Effects of temperature and oxygen tension on growth of Escherichia coli in milk.

An in vitro system was developed to mimic conditions within normal and mastitic mammary glands. The system consisted of a modified batch fermenter that allowed for manipulation of temperature, oxygen tension, and pH. Experiments in tryptose-soy broth and UHT-treated milk were conducted to evaluate growth characteristics of Escherichia coli P4 as physical conditions were manipulated. The effect of bacterial growth on oxygen tension and pH were also evaluated. Growth of E. coli was inhibited as temperature was increased from 37 to 41 degrees C and as oxygen tension was decreased from microaerophilic to anaerobic levels. At bacterial populations > 6 log10 cfu/ml, microaerophilic cultures became anaerobic. The pH followed a similar trend; however, after a significant decrease in pH, mean bacterial populations were 7.1 log10 cfu/ml in tryptosesoy broth and 8.2 log10 cfu/ml in UHT-treated milk. This dynamic model demonstrated potential use in evaluation of growth characteristics of mammary gland pathogens in the lactating mammary gland.