EVALUATION OF ANTIBACTERIAL SOAP BARS 345 containing 2% of a mixture of the antibacterials: 3,5-di- and 3,4',5- tribromosalicylanilides (BSA), 4,4'-dichloro-3-(trifluoromethyl) car- banilide (TFC), and 3,4,4'-trichlorocarbanilide (TCC). Antibacterial Soap B was a milled bar containing 0.75% 3,4,4'-trichlorocarbanilide (TCC) plus 0.75% hexachlorophene (G-11). Considerable variation among the organisms in sensitivity to both soap bars was evident. Strain 22 required over four times as much of either soap for complete inhibition of growth as did Strain 32. Overall, the data show that the soaps were similar in regard to bacteriostatic TABLE I Minimum Inhibitory Concentration Against Staphylococcus aureus Strains mg./100 g. of product Antibacterial Soap Antibacterial Soap Strain A a B b Strain A B 26 6 8 32 4 4 20 6 8 34 8 8 19 6 6 35 8 8 21 6 6 36 6 6 22 16 16 37 6 6 24 6 6 38 6 6 27 6 6 39 6 6 29 6 6 23 8 6 30 8 8 25 12 8 31 6 6 28 8 6 Antibacterial additive: 2% mixture of BSA, TFC, and TCC. Antibacterial additive: 0.75% TCC q- 0.75% G-11. activity. If, however, either Strains 20 or 26 had been chosen as the only test organisms, the conclusion would have been that Soap A was superior to B. Had either Strains 25 or 28 been the only test organ- isms, Soap B would have been judged superior. With each of these strains, the recorded differences between the soap bars were reproducible, but, if the experiment were to be repeated with another group of strains of this same bacterial species, the results might very well be different. The problem of interpretation of MIC data in terms of the relative skin degerming effectiveness of two products is further complicated when other species of bacteria are used as test organisms. Data in Table II illustrate this complication. MIC values were obtained for Soaps A and B with a group of 20 strains of Corynebacterium minutis- sireurn isolated from toe webs of individuals with erythrasma. Overall, the data show Bar A to be superior to Bar B in control of these strains.

346 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS TABLE II Minimum Inhibitory Concentration Against Corynebacterium minutissimum Strains mg./100 g. of product Antibacterial Soap Antibacterial Soap Strain A s B • Strain A B P17-1 8 14 Pi-1 11 16 P16-1 8 14 P3-3 11 14 P6-1 8 14 P8-2 16 16 1-2 8 16 2A 14 16 10289 8 11 7A 12 16 3A 8 16 P22-1 16 16 12A 6 8 P7~3 16 16 4R 8 16 P1-4 16 16 8L 8 16 P20-1 16 16 P13-1 11 14 P26-3 14 12 Antibacterial additive: 2% mixture of BSA, TFC, and TCC. Antibacterial additive: 0.75% TCC q- 0.75% G-11. TABLE III Skin Degenning Effectiveness of an Antibacterial Bar Soap: Constancy of Results Handwashing--Fifth Basin--Four Day Regimented Usage Mean Bacterial Count Test Product Test Date Per Liter Antibacterial soap A s 1-9-61 9,000 4-17-61 17,800 3-11-63 11,300 1-27-64 13,100 3-9-64 13,800 10-23-64 8,900 10-26-64 1,900 11-9-64 11,000 11-9-64 5,700 Control soap • 1,300,000 Antibacterial additive: 2% mixture of BSA, TFC and TCC. No antibacterial additive. However, if Strain P26-3 had been selected as the only test organism, Soap B would have been judged superior. Had any of the four strains just above it in the table been used, the bars would have been judged equally effective. Obviously, decisions regarding relative efficacy of antibacterial products based on MIC data are capricious. Results are too dependent upon the bacterial strains that happen to be chosen for the test. For