650. The influence of temperature on the generation time of bacteria commonly found in milk: II. Examination of partial contributions over the full lactation period of two cows

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Abstract
An attempt to show the effect of temperature on the rate of growth of bacteria in milk was made by finding the generation times ofSalmonella typhosa, Shigella dysenteriae, Streptococcus haemolyticus, Micrococcus pyogenes aureus, Lactobacillus acidophilus, Escherichia coli, Bacillus subtilisandAlcaligenes faecalisat temperatures ranging from 4 to 60°C. Growth was quantitatively measured by means of plate counts during the logarithmic period which was previously determined for each organism. The following is a summary of the results obtained:At 4° C. none of the micro-organisms showed evidence of multiplication during the 6hr.incubation.As temperatures of 5–45° C. were approached the generation time decreased until the optimum temperature for each organism was reached; beyond this point a slowing of growth was observed, until at 60° C. viability was apparently lost by all the organisms.Streptococcus haemolyticusandMicrococcus pyogenes aureushave a generation time of 37–23 min.Salmonella typhosaandShigella dysenteriaehave a generation time of 50–26 min.Escherichia coliandAlcaligenes faecalishave a generation time of 41–16 min.Bacillus subtilisgrows at about the same rate asAlcaligenes faecalis.The slowest organism of all appears to beLactobacillus acidophiluswith a generation time of 52–125 min.