Species distribution and susceptibility of Nocardia isolates in New Zealand 2002–2021

Abstract

The aim was to record the distribution and susceptibility of Nocardia species in New Zealand. Local and referred isolates were identified by an evolving approach over the study period including conventional phenotypic methods, susceptibility profiles, matrix-assisted laser desorption ionisation-time of flight mass spectrometry (MALDI-TOF) and molecular sequencing. Isolates previously identified as a Nocardia sp. or part of the N.asteroides complex were reidentified by MALDI-TOF and/or molecular methods. Antimicrobial susceptibility to eight antibiotics was performed by standard microbroth dilution. The site of isolation, susceptibility profiles and species distribution were analysed. A total of 383 isolates were tested: N.brasiliensis 23 (6%), N.cyriacigeorgica 42 (11%), N.farcinica 41 (11%), N.nova complex 226 (59%), and 51 (13%) other species/complexes. The respiratory tract was the most common site of infection (244, 64%), with skin and soft tissue the second most common site (104, 27%). All 23 N.brasiliensis isolates were from skin and soft tissue specimens. Almost all isolates (≥98%) were susceptible to amikacin, linezolid and trimethoprim-sulfamethoxazole; 35% and 77% were resistant to clarithromycin and quinolones, respectively. The expected susceptibility profiles of the four common species and complex were observed for most agent-organism parings. Multi-drug resistance was uncommon (3.4%). The spectrum of Nocardia species in New Zealand is similar to overseas reports and our most common group is the N.nova complex. While amikacin, linezolid and trimethoprim-sulfamethoxazole remain good empiric treatment choices, other agents should have their activity confirmed before use.