Fluorescence in Situ Hybridization for Visualization and Identification of Microorganisms in Endocarditic Heart Valve Tissue Improves Diagnosis of Endocarditis

Objectives: In infective endocarditis (IE) early diagnosis of the causative microorganism (MO) and consecutive treatment is crucial for patient survival. While during valve surgery the macroscopic aspect resembles an infected heart valve, standard diagnostic tests often fail to pick up the causative MO, resulting in inadequate postsurgical treatment. Fluorescence in situ hybridization (FISH) is a molecular, culture-independent technique, which allows identification and visualization of MO within tissue, also providing information of morphology, number and activity. It is able to detect fastidious or yet-uncultured organisms, thus identifying pathogens in culture-negative IE.

Methods: From 09/2015 to 09/2017, ninety-three patients with suspected/diagnosed IE were referred to our institution for valve surgery. Patients were assigned into 3 groups, namely, definite (n = 39), possible (n = 29) or rejected (n = 25) IE, according to the modified Duke criteria. Clinical data including blood culture and antibiotic treatment pre-surgically were collected from all patients. Surgical valve tissue specimen were send for PCR and FISH/PCR analysis in addition to standard diagnostic tests. All obtained results were correlated to the Duke IE groups.

Results: Blood culture prior to antibiotic treatment detected MO in 35/39 definite, 19/29 possible and 2/25 rejected IE cases. Culture of valve tissue detected bacteria in 9/39 definite, 8/29 possible and 4/25 rejected IE only. All definite and possible as well as 11 rejected IE patients received antibiotics pre-surgically. FISH/PCR was able to detect MO in 36/39 definite, with 13 cases of highly active IE despite treatment including 2 cases of highly active IE solely detected by FISH and PCR. FISH/PCR detected MO in 23/29 possible IE with 8 cases of highly acute IE despite treatment and MO in 19/25 rejected IE cases, with the remaining 6 cases showing no signs of IE in any of the performed testing. PCR alone detected bacteria in 30/39 definite, 16/29 possible and 4/25 rejected IE.

Conclusion: Due to the combination of histopathologic visualization and molecular detection, FISH/PCR proved to be the most sensitive diagnostic technique to identify the causative agent in IE. We believe this makes it a valuable diagnostic tool especially in culture-negative IE alongside with standard diagnostic tests.

No conflict of interest has been declared by the author(s).