Streptococcus gallolyticus and Bacterial Endocarditis in Swine, United States, 2015-2020

Abstract

To evaluate trends in bacterial causes of valvular endocarditis in swine, we retrospectively analyzed 321 cases diagnosed at Iowa State University Veterinary Diagnostic Laboratory (Ames, IA, USA) during May 2015--April 2020. Streptococcus gallolyticus was the causative agent for 7.59% of cases. This emerging infection in swine could aid study of endocarditis in humans.

Keywords: Streptococcus bovis; Streptococcus gallolyticus; United States; bacteria; bacterial endocarditis; swine.

Figure 1

Five selected Streptococcus gallolyticus isolates from swine vegetative valvular lesions (2019018903, 2020037125, 2020062826, 2020064948, and 2020066722) characterized as S. gallolyticus subspecies pasteurianus on the basis of reference 16S ribosomal RNA sequences. Samples were collected in the United States during 2015–2020. Scale bar indicates nucleotide substitutions/site.

Figure 2

Lesions associated with swine vegetative endocarditis, United States, 2015–2020. A) Macroscopic findings of vegetative growth on the left atrioventricular heart valve leaflets. B) Histopathologic findings of inflammation characterized by necrotic leukocytes (N), fibrin (F), mineralization (M), and myriad bacterial colonization (yellow outline) along the surface of the heart valve (hematoxylin and eosin staining); original magnification ×40. Higher magnification image (inset) shows cocci bacteria in clusters and long chains; original magnification ×1,000. C) Streptococcus gallolyticus directly detected (red) on the surface of the heart valve by RNA in situ hybridization with a probe targeting the helix-hairpin helix domain–containing protein, ComEC/Rec2, and DNA pol III subunit delta genes specific to S. gallolyticus; original magnification ×40. Higher magnification image (inset) shows the bacteria labeled by the in situ hybridization probe; original magnification ×1,000.