728 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Simple aqueous solutions Some moulds will grow on such unlikely media as strong solutions of copper sulphate or sulphuric acid and simple solutions of inorganic com- pounds will support the growth of many sorts of microbe. The presence of organic material greatly increases the chance of growth occurring as it not only provides a utilizable substrate but may serve to introduce contamin- ants into the solutions. We have detected deposits of turbidity due to algae, moulds, bacteria or yeasts in a multiplicity of different solutions including ammonium carbonate, neutral ammonium tartrate, calcium digluconate, potassium citrate and Amaranth Solution B.P., even when apparently preserved with chloroform. Many solutions are included in the great diversity of mixtures in the B.P.C. and other formularies. These are often prepared from aqueous con- centrates which are themselves adequately preserved. However, the pre- servative can be diluted out on mixing and the resulting preparation is then at risk. An example of recent interest is peppermint water which has been implicated as a source of contaminants in formulations containing this ingredient. In at least one case there is evidence that potential pathogens have been transmitted to patients from it (12). Suspensions Aqueous suspensions of inorganic material for pharmaceutical use fre- quently support microbial growth, particularly as added preservatives tend to be absorbed and inactivated by the suspended matter. Unless growth is at the surface, as with mould contaminants, it is not easily detected visually because of the opacity of these products. When the lid is removed spoilage is sometimes manifested by an offensive odour or an unpleasant taste, but otherwise large numbers of bacteria may unwittingly be taken with the preparation. Thus, a medicament for the treatment of an intestinal disorder may exacerbate, rather than alleviate, the condition. However, apart from visible growth, a variety of other changes in appear- ance may be seen and preparations of this type can thin, separate, de- colourize, or change colour. The sequential growth of an aerobic organism, particularly a pseudomonad, followed by an anaerobe can cause striking changes in pharmaceutical products. The sequence occurring in cutting oil emulsions, used for cooling during drilling operations in the engineering industry, has been studied by several workers (13). The oils often become blackened due to bacterial action, the first organism lowering the redox potential and allowing the proliferation of anaerobic sulphate-reducing

MICROBIOLOGICAL SPOILAGE IN PHARMACEUTICALS AND COSMETICS 729 bacteria, Desulphovibrio or Desulphotomaculum species, which oxidize simple organic compounds and reduce sulphates to hydrogen sulphide. This then deposits iron sulphide due to the abundance of iron present in the environment where the oil is used. Emulsions O/w emulsions are particularly susceptible to spoilage as the water in the continuous phase allows contaminants to spread throughout the pro- duct. Preservatives generally exert their influence only within this phase, and at its boundaries, but their concentration depends on their relative solubilities in the particular oil and in water and on the oil water ratio in the emulsion (14). In addition to partition effects the activity of preservatives may be further diminished due to inactivation by compounds such as the nonionic emulgents. These possess little bactericidal adtivity and may even be utilized by pseudomonads (15, 16). In a comprehensive review Wedder- burn (17) pointed out that many other materials used in emulsions are susceptible to microbial degradation. Spoilage in emulsions can be manifest by changes in rheological proper- ties, including separation or 'breaking down'. Discolouration, decolouriza- tion, changes in odour and taste and signs of visible growth also occur. Creams and lotions A wide variety of complex cosmetic and toiletry preparations are included under this heading. Apart from the usual ingredients there is a current tendency to employ substances of natural origin including animal proteins and vitamins. These materials are not only highly nutrient to micro-organisms but may inactivate preservatives and even serve as a source of contamination. Glycerol is commonly used in both pharmaceutical and cosmetic formulations and may be metabolized by organisms frequently found in water. For instance, Klebsiella species will frequently produce gas in poorly preserved products when used to challenge creams and lotions containing this component. Mould growth is one of the most common causes of spoilage of creams of all types and can occur in products as varied as antifungal, calamine, baby and hair creams and a number of other cosmetic formulations including moisture and cleansing creams. The difficulties of preserving these products against mould growth are enhanced by the risk of contamination from containers, the presence of large air spaces and poor storage con- ditions.