Background/Purpose
Mutations in rpsL and rrs genes are associated with resistance to streptomycin in tuberculosis, but important geographical variation exists in these mutations. The goal of this study was to characterize these mutations in isolates of streptomycin-resistant mycobacteria originating from southeast Mexico.
Methods
Mycobacteria were isolated from patients with suspected drug-resistant tuberculosis. Susceptibility tests were carried out using the fluorometric method, and rrs and rpsL DNA sequencing was performed by capillary electrophoresis.
Results
Some 136 drug-resistant isolates were recovered, of which 91(67%) exhibited resistance to streptomycin. Mutations in rpsL were observed in 18 isolates (19%) in codons 43 (A→G, K/R, n = 12) and 88 (A→G, K/R, n = 4; A→C, K/Q, n = 2). Mutations in rrs were observed in 26 isolates (28%). These were at nucleotides 513 (A→C, n = 8) and 516 (C→T, n = 6), and six novel mutations at nucleotides 483 (A→T, n = 2), 485 (A→G, n = 2), 496 (G→A, n = 2), 795 (C→T, n = 6), 870 (C→T, n = 3), and 907 (A→C, n = 3), with some isolates showing more than one mutation. Finally, 47 (52%) of the isolates showed no mutation.