158 Fusobacterium Varium in Liver Abscesses, Ruminal and Colonic Contents and Tissues: Does It Have a Role in Liver abscesses?
Authors: Deters Alyssa K , Abbasi Mina , Shi Xiaorong , Mathieu Jacques , Nagaraja T G 
Published: November 2023

Abstract
Fusobacterium necrophorum, an anaerobic ruminal bacterium, is the primary causative agent of liver abscesses in cattle. Another species of Fusobacterium, i.e., varium, shares many morphological and biochemical similarities with F. necrophorum and is also a normal ruminal inhabitant. Fusobacterium varium is a known human and animal pathogen, isolated from a variety of necrotic infections, and in humans is implicated in ulcerative colitis. Previously, we determined F. varium prevalence and concentrations in ruminal contents of feedlot cattle with and without liver abscesses (63%, 2.1 x 104 CFU/ml and 49%, 2.7 x 104 CFU/ml, respectively) at slaughter. Therefore, it is of interest to assess involvement of F. varium in liver abscess formation. Our objectives were to determine prevalence and concentrations of F. varium in liver abscesses and corresponding ruminal and colonic contents and/or tissues. Liver abscesses (n = 144), ruminal contents (n = 98), ruminal epithelial tissues (n = 144), colonic contents (n = 98), and colonic epithelial tissues (n = 98), were collected from feedlot cattle at the time of slaughter. Ruminal and colonic (diluted 1:1 with sterile phosphate-buffered saline; PBS) content samples were strained through 4 layers of cheesecloth. Tissue samples were homogenized in sterile PBS. Homogenized tissue samples were plated onto blood agar and peptone-yeast agar containing lactate (100 mM; PY-La JVN) or lysine (100 mM; PY-Ly JVN) as a major carbon source and supplemented with josamycin, vancomycin, and norfloxacin. Inoculated plates were incubated anaerobically for 48 hours, putative colonies were picked and streaked on blood agar, and species was confirmed by a qPCR assay targeting the hgdA gene, which encodes for 2-hydroxyglutarylCoA dehydratase subunit alpha. Additionally, tissue homogenates were enriched in PY-la JVN and PY-Ly JVN broths and plated onto blood agar for F. varium isolation. DNA was extracted from tissue homogenates and from strained content samples, before and after enrichment in PY-La JVN and PY-Ly JVN for use in the qPCR assay for detection and quantification of F. varium. Based on qPCR, F. varium was prevalent in 19 of 144 (13%) liver abscess samples. Fusobacterium varium was also frequently detected in ruminal epithelial (88/144; 61%), and colonic epithelial (42/98; 43%) tissues. Additionally, the qPCR assay showed a high prevalence of F. varium in ruminal (83/98; 85%) and colonic (68/98; 70%) content samples. A total of 25 F. varium isolates were recovered from enriched liver abscesses (17%) and none from direct plating. In addition, F. varium was isolated from 91 ruminal epithelial samples (63%), with 37 from direct plating, and 30 colonic epithelial samples (30%), with 3 from direct plating. The prevalence of F. varium in ruminal and colonic tissues suggested invasive abilities of the species, and further research is needed to determine the potential role of F. varium as an etiologic agent in liver abscess pathogenesis.