Bacterial Communities Identified by Standard Culture and 16S rRNA Amplicon Sequencing in Ophthalmic Preservative‐Free Dexamethasone SP Used in Canine Cataract Surgery

OBJECTIVE: To assess different lots and brands of sterile preservative-free dexamethasone sodium phosphate (dexamethasone SP) for evidence of bacterial contamination via culture-dependent and independent methods, and quantify endotoxin. Broadly, the objective is to further investigate potential causes for fibrin web (FW) development after canine cataract surgery. PROCEDURES: Five samples from two lots of three brands of dexamethasone SP (30 samples total) and reagent controls were collected. All samples underwent conventional aerobic and capnophilic bacterial culture, as well as kinetic chromogenic endotoxin quantification. Deoxyribonucleic acid (DNA) extraction, 16S ribosomal ribonucleic acid (rRNA) sequencing, sequence analysis, and classification were performed on all samples. Statistical analysis assessed DNA concentration, α and β diversity, and sample biomarkers. RESULTS: Bacterial cultures were positive in 0/10 Auromedics, 1/10 Fresenius Kabi, and 4/10 Somerset Pharma LLC dexamethasone SP samples. The bacteria identified (Bacillus thuringiensis, Staphylococcus epidermidis, and Staphylococcus oralis) were likely present due to contaminants during plating. Endotoxin quantification was below the limit of detection of the assay (0.5 EU/mL). There were no statistically significant differences in α or β diversity between brands. Differential abundance testing found Lactococcus and Acetitomaculum as genus-level biomarkers for the Auromedics brand and Solobacterium for the Somerset brand of dexamethasone SP. The most common bacterial families recovered were Bacillaceae, Clostridiaceae, Enterobacteriaceae, Lachnospiraceae, Lactobacillaceae, Muribaculaceae, Propionilbacteriaceae, Staphylococcaeae, and Xanthobacteraceae. CONCLUSIONS: There were no significant dexamethasone SP brand-specific differences. Endotoxin was below the limit of detection of the assay.