2026 Volume 75 Issue 2 Pages 440-445
In most cases, positive blood cultures yield a single bacterial species. Polymicrobial blood culture positivity involving gram-positive cocci, gram-negative rods, or anaerobes is occasionally observed in critically ill patients with gastrointestinal perforations or malignancies. However, simultaneous detection of general bacteria and mycobacteria in blood cultures is rare. Here, we present a case in which S. aureus and Mycobacterium abscessus complex (MABC) were concurrently isolated from a single blood culture sample. The patient, a 92-year-old man, was referred to our hospital with anorexia, fever, melena, and impaired activities of daily living. A urinary tract infection was suspected; therefore, two sets of blood cultures were obtained, and empirical treatment with ceftriaxone was initiated. On day 3, S. aureus was isolated from the first set. On day 4, Gram staining of the second set revealed unstained bacilli that were positive for acid-fast staining (Ziehl–Neelsen stain). A retrospective review of smears that yielded S. aureus also demonstrated similar bacilli, which were subsequently confirmed as acid-fast. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) identified the organism as MABC. MABC is a rapidly growing mycobacterium (RGM) that has been increasingly reported in recent years and can be detected in standard blood culture bottles. Given the potential for co-detection with general bacteria and NTMs, clinicians should remain vigilant for the presence of mycobacteria, which are at risk of being overlooked in routine blood culture assessments.
