A hemolysin-encoding plasmid contributes to bacterial virulence in experimental Enterococcus faecalis endophthalmitis

Area of Science:

• Ophthalmology
• Microbiology
• Infectious Diseases

Background:

• Beta-hemolysin production is a variable trait in Enterococcus faecalis, a Lancefield group D streptococcus.
• The hemolysin in E. faecalis is encoded by large, transmissible plasmids, suggesting a potential role in virulence.

Purpose of the Study:

• To investigate the contribution of the hemolysin-encoding plasmid to the severity of experimental endophthalmitis.
• To compare isogenic E. faecalis strains with and without the hemolysin plasmid in a rabbit model.

Main Methods:

• Induction of experimental endophthalmitis in rabbits using varying concentrations of E. faecalis strains.
• Comparison of disease severity between strains harboring the hemolysin-encoding plasmid and plasmid-free strains.
• Assessment of retinal function using electroretinography (ERG) and clinical examination (indirect ophthalmoscopy, slit-lamp examination).

Main Results:

• Infections with hemolysin-producing E. faecalis led to a 98% loss of retinal function by day 3.
• Plasmid-free E. faecalis infections resulted in retained retinal function (23% by ERG) and a visible red reflex.
• Microscopy and ophthalmoscopy confirmed a more aggressive endophthalmitis with hemolysin-encoding plasmid-containing strains.

Conclusions:

• The hemolysin-encoding plasmid significantly enhances the virulence of E. faecalis in experimental endophthalmitis.
• This study establishes a novel endophthalmitis model for evaluating bacterial virulence using isogenic strains.
• The findings highlight the role of plasmid-mediated factors in bacterial pathogenesis of ocular infections.