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

354 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 7O 6O rr •3 50 o z 4o • 2o 10 984 M P 984 ß tip TE8T SYSTEM Figure 2. Comparison of D-values for P. aeruginosa 9027, P. cepacia 13945, P. fluorescens 13525, and P. puti&• 12633, determined by preservative efficacy testing of the nonionic lotion containing 0.2% MP, 0.2% 934, or both 0.2% MP and 0.2% 934. be much more resistant to the preservative system of the lotion containing 0.2% MP q- 0.2% 1342. Even though the ?. stutzeri inoculum contained 1.7 x 107/ml, this or- ganism was not recovered from the initial sampling in the MP q- Na2EDTA solution. Similarly, ?. stutzeri was inactivated more rapidly than all other test organisms in the lotion containing MP q- 1342 (Table II). Hardness analyses of tap water, tap water containing 0.01% Na2EDTA, and deionized water gave mean hardness values of 137 (s = 5.0), 109 (s = 1.4), and 20 (s = 14) ppm CaCO 3, respectively. These means were significantly different (p 0.05). The STs obtained in Table V were used to calculate survivor curve slopes and D-values and to demonstrate synergy for all Pseudomonas test organisms in 0.1% MP q- 0.01% Na2EDTA solutions, except for ?. cepacia 13945 (Table VI). It was possible to calculate a slope and D-value where STs were known, as in the case for ?. cepacia 13945 in 0.2% Table IV Effect of 0.1% CaC12 on Preservative Efficacy Test Results of Nonionic Lotion Containing 0.2% MP and 0.2% 1342 Challenged With P. aeruginosa 9027, P. cepacia 13945, P. fluorescens 13525, and P. putid• 12633 Test organism Lotion Lotion with CaCl2 P. aeruginosa 1.8 (0.8) 10' (0) P. cepacia 90* (16) 13' (0.7) P. fluorescens 2.0 (0.07) 8.5 (0.4) P. puti&• 2.2 (0.28) 11' (1.0) Table values are mean D-values from duplicate experiments, with standard deviations in parentheses. * D-values over 10 hr were rounded to the nearest whole number.