The Mode of Action of Antibiotics in the Nutrition of the Dairy Calf. II. Effect of Aureomycin Administered Orally to Young Dairy Calves on the Sensitivity of Intestinal Bacteria to Phagocytosis

MODE OF ACTION OF ANTIBIOTICS IN THE NUTRITION OF THE DAIRY CALF IV.Escherichia coli

“…In two previous studies (Radisson et al, 1956a;MacFadden and Bartley, 1959), it was shown that leucocytes from newborn calves had a lower phagocytic activity than did leucocytes from older calves. The greatest growth response to antibiotics was obtained during the early life of the calf when it was most susceptible to intestinal disturbances.…”

“…The antibiotic may become ineffective against the microorganism toward which the drug is directed, or the organism which is inhibited may be replaced by another pathogen that is resistant to the drug. Radisson et al (1956a) and MacFadden and Bartley (1959) showed that low level feeding of chlortetracycline to dairy calves aids the host defense mechanism of phagocytosis by reducing the virulence of the pathogen. Also, McKee and Houck (1943), Blair, Carr, and Buchman (1946), and Radisson et al (1956b) observed that certain biological changes, such as in morphology and physiology, occurred in drug-resistant bacteria and that these changes were often accompanied by a reduction in virulence.…”

Effect of Antibacterials, Antibiotics, Enzymes and Steroids on Phagocytosis

“…In another study, the oral administration of chlortetracycline did not materially affect the phagocytic activity of the leukocytes in the blood of calves. However, the bacteria isolated from the feces of calves receiving this antibiotic were more sensitive to phagocytosis than were bacteria isolated from the feces of calves not receiving this antibiotic (29). phagocytic sensitivity was further increased when bacteria were grown in vitro in the presence of sub bacteriostatic concentrations of the antibiotic.…”

Antibiotics and other growth–promoting substances

“…There is also evidence to show that the continual administration of chlortetracycline to the calf may influence the metabolism of the microflora of the gut in such a way as to make the bacterial cell more susceptible to the normal process of phagocytosis (Radisson, Bartley, Lord & Swenson, 1956). Modification of the intestinal flora may either permit increased synthesis or availability of nutrients, depress bacterial toxin production or control organisms which in limited numbers may depress growth and in excess may bring about severe clinical disease.…”