O01 ‘Matters of the heart’: navigating resistance and allergies in <i>Granulicatella adiacens</i> endocarditis

Abstract Background Nutritionally variant streptococci (NVS), including Granulicatella and Abiotrophia genera, are fastidious Gram-positive cocci requiring pyridoxal or thiol for growth. They are implicated in 1%–2% of infective endocarditis (IE) cases and associated with large vegetations and poorer outcomes.¹ Multiple reports describe treatment of Granulicatella adiacens IE with guideline-supported regimens such as penicillin, ceftriaxone, and vancomycin.2–4 We present a case of G. adiacens IE in a patient with aortic homograft, with ceftriaxone resistance and allergies to penicillin and vancomycin, and review literature on treatment of NVS IE with alternative agents outside of recognized guidelines. Case report A 45-year-old female with Turner’s syndrome, prior bioprosthetic aortic valve replacement and aortic homograft presented with one month of malaise, dyspnoea and fever. Echocardiography revealed severe aortic regurgitation with a 9×4 mm aortic valve vegetation. Four sets of blood culture cultured G. adiacens on standard blood agar without pyridoxal supplementation. Empirical ceftriaxone, vancomycin and gentamicin were commenced, pending susceptibility testing. She underwent aortic valve replacement. Valve culture was negative, but 16S PCR detected G. adiacens. Reference laboratory susceptibility testing demonstrated ceftriaxone resistance and penicillin/vancomycin susceptibility. Amoxicillin and vancomycin were then initiated, while amoxicillin susceptibility result was awaited. The patient developed a severe cutaneous reaction with eosinophilia of 0.93×10⁹/L, meeting criteria for DRESS syndrome (drug rash with eosinophilia and systemic symptoms), with β-lactams suspected as culprits. Amoxicillin was stopped; however the rash worsened, prompting vancomycin discontinuation also. Due to fastidious growth of G. adiacens and delayed susceptibility results, meropenem and linezolid were trialled empirically. Thrombocytopenia subsequently developed on linezolid (nadir platelet count 114×10⁹/L), which was ceased. Ultimately, she completed 6 weeks of therapy post-surgery with ertapenem and levofloxacin, with good clinical response. MICs were 0.064 for ertapenem and 0.5 for levofloxacin—while no EUCAST breakpoints exist for G. adiacens, the reference laboratory suggested both may be considered for therapy . Surveillance blood cultures one month after completing therapy were negative and repeat echocardiography showed a well-seated prosthetic valve with no vegetation. Discussion Infective endocarditis guidelines from AHA, ESC and BSAC recommend penicillin, ampicillin, or ceftriaxone with gentamicin for six weeks in penicillin-susceptible Granulicatella IE, or vancomycin with gentamicin in β-lactam allergy.2,3,4 Data on daptomycin, linezolid and fluoroquinolone use for NVS IE are limited. One study found 87% of G. adiacens isolates meropenem-susceptible.⁵ Fastidious growth, prolonged turnaround for susceptibilities and lack of formal EUCAST breakpoints complicated antimicrobial selection in this case. Recurrence of NVS IE is common (17%–27%),⁶ and the retained aortic homograft raised relapse risk. Long-term oral suppressive therapy was avoided due to limited options and fluoroquinolone toxicity concerns. Instead, close outpatient monitoring was instituted. Conclusions The management of NVS endocarditis is already challenging due to its fastidious growth, more severe prognosis, high relapse rates and antibiotic resistances. This case was further complicated by severe antibiotic hypersensitivity reactions to guideline-supported antibiotic regimens. Guided by case series and MDT input, a non-guideline-supported regimen achieved successful outcomes. Publication of such cases is essential to inform future management strategies for rare and difficult infections.