The genotypic study of Mycobacterium tuberculosis complex resistant to isoniazid: Galicia, Spain (2008-2013)

Incorporation of rapid detection systems to identify mutations in M. tuberculosis complex that confer resistance to isoniazid and rifampicin has potentiated the knowledge of their distribution, given the geographical variability. We performed antibiograms of the 2,993 strains isolated in Galicia, Spain (2008-2013). In the strains resistant to isoniazid, a concentration of 0.4 mg/mL and MTBDRplus Genotype test (Hain Lifescience, Germany) were used. We found that 3.64 % of strains were resistant to isoniazid, while 0.43 % were resistant to isoniazid and rifampicin (multidrug resistant, MDR). The MTBDRplus test showed an overall sensitivity of 72.48 %, with 62.5 % sensitivity for non MDR isoniazid-resistant strains and 100 % sensitivity for MDR strains. The katG gene mutation was detected at codon 315 in 38.53 % of strains. The S315T mutation appeared in 61.54 % of MDR strains and 34.38 % of non-MDR strains. The 28.44 % had mutations in inhA, (93.55 % in C15T), and 38.46 % of MDR strains were mutated. In non-MDR strains, 37.50 % were wild-type, 35.42 % and 27.08 % had mutations in katG and inhA, respectively. The most frequent mutation in rpoβ was S531L (46.15 %). The 38.71 % and 41.9 % of strains with resistance to isoniazid and streptomycin had mutations in katG and inhA, respectively (2 strains with mutations in T8C and T8A). The distribution pattern of resistance among strains with high and low concentrations of isoniazid showed statistically significant differences in relation to the mutation in katG and wild-type. The sensitivity of the Genotype MTBDRplus test for non-MDR strains in our area was at the lower threshold described.