Infective endocarditis caused by penicillin-resistant viridans group streptococci: a series of nine cases from a Spanish cohort

Background: Infective endocarditis (IE) caused by viridans and gallolyticus group streptococci (VGS-GGS) resistant to penicillin (PEN-R; minimum inhibitory concentration ≥4 mg/L) is rare but poses therapeutic challenges.

Objectives: To describe the characteristics of patients with IE caused by PEN-R VGS-GGS, focusing on antimicrobial management.

Methods: Retrospective analysis of a prospective cohort of definite IE caused by PEN-R VGS-GGS between 2008 and 2023 in 40 Spanish hospitals. We describe clinical characteristics, management and outcome of the cases, and compare them to IE caused by VGS-GGS with susceptibility or susceptibility with increased exposure to penicillin (PEN-I).

Results: We identified nine cases of PEN-R VGS-GGS IE in a cohort of 1563 streptococcal IE (0.58%). All isolates belonged to S. mitis group. Three cases died during hospitalization and no relapse occurred at 3 months of follow-up. Compared to cases with susceptibility or PEN-I, PEN-R showed a higher rate of mitral location (78% versus 51%), surgical indication (67% versus 51%), and in-hospital mortality (33% versus 12%). Most cases (86%) showed resistance to third-generation cephalosporins. The preferred antibiotic regimen was beta-lactam-based: ceftriaxone plus gentamicin, penicillin plus gentamicin, ceftriaxone plus levofloxacin, and ceftaroline plus daptomycin. Two cases received a combination of vancomycin plus gentamicin. Levofloxacin was used in two cases in combination with ceftriaxone or daptomycin. All patients that received cardiac surgery were cured at the end of follow-up.

Conclusions: IE caused by PEN-R VGS-GGS was rare and only affected mitis group streptococci. Antibiotic combination including a beta-lactam seems to be effective in its management.