BACKGROUND: Few studies have assessed microflora and their antibiotic sensitivity in normal bile and lithogenic bile with different types of gallstones. 
METHODS: We performed a case control study of 70 bile samples (35 cholesterol and 35 pigment stones from 51 females and 19 males, aged 21-72 years with a median age of 37 years) from patients who underwent laparoscopic cholecystectomy for uncomplicated cholelithiasis, and 20 controls (14 females and 6 males, aged 33-70 years with a median age of 38 years) who underwent laparotomy and had no gallbladder stone shown by ultrasound scan. The bile samples were aerobically cultured to assess microflora and their antibiotic susceptibility. The procedures were undertaken under sterile conditions. 
RESULTS: Thirty-eight (54%) of the 70 patients with gallstones had bacterial isolates. Nine isolates (26%) were from cholesterol stone-containing bile and 29 isolates (82%) from pigment stone-containing bile (P=0.01, t test). Twenty-eight of these 38 (74%) bile samples were shown positive only after enrichment in brain heart infusion medium (BHI) (P=0.02, t test). The overall bacterial isolates from bile samples revealed E. coli predominantly, followed by P. aeruginosa, Enterococcus spp., Klebsiella spp. and S. epidermidis. There were no bacterial isolates in the bile of controls after either direct inoculation or enrichment in BHI. 
CONCLUSIONS: Bacterial isolates were found in pigment stone-containing bile. Non-lithogenic bile revealed no bacteria, showing an association between gallstone formation and the presence of bacteria in bile. Antibiotic sensitivity patterns of isolated organisms were similar irrespective of the type of stone.