Abstract
Purpose :
Alpha-hemolytic streptococci, especially viridans group streptococci (VGS), have been increasingly associated with endophthalmitis. The prevalence and diversity of toxins secreted by alpha-hemolytic streptococci are largely uncharacterized. The purpose of this study was to identify and characterize the toxicological profiles of recent alpha-hemolytic streptococci recovered from endophthalmitis.
Methods :
Twenty ocular streptococcal isolates recovered from endophthalmitis between January 10, 2019 and October 29, 2021 were included in this study. PCR and DNA sequencing were conducted to confirm genotype identification and screen for 3 toxins: autolysin, hyaluronidase, and pneumolysin. Isolates’ genotypes were compared to phenotypes generated using Vitek2 and/or API kits. E tests were used to confirm antibiotic susceptibility profiles for cefuroxime, vancomycin, levofloxacin, benzylpenicillin, and moxifloxacin.
Results :
Nineteen (95%) isolates were identified as members of the alpha-hemolytic group. Thirteen (68.4%) isolates of this group included members of the VGS group. S. mitis/oralis (n=8, 57.1%) was the most common isolate among VGS species. Other members included S. sanguinis (n=3), and 1 each of S. mutans, S. pseudopneumoniae, and S. thermophilus. S. pneumoniae (n=5) was the most common isolate among non-VGS group isolates. Streptococcus dysgalactiae was the sole non-alpha-hemolytic strain. Phenotype-genotype identification agreement was present among 15 (75%) of the 20 isolates.
At least one toxin was found among 9 (45%) isolates, with 5 (55.5%) identified as members of VGS. Hyaluronidase was identified in 5 (25%) samples, pneumolysin in 4 (20%) samples, and autolysin in 2 (10%) samples. Dual toxins (hyaluronidase, pneumolysin) were identified in a S. pneumoniae and S. mitis/oralis strain. No isolate was positive for all three toxins. In vitro susceptibility profiles included: vancomycin (100%, MIC90-1 mcg/mL), moxifloxacin (90%, MIC90-0.642 mcg/mL), levofloxacin (90%, MIC90-5 mcg/mL), cefuroxime (80%, MIC90-3.3 mcg/mL), and benzylpenicillin (75%, MIC90-0.492 mcg/mL).
Conclusions :
Definitive laboratory identification of alpha-hemolytic streptococci may be challenging. The high level of toxin production among endophthalmitis VGS isolates could contribute to their aggressive clinical course and poor patient outcomes.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.