Background: Bacteria are traditionally accorded a role in the formation of brown but not black pigment gallstones. Black pigment stones are thought to be the predominant pigment stone in western populations. We previously reported that most pigment stones contain bacteria, detectable by culture or scanning electron microscopy (SEM). This study examined in a large western population the incidence of infected pigment stones, and their chemical and bacterial composition.
Methods: 382 gallstones were prospectively obtained under aseptic conditions, 178 were pigment stones (from 159 patients). Pigment stones were classified as follows: Black - jet black stones, Brown - brown, or brown and black stones. Bacteria were detected using SEM (125 stones) and gallstone culture (108 stones). Chemical composition was determined with IR spectroscopy (84 stones).
Results: 72% of 178 stones contained bacteria. Bacteria were present in 19% of 58 black pigment stones and 98% of 120 brown pigment stones (p<0.0001, Chi-square). Of stones confined to the gallbladder (GB), 50% contained bacteria, 60% of which were black. Of stones located in both the GB and CBD, 89% contained bacteria, of which 85% of were brown. All primary CBD stones were brown and contained bacteria. Ca-bilirubinate was present in all pigment stones. 98% of stones containing Ca-palmitate possessed bacteria and 96% of these were brown. Of stones containing Ca-carbonate, 50% contained bacteria, and 79% were black. Composition alone, however, could not predict bacterial presence or stone character (brown or black). Pure Ca-bilirubinate stones could be black or brown, and 68% contained bacteria. 92% of bacteria recovered from pigment stones and produced slime and 70%% produced beta-glucuronidase. There were no differences in the incidence of bacterial slime and beta-Glucuronidase production of bacteria from brown or black stones (p=0.965 and p=0.87, respectively, Chi-squared).
Conclusions: Most (72%) pigment stones contained bacteria. And, the majority of pigment stones were brown, not black. Mineral composition correlated with the presence of bacteria, but was not always predictive. Pigment CBD stones usually contained bacteria, but black stones and stones confined to the gallbladder also contained bacteria in many cases. These data suggest that bacteria play an integral role in the pathogenesis of pigment gallstones in a typical U.S. population.