Mycobacterium fortuitum: A Neglected Cause of Culture-Negative Prosthetic Valve Endocarditis and a Literature Review

TL;DR

This paper reports a rare case of prosthetic valve endocarditis caused by Mycobacterium fortuitum, which was diagnosed only after prolonged incubation and molecular testing.

Contribution

The paper presents a novel clinical case highlighting the importance of prolonged incubation for diagnosing M. fortuitum endocarditis.

Findings

M. fortuitum was identified after routine blood cultures were negative, requiring extended mycobacterial cultures.

The patient improved with an amikacin-based combination therapy.

Prolonged incubation and targeted microbiological workflows are critical for diagnosing culture-negative endocarditis.

Abstract

Background/Objectives: Prosthetic valve endocarditis caused by non-tuberculous mycobacteria is a rare but serious condition and is often associated with delayed diagnosis due to initially negative routine blood cultures with late positivity after prolonged incubation. Mycobacterium fortuitum, a rapidly growing mycobacterium, is an uncommon cause of endocarditis but may result in significant morbidity if not promptly identified. Methods: We report a 67-year-old man with prior cardiac surgery who presented 18 months later with recurrent fever, weight loss, and renal dysfunction. Initial blood cultures, echocardiography, and standard imaging were non-diagnostic. Ongoing clinical suspicion prompted extended mycobacterial cultures with prolonged incubation and molecular identification performed at a reference laboratory, which revealed M. fortuitum. Results: Antimicrobial susceptibility testing demonstrated susceptibility to amikacin, ciprofloxacin, and clarithromycin, and treatment was initiated with an amikacin-based combination regimen. The patient showed marked clinical and laboratory improvement, including resolution of fever and stabilization of renal function. Conclusions: This case highlights the diagnostic and therapeutic challenges of M. fortuitum prosthetic valve endocarditis and underscores the limitations of routine diagnostic methods in culture-negative endocarditis. It also emphasizes the importance of prolonged incubation and targeted microbiological workflows in suspected cases.

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