First report of isolation of Fusobacterium varium from liver abscesses and ruminal and colonic epithelial tissues of feedlot cattle*

Objective

Our objective was to isolate and determine prevalence of Fusobacterium varium in liver abscesses and the corresponding ruminal and colonic epithelial tissues and ruminal and colonic contents of feedlot cattle.

Materials and Methods

A total of 96 intact liver abscess samples and matched ruminal and colonic tissues and contents from cattle, originating from feedlots that did not receive in-feed tylosin, were collected at slaughter. Liver abscesses and ruminal and colonic tissue were ho- mogenized and then plated, before and after enrichment in lactate or lysine medium with selective antibiotics, onto blood agar and selective lactate or lysine agar for isolation of Fusobacterium and to determine prevalence and concentration. Putative colonies were tested by a quantitative PCR assay targeting the hgdA gene for species confirma- tion.

Results and Discussion

None of the liver abscess samples yielded F. varium by direct plating; however, F. varium was isolated from 3 of 96 (3.1%) following enrich- ment of the homogenate in lactate or lysine medium. In contrast to liver abscesses, F. varium was isolated by direct plating from 27.1% (26/96) of ruminal epithelial and 3.1% (3/96) of colonic epithelial tissue homogenates. Overall, 10.1%, 77.1%, 44.8%, 86.5%, and 70.1% of liver abscess, ruminal, and colonic epithelial tissues and ruminal and colonic contents were positive for F. varium, respectively.

Implications and Applications

The increased fre- quency of isolation and high prevalence of F. varium in ruminal tissue and, to a lesser extent, in the colonic tissue confirms its ability to invade tissues and possibly cause bacterial ruminitis. However, the relatively low frequency of F. varium isolation and low prevalence in liver abscesses suggest that it is unlikely to be an etiologic agent. Inter- estingly, there is some evidence that ruminal strains of F. varium were resistant to tylosin; therefore, it would be of interest to determine the prevalence in cattle receiving in-feed tylosin.