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 fer menter that allowed for manipulation of temperature, oxygen tension, a nd pH. Experiments in tryptose-soy broth and UHT-treated milk were con ducted to evaluate growth characteristics of Escherichia coli P4 as ph ysical conditions were manipulated. The effect of bacterial growth on oxygen tension and pH were also evaluated. Growth of E. coli was inhib ited as temperature was increased from 37 to 41 degrees C and as oxyge n tension was decreased from microaerophilic to anaerobic levels. At b acterial populations >6 log(10) cfu/ml, microaerophilic cultures becam e anaerobic. The pH followed a similar trend; however, after a signifi cant decrease in pH, mean bacterial populations were 7.1 log(10) cfu/m l in tryptose-soy broth and 8.2 log(10) cfu/ml in UHT-treated milk. Th is dynamic model demonstrated potential use in evaluation of growth ch aracteristics of mammary gland pathogens in the lactating mammary glan d.