Bacterial DNA in non-leukocytic ascites, identification of risk factors

Background: As culture-dependent bacterial identification methods are still limited to capture colonisation or infection of ascites fluid we established a culture-independent PCR-based method for the detection, quantification and differentiation of bacterial DNA (bactDNA). This report aims to characterize risk factors for bactDNA identification in non-leukocytic ascites fluid (nlAF) and for progression to SBP.

Methods: 299 nlAF samples of 142 patients were collected between 02/2011 and 12/2012. BactDNA was detected using real-time PCR with primers targeting the 16S-rRNA-gene and differentiated by direct sequencing. Genetic polymorphisms (SNP) of receptors recognising bacterial components such as TLR subtypes, CD14, NOD2 and MBL2 were identified by detecting and amplifying corresponding genes. Patients' characteristics like liver function and underlying disease were correlated with PCR-results.

Results: BactDNA was detected in 37% of nlAF after index-paracentesis. Risk of bactDNA detection was associated with variants of TLR2-SNP rs5743708 (G(wildtype)/A, OR 0.241, p = 0.054) and TLR6-SNP rs5743810 (C(wildtype)/T, OR 2.241, p = 0.030). An association with median bactDNA quantity was observed for the variants of TLR1-SNPs rs4833095 (T(wildtype)/C, p = 0.016), and rs5743618, G(wildtype)/T, p = 0.021). After detection of bactDNA in nlAF 40.7% did not develop SBP (group1), 59.3% proceeded to SBP or received antibiotics (group2). Group2 was characterized by a lower prothrombin time and increased CRP level but no significant association was found regarding SNPs and bactDNA quantity.

Conclusion: These results emphasise that the susceptibility to bacterial colonisation or ascites infection in patients with cirrhosis might be genetically determined. However, further risk factors and mechanisms favouring the progression from colonisation to overt SBP still have to be clarified.