Antibiotic Susceptibility of Nocardia Clinical Isolates Collected from Chinese Patients - China, 2014-2024.

Introduction: Nocardia species are found worldwide in soil rich in organic matter and can cause nocardiosis in humans. Trimethoprim-sulfamethoxazole has long been the first-line treatment for Nocardia infections; however, resistance to this therapy has recently been reported. Methods: Sixty-three clinical Nocardia isolates collected in China were tested against 32 antimicrobial agents using the broth microdilution method. Phylogenetic analysis of the 16S rRNA gene was performed to identify the species. Results: Three sequences from samples collected in Hainan Province did not match any known Nocardia species, suggesting significant genetic diversity among Nocardia isolates. Nocardia strains generally exhibited high resistance to clarithromycin, clindamycin, and isoniazid. Clinical and reference strains of N. farcinica and N. otitidiscaviarum were susceptible to amikacin and linezolid. Amoxicillin-clavulanate and imipenem were effective against all clinical and reference strains of N. farcinica, whereas gentamicin was effective against all clinical and reference strains of N. otitidiscaviarum. Conclusions: Linezolid and amikacin were the most consistently active drugs among the analyzed species. Variability of antimicrobial susceptibility was observed among clinical isolates of the same species and between clinical and reference isolates of the same species. Overall, this study highlights the need for better assessment of the burden of nocardiosis in China and for continuous monitoring of antimicrobial resistance among Nocardia isolates.