FUNDAMENTALS OF MICROBIOLOGY IN RELATION TO CLEANSING According to Monori and Varga (5) even apparently innocuous deter- gents such as the anionics, non-ionics and trisodium phosphate can exert a powerful killing effect against most pathogens but not against tubercle bacilli or spores. The effectiveness of alkaline detergents can be improved by incorpor- ation of anionic wetting agents if foaming problems are not likely to arise. The alkyl-aryl sulphonates may improve not only wetting, emulsifying and deflocculating but also the bactericidal action (6). It is generally accepted that there is no reliable method of testing efficiency of detergent action suitable for application under all conditions or relevant to all problems, although standard test methods for detergents as such can be devised. Comparison of sterilants All sterilants have their characteristic advantages and disadvantages, and it is quite unsound to attempt to compare them unless consideration is given to the conditions of use. The following factors should be taken into consideration when deciding on the best method for sterilizing equipment: (a) Material of construction. Stainless steel and glass are best from the hygiene point of view (7). (b) Adequacy of supply of steam and/or hot water (85-90øC). (c) Time available for cleaning and sterilizing. A quick turnover (e.g. for a tanker) may make the use of steam impossible. (d) Type of equipment, e.g. large tank, long pipeline, equipment susceptible to heat distortion. The advantages and disadvantages of heat and chemical sterilizing methods are summarized in Table II {8). Recommendations for choice of sterilant are given in Table III (8). Chlorine compounds are particularly indicated where a quick drastic action is required. The QAC are not recommended where serious gram-negative con- tamination is possible, or where rinsing is difficult, e.g. where surfaces are rough or absorbent. One danger with QAC preparations is that they may be used as detergents although they are sold only as a sterilant.

58 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table II. Sterilizing agents--advantages and disadvantages Chlorine- Quaternary Hot water releasing ammonium Steam (90øC) compounds compounds Iodophors Cost Varies Varies Convenience Depends on Recirculatory lay-out system necessary Penetration Good if Good Clean plant adequate essential supply Heating Tanks, etc. Les• than None effect may require steam hours to cool.-Un- desirable stresses may be set up Suitability Very suitable Very suitable for enclosed for pipelines systems and small articles in chests Persistence Not persistent Not persistent Not persistent Corrosion None None Very corrosive unless main- - - rained at pH 9 or above -Odour None None Marked Rinsing Unnecessary Unnecessary Low High Very Very convenient convenient Clean plant essential According to temper- ature Intermediate Very convenient Has detergent action None All purposes All purposes All purposes Persistent None Not persistent Not corrosive if thoroughly rinsed away None None below 50øC Good rinsing Good rinsing Good rinsing essential essential essential All chemical sterilants can be corrosive if improperly used, e.g. at too high a concen- tration, at too high a temperature, for too long, and/or not adequately rinsed away. Table III. Recommendations on types of sterilant Circumstances Circumstances where Sterilant where indicated inadvisable Hypochlorites, chloro- cyanuric acids and sodium phosphate hvpochlorite. Where drastic action required. Where low cost is important. Where all types of micro- organisms are likely to be encountered. Where alkaline detergent required Where odour inadvisable. Where corrosion likely Continued page 59