Liver abscess bacterial pathogens in healthy liver tissues, normal tissues of abscessed livers, and corresponding ruminal epithelial tissues of beef-on-dairy cattle*

Objective

Our objective was to determine the prevalence of Fusobacterium necrophorum ssp. necrophorum and ssp. funduliforme, Trueperella pyogenes, Salmonella enterica, and Escherichia coli and quantify F. necrophorum in parenchymal tissues of healthy livers and abscessed livers and ruminal epithelial tissues of beef-on-dairy cattle.

Materials and Methods

Samples, collected at slaughter, included 107 healthy livers and 110 abscessed livers, and 101 matched ruminal tissues each from cattle with healthy or abscessed livers. Culture methods to isolate the bacterial species and quantitative PCR to determine prevalence and concentrations of F. necrophorum were used. Statistical analyses included Fisher’s exact test for prevalence and ANOVA for bacterial concentration comparisons.

Results and Discussion

Culture and quantitative PCR data indicated prevalence of the 4 species of pathogens and E. coli in tissues of healthy livers and abscessed livers. The prevalences of the 2 subspecies were greater in ruminal than liver tissues. Fusobacterium necrophorum ssp. funduliforme was the dominant subspecies in both tissues, likely because it is the most prevalent subspecies in ruminal contents of cattle. Only one healthy liver yielded T. pyogenes. Both tissue types yielded S. enterica, and the dominant serotype was Montevideo. The prevalence of E. coli, an indicator of bacterial flow from the gut, ranged from 55% to 100%. Approximately, 8% of the liver tissues had quantifiable concentrations of F. necrophorum. More ruminal tissues from cattle with abscessed livers (76%) had quantifiable concentrations of the 2 subspecies than those from cattle with healthy livers (57.4%). Our data suggest that healthy livers harbor pathogens and ruminal tissues serve as a reservoir of pathogens that enter the portal blood.

Implications and Applications

Tissue-embedded pathogens exist in healthy livers, normal regions of abscessed livers, and ruminal epithelium of cattle. There is likely a threshold of concentration required to initiate abscess development, and delineating factors that trigger this process may aid in novel intervention strategies.