352 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table II Preservative Efficacy Test Results Obtained With Nonionic Lotion Containing 0.2% MP and 0.2% 1342 Challenged With S. aureus, B. cereus, E. coli, and Several Different Species of Pseudomonas Test organism D-value P. aeruginosa 9027 0.9 (0.3) P. aeruginosa 10145 1.1 (0.1) P. cepacia 13945 24* (4) P. cepacia 25416 11' (0) P. fluorescens 13525 1.1 (0.9) P. putida 12633 1.0 (0.6) P. stutzeri 17588 0.5 (0) Pseudomonas sp. 9230 9.3 (0.9) S. aureus 6538 26* (0) B. cereus 11778 7.2 (0.4) E. coli 8739 78* (28) Table values are mean D-values in hours, with the standard deviations in parentheses. * D-values over 10 hr were rounded to the nearest whole number. of the preservative system, as indicated by the larger D-values obtained with these organisms. The D-values and slopes of the survivor curves obtained with P. aeruginosa, P. cepacia, ?. fluorescens, and ?. putida in the nonionic lotion with MP with 934, 941, or 1342 and no MP and with MP and 934, 941, or 1342 are presented in Table III. All lotions were adjusted to pH 7.0 with TEA. The D-values were much smaller (i.e., the rates of death of the test organisms were much faster) in all lotions containing 934, 941, or 1342 with MP than in lotions containing only MP or acrylic acid homopolymer/copolymer. The dramatic anti-?seudomonas effect obtained with MP + 934, in comparison with MP or 934, is illustrated in Figure 2. In this work, a synergistic effect in multicomponent preservative systems was defined as one in which the slope (i.e., rate of death of the population of test organisms) was a larger negative number in the presence of two or more agents than the sum of the slopes in the presence of each agent by itself. Thus, a synergistic effect was obtained when the slope in the presence of the MP and acrylic acid homopolymer/copolymer was a larger negative number than the sum of the slopes in the presence of MP (without 934, 941, or 1342) and 934, 941, or 1342 (without MP). The test systems that produced syner- gistic anti-?seudomonas activity are indicated by an asterisk in Table III. All test systems, except the 1342/MP system challenged with ?. cepacia, exhibited synergistic antibacterial activity. The antibacterial action of MP and 1342 for ?. cepacia was addi- tive in this test lotion. The results of preservative efficacy testing of the nonionic lotion containing 0.2% 1342 and 0.2% MP, with and without 0.1% CaCI2, are shown in Table IV. The addition of CaCI 2 to the lotion significantly increased the D-values and eliminated the anti-?seudo- toohas synergy for P. aeruginosa, P. fluorescens, and P. putida. The CaCI 2 significantly decreased the D-values for P. cepacia (Table IV). No attempt was made to demonstrate synergy or antagonism in the experiments done with CaCI 2 test systems. Addition of CaCI 2 to the lotion decreased the viscosity to a water-thin consistency and decreased the pH from 6.8 to 5.7, but no phase separation was apparent during the

SYNERGY OF PRESERVATIVES 353 Table III Synergism of MP and Polyacrylic Acid Homopolymer/Copolymer: Preservative Efficacy Test Results in Nonionic Lotion Containing 0.2% MP 0.2% 934, 941, or 1342 and 0.2% MP + 0.2% 934, 941, or 1342, Challenged With P. aeruginosa 9027, P. cepacia 13945, P. fluorescens 13525, and P. putida 12633 934 Test system: MP 934 MP + 934 Test organism D-value Slope D-value Slope D-value Slope P. aeruginosa 6.3 - 0.16 25 - 0.04 0.5 - 2.0* P. cepacia 52 - 0.02 35 - 0.03 11.5 - 0.09* P. fluorescens 31 - 0.03 64 - 0.02 0.4 - 2.5* P. putida 34 - 0.03 9.3 - 0.11 0.8 - 1.2' 941 Test system: MP 941 MP + 941 Test organism D-value Slope D-value Slope D-value Slope P. aeruginosa 6.3 - 0.16 390 - 0.003 1.7 - 0.59* P. cepacia 52 - 0.02 45 - 0.02 17 - 0.06* P. fluoroescens 31 - 0.03 400 - 0.003 0.004 - 250* P. putida 34 -0.03 8 -0.13 1.1 -0.91' 1342 Test system: MP 1342 MP + 1342 Test organism D-value Slope D-value Slope D-value Slope P. aeruginosa 6.3 -0.16 60 -0.02 0.9 - 1.1' P. cepacia 52 - 0.02 48 - 0.02 24 - 0.04 P, fluorescens 31 - 0.03 110 - 0.01 1.1 - 0.9* P. putida 34 - 0.03 16 - 0.06 1.0 - 1.0' Table values are D-values in hours and the corresponding slopes of the survivor curves in hours-•. * Synergistic anti-Pseudomonas activity is indicated by a larger negative slope with MP + acrylic acid derivative than with the sum of slopes obtained with MP and polyacrylic acid homopolymer/copolymer. course of the preservative testing. A 0.1% solution of unneutralized 1342 in tap water had moderate chelating ability. The mean hardness of duplicate tap water samples was 109 (s = 0.71) ppm as CaCO3, and the mean hardness of duplicate 0.1% 1342 solu- tions was 75 (s = 1.5) ppm as CaCO 3. These means were significantly different (p 0.01). The STs of the test organisms in MP, Na2EDTA , and MP + Na2EDTA solutions were determined. The 0.2% MP solutions were not rapidly bacteriocidal because all test organisms (including S. aureus and E. coli) were viable at 24 hr. P. cepacia 13945 and P. putida were not recovered at 48 hr (Table V). Similarly, all but two of the pseudomonad test organisms were recovered from the Na2EDTA solutions at 48 hr. In contrast, the combination of 0.01% Na2EDTA + 0.2% MP showed marked anti-Pseudomonas ac- tion, because all test organisms, except P. cepacia 13945 and 25416 and Pseudomonas sp. 9230, had STs 4 hr. P. cepacia 13945 was the only pseudomonad recovered at the 24-hr sampling. S. aureus and E. coli had STs 48 hr. These results parallel the results obtained in Table II, in which both P. cepacia strains and Pseudomonas sp. were found to