Phagocytic and postphagocytic activities of bovine neutrophils for pure and mixed bacterial cultures.

A comparative study of phagocytosis and postphagocytic oxidative metabolic activity of bovine blood neutrophils incubated with pure and mixed cultures of Escherichia coli, Staphylococcus aureus, and Streptococcus agalactiae was preformed. Most neutrophils when incubated with mixed cultures showed preferential phagocytosis for one species and a smaller number phagocytized both species of microorganisms. Percent phagocytosis for E. coli in pure culture was similar to that of Strep. agalactiae in pure culture and higher than that for Staph. aureus in pure culture. Neutrophils incubated with mixed cultures of E. coli and Staph. aureus or E. coli and Strep. agalactiae showed greater than expected phagocytosis of each microorganisms alone and reduced phagocytosis of both microorganisms together. Postphagocytic oxidative metabolic activity of neutrophils, measured by percent nitroblue tetrazolium reduction, did not differ following phagocytosis of these three microorganisms in pure cultures. In comparison, a synergistic effect on nitroblue tetrazolium reductive activity was seen in mixed cultures as evidenced by higher percent nitroblue tetrazolium reduction following phagocytosis of both E. coli and Staph. aureus or E. coli and Strep. agalactiae. These observations indicate that the phagocytic and metabolic activities of neutrophils for bacteria in mixed cultures may not be identical to those in pure cultures.