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Bahram Nasr Esfahani, Hossein Mirhendi, Fatemeh Riyahi Zaniani, Mahshid Salehi and Sediqeh Karimi
Drug-resistant tuberculosis is considered a major universal problem. Based on knowledge on certain mutations occurring in Mycobacterium tuberculosis genome, drug resistance could be detected timely. The goal of this study was to determine the prevalence of the most common mutations likely to result from resistance to streptomycin in M. tuberculosis isolates, as well as genetic patterns of rpsL and rrs genes, in the province of Isfahan, Iran.
Clinical specimens were collected from individuals suspected of tuberculosis who referred to the Tuberculosis Center of Isfahan among whom 205 isolates were diagnosed with M. tuberculosis by conventional methods. The minimum inhibitory concentration of streptomycin in these isolates was determined with proportion method using Lowenstein- Jensen medium from which 10 isolates were recognized with streptomycin-resistant tuberculosis. The nucleotide sequence of rpsL and 530 loop of rrs genes were analyzed in all streptomycin-resistant isolates, in addition to five randomly selected streptomycin-susceptible isolates.
Six (6/10, 60%) streptomycin-resistant isolates represented a mutation in either rpsL gene and/or rrs530 loop. Four (40%) isolates showed rpsL mutations (codons 43 and 88), and two (20%) of them alterations in rrs gene (A514C and C517T). However, no mutation was found in streptomycin-susceptible isolates in either of the genes.
The study could successfully highlight the positive effects of rpsL and rrs mutations as molecular markers of streptomycin resistance in M. tuberculosis strains. Diversity and presence or absence of mutations suggested possible circulation of a variety of strains and the role of additional mechanisms contributing to strstreptomycin resistance in various regions.