Nocardia gipuzkoensis: clinical characterization, identification, and antimicrobial susceptibility

Abstract

Nocardia gipuzkoensis was first described as a novel species in 2020. To date, infections caused by N. gipuzkoensis have rarely been reported. The prevalence of N. gipuzkoensis may be severely underestimated because N. gipuzkoensis was misidentified as Nocardia abscessus with 16 S rRNA gene sequencing in a previous study. The study aimed to systematically analyze the clinical characteristics, identification, and antimicrobial susceptibility profiles of N. gipuzkoensis to improve our understanding of this pathogen. We examined 23 strains of N. gipuzkoensis that were isolated from clinical cases in China between 2017 and 2025. These isolates were identified with 16 S rRNA and whole-genome sequencing (WGS). Clinical data were collected from medical records, and the susceptibility of Nocardia species for 14 antibiotics was tested with the broth microdilution method. The 23 N. gipuzkoensis isolates and N. abscessus NBRC 100,374 shared 16 S rRNA gene sequence similarity ranging from 99.9% to 100%, indicating that routine 16 S rRNA sequencing does not distinguish the two species accurately. All 23 isolates were ultimately identified as N. gipuzkoensis with WGS. Of the 23 N. gipuzkoensis isolates identified, 20 (87.0%) were isolated from the lower respiratory tract, two (8.7%) from the eye, and one (4.3%) from skin pus. The susceptibility rate was highest (100%) to trimethoprim–sulfamethoxazole, linezolid, and amikacin, followed by ceftriaxone, tobramycin, and minocycline, with rates exceeding 90%. However, susceptibility rates were 100% for meropenem and 56.5% for imipenem. Relatively low inhibitory rates were observed for ciprofloxacin, levofloxacin, and moxifloxacin, followed by clarithromycin. Conventional 16 S rRNA sequencing contributes to the misidentification of N. gipuzkoensis. In this study, we clarified the clinical characteristics, identification and antimicrobial susceptibility profile of N. gipuzkoensis.