EFFECT OF OXYGEN-TENSION ON KILLING OF ESCHERICHIA-COLI BY BOVINE POLYMORPHONUCLEAR NEUTROPHIL LEUKOCYTES IN-VITRO

A batch fermenter modified to simulate the physical conditions of an i nflamed v. uninflamed mammary gland was utilized to evaluate the effec t of oxygen tension on killing of Escherichia coli P4 by bovine polymo rphonuclear neutrophil leucocytes. Leucocytosis was simulated in vitro 4 h after inoculation with Escherichia coli by adding bovine neutroph ils isolated from peripheral blood to the culture medium. Experiments were conducted at 39 degrees C in UHT treated milk. At microaerophilic oxygen tension (oxygen partial pressure, 3.11 kPa), bacterial numbers declined during the first hour following addition of the neutrophils. Oxygen tension declined rapidly following PMN addition. Once oxygen w as depleted, neutrophil activity was presumably diminished and Esch. c oli numbers began to increase. Under anaerobic conditions (oxygen part ial pressure, 0.17 kPa), no reduction in population was observed. Phot omicrographs taken at the time of neutrophil addition and at subsequen t time intervals demonstrated a specific association between neutrophi ls and the pathogen. Subsequent lysis of neutrophils associated with E sch. coli growth was seen coincident with oxygen depletion.