Abstract
The viridans group streptococci comprise multiple species and have gained more recognition in recent years as common etiologic agents of bacterial endophthalmitis. The purpose of this study was to identify the species of human endophthalmitis isolates of viridans streptococci and to characterize their potential virulence attributes. The species of 22 endophthalmitis strains of viridans streptococci were identified by Matrix Assisted Laser Desorption Ionization Time-of-Flight. Susceptibilities to 3 antibiotics commonly used for bacterial endophthalmitis were determined. The extracellular milieu of each strain was tested for cytotoxicity of retinal pigmented epithelial cells, hemolysis of sheep erythrocytes, and protease activity using gelatin zymography. Identified species were Streptococcus mitis/oralis, S. salivarius, S. vestibularis, S. parasanguinis, S. mutans, S. constellatus, and S. gordonii. One strain of S. pseudoporcinus was also identified. All strains were sensitive to vancomycin, 77% were resistant to amikacin, and 27% had intermediate resistance to ceftazidime. Extracellular milieu from all strains except one (S. pseudoporcinus) were largely devoid of toxicity to retinal pigmented epithelial cells and sheep erythrocytes. Twelve strains, 10 of which were S. mitis/oralis, produced protease activity. Interestingly, not all of the S. mitis/oralis strains were proteolytic. These findings highlight the diversity of virulence factor production in ocular strains of the viridans streptococci not only at the group level but also at the species level.
Highlights
The term “viridans group streptococci (VGS)” is often used to describe a large group of Streptococcus species that historically did not fit into the Lancefield typing scheme
Twenty-one strains were identified by MALDI-TOF and one strain (E618) was identified by biochemical characteristics (Table 1)
The remainder of the strains were species commonly located in the oral cavity, with the exception of E618, which was identified as S. pseudoporcinus
Summary
The term “viridans group streptococci (VGS)” is often used to describe a large group of Streptococcus species that historically did not fit into the Lancefield typing scheme. The VGS have been identified as mostly exhibiting alphahemolysis on blood agar similar to Streptococcus pneumoniae, but having resistance to optochin and insolubility in bile salts which are opposite characteristics of S. pneumoniae. Further complicating classification is the reactivity of some species to Lancefield sera. This overarching collection of VGS is divided into 5 major groups (mitis, anginosus, sanguinis, salivarius, and mutans) each consisting of multiple different species [2]. Many species from these groups are commensals of the human oral cavity
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