Antimicrobial susceptibility and clinical characteristics of Nocardia isolates from a tertiary care centre diagnostic laboratory in Pakistan

Objectives: Nocardiosis is an opportunistic infection that can present as cutaneous, pulmonary and/or disseminated disease depending on the host immunity. Treatment choices include trimethoprim/sulfamethoxazole (co-trimoxazole; SXT) and imipenem along with some other antibiotics. The Clinical and Laboratory Standards Institute (CLSI) recommends the broth microdilution (BMD) method to determine antimicrobial susceptibility, however there is a lack of susceptibility data using this method in Pakistan. Therefore, this study was undertaken to outline the susceptibility profile of Nocardia isolates in Pakistan. Methods: From November 2014 to June 2016, 52 consecutive isolates of Nocardia obtained from clinical specimens cultured at the clinical microbiology laboratory of Aga Khan University Hospital (Karachi, Pakistan) were tested for susceptibility to recommended antibiotics using the CLSI-recommended BMD method. The frequency and percentage of susceptibility and resistance of Nocardia to antimicrobials recommended by CLSI were calculated. The susceptibility profiles of pulmonary and extrapulmonary specimens were compared by χ² test. Results: Of the 52 isolates, 47 (90.4%) were susceptible to SXT, 20 (38.5%) to imipenem, 49 (94.2%) to amikacin and 52 (100%) to linezolid. No significant differences were found when susceptibilities were compared between pulmonary and extrapulmonary isolates. Conclusion: This study highlights the importance of using the gold-standard BMD method for susceptibility testing of Nocardia isolates. Larger studies are needed in the region to establish susceptibility profiles of Nocardia spp. using the BMD method in order to monitor resistance trends and to inform empirical therapy choices.