COMPARISON OF METHODS OF IDENTIFYING HELICOBACTER-HEPATICUS IN B6C3F(1) MICE USED IN A CARCINOGENESIS BIOASSAY

In a long-term rodent bioassay evaluating the carcinogenicity of triet hanolamine, there,cns equivocal evidence of carcinogenic activity in m ale B6C3F(1) mice, based on a marginal increase in the number of hepat ocellular adenomas and hepatoblastomas. Interpretation was complicated by the presence of Helicobacter hepaticus in selected silver-stained liver sections which also had histological evidence of karyomegaly and oval cell hyperplasia. An increase in numbers of liver tumors, as evi dence of carcinogenic activity, was also noted in female mice. However , H. hepaticus was not considered a complicating factor, because the l ivers of the female mice did not have histological features compatible with H. hepaticus infection, A retrospective analysis of 51 liver tis sue samples from the original carcinogenicity study was conducted to d etermine the incidence of H. hepaticus infection and to evaluate diffe rent diagnostic approaches for assessing the presence of H. hepaticus in livers lacking characteristic lesions. In an initial evaluation of seven mice with liver tumors, argyrophilic bacteria resembling H. hepa ticus were observed in liver sections, associated with characteristic liver lesions of hepatocytic karyomegaly and oval cell hyperplasia, Fr ozen liver tissue was available from four of these mice; all were conf irmed to be infected with H. hepaticus by culture and PCR, In a larger subsequent analysis using frozen liver tissues from 44 mice without c haracteristic hepatic lesions, H. hepaticus-specific DNA was amplified from the livers of 21 of 44 of the mice (47%), compared to 14 of 44 o f the mice (32%) having H. hepaticus cultured from their frozen liver tumors. The results of H. hepaticus culture and H. hepaticus-specific PCR concurred (i.e., both positive and negative results) in 84% of the cases. Microscopic detection of immunofluorescence-labeled or silver- stained bacteria in liver sections was relatively insensitive compared to either culture or PCR detection, This study confirms the widesprea d prevalence of H. hepaticus in mice, its potential to confound experi mental results, and the need to include diagnostic testing for H. hepa ticus in a murine health monitoring program.