FUNDAMENTALS OF MICROBIOLOGY IN RELATION TO CLEANSING 67 conditions of testing. The only ultimate criterion which is of any value to the user is whether the substance fulfils the claims made for it under the condition of use. Any laboratory test used should therefore simulate as closely as possible these conditions. Choice of end-point It should be realized that there is nothing definite about disinfectant studies everything is arbitrary. Such terms as 'complete kill' or '99.99 per per cent kill' are quite arbitrary and can only be defined in terms of the particular technique used. There are many factors capable of affecting the result of any disin- fectant test, irrespective of its nature (Table V). In a laboratory test, these can at least be standardized but under conditions of use such factors may Table V. Factors influencing the result of any disinfectant test 1. Type of organism (e.g. Staph. aureus) 2. Particular strain used 3. Physiological condition--long term (e.g. how long in artificial culture) 4. Physiological condition--short term (e.g. 24 h at 37øC) $. Composition of medium used for growth (e.g. nutrient broth) 6. Physical state of medium used for growth (e.g. agar medium) 7. Temperature, humidity, etc. of growth 8. Concentration of disinfectant 9. Stability of disinfectant to moisture, oxygen, etc. 10. Temperature of test 11. Time of contact 12. pH value 13. Osmotic pressure 14. Synergistic effects with other substances, e.g. acids, surfactants, salts. 15. Concomitant substances (e.g. in hard water) compatibility with other substances present 16. Physical nature of suspending fluid, e.g. emulsion 17. Surface tension of suspending liquid (e.g. Teepol) 18. Nature of solvent (e.g. part isopropyl alcohol) 19. Method of mixing disinfectant and cells 20. Type, physical nature and concentration of soiling matter 9,1. Choice and concentration of inactivator (e.g. Lubrol W) 9,2. Medium for growing survivors 9.3. Incubation temperature for plates Surface film tests 9,4. Soiling material used (e.g. whole milk) 9,5. Method of fixing to surface (e.g. drying at 87øC) 9.6. Chemical nature of surface used (e.g. stainless steel) 9,7. Condition of surface (e.g. highly polished)

68 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS vary considerably, e.g. temperature, time of contact, nature and amount of soilage, hardness of water. Reports of microbiological examinations In my opinion many reports and claims for disinfectant power, etc. by manufacturers, are unscientific and even sloppy. Such statements as 'kills typhoid in 2 min', 'coli absent', etc., are meaningless, and in fact may even be misleading. The conditions of testing should always be stated, and reports should state results in a form such as 'coli not detected in 1 ml', etc. Some recommended microbiological control methods for cosmetic products are given in Table VI. Table VI. Recommended bacteriological control methods for cosmetic products Organism Medium Total (public health) Total (general) Staphylococcus aureus Pseudomonas aeruginosa Presumptive coliforms Faecal coli (follow-up tests) Candida albicans, yeasts and moulds Yeasts and moulds Streptococcus faecalis Salmonella Clostridium spores Blood agar Glucose tryprone agar Mannitel salt (21) Egg yolk (22) Phenol phthalein phosphate (23) Acotamide agar (24) Cetrimide agar (39) MacConkey broth Eosin methylene blue agar } Escherichia and (25) Aerobacter can Violet red bile agar (26) bo differentiated on these media MacConkey broth (both must be used) Peptone water Malt agar pH $.4 Malt or buffered beerweft agar pH 3.5 (27) Buffered citric acid agar rH 3.S (28) Crystal violet azide blood agar (29) Selenite broth (for enrichment) (30) Desoxycholate (31) Brilliant green (32) or Bismuth sulphite agax (33) Kligler iron agax (32), (35}) or Kohn-Gillics broths (36), (37) Final serological confirmation Meat broth Reinforced clostridial medium {38) Temperature 'C 37 27 37 37 37 37 (42) 37 3O 3O 3O 44 44 27 27 27 37 37 (43) 37 37 37 37 Oxoid or Difco media (see Manuals issued by these firms)