Determinants of bacterial replication rates in mastitic whey

Bacterial growth was measured by a turbidimetric microtechnique in the whey of milk samples from quarters of cows with subclinical mastitis. Samples were grouped according to bacterial isolates recovered and the effects of bacterial species and whey on bacterial growth rates were analysed. Different strains of bacteria and different whey samples gave highly significant differences in bacterial replication rates. Except for penicillin-resistant Staphylococcus aureus, bacteria grew better in whey from mastitic milk where the inflammation was caused by the same bacterial species than in other mastitic milk samples. Inflammation caused by major pathogens generally enhanced the growth in whey of any type of major pathogen. Since mastitis pathogens showed enhanced growth in whey prepared from the same milk from which they were isolated, specific antibacterial factors in the whey did not appear to restrict bacterial growth in whey. The nutritional quality of the medium seems to be the important determinant of bacterial growth.