Objective—To evaluate chemotactic, phagocytic, and
bactericidal activities of bovine and porcine alveolar
macrophages (AM) exposed to tilmicosin.
Animals—12 healthy calves and 12 healthy pigs.
Procedure—Lungs were obtained immediately after
euthanasia; AM were collected by means of bronchoalveolar
lavage and density gradient centrifugation.
Chemotactic activity was evaluated by exposing
AM to lipopolysaccharide or macrophage inhibitory
peptide during incubation with tilmicosin. Phagocytic
activity was evaluated by incubating AM with tilmicosin
for 24 hours and then with tilmicosin-resistant
Salmonella serotype Typhimurium. Bactericidal activity
was evaluated by incubating AM with tilmicosin (0,
10, or 20 µg/ml for bovine AM; 0 or 10 µg/ml or 10
µg/ml but washed free of tilmicosin for porcine AM)
and then with Mannheimia haemolytica (bovine AM)
or with Actinobacillus pleuropneumoniae or
Pasteurella multocida(porcine AM).
Results—Tilmicosin had no significant effects on
chemotactic or phagocytic activities of bovine or
porcine AM. The time-course of bactericidal activity
was best described by polynomial equations. Time to
cessation of bacterial growth and area under the time
versus bacterial number curve were significantly
affected by incubation of AM with tilmicosin.
Conclusion and Clinical Relevance—Results show
that bactericidal activity of bovine and porcine AM
was enhanced by tilmicosin, but not in proportion to
the reported ability of AM to concentrate tilmicosin
intracellularly. With or without exposure to tilmicosin,
the time-course of bactericidal activity of bovine AM
against M haemolytica and of porcine AM against
A pleuropneumoniae or P multocida was too complex
to be reduced to a simple linear equation. (Am J Vet