The source of bacteria in fresh cream, and the methylene blue reduction test as a guide to hygienic quality

Abstract

SUMMARYOne hundred and twenty-nine samples of fresh cream collected in Worcestershire were examined bacteriologically. Sixty (46·5 %) creams had counts of over 100,000 bacteria/ml. The bacteria present were of many varieties, the commonest being Bacillus spp. (aerobic spore formers), Gram-negative bacilli, staphylococci and micrococci. Since most of the creams had been either pasteurized as cream or manufactured from pasteurized milk it was thought that the many bacteria were present because of contamination after pasteurization due to three main causes; unsatisfactory or unhygienic premises, unsuitable equipment, manual handling during the filling and capping process.The methylene blue test results related well with bacterial counts but there were seven (5·4 %) anomalous results. Although the methylene blue reduction test therefore could serve as a simple and reasonable guide to the hygienic quality of fresh cream, 5·4 % of anomalous results would perhaps make it unsuitable as a statutory test.We thank Mr R. Colenso, M.A.P.H.E., M.A.P.H.I., Chief Public Health Inspector, and Mr H. Beckett, Milk Sampling Officer of the Worcestershire County Council, for arranging the supply of samples.