Predominance of Beijing lineage among pre-extensively drug-resistant and extensively drug-resistant strains of Mycobacterium tuberculosis: A tertiary care center experience.

OBJECTIVE/BACKGROUND: Increasing resistance to various first-line and second-line drugs has become a major concern in India. However, it is not known if some genotypes are more associated with second-line drug resistance. Thus, the main aim of this study was to find out the predominant genotype associated with second-line drug resistance.

METHODS: During the study, a total of 234 multidrug resistant (MDR) strains of Mycobacterium tuberculosis, isolated between 2008 and 2015, were randomly selected and screened for pre-extensively drug-resistant (XDR) and XDR patterns using second-drug susceptibility testing with BACTEC MGIT 960. All the MDR isolates were tested against ofloxacin (2μg/mL), kanamycin (2.5μg/mL), amikacin (1μg/mL), and capreomycin (2.5μg/mL). Based on the resistance pattern pre-XDR was defined as M. tuberculosis isolates resistant to fluoroquinolone alone. The identified pre-XDR and XDR isolates were further characterized using spoligotyping. The spoligo patterns obtained were compared and analyzed using SITVIT_WEB Unweighted Pair Group Method with Arithmetic Mean, and Minimum Spanning Tree was derived using MIRU-VNTRplus.

RESULTS: Among the 234 MDR strains of M. tuberculosis, 85 (36.3%) were detected as pre-XDRs and 15 (6.4%) as XDRs. All the pre-XDR strains were ofloxacin resistant, whereas among the XDR strains, 10 (66.6%) were resistant to ofloxacin, kanamycin, and capreomycin, four (26.6%) were resistant to ofloxacin, kanamycin, and amikacin, and one (6.6%) isolate was resistant to ofloxacin and kanamycin. Upon spoligotyping analysis, the Beijing lineage was found to be the single most dominant lineage among the pre-XDR strains (38.8%) followed by CAS (30.5%), X (7%), T (5.8%), Haarlem (3.5%), EAI (2.3%), and MANU (2.3%). Among the XDR isolates, seven (46.6%) belonged to Beijing, three (20%) belonged to CAS, and one (6.6%) to each of the EAI, T, URAL, and X lineages. Within the Beijing family, ST1 was the most common in both pre-XDR (94%) and XDR isolates. All the isolates belonged to the ST1 sublineage.

CONCLUSION: The Beijing lineage was found to be the single most dominant genotype among the pre-XDR and XDR isolates.