Attempted measurement of the activity of selected preservative combinations

The rates of kill of four commonly used preservatives, either alone or in pairs, have been determined against Escherichia coli using the viable count method. The four preservatives, employed as aqueous solutions at 25 degrees C, were benzalkonium chloride, phenylmercuric nitrate, benzyl alcohol and 2-phenylethanol. An attempt was made to quantify the results in terms of antagonism or potentiation of summed pairs, and reduction times were calculated. The usefulness of preservative combinations with regard to an improved rate of kill is demonstrated, and the use of combinations can, with wise selection, broaden the spectrum of antimicrobial activity.