Abstract
As one of the various means purported to differentiate the undulant fever bacteria of caprine, bovine, and porcine types, the inhibitory effect of certain dyes, particularly gentian violet and thionin, has been suggested. As with other means of differentiation, there is no absolute scale for comparison, inasmuch as not all strains fall consistently into any one group by all differentiating tests. 1 The present study attempts to throw some light on the discrepancies in so far as the bacteriostatic effect of dyes is concerned.
The technic, briefly described, consisted of making appropriate dye concentrations in melted liver hormone agar, from which plates were poured, and cultures streaked on a sector from a broth suspension of an agar slant culture, to insure a degree of uniformity in inoculum. The results were most clearly observed after 72 to 96 hours of incubation at 37° C. The cultures used were obtained from Tunis, Austria, Italy, Denmark, Germany, and from the western part of the United States, and represented a variety of animal and human sources.
The correlation between the original sources of cultures and the bacteriostatic effect of gentian violet, basic fuchsin, brilliant green, thionin, and methylene blue, considered individually or collectively, was found to have a number of discrepancies. Gentian violet in dilutions of 1:50,000 allowed growth with some strains, and inhibited completely in a 1:250,000 dilution with others. Basic fuchsin, chemically related to gentian violet, in most instances allowed virtually normal growth in a 1:50,000 dilution, or even lower, but in some instances inhibited completely in a dilution of 1:100,000. Brilliant green possessed a marked inhibitory quality, permitting on occasion a moderate growth in a 1:1,250,000 dilution; other cultures were almost entirely inhibited in a dilution twice as great.
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