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Surface active agents and their application in bacteriology.

After the introduction of phenols of high germicidal potency as disinfectants, various laboratories began to experience discrepancies in results obtained by the F. D. A. phenol coefficient procedure. These variations were particularly marked when the test organism, Staphylococcus aureus, was used. The increased demand for disinfectants and antiseptics for war use and the increased emphasis on S. aureus as a test organism have caused these variations to become more evident and important. The U. S. Food and Drug Administration (1931) established an official pro cedure for the phenol coefficient test. Liebig's beef extract and Armour's special peptone were specifically designated as components of the culture medium for the test organisms, Eberthella typhosa and S. aureus. At the present time, Liebig's beef extract is practically unobtainable. Wright (1917) and Reddish and Burlingame (1938) have shown that different brands of peptone used in the culture medium may cause differences in coefficient values. Brewer (1943) demonstrated that different lots of the same brand of peptone caused as much as 100 per cent variation in phenol coefficient values. The English workers, Gladstone (1937), Knight (1937a, 1937b), Richardson (1936), and Fildes et al. (1936) have proved that S. aureus can grow in a synthetic medium in which amino acids furnish the sole source of nitrogen with the exception of that contained in the added growth factors. However, the use of the amino acids as a source of nitrogen is rather expensive, and, in some cases, their sterilization is laborious. Woolley and White (1943), in a study of microbial inhibition of several organisms including S. aureus, used an acid hydrolyzate of casein (\"casamino acids\"') as the main source of nitrogen for bacterial growth. The complete medium is as follows: glucose, 0.25 per cent; K2HPO4, 0.50 per cent; NaCl, 0.25 per cent; casamino acids (Difco), 0.25 per cent; 1(-)tryptophane, 25 mg per L; uracil, 5 mg per L; niacin, 1 mg per L; thiamine, 0.01 mg per L; biotin, 0.001 mg per L; and 2.5 ml per L of salt solution (Snell and Strong, 1939). As this medium seemed to have promise of being more nearly reproducible than the F. D. A. peptone medium, it was used as a starting point in this study. The various components of the mixture were studied in order to find whichwere

A Medium Containing an Acid Casein Hydrolyzate for Use in Testing Disinfectants

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A study of certain factors which influence the resistance of Staphylococcus aureus when grown in beef extract broth

1. The bacteriostatic properties of sulphanilamide and five N 1 -substituted sulphanilamides, and of three anionic surface-active compounds, have been studied, singly and together, against the organisms, S. aureus, E. coli, and E. typhosa, using peptone-broth and a synthetic medium. 2. With incubation temperatures of 37° and 43° the concentration of sulphanilamide for bacteriostasis in peptone medium is independent of the age of the culture and the concentration of the inoculum at the higher temperature only. In the synthetic medium, the effects of age of cells and size of inocula are less pronounced at both temperatures of incubation. 3. The minimum effective concentrations of sulpha drugs needed for growth inhibition are more in peptone broth than in the synthetic medium. Similar but less pronounced differences are seen with the surface-active compounds against S. aureus. 4. While the surface-active compounds are by themselves ineffective against the Gram-negative organisms, they have potentiating activity with the sulpha drugs. 5. The synergic effects of sulphanilamide and surface-active compound are unaltered even when the organism is rendered resistant to sulphanilamide or when the antibacterial property of the surface-active compound is neutralized by lecithin.

Ella M. Burlingame

Papers

The Effect of Peptone on the Resistance of Staphylococcus Aureus