Development of a new in situ hybridization method for the detection of global bacterial DNA to provide early evidence of a bacterial infection in spontaneous bacterial peritonitis

Abstract

Despite the importance of identifying the causative pathogen(s), ascitic fluid cultures are occasionally negative in patients with spontaneous bacterial peritonitis (SBP). A novel strategy using the in situ hybridization (ISH) method was introduced to detect the bacterial genomic DNA phagocytized in the blood of patients with sepsis. In the present study, we developed a new ISH probe to detect global bacterial DNA (named as GB probe) and evaluated its utility for detecting the phagocytized bacterial DNA in SBP ascites. Hybridization of bacterial DNA with the GB probe was examined by dot-blot and ISH tests. In addition, the utility of the ISH method to detect the bacterial DNA in the leukocytes of SBP ascites was evaluated. The GB probe hybridized with the genomic DNA of all 59 bacterial strains tested (59 species of 36 genus). Eleven of 51 patients with ascites (out of total 542 cirrhotic inpatients) were categorized as SBP. The ISH tests showed positive results in 10 of 11 SBP cases. However, the ISH tests all showed negative results in the 40 non-SBP ascitic samples. Therefore, the ISH tests yielded highly sensitive and specific results for detecting the phagocytized bacterial DNA in the leukocytes of SBP ascites. Moreover, all of the ISH test results were obtained within only one day. Our newly established ISH method was found to provide both a rapid and sensitive detection of bacterial DNA in SBP ascites, thus suggesting its utility for providing early and direct evidence of bacterial infection in SBP ascites.