Fusobacterium necrophorum was the
predominant bacterial isolate from liver
abscesses of feedlot cattle fed with or without
tylosin. The major difference in the bacterial
flora of liver abscesses between cattle groups
was the higher incidence of Actinomyces
pyogenes in the tylosin-fed cattle. Because the
minimum inhibitory concentration of tylosin
was not different between bacterial isolates
from cattle in the two treatments, we concluded
that continuous feeding of tylosin does not
induce resistance. The source of A. pyogenes
infection and significance of A. pyogenes
interaction with F. necrophorum in tylosin-fed
cattle are not known.
