OBSERVATIONS ON THE EFFECT OF ADDED HYPOCHLORITE ON THE NUMBERS AND KINDS OF BACTERIA IN MILK

SUMMARY: In an investigation of the effect of added hypochlorite on the bacterial flora and bacterial numbers of milk no bactericidal action was apparent within 15 min of adding the disinfectant unless at least 500 p/m available chlorine had been added. After 24 hr storage at atmospheric temperature a reduction in numbers was found with 10 p/m available chlorine and this became more pronounced with increased concentrations. Micrococci seemed more susceptible to the bactericidal effect than streptococci, which formed, after 24 hr storage, the predominant residual flora where 250 and 500 p/m available chlorine had been added. Acid production by lactic streptococci was retarded at concentrations greater than 50 p/m available chlorine in a 5 hr incubation period at 30°, but after a 24 hr incubation the decrease in acid production was only apparent when 500 or 1,000 p/m available chlorine was present. Little effect on acid production by lactic streptococci was found when less than 50 p/m available chlorine had been added. The residual chlorine content of rinses of equipment sterilized in hypochlorite solutions was negligible.     

THE ASSOCIATIVE GROWTH OF SOME THERMODURIC BACTERIA IN PASTEURIZED MILK

SUMMARY: Three strains of aerobic spore forming bacteria have been studied in association with thermoduric streptococci in pasteurized milk at different temperatures. Generally the development of each component organism of the mixtures was unaffected in the initial stages by the presence of the other, though later the spore formers were frequently adversely affected. Acid production by the mixed cultures was compared with that of the pure cultures under the same conditions of incubation. Generally more acid was formed by the mixtures, particularly at the higher temperatures of incubation. Gas formation was noted by a culture of Streptococcus faecalis in association with the spore formers.     

THE RATES OF GROWTH OF SOME THERMODURIC BACTERIA IN PURE CULTURE AND THEIR EFFECTS ON TESTS FOR THE KEEPING QUALITY OF MILK

SUMMARY: The growth rates of eleven representative thermoduric bacteria, comprising 3 aerobic spore formers, 3 streptococci, 1 Corynebacterium lacticum and 4 micrococci, have been determined in glucose broth and sterile pasteurized milk at 37·5°, 26° and 15°. The spore formers and streptococci were generally not affected by the presence of inhibitory factors in pasteurized milk. When multiplication of micrococci and C. lacticum occurred in milk this was only after a lag period. One micrococcus showed an unusual series of growth phases in glucose broth at 37·5°, possibly due to the appearance of mutants or to adaptation of the organism to growth at that temperature. This was not observed in pasteurized milk. C. lacticum died off when incubated in glucose broth at 37·5°.
None of the keeping quality tests was more effective than any other in detecting these organisms in milk. The micrococci and C. lacticum had little effect on the keeping quality of pasteurized milk within the period of 'commercial life'. Some of the spore formers and streptococci showed marked differences in the end-points with the clot-on-boiling and the alcohol precipitation tests.     

EFFECT OF PROTEOLYTIC ATTACK ON THE STRUCTURE OF CNS MYELIN MEMBRANE

Rat CNS myelin particles have been incubated with trypin and acetyltrypsin under conditions which ensured a selective and substantial removal of the basic proteins leaving acidic Wolfgram and proteolipid proteins. Some trypsin became associated with the basic protein denuded pellet while no attachment of acetyltrypsin was observed. The removal of basic proteins ‘solubilized’ some myelin and produced a lighter ‘fluff’ layer on top of the myelin pellet, but this amounted to no more than 10 per cent of the total myelin lamellae. Electron microscopy indicated a more dense-straining interperiod line in a small percentage of lamellae which otherwise remained normal. Selective extraction of complex lipids with solvents of increasing polarity, nuclear magnetic resonance spectra and X-ray diffraction patterns showed no significant changes on removing basic proteins from myelin. The results are interpreted as suggesting that the basic proteins are not uniformly distributed in myelin but preferentially located in the outside layers of the myelin sheath and that they play little part in stabilizing the bulk of the myelin membrane structure.     

COLI-AEROGENES BACTERIA FROM FARM DAIRY EQUIPMENT AND RAW MILK

SUMMARY: A series of 1,040 cultures of coli-aerogenes bacteria isolated at 30° from farm dairy equipment and raw milk was classified according to the recommendations of the Coliform Sub-Committee of the Society for Applied Bacteriology (Report, 1949). The distribution of species and types isolated from milk did not differ materially from that for dairy equipment, Klebsiella cloacae, K. aerogenes and Citrobacter freundii being the dominant species, while the incidence of Escherichia coli was relatively low. There was no marked seasonal incidence of any type, though E. coli I formed a slightly higher proportion of the coli-aerogenes microflora in winter, whereas K. aerogenes I was slightly higher in summer. Many of the cultures of the dominant types, K. cloacae, K. aerogenes I and Cit. freundii I, did not form acid and gas from lactose in two days at 37°. Consequently 37° negative, anaerogenic and paracolon strains constituted a relatively high proporton (49%) of the coli-aerogenes microflora.