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In vivo effects of chloramphenicol, tetracycline, and gentamicin on bovine neutrophil function and morphologic
M J Paape1, S C Nickerson, G Ziv
1Milk Secretion and Mastitis Laboratory, US Department of Agriculture, Beltsville, MD 20705.
Abstract:
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-beta-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 less than 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 less than 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 less than 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 nonsignificantly (P greater than or equal to 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.
Insights
Certain antibiotics negatively impact bovine immune cells, potentially weakening their ability to fight infections. This study investigated the effects of common antibiotics on cow immune cells and milk quality.
Area of Science:
- Veterinary Immunology
- Bovine Mastitis Research
- Pharmacology
Background:
- Antibiotic use in dairy cows can affect udder health.
- Bovine polymorphonuclear leukocytes (PMNL) are crucial for mammary gland defense.
- In vitro studies suggest some antibiotics impair PMNL function.
Purpose of the Study:
- To evaluate the in vivo effects of intramammary antibiotic administration on bovine PMNL function.
- To assess the impact of chloramphenicol, tetracycline, and gentamicin on milk somatic cell count and enzyme activity.
- To determine how these antibiotics affect PMNL morphology and key immune responses like phagocytosis and chemiluminescence.
Main Methods:
- Four cows received intramammary infusions of chloramphenicol, tetracycline, gentamicin, or phosphate-buffered saline solution (PBSS) into uninfected quarters.
- Milk somatic cell count and N-acetyl-beta-D-glucosaminidase (NAGase) activity were measured.
- PMNL ultrastructure, phagocytosis, nitroblue tetrazolium reduction, and chemiluminescence were analyzed in vitro.
- Data were compared to baseline and PBSS control values.
Main Results:
- Chloramphenicol and tetracycline significantly increased milk somatic cell counts.
- All tested antibiotics altered PMNL morphology, with tetracycline causing the most abnormalities.
- Tetracycline and gentamicin significantly reduced phagocytosis, and tetracycline abolished chemiluminescence.
- NAGase activity was not affected in the initial 12 hours post-treatment.
Conclusions:
- Intramammary administration of certain antibiotics can impair bovine PMNL function.
- This impairment of phagocyte function may compromise the cow's natural defense mechanisms against mammary pathogens.
- Further research is needed to understand the long-term implications of antibiotic-induced immune suppression in dairy cows.