Detection of bacterial DNA in cholesterol gall stones

Abstract

Introduction: Recently, bacterial infection has been shown to play an important role in the formation of cholesterol gallbladder stones. This led us to investigate the presence of bacterial structures in cholesterol gallstones by means of bacterial culture and DNA detection. Method: Gallstones were obtained from 31 consecutive patients operated from May 2005 to October 2006 in the department. Culture study was done using standard bacteriological methods. Cholesterol was estimated by spectrophotometry and stones were divided into cholesterol stones (>70% cholesterol) and mixed/pigment stones (<70% cholesterol). DNA for organisms was extracted from the core of the stone and confirmed by agarose gel electrophoresis. Sterile stones were subjected to PCR amplification. Results: Age of patients ranged from 27 to 66 years (mean = 46.58 years); 14/31 stones were pure cholesterol stones (45%), and 17 (55%) were mixed and pigment stones. On culture, 12 stones (39%) were sterile, while 19 (61%) showed presence of viable bacteria; amongst cholesterol stones, 11 out of 14 were sterile (79%), while only 1 (6%) out of 17 pigment and mixed stone was sterile. E.coli was the most common bacterium isolated (42%) followed by Pseudomonas and Salmonella. DNA extraction was positive in all 31 of the stone samples collected (100%). PCR amplification was positive in all the bacteriologically sterile stones. Discussion: All gallstones, including cholesterol stones, revealed bacterial DNA; suggesting that bacterial infection is associated even with cholesterol gallstones.