DIFFERENCES IN OUTER-MEMBRANE CHARACTERISTICS BETWEEN GALLSTONE-ASSOCIATED BACTERIA AND NORMAL BACTERIAL-FLORA

Previous studies with scanning electron microscopy (SEM) have suggeste d that pigment gallstones contain bacteria. We set out to culture thes e bacteria and to study their membrane characteristics. We studied gal lstones from 54 patients (36 men, 18 women; mean age 55.4 years) admit ted consecutively to two hospitals for cholecystectomy. SEM detected b acteria in all of 14 brown pigment stones, 2 of 14 black pigment stone s, and in the pigmented centres of 9 of 19 mixed cholesterol stones; n o bacteria were detected in 14 pure cholesterol stones or within the c holesterol portions of mixed stones. We were able to culture bacteria from all gallstones with bacteria seen on SEM and for which sufficient material was available (n=16). 20 bacterial species were recovered fr om these stones. Gallstones containing bacteria were associated with c linical sepsis and cholangitis. All bacteria obtained from gallstones agglutinated human O P1 erythrocytes, which reflects the presence of P 1-specific fimbriae. 5 strains were positive for Forssman-antigen-spec ific fimbriae. None showed evidence of mannose-specific fimbriae. All of the organisms bound anti-Gal, a ubiquitous naturally occurring IgG specific for a-galactosyl residues. The presence of P1 fimbriae and al pha-galactosyl residues and the absence of mannose-specific fimbriae d istinguish these organisms from gut flora. We postulate that possessio n of these unusual properties may enhance the ability of bacteria to c olonise the biliary tree and initiate pigment gallstone formation.