Escherichia coli induces apoptosis and proliferation of mammary cells

Mammary cell apoptosis and proliferation were assessed after injection of E scherichia coli into the left mammary quarters of six cows. Bacteriological analysis of foremilk samples revealed coliform infection in the injected q uarters of four cows. Milk somatic cell counts increased in these quarters and peaked at 24 h after bacterial injection. Body temperature also increas ed, peaking at 12 h postinjection, The number of apoptotic cells was signif icantly higher in the mastitic tissue than in the uninfected control. Expre ssion of Bax and interleukin-1 beta converting enzyme increased in the mast itic tissue at 24 h and 72 h postinfection, whereas Bcl-2 expression decrea sed at 24 h but did not differ significantly from the control at 72 h posti nfection, Induction of matrix metalloproteinase-g, stromelysin-1 and urokin ase-type plasminogen activator was also observed in the mastitic tissue. Mo reover, cell proliferation increased in the infected tissue, These results demonstrate that Escherichia coli-induced mastitis promotes apoptosis and c ell proliferation.