Detection of streptomycin and quinolone resistance in Mycobacterium tuberculosis by a low-density DNA array

In cases of multidrug-resistant tuberculosis, it is crucial to rule out resistance to second-line antituberculous (anti-TB) agents. In the present study, a low-cost low-density DNA array including four genetic regions (rrs 530 loop, rrs 1400, rpsL and gyrA) was designed for the rapid detection of the most important mutations related to anti-TB injectable drugs (mainly streptomycin) and fluoroquinolone resistance (LD-SQ array). A total of 108 streptomycin- and/or ofloxacin-resistant and 20 streptomycin- and ofloxacin-susceptible Mycobacterium tuberculosis clinical isolates were analysed with the array. The results obtained were compared with sequencing data and phenotypic susceptibility pattern. The LD-SQ array offered a good sensitivity compared to sequencing, especially among resistant strains: 92.5% (37/40) for streptomycin and 87.5% (7/8) for fluoroquinolones. Therefore, this array could be considered a good approach for the rapid detection of mutations related to streptomycin and fluoroquinolone resistance. On the other hand, there were discordant results in 16 resistant strains and six susceptible isolates, mostly concerning the gyrA region, in which the existence of polymorphisms next to informative positions might cause cross-hybridization. These discrepancies were caused by some technical limitations; consequently, the present array should be considered as a first-step prior to a forthcoming optimized version of the array.