WATER-BORNE BACTERIA AND SHAMPOO SPOILAGE 283 the same bacterial populations. After 14 days the populations were still similar but lower, by a factor of approximately 10, than at 7 days. Influence of shampoo volume on the survival of bacteria As few as 50 organisms were necessary to contaminate 1000 g of sham- poo so that after 4 days' incubation a population of 106 bacteria g4 was obtained (Fig. 2). 8,0 - 7'0 5'0 4.0 3.0 •.o I'O -- 1 04h I 2 3 4 5 6 7 14 Time (doys) Figure 2. Influence of inoculum size and shampoo volume on the survival and multiplication of E. cloacae in a model shampoo. Initial inoculum: --.O = 50 bacteria in 10 g shampoo ---O .... 400 bacteria in 10 g shampoo • = 50 bacteria in 100 g shampoo ---• - 400 bacteria in 100 g shampoo ß = 50 bacteria in 1000 g shampoo ---I .... 400 bacteria in 1000 g shampoo. As might be expected the maximum supportable population was achieved most rapidly in the system in which the initial number g-• was highest but all systems were in the early stationary phase of the growth cycle within 4 days of inoculation. After 7 days the total number of bacteria in each system was proportional to the volume of shampoo inoculated (Fig. 3).

284 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 9.0 .c_ 7-0 'F,_, '• 6.0 'B 5.0 "• ,4.0 .• 3-0 • z.o I'0 o 4h I I I I I I I // I I 2 3 4 5 6 7 14 Time {doys) Figure 3. Influence of inoculum size and shampoo volume on the total popula- tion of E. cloacae in a model shampoo. Initial inoculum: --O---- = 50 bacteria in 10 g shampoo ---O .... 400 bacteria in 10 g shampoo • = 50 bacteria in 100 g shampoo ----• .... 400 bacteria in 100 g shampoo , l-- 50 bacteria in 1000 g shampoo ---1 - 400 bacteria in 1000 g shampoo. Isolation from mains water of bacteria capable of multiplying in a model shampoo Inoculation of shampoos with filters derived from filtration of 1000 ml of water or less did not result in contamination with bacteria capable of multiplying in the shampoo. Of five inoculations with filters derived from l0 1 volumes two resulted in contamination of the shampoo (Table I). Viable counts on the shampoos immediately after inoculation in every case failed to reveal the presence of bacteria. Despite the relatively low population which developed in the contaminated shampoos (2.7 x 105 and 3.6 x 103 g-•) contamination was associated with obvious visual changes, i.e. the production ooe turbidity and strings of slime, after only 7 days' incubation.