Phagocytic and nitroblue tetrazolium reductive properties of bovine neutrophils for mammary pathogens

A comparative evaluation of in vitro phagocytic and metabolic activities of freshly isolated bovine blood neutrophils from 26 cows was performed. Degrees of phagocytosis and nitroblue tetrazolium reduction by neutrophils were measured using zymosan, Escherichia coli, Staphylococcus aureus, Streptococcus agalactiae, Mycoplasma bovis, Salmonella sp., and Brucella abortus opsonized with fresh bovine serum. Percent phagocytosis and nitroblue tetrazolium reduction by the neutrophils were determined by microscopic evaluation of stained coverslip smears. Individual variation among cows was found in parameters measured, but age was not a contributing factor. Phagocytosis was high (73 to 81%) for E. coli, Salmonella sp., Strep. agalactiae, and zymosan; intermediate (64%) for Staph. aureus; and low (24 to 40%) for M. bovis and B. abortus. Nitroblue tetrazolium reduction was distinctly lower than zymosan (74%) for all microorganisms. Similar percentages (32 to 41%) of nitroblue tetrazolium reduction were observed for E. coli, Staph. aureus, Strep. agalactiae, and M. bovis; intermediate (28%) was obtained for Salmonella sp. and lowest (11%) for B. abortus.