Effect of antibiotics and vehicles on bovine mammary polymorphonuclear leukocyte morphologic features, viability, and phagocytic activity in vitro

Effects of antibiotics and antibiotic vehicles on polymorphonuclear leukocytes (PMNL) isolated from bovine mammary glands were studied in vitro. Amikacin, dicloxacillin, erythromycin, gentamicin, lincomycin, nitrofurantoin, novobiocin-penicillin, polymyxin B, rifampin, tetracycline, or tiamulin was added to culture medium at 1 mg/ml and chloramphenicol was added at 4 mg/ml. Drug concentrations were equivalent to those detected in milk immediately after injection into the mammary gland. Vehicles included mineral oil and peanut oil, each at a dilution of 1:100 in culture medium. The PMNL morphologic features, viability, and phagocytic activity were evaluated. In comparison with the phosphate-buffered saline solution (PBSS) control, significant (P less than 0.05) alterations in normal cell morphologic features were observed in PMNL cultured with tetracycline, nitrofurantoin, erythromycin, polymyxin B, rifampin, novobiocin-penicillin, chloramphenicol, tiamulin, or peanut oil. Viabilities of PMNL cultured with chloramphenicol, novobiocin-penicillin, or tiamulin were significantly (P less than 0.05) reduced when compared with those of PBSS controls. Addition of Staphylococcus aureus to culture medium enhanced morphologic alterations and reduced viabilities of PMNL. Phagocytosis of S aureus by PMNL was significantly (P less than 0.05) depressed in medium containing novobiocin-penicillin, amikacin, rifampin, chloramphenicol, tiamulin, or peanut oil in comparison with that of PMNL incubated in PBSS.