Detection of Coxiella burnetii in heart valve sections by fluorescence in situ hybridization

Purpose. Infective endocarditis is a severe and potentially fatal disease. Nearly a third of all cases remain culture-negative, making a targeted and effective antibiotic therapy of patients challenging. In the past years, fluorescence in situ hybridization (FISH) has proven its value for the diagnosis of infective endocarditis, particularly when it is caused by fastidious bacteria. To increase the number of infective endocarditis causing agents, which can be identified by FISH, we designed and optimized a FISH-probe for the specific detection of Coxiella burnetii in heart valve tissue. Methodology. Even with specific probes the detection and identification of bacteria can be complicated by the high autofluorescence due to calcification of the analysed tissue. To overcome this problem, we developed a protocol to detect C. burnetii by hybridizing, stripping and reprobing the identical section with different species-specific probes repeatedly. Results/Key findings. The newly designed specific FISH probe and the developed protocol exemplarily allowed us to unequivocally identify C. burnetii in tissue sections of a patient with infective endocarditis. Conclusion. This method provides an add-on to existing protocols for the unambiguous diagnosis of bacteria directly within tissues or other difficult tissue samples in cases with small sample size and limited sections.