Effects of florfenicol, chloramphenicol, and thiamphenicol on phagocytosis, chemiluminescence, and morphology of bovine polymorphonuclear neutrophil leukocytes.

Florfenicol, chloramphenicol, and thiamphenicol were tested in vitro to determine their potential toxic effects on bovine neutrophils. Antibiotics were tested at 4000, 2000, and 10 micrograms/ml of incubation mixture. Percentage phagocytosis was determined by incubations with neutrophils isolated from milk of five cows and 32P-labeled Staphylococcus aureus and 5% skim milk. The effect of 4000 micrograms of each antibiotic on chemiluminescence was determined on neutrophils isolated from mammary secretions of three nulliparous heifers. Morphological evaluation by transmission and scanning electron microscopy was performed on neutrophils isolated from two heifers at antibiotic concentrations of 4000 and 10 micrograms/ml. Chloramphenicol depressed phagocytosis at the high and medium doses and blocked chemiluminescence activity at the high dose. No effects were observed for florfenicol and thiamphenicol. Transmission electron microscopic examination showed that at the high concentration of drugs, 99, 99, 97, and 76% of the neutrophils treated with florfenicol, chloramphenicol, thiamphenicol, and dimethyl sulfoxide were abnormal. Examination by scanning electron microscopy showed that the percentage of neutrophils without pseudopodia averaged 67, 94, 32, and 16%, respectively. Results indicated that neither florfenicol nor thiamphenicol altered neutrophil function, but they did alter neutrophil morphology, although to a lesser extent than did chloramphenicol.