeated collisions between the abrasive particles and the bacteria is a gradual disintegration of the cells. This is attended by a decrease in opacity of the suspension. When the shaking is performed at a fixed speed and a constant volume of suspension employed the rapidity with which spores are destroyed differs greatly with the nature and quantity of the abrasive used, the size of the particles and the species and density of the spore suspension. Highest sporicidal efficiency was obtained with small glass beads (sieves 60/80). Apart from their greater germicidal efficiency, glass beads are superior to the angular abrasives studied, in that they undergo no disintegration with prolonged shaking. Sporicidal efficiency was progressively increased as the speed of shaking was increased between 330 and 570 shakes per min. Vegetative bacteria are more rapidly killed by shaking procedures than are spores; foam producing substances reduce somewhat the germicidal efficiency of such procedures. Resistance of spores to mechanical destruction is not correlated with thermal resistance. Some possible applications of the shaking technique are indicated.