Aerococcus urinae - A potent biofilm builder in endocarditis.

Berrin Yaban,Judith Kikhney,Julia Schmidt,Annette Moter,Volkmar Falk,Annett Petrich,Michele Musci,Felix Schoenrath,Maria Hajduczenia,Cécile Oury

doi:10.1371/journal.pone.0231827

Abstract

The diagnosis of infective endocarditis (IE) remains a challenge. One of the rare bacterial species recently associated with biofilms and negative cultures in infective endocarditis is Aerococcus urinae. Whether the low number of reported cases might be due to lack of awareness and misidentification, mainly as streptococci, is currently being discussed. To verify the relevance and biofilm potential of Aerococcus in endocarditis, we used fluorescence in situ hybridization to visualize the microorganisms within the heart valve tissue. We designed and optimized a specific FISH probe (AURI) for in situ visualization and identification of A. urinae in sections of heart valves from two IE patients whose 16S rRNA gene sequencing had deteced A. urinae. Both patients had a history of urinary tract infections. FISH visualized impressive in vivo grown biofilms in IE, thus confirming the potential of A. urinae as a biofilm pathogen. In both cases, FISH/PCR was the only method to unequivocally identify A. urinae as the only causative pathogen for IE. The specific FISH assay for A. urinae is now available for further application in research and diagnostics. A. urinae should be considered in endocarditis patients with a history of urinary tract infections. These findings support the biofilm potential of A. urinae as a virulence factor and are meant to raise the awareness of this pathogen.

Highlights

Infective endocarditis (IE) is a life-threatening infection of the endocardium and is associated with high morbidity and mortality [1]
The patient had an uneventful postoperative course. Both heart valves were embedded and analyzed by fluorescence in situ hybridization (FISH) using the pan-bacterial probe EUB338 in order to screen for bacterial colonization including yet uncultivated or fastidious bacterial species
We found extensive areas with bacterial colonization and formation of Aerococcus urinae biofilms in endocarditis microorganisms resembling structured biofilms, which were in part FISH-positive

Summary

Introduction

Infective endocarditis (IE) is a life-threatening infection of the endocardium and is associated with high morbidity and mortality [1]. Culture-negative endocarditis, where the causative pathogens remain elusive in the routine microbiological diagnostic work-up, represents a serious risk for the patient. Culture-negative results in routine microbiology diagnostics may be caused by biofilm growth of bacteria, prior antibiotic treatment of the patient, or by fastidious or slow-growing bacteria [3]. In recent years molecular biological methods such as nucleic acid amplification techniques (NAT) and fluorescence in situ hybridization (FISH) have helped detect microorganisms that might otherwise be missed by routine culture methods [4]. The direct detection of microorganisms in valve specimens by FISH enables the simultaneous visualization and identification of the causative agent in situ, in culture-negative cases [5]. One of the rare bacterial species recently associated with culture-negative IE is Aerococcus urinae (A urinae) [6,7,8,9,10]

Methods

Results

Conclusion