Genotypic Differences Among Bacillus cereus Ocular and Gastrointestinal Isolates and the Relationship to Endophthalmitis Pathogenesis

Abstract

Purpose : To test the hypothesis that clinical ocular and gastrointestinal Bacillus cereus (BC) isolates differ in terms of genotype and endophthalmitis virulence.

Methods : Twenty-nine BC isolates were used in this study, including: ATCC 14579 and 2 other laboratory isolates, clinical ocular isolates (7 post-traumatic endophthalmitis, 1 endogenous endophthalmitis, 2 keratitis, 3 blepharitis, 3 cataract lens) and clinical gastrointestinal isolates (5 diarrheal, 3 emetic, 1 atoxic, and 1 unspecified). In vitro hemolysis assays were performed to assess the difference in hemolytic activity among the strains. Virulence factor profiling of each strain was completed using polymerase chain reaction (PCR) with primers specific for common BC virulence genes including multiple toxins, gene regulators, metalloproteases, and superoxide dismutase. A murine model of BC endophthalmitis was used to assess differences in retinal function retention measured by electroretinography and intraocular bacterial counts among the different isolate origins.

Results : BC isolates from clinical ocular infections had a higher rate of PCR positivity for the virulence genes examined in this study (92% cumulative PCR positivity of all genes) compared to the GI isolates (72% PCR positivity). However, hemolytic activity against rabbit erythrocytes between ocular and gastrointestinal BC isolates was similar (p = 0.9989). In the murine experimental endophthalmitis model, while growth of the GI isolates was significantly lower than a commonly used laboratory strain of BC (ATCC14579) (p ≤ 0.0303), no difference in retinal function retention among laboratory, ocular, and GI isolates was observed at 8 hours postinfection (p ≥ 0.1175).

Conclusions : Though ocular isolates tested in this study were PCR-positive for a higher percentage of important virulence genes compared to GI isolates, ocular and GI isolates were similar in their ability to cause severe endophthalmitis.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.