Clinico-microbiological analysis of streptococcal isolates from blood cultures with focus on infective endocarditis

Background: Infective endocarditis (IE) is an infection of the endocardium, most commonly caused by Streptococcus . The study aims to evaluate the clinical features, blood culture yields, species distribution, and antibiotic susceptibility patterns of streptococcal isolates, with a focus on IE. Materials and Methods: Fifty streptococcal blood culture isolates from clinically suspected cases of bloodstream infection (BSI) were analyzed from January 2022 to December 2024. Species identification was performed using the VITEK 2 compact system, and matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry. Clinical data, association with IE, number of blood culture sets, and antimicrobial susceptibility patterns were analyzed descriptively. Results: Out of 8757 blood samples processed, 900 were culture positive. Streptococcal species accounted for 50 (5%) of these isolates. Streptococcus agalactiae was the most frequently identified species ( n = 20, 40%). Most of the patients were >40 years, with male predominance ( n = 34, 68%). Of the 50 culture-proven streptococcal BSIs, 18 (36%) were clinically suspected to have IE. Of these, 8 (44%) had positive blood cultures, with viridans streptococci being the most common isolate. Diagnostic yield correlated with the number of blood culture sets. Echocardiography revealed vegetations in 75% of IE patients, the most common being mitral valve involvement (63%). Streptococcal isolates showed high susceptibility to b-lactams (ampicillin, ceftriaxone) and vancomycin. Conclusion: Viridans streptococci remain the most common cause of streptococcal IE, while S . agalactiae is increasingly implicated in adult bacteremia. Obtaining multiple blood culture sets significantly improves IE diagnostic yield. Species-level identification and adherence to Duke International Society for Cardiovascular Infectious Disease criteria are essential for accurate diagnosis and effective management of streptococcal IE.