An accurate and rapid microbiological method for assaying chemical preservatives of nonantibiotic nature has been developed which employs a time-tested, proven procedure. Preservative concentration is measured by a turbidimetric procedure using Escbwicbia coli as the test organism. The method has been applied to chlorobutanol, phenol, and -chloro-beta-phenylethyl alcohol and compares favorably with chemical analytical methods.
N CARRYING out stability studies on chemical I preservatives in pharmaceutical solutions, it is essential that the methods employed accurately establish the preservative content. Analytical methods invariably have involved chemical procedures of varying degrees of complexity. Although regarded as possessing reliability, such assays may require chemical manipulation and equipment which are not always readily available.
From a theoretical standpoint it is conceivable that while a chemical analysis may indicate appreciable loss of preservative content because of degradation, the breakdown products per se may possess intrinsic antibacterial activity.
In view of the generally accepted concept that preservative as well as antibiotic content is best expressed on the basis of antimicrobial activity, an attempt was made to develop an accurate and rapid turbidimetric assay similar to those generally employed for antibiotics. An extensive search of the literature has revealed no reports on the existence of a bioassay for chemical preservatives of nonantibiotic nature.
Initial attempts on our part (1) to arrive at a bioassay method involved the addition to the sample being assayed of a standardized number of E. coli organisms. At intervals, 1-ml. portions were removed, which were immediately plated for survivor count. Curves were then plotted of per cent survivors 0s. time for each concentration of preservative. The time required to produce 50% killing was obtained from the plots. A standard curve was then drawn of the time required to destroy 50% of the organisms vs. the corresponding concentrations of preservative.