Bacteriologic analyses of bile and brown pigment stones in patients with acute cholangitis

Background. Bacteria play an important role in the formation of brown pigme nt stones through adherence and biofilm formation. Scanning electron micros copy of cross sections of these stones reveals a laminated appearance and v arious bacteria in the different layers. Our postulation was that different bacteria might be involved at different stages of stone formation. Methods: By using standard bacteriologic cultures, the composition, morphol ogy, and antibiotic sensitivity patterns of bacteria isolated from paired s tone were compared with bile samples from 70 patients with acute cholangiti s. A further comparison was made between bacteria isolated from the periphe ry and center of 3 randomly selected brown pigment stones. Results: Ninety-one percent of bile and 99% of stone samples yielded positi ve cultures, with a total of 151 and 149 bacteria isolated from bile and st ones, respectively. In 22 patients (33%), the bacteria isolated from the pa ired bile and stone samples were totally different. The mean percentage sim ilarity of bacteria isolated from bile and stones was 39% (range 0%-100%). Of the 59 pairs of similar bacteria isolated, the antibiotic sensitivity pa tterns were different in 24 (41%) cases. Of the 3 brown stones studied, eit her different bacterial species or the same bacteria but different strains with different antibiotic sensitivities were isolated from the center and p eriphery of the stones. Conclusions: Bacteria present in the different layers of brown pigment ston es may represent the bacterial flora in bile at different times. Simple bil e culture may not identify bacteria trapped inside the stone.