Illustration of the Difficulty of Identifying Streptococcus equi Strains at the Subspecies Level through a Case of Endocarditis in an Immunocompetent Man

Abstract

dWe report a case of endocarditis caused by Streptococcus equi in an immunocompetent patient who was subsequently cured after appropriate antibiotherapy and cardiac surgery. However, it was challenging to identify the strain to the subspecies level, which highlights the necessity of developing reliable molecular tools to discriminate between the subspecies. CASE REPORT In January 2012, a 63-year-old man presented to the emergency room with a 2-week history of low-grade fever but without other symptoms and reported self-treatment with paracetamol. Past medical history included pituitary adenoma, which was treated by surgery in 1989, and a mechanical aortic valve replacement in December 2008 as treatment for severe aortic insufficiency.At admission, he had no fever (37.2°C), was under treatment with paracetamol, and had a pulse rate of 71/min. His blood pressure was 128/91 mm Hg, and oxygen saturation was 97% on air. An erythematous skin rash on his forehead extending to his right infraorbital area, which appeared a few hours before admission, was noted. No other skin lesions were apparent by physical examination. Cardiac auscultation was normal, and no signs of cardiac failure were found. Electrocardiogram revealed a second-degree atrioventricular block, while neurological, abdominal, and respiratory examinations were normal. The thoracic computed tomography scan was normal, transthoracic and transesophageal echocardiographies (TTE and TEE) did not show any vegetation or signs of endocarditis, and the mean transaortic valve gradient was close to 35 mm Hg without pathological regurgitation.Initial laboratory investigations revealed a leukocyte count of 10,100/mm 3 (75% neutrophils) (8,000 to 10,000/mm 3 ), the C-reactive protein concentration was 30 mg/liter (normal, Ͻ4 mg/liter), and his serum electrolyte assay results, troponin level, and international normalized ratio (INR) were normal. On the third day, pyrexia and confusion were observed. Blood cultures were performed daily, and cultures were incubated in a BacT/Alert automated system (Organon Teknika, bioMéri-eux). Aerobic and anaerobic bottles (eight out of nine sets) obtained during the febrile period were positive within 24 h, and Gram-positive coccus chain formation suggestive of Streptococcus was seen upon Gram staining.A subculture of the bacterium was obtained within 24 h of incubation on horse blood agar and on chocolate agar (bioMérieux, Marcy l'Etoile, France). The colonies were 0.5 to 1 mm in diameter, round, mucoid, glistening, nonpigmented, catalase negative, and beta-hemolytic. Gram staining demonstrated thin, short to medium-length, Gram-positive, non-spore-forming cocci suggestive of Streptococcus. The strain was identified as Lancefield group C, and rapid ID 32 Strep and API 20 Strep (bioMérieux) results were Streptococcus equi subsp. zooepidemicus (probability, 99.7%). However, the following phenotypical characteristics led to an identification as Streptococcus equi subsp. ruminatorum: the CAMP reaction was positive, and the strain hydrolyz...

Artritis séptica por Streptococcus equi: reporte de un caso y revisión de la literatura

“…Desafortunadamente, en muchos de los casos publicados de infección por S. equi no ha sido posible la identificación más allá de la especie, por lo que la frecuencia real de las infecciones producidas por cada subespecie es desconocida, limitando el conocimiento de los factores de riesgo ligados a cada una de ellas. La identificación de las supespecies de S. equi requiere procedimientos microbiológicos que pueden diferenciar S. equi subsp equi, pero que frecuentemente fallan en discriminar S. equi subsp ruminatorum y S. equi subsp zooepidemicus 8 . Recientemente las nuevas técnicas de Matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF), la reacción en cadena de polimerasa o la secuenciación de la 16S ARN han permitido la detección e identificación más precisa de las subespecies de S. equi 8,9 .…”

“…La identificación de las supespecies de S. equi requiere procedimientos microbiológicos que pueden diferenciar S. equi subsp equi, pero que frecuentemente fallan en discriminar S. equi subsp ruminatorum y S. equi subsp zooepidemicus 8 . Recientemente las nuevas técnicas de Matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF), la reacción en cadena de polimerasa o la secuenciación de la 16S ARN han permitido la detección e identificación más precisa de las subespecies de S. equi 8,9 . En este caso, las dos herramientas microbiológicas empleadas para hacer la identificación reportaron subespecies diferentes.…”

Type A Aortic Dissection With Concurrent Aortic Valve Endocarditis, Subarachnoid Hemorrhage, and Disseminated Intravascular Coagulation

“… 5 There are several reports of S. equi endocarditis in Europe. 6 , 7 , 8 Notably, most patients who contract group C streptococci (GCS) bacteremia have an underlying malignancy, cardiovascular disease, recent consumption of unpasteurized dairy products, or contact with horses. 4 One report described canine to human transmission of GCS; however, the canine in the case report developed respiratory symptoms.…”

“…Subspeciation of S. equi was not available, and has proven difficult for many laboratories caused by frequent misidentification. 8 …”

leBIBIQBPP: a set of databases and a webtool for automatic phylogenetic analysis of prokaryotic sequences

“…Since its introduction, the system has evolved to a more sophisticated version called leBIBI, and it has become widely used for identification of Bacteria and Archaea, with about 150,000 identifications annually. The website is also mentioned as the source of bacterial identification in more than 100 articles dealing with the identification of newly described or rarely encountered pathogens in humans [ 66 – 69 ], animals [ 70 – 75 ], or environmental microbiology [ 76 , 77 ]. It has also been analyzed in reviews of the sequence based identification approach [ 5 , 55 , 78 – 82 ].…”