8OO JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 25øC and at a pH of 7-8. They are micro-aerophilic and few organisms have their capacity for growth at 0 øC (16). The susceptibility of some formulations to pseudomonas contamina- tion may be specific. A pseudomonad isolated from one preparation may not readily grow in any other. Pseudomonads that have been iso- lated from a make-up product, for example, will only grow within the specific product. Pseudomonads isolated from a cream could only grow within that cream. It has been necessary on occasion to prepare prod- uct-containing culture media to achieve profuse growth and after adapta- tion to laboratory media, the pseudomonad organism must frequently be inoculated into the original cream to maintain the resistance of the or- ganism. Because of these properties, it is a practice of the author's lab- oratories to name isolated pseudomonads according to the product of origin. For example, there is a culture named Pseudornonas aquasolarus, a variety of aeruginosa, whose name indicates the origin of the culture. PSEUDOMONIASIS, AN INDUSTRIAL DISEASE AND ITS CONTROL The growth of pseudomonads in a product becomes an infection and the termination of which is the destruction of the product. The mecha- nisms of industrial control are similar to those used by a health depart- ment in a communicable disease program. 1. Preservatives increase the resistance of products to infection. 2. Manufacturing at 180 øF reduces or eliminates the microbial con- tent of the ingredients. 3. Sanitary compounding and filling minimizes contamination of the preparation. 4. Housekeeping and sanitation is enhanced by company issued san- itary regulations and periodic inspection by sanitarians. 5. Education of manufacturing personnel can help achieve a high level of sensible, clean production methods. Successful results can most readily be obtained when plant personnel understand the reasons for sanitation of equipment and for clean manufacture. 6. An investigative microbiology program tests the adequacy of product preservation, controls the microbiological quality of products at the time of manufacture, conducts shelf studies, and examines partially used products secured from consumers. In sum, the mechanisms which insure the microbiological quality of manufactured products are: 1. Microbiological control 3. Sanitary inspection 2. Sanitary manufacturing 4. Personnel education

PSEUDOMONADS IN COSMETICS 801 Preservation Regardless of sanitary manufacturing methods, a poorly preserved preparation provides many opportunities for microbial infection. As described earlier an O/W emulsion at a pH of 7-8 containing nonionics provides a particularly suitable menstruum for pseudomonas growth. Preservatives used to restrain growth are the well known phenolics, parabens, bisphenols, and organo-metals. Organic acids can be effective at pH 7 while quaternaries tend to be incompatible with a nonionic slightly alkaline system. It is necessary to bear in mind that few cosmetically acceptable bacteriocides are active against pseudomonads specifically, even in the absence of surfactants. Anionics in general ap- pear to inhibit selectively the metabolism of gram-positive organisms, and those which are bacteriocides tend to have a narrower spectrum than cationics. The bacterial action of anionics is influenced to a greater ex- tent by changes in pH. Some nonionics actually inactivate the bacteriostatic action of bisphenols and Tween © 80,* for example, is a more effective antidote than blood serum for nullifying the antibacterial properties of these com- pounds (17). However, Tween 80 in low concentrations, such as 0.02%, render pseudomonads actually more susceptible to antimicrobial agents. This enhancing effect at low levels is noteworthy since at higher levels the surfactant was found by Kohn et al. (18) to be an antagonist to the very same bacteriostatic agents. Studies have shown that Pseudornonas aeruginosa is capable of growth in solutions and dispersions of nonionic surfactants of the Tween type and can split the ester linkages of these agents (19). Practically all the nonionics of ethylene oxide or propylene oxide condensates of fatty acids and alcohols inactivate many pre- servatives in current use. It was found, in a study of 36 nonionics and 26 preservatives, that the nonionic surfactants reduced the efficiency of all preservatives when the ratio of surfactant to preservative ex- ceeded certain critical values (20). Of course, one is now cognizant that with time, inactivation of many biostats occurs and what appears as a well-preserved preparation today can be spoiled by an inoculum 2-3 months after manufacture (21). Emulsions of the water-in-oil type are relatively resistant to natural pseudomonas attack since the continuous oil phase acts as a barrier to penetration of the organism into the water phase, and impedes the spread of growth through the system. However, the features which pre- * Tween 80 is a registered trademark of Atlas Powder Company, Wilmington, Del.