Bactericidal Power of Dried Painted Surfaces. ∗ (I)

Abstract

The development of a paint which has bactericidal properties after drying has been reported recently by Wetchler, Lewis and Battline. 1 This paint has, as the binder, a 4% halogenated oil base. The present study deals with bactericidal tests on this type of paint after prolonged periods of drying in comparison with a number of ordinary commercial paints bought in the open market. The cultures used for testing have been B. typhosus, “Hopkins” (U.S. Food and Drug Administration strain), and Staphylococcus aureus, 4 strains, namely, No. 209 (U.S.F.D.A. strain), No. 3 (stock strain of the Bureau of Laboratories, N.Y.C. Dept of Health), and 2 freshly isolated from boils. Work on bactericidal paints has been reported by Portier and Kling, 2 Trouissant, 3 and Vallée. 4

Two methods were used for determining bactericidal action as judged by the lack of growth on media. The method on which the majority of results given in this paper were based, consisted in the use of painted glass rods, 10 mm. in diameter, which were allowed to dry in the air for various periods of time. Baking at 100° C. and 125° C. was employed to simulate longer periods of air-drying; this method of aging is a common practice in paint technology. For the tests, the rods were immersed in test tubes containing 4 cc. of saline (0.85%) suspension of the culture (18 hour agar slant) and kept at room temperature for a given time. The rods were then removed and 0.2 cc. of the culture suspension placed on the surface of extract agar plates. Observation of the amount of growth was made after 18 and 42 hours'incubation at 37° C. Prolonged incubation for 4 days did not show any appreciable increase in the number of colonies. Dilution pour plates were made in a number of instances to eliminate the possibility of an inhibitory factor which would be removed by further dilution. The density of the bacterial suspension used in each test was determined by comparison with barium sulfate standards and by plate count made from serial dilution in salt solution.