Bacteriological and electron microscopy examination of brown pigment stones.

Bacteriological and morphological studies of 38 brown pigment common duct stones were performed. Stone cultures were positive for bacteria in 80.5% of those studied. Enterococci were the most common organisms that were isolated. Scanning electron microscopy showed the presence of bacteria in 84.2% of the stones. The bacteria were seen embedded within an amorphous matrix in alternating layers of flakelike crystals. Transmission electron microscopy showed the presence of gram-positive and gram-negative bacteria surrounded by a ruthenium red-stained exopolysaccharide material. Results of the bacteriological and morphological studies confirmed the close relationship between the presence of bacteria and the development of brown pigment stones.