Characterization of a bacterial strain Lactobacillus paracasei LP10266 recovered from an endocarditis patient in Shandong, China

Qi Tang,Yingying Hao,Xiaoben Wu,Chao Lu,Lu Wang,Zaifeng Si,Ming Li,Zhiming Lu

doi:10.1186/s12866-021-02253-8

Abstract

BackgroundLactobacilli are often recognized as beneficial partners in human microbial environments. However, lactobacilli also cause diseases in human, e.g. infective endocarditis (IE), septicaemia, rheumatic vascular disease, and dental caries. Therefore, the identification of potential pathogenic traits associated with lactobacilli will facilitate the prevention and treatment of the diseases caused by lactobacilli. Herein, we investigated the genomic traits and pathogenic potential of a novel bacterial strain Lactobacillus paracasei LP10266 which has caused a case of IE. We isolated L. paracasei LP10266 from an IE patient’s blood to perform high-throughput sequencing and compared the genome of strain LP10266 with those of closely related lactobacilli to determine genes associated with its infectivity. We performed the antimicrobial susceptibility testing on strain LP10266. We assessed its virulence by mouse lethality and serum bactericidal assays as well as its serum complement- and platelet-activating ability. The biofilm formation and adherence of strain LP10266 were also studied.ResultsPhylogenetic analysis revealed that strain LP10266 was allied with L. casei and L. paracasei. Genomic studies revealed two spaCBA pilus clusters and one novel exopolysaccharides (EPS) cluster in strain LP10266, which was sensitive to ampicillin, penicillin, levofloxacin, and imipenem, but resistant to cefuroxime, cefazolin, cefotaxime, meropenem, and vancomycin. Strain LP10266 was nonfatal and sensitive to serum, capable of activating complement 3a and terminal complement complex C5b-9 (TCC). Strain LP10266 could not induce platelet aggregation but displayed a stronger biofilm formation ability and adherence to human vascular endothelial cells (HUVECs) compared to the standard control strain L. paracasei ATCC25302.ConclusionThe genome of a novel bacterial strain L. paracasei LP10266 was sequenced. Our results based on various types of assays consistently revealed that L. paracasei LP10266 was a potential pathogen to patients with a history of cardiac disease and inguinal hernia repair. Strain LP10266 showed strong biofilm formation ability and adherence, enhancing the awareness of L. paracasei infections.

Highlights

Lactobacilli are often recognized as beneficial partners in human microbial environments
Strain LP10266 was a conditional pathogen to patients with a history of cardiac disease and inguinal hernia repair
The present study reported a rare case of infective endocarditis caused by a novel bacterial strain of L. paracasei LP10266

Summary

Introduction

Lactobacilli are often recognized as beneficial partners in human microbial environments. Lactobacilli are Gram-positive, microaerophilic, or facultatively anaerobic, non-spore-forming rods [1] They form a part of the normal human microbiota of the oral, gastrointestinal, and female genital tracts [2, 3]. An increasing number of studies have reported clinical infections caused by lactobacilli, including peritonitis, bacteraemia, and endocarditis [8,9,10]. These infections are attributable to defective host defense mechanisms and severe underlying diseases. Bacterial biofilm formation [14] and adhesion to human vascular endothelial cells (HUVECs) [15] are potential pathogenic traits for the progression of infective endocarditis (IE)

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