Streptococcus hillyeri isolated from septic pleuritis in a horse

Here we report the isolation of Streptococcus hillyeri from a thoracic sample from a horse. A 17-y-old Hungarian Sport Horse mare was referred to the equine clinic of the University of Veterinary Medicine Budapest, Hungary, with suspected pleuritis. Upon arrival, the horse was febrile and had tachycardia, severe inspiratory dyspnea, and tachypnea. Thoracic ultrasonography revealed severe bilateral pleural effusion, and a large area of lung consolidation. After sampling of both hemithoraces, 66 L of turbid exudate were drained. Based on these findings, a tentative diagnosis of septic pleuritis was made, and the horse was immediately started on a course of broad-spectrum antibiotics, a NSAID, an anticoagulant, and intravenous fluids. Despite intensive care, the clinical parameters deteriorated, and the horse was euthanized 6 d later. Cytology confirmed septic pleuritis, with short chains or groups of coccoid bacteria. Anaerobic culture yielded gram-positive cocci from both hemithoraces in almost pure culture, which we identified as S. hillyeri by 16S rDNA and whole-genome analysis. Additionally, we identified 4 previously unassigned Streptococcus sp. sequences as S. hillyeri. Of these, 3 were obtained from aborted equine fetuses and a fourth from a donkey mastitis case, supporting the pathogenic nature of S. hillyeri in these host species.