2.3. Preservative efficacy evaluation
Products found to be free of microbial contamination were challenged with P. aeruginosa ATCC 9027. This test organism is one of the bacterial strains recommended by the ISO/WD 11930 for the
evaluation of antimicrobial protection of cosmetic products. Inoculae for this test were prepared by harvesting colonies of the test organism grown on SBCD agar with sterile phosphate buffer, pH 7. The absorbance of this suspension was adjusted spectrophotometrically at 625 nm to match that of 0.5 McFarland standards using similar buffer (Sutton, 2006a). This suspension contained 2 108 CFU ml1 as determined by plate count. The challenge test procedure involved the inoculation of 0.1 ml test suspension into 20 g of the product under investigation; thus the challenged product contained 106 CFU ml1. Inoculated aliquots were incubated in a shaking water bath at 27 C and samples were aseptically removed at days 0, 7, 14, 21, and 28 for viable counting as described above. Un-inoculated sample of each preparation was treated as described above to serve as a control. The product was considered as adequately preserved when 99.9% reduction of the initial inocula count was obtained on the 7th day of incubation and remained
with no increase up to the 28th day of the experiment (Anon,2008). Microbiological culture media used were all derived from Difco, USA.
2.3. Preservative efficacy evaluation
Products found to be free of microbial contamination were challenged with P. aeruginosa ATCC 9027. This test organism is one of the bacterial strains recommended by the ISO/WD 11930 for the
evaluation of antimicrobial protection of cosmetic products. Inoculae for this test were prepared by harvesting colonies of the test organism grown on SBCD agar with sterile phosphate buffer, pH 7. The absorbance of this suspension was adjusted spectrophotometrically at 625 nm to match that of 0.5 McFarland standards using similar buffer (Sutton, 2006a). This suspension contained 2 108 CFU ml1 as determined by plate count. The challenge test procedure involved the inoculation of 0.1 ml test suspension into 20 g of the product under investigation; thus the challenged product contained 106 CFU ml1. Inoculated aliquots were incubated in a shaking water bath at 27 C and samples were aseptically removed at days 0, 7, 14, 21, and 28 for viable counting as described above. Un-inoculated sample of each preparation was treated as described above to serve as a control. The product was considered as adequately preserved when 99.9% reduction of the initial inocula count was obtained on the 7th day of incubation and remained
with no increase up to the 28th day of the experiment (Anon,2008). Microbiological culture media used were all derived from Difco, USA.
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