Byline: Priya. Rajendran, Chandrasekaran. Padmapriyadarsini, Vaishnavee. Vijayaraghavan, Tamizhselvan. Manoharan, Lakshana. Lokanathan, Parveen. Kadhar, Lavanya. Jayabal, Gomathy. Sivaramakrishnan
OBJECTIVES: With the introduction of newer molecular diagnostic tools to identify Mycobacterium tuberculosis, an increasing number of nontuberculous mycobacterium (NTM) is being identified. However, the drug resistance pattern of the NTM species identified is less explored. The objective of this study is to study the drug resistance patterns of Mycobacterium kansasii species isolated in a tuberculosis-endemic setting at South India. METHODS: A wide profile of NTM species were reported earlier from a prospective cohort of adults during 2017-2020. Out of this profile, a total of 22 M. kansasii species were subjected to drug susceptibility testing by two different methods: proportion sensitivity testing method and Sensititre testing method. RESULTS: Out of the 18 strains of M. kansasii subjected to Sensititre method of testing, the resistance pattern was demonstrated to be high for doxycycline (13) followed by rifampicin and trimethoprim/sulfamethoxazole (7). Out of the 22 strains subjected to proportion sensitivity testing method, 20 and 10 were resistant to isoniazid and ethambutol, respectively. CONCLUSION: There was a poor correlation between the treatment outcome and the resistance pattern of the antibiotics tested. With increasing numbers of NTM being reported, early and correct identification of NTM species is essential for the prompt initiation of appropriate treatment to achieve better outcome.
Nontuberculous mycobacteria (NTMs) that were earlier considered as the nonpathogenic, environmental mycobacteria are gaining importance in recent years. Mycobacterium kansasii , known to cause both pulmonary and extrapulmonary infection, is one of the six most frequently isolated NTMs. This species is considered to be the most pathogenic NTM, with the majority of culture-positive cases presenting with clinical disease, along with the colonization.,,, Among the seven subtypes (I-VII) identified so far, subtype I is associated with human infections, and subtype II is associated with HIV-infected patients indicating its role as an opportunistic pathogen. The other five subtypes are, in general, documented as environmental isolates rather than pathogenic species. The perceptible similarities between clinical presentations of pulmonary Mycobacterium tuberculosis (MTB) and M. kansasii have made the physicians to rely on microbiological confirmation to distinguish between these infections.,, To diagnose pulmonary NTM, a minimal radiological evaluation with a chest X-ray (or computed tomography), combined with positive cultures and clinical exclusion of other diagnoses, is recommended by the American Thoracic Society/Infectious Disease Society of America (ATS/IDSA) guidelines. Identification of pulmonary M. kansasii with this combined diagnostic algorithm of clinical and microbiological investigation along with its drug susceptibility testing (DST) could facilitate timely and proper management of the symptomatic patient.
The different types of DST methods currently used for M. kansasii include broth microdilution, agar proportion, and E-test methods. These methods vary by different factors such as inoculums and medium used, incubation conditions, and interpretation of the results, thereby influencing the outcomes. DST of M. kansasii is a less explored topic, and as of other mycobacteria, the Clinical and Laboratory Standards Institute (CLSI) recommends the microdilution method in Mueller-Hinton medium with drugs rifampicin...