THE INFLUENCE OF BILE ON AUTOLYSIS

Epithelial Inclusions in Gallbladder Specimens Mimic Parasite Infection: Histologic and Molecular Examination of Reported Cystoisospora belli Infection in Gallbladders of Immunocompetent Patients

Recent publications have described epithelial cytoplasmic vacuoles and inclusions incidentally noted within gallbladder epithelium and concluded that they represent coccidian parasite infection, in particular, Cystoisospora belli. We identified 8 gallbladder specimens from our institution in the past 3 years in which this diagnosis was suggested or in which similar epithelial alterations were prominent. Molecular analysis was performed on the 8 gallbladder specimens and on 3 positive control specimens: small bowel biopsies from acquired immunodeficiency syndrome patients with diarrhea. Polymerase chain reaction using primers designed to amplify an internal transcribed spacer (ITS2) in the C. belli ribosomal gene cluster was performed on the DNA samples. All 8 gallbladder specimens were negative for amplification, while a product consistent with C. belli was amplified from all 3 positive controls. Histologically, the gallbladder cytoplasmic inclusions stained diffusely positive for Grocott-Gomori's methenamine silver and Periodic acid-Schiff with diastase. In contrast, sections from a positive control small bowel biopsy demonstrated organisms that were negative for Grocott-Gomori's methenamine silver and showed a distinct capsular and punctate internal staining on Periodic acid-Schiff with diastase in various parasite forms. Together, the lack of molecular evidence of C. belli and the distinct morphologic and special staining patterns in these gallbladders compared with positive control small bowel suggest that these epithelial changes do not represent true C. belli infection. Our results suggest that gallbladders of immunocompetent patients may occasionally show epithelial changes that can morphologically mimic C. belli infection. Pathologists should be aware of this histologic variant to minimize unnecessary treatment, testing, and patient anxiety.

The novel Listeria monocytogenes bile sensor BrtA controls expression of the cholic acid efflux pump MdrT

Mammalian bile has potent anti-microbial activity, yet bacterial pathogens of the gastrointestinal tract and hepatobiliary system nonetheless persist and replicate within bile-rich environments. Listeria monocytogenes, a Gram-positive pathogen, encounters bile at three stages throughout its infectious cycle in vivo: in the gut during initial infection, in the liver where it replicates robustly and in the gallbladder, from which it can return to the intestine and thence to the environment. The mechanisms by which L. monocytogenes senses mammalian bile and counteracts its bactericidal effects are not fully understood. In this report, we have determined the L. monocytogenes bile-induced transcriptome, finding that many critical virulence factors are regulated by bile. Among these, the multidrug efflux pumps MdrM and MdrT, previously shown to be critical for the bacterial provocation of a pathogenesis-promoting host innate immune response, are robustly and specifically induced by the bile component cholic acid. This induction is mediated by BrtA, the first identified L. monocytogenes sensor of bile, which loses the ability to bind to and repress the mdrT promoter in the presence of cholic acid. We show that MdrT can export cholic acid, and that ΔmdrT bacteria are significantly attenuated both in vitro when exposed to cholic acid or bile, and in vivo in the gallbladders and livers of infected mice.