748 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 1.31 1.311 Nutrient Agar or Plate Count Agar 1.312 Nutrient Broth 1.313 Blood Agar 1.314 MacConkey Agar 1.3 Recommended test media and incubating conditions Detection of aerobic bacteria (Mesophiles) Incubation temperature 28-32 ø 28-32 ø 37 ø 28-32 o Examine at 24-48 h intervals and continue incubation up to 7 days. 1.32 Detection of Escherichia coli (Type 1) 1.321 Sub-culture in MacConkey Broth (with Durham tube) 44 ø Examine for acid and gas at 48 h. 1.33 Detection of Psychrophiles 1.331 Tryptone Glucose Yeast Extract Agar 10 ø Examine at 5 and 10 days. Continue incubation as necessary. 1.34 Detection of Thermophiles 1.341 Tryptone Glucose Yeast Extract Agar 55-63 ø Incubate for 36 - 48 h in an atmosphere sufficiently humid to prevent drying of the medium. Continue incubation as necessary. 1.35 Detection of Clostridia 1.351 Cooked Meat Broth 37 ø Incubate 3 to 4 days and sub-culture to suitable plate media and incu- bate anaerobically. Tubes of cooked meat broth not used the day they are prepared should be placed in a boiling water bath or flowing steam for a few minutes to drive off dissolved oxygen then cooled to 37 ø before inoculating. 1.352 Thioglycolate Broth 37 ø 1.353 Reinforced Clostridial Agar and Broth 37 ø Incubate anaerobically. 1.36 Detection of yeasts and moulds 1.361 Sabouraud Liquid Medium/Malt Extract Broth 22-25 ø 1.362 Sabouraud Dextrose Agar 22-25 ø 1.363 Malt Extract Agar 22-25 ø Inspect at 24-48 h intervals and continue incubation up to 10 days.

HYGIENIC MANUFACTURE AND PRESERVATION 749 1.37 Selective enrichment media for the isolation of pathogens 1.371 Staphylococcus aureus (a) Salt Meat Broth 37 ø Sub-culture to Nutrient Agar at 24 h. Carry out slide and coagulase test from Nutrient Agar (see 1.88 below). (b) Baird-Parker Medium (Oxoid code CM275) 37 ø For further details see 5.3 Ref. (13) (Appendix E). 1.372 Pseudomonas aeruginosa (Ps. pyocyanea) 37 ø Plate on Cetrimide Agar from broth at 24 h. 1.373 Salmonellae Selenite F broth 37 ø 43 ø Subculture on brilliant green agar (Bacto) after 24 and 48 h. Incubate at 37 ø and examine the plates for colonies with Salmonella characteristics and identify by standard biochemical and serological methods [see Selected Bibliography. Appendix E, 5.3, Refs. (4, t3)• 1.38 Staphylococcal coagulase test This test is used to differentiate pathogenic Staph. aureus from non- pathogenic staphylococci. 1.381 Test reagent Human or rabbit plasma. Dried rabbit plasma, reconstituted and diluted 1:5 in isotonic saline is satisfactory. 1.382 Slide test Use an 18-24 h Nutrient Agar Culture (not a broth culture). Mark a clean slide into two sections. Place a loopful of water (not saline) on each section and emulsify a colony or small amount of culture in each drop until a homogeneous suspension is obtained. If no clumping occurs in 10-20 s, add and mix a loopful of neat reconstituted plasma. Avoid excess plasma as this may give false positives. The second suspension serves as a control. A positive result is indicated by visible clumping within 10 s. Delayed clumping does not constitute a positive result. 1.383 Tube test Use an 18-24 h plain Nutrient Broth Culture. Place 0.5 ml of diluted plasma in each of two small test tubes. To one tube add 0.5 ml of an 18-24 h