In vivo effects of chloramphenicol, tetracycline, and gentamicin on bovine neutrophil function and morphologic features

M. J. Paape From the Milk Secretion and Mastitis Laboratory, Agricultural Research Service, US Department of Agriculture, Beltsville, MD 20705 (Paape), Hill Farm Research Station, Louisiana State University Agricultural Center, Route 1, Box 10, Homer, LA 71040 (Nickerson), and Ministry of Agriculture, Kimron Veterinary Institute, Bet-Dagan, Israel (Ziv).

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S. C. Nickerson From the Milk Secretion and Mastitis Laboratory, Agricultural Research Service, US Department of Agriculture, Beltsville, MD 20705 (Paape), Hill Farm Research Station, Louisiana State University Agricultural Center, Route 1, Box 10, Homer, LA 71040 (Nickerson), and Ministry of Agriculture, Kimron Veterinary Institute, Bet-Dagan, Israel (Ziv).

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G. Ziv From the Milk Secretion and Mastitis Laboratory, Agricultural Research Service, US Department of Agriculture, Beltsville, MD 20705 (Paape), Hill Farm Research Station, Louisiana State University Agricultural Center, Route 1, Box 10, Homer, LA 71040 (Nickerson), and Ministry of Agriculture, Kimron Veterinary Institute, Bet-Dagan, Israel (Ziv).

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SUMMARY

Antibiotics that have been shown in vitro to have a detrimental effect on bovine polymorphonuclear leukocytes (pmnl) were injected into the mammary gland. Chloramphenicol, tetracycline, gentamicin, or phosphate-buffered saline solution (pbss) were administered to uninfected mammary quarters of four cows at recommended doses. Each cow received each of the 4 treatments. Total milk somatic cell count and N-acetyl-β-d-glucosaminidase activity in milk in response to drug, changes in ultrastructure of pmnl, and effects on in vitro percentage phagocytosis, reduction of nitroblue tetrazolium, and chemiluminescence were studied.

Chloramphenicol and tetracycline caused a significant (P < 0.01) increase in somatic cell count, compared with baseline values. During the first 12 hours, no effect on NAGase activity was observed. All 3 antibiotics caused a significant (P < 0.05) alteration of pmnl morphologic features. More abnormal pmnl (63%) were found in tetracycline-injected quarters. Gentamicin-injected quarters contained 33% abnormal pmnl, compared with only 5% for pbss-injected quarters. A significant (P < 0.01) decrease in percentage phagocytosis was observed for tetracycline and gentamicin. Tetracycline inhibited all chemiluminescence activity, whereas no effect was observed for the other 2 drugs. Nitroblue tetrazolium reduction was nonsignificant (P ≥ 0.05) decreased for the 3 drugs, compared with that for pbss controls. On the basis of our findings, we concluded that some antibiotics may be inhibitory to phagocyte function and, thereby, impair host defense mechanisms against invading microbes.

SUMMARY

Antibiotics that have been shown in vitro to have a detrimental effect on bovine polymorphonuclear leukocytes (pmnl) were injected into the mammary gland. Chloramphenicol, tetracycline, gentamicin, or phosphate-buffered saline solution (pbss) were administered to uninfected mammary quarters of four cows at recommended doses. Each cow received each of the 4 treatments. Total milk somatic cell count and N-acetyl-β-d-glucosaminidase activity in milk in response to drug, changes in ultrastructure of pmnl, and effects on in vitro percentage phagocytosis, reduction of nitroblue tetrazolium, and chemiluminescence were studied.

Chloramphenicol and tetracycline caused a significant (P < 0.01) increase in somatic cell count, compared with baseline values. During the first 12 hours, no effect on NAGase activity was observed. All 3 antibiotics caused a significant (P < 0.05) alteration of pmnl morphologic features. More abnormal pmnl (63%) were found in tetracycline-injected quarters. Gentamicin-injected quarters contained 33% abnormal pmnl, compared with only 5% for pbss-injected quarters. A significant (P < 0.01) decrease in percentage phagocytosis was observed for tetracycline and gentamicin. Tetracycline inhibited all chemiluminescence activity, whereas no effect was observed for the other 2 drugs. Nitroblue tetrazolium reduction was nonsignificant (P ≥ 0.05) decreased for the 3 drugs, compared with that for pbss controls. On the basis of our findings, we concluded that some antibiotics may be inhibitory to phagocyte function and, thereby, impair host defense mechanisms against invading microbes.

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