Genotyping of Nocardia farcinica with multilocus sequence typing

Nocardia are aerobic Gram-positive saprophytes that are widely distributed in nature, but some species cause nocardiosis, especially opportunistic infections that affect immunocompromised patients mostly. In this study, we developed a multilocus sequence typing (MLST) scheme using seven housekeeping genes (gyrB, hsp65, secA1, rpoB, rpoA, recA, and trpB) for genotyping the most common clinical species, Nocardia farcinica (37 clinical isolates from the patients with nocardiosis and seven from animals in China and 15 reference strains). The results showed that using these loci could perform accurate identification among different species, and high discriminative power within the N. farcinica species. Of the 59 N. farcinica isolates, 44 sequence types have been identified; 32 STs covering 46 isolates could be assigned to six clonal complexes that encompassed most of the collected strains. The results showed that these strains displayed a sufficiently informative population structure using this method. Our study also provided a suitable approach for epidemiological studies of N. farcinica. A large clonal complex comprising 16 strains was identified, and was notable for its wide distribution and host adaptation. This complex should be monitored closely and merits further study.