The role of bacteria in gallbladder and common duct stone formation

Debate continues as to the role that bacteria play in gallstone pathogenesis in Western countries. We therefore, examined gallbladder and common duct stones from 67 consecutive patients undergoing cholecystectomy and/or common bile duct exploration. Bile was cultured and stone cholesterol content was measured. Stones were examined by scanning electron microscopy (SEM) for bacteria. Individual calcium salts were classified by windowless energy-dispersive x-ray microanalysis. Gallbladder stones in 65 patients were identified as cholesterol in 46 (71%), black pigment in 17 (26%), and brown pigment in 2 patients (3%). Common bile duct stones from ten patients were cholesterol in 4, black pigment in 2, and brown pigment in 4 patients. The five patients with brown pigment stones were significantly (p less than 0.05) older, more likely to be men and to present with bile duct obstruction. Bile cultures were positive in 13% of patients with cholesterol stones, in 14% of those with black pigment stones, and in all of the patients with brown pigment stones (p less than 0.001). By SEM, bacteria were observed only within the calcium bilirubinate-protein matrix of brown pigment stones (p less than 0.001). In comparison to black pigment stones, brown stones were more likely to contain calcium palmitate (p less than 0.005) and cholesterol (p less than 0.001). We conclude that black and brown pigment stones have different pathogenic mechanisms and that bacterial infection is important only in the formation of brown pigment stones.