Correlations of mutations in katG, oxyR-ahpC and inhA genes and in vitro susceptibility in Mycobacterium tuberculosisclinical strains segregated by spoligotype families from tuberculosis prevalent countries in South America

Abstract

BackgroundMutations associated with resistance to rifampin or streptomycin have been reported for W/Beijing and Latin American Mediterranean (LAM) strain families of Mycobacterium tuberculosis. A few studies with limited sample sizes have separately evaluated mutations in katG, ahpC and inhA genes that are associated with isoniazid (INH) resistance. Increasing prevalence of INH resistance, especially in high tuberculosis (TB) prevalent countries is worsening the burden of TB control programs, since similar transmission rates are noted for INH susceptible and resistant M. tuberculosis strains.ResultsWe, therefore, conducted a comprehensive evaluation of INH resistant M. tuberculosis strains (n = 224) from three South American countries with high burden of drug resistant TB to characterize mutations in katG, ahpC and inhA gene loci and correlate with minimal inhibitory concentrations (MIC) levels and spoligotype strain family. Mutations in katG were observed in 181 (80.8%) of the isolates of which 178 (98.3%) was contributed by the katG S315T mutation. Additional mutations seen included oxyR-ahpC; inhA regulatory region and inhA structural gene. The S315T katG mutation was significantly more likely to be associated with MIC for INH ≥2 μg/mL. The S315T katG mutation was also more frequent in Haarlem family strains than LAM (n = 81) and T strain families.ConclusionOur data suggests that genetic screening for the S315T katG mutation may provide rapid information for anti-TB regimen selection, epidemiological monitoring of INH resistance and, possibly, to track transmission of INH resistant strains.

An <em>In Silico</em> Study of a Novel rpoB Insertion in a Cluster of Clinical Strains of <em>Mycobacterium tuberculosis</em> Highly-Rifampicin Resistant

“…DNA isolation and amplification of genes regions were carried out as described previously (Dalla Costa et al, 2009;Telenti et al, 1993;van Soolingen et al, 1994).…”

Review: The Molecular Basis of Resistance in &lt;i&gt;Mycobaterium tuberculosis&lt;/i&gt;

“…Beijing families isolated from several countries usually carry a higher percentage of the katG S315T shift, compared to non-Beijing family isolates [15,[31][32][33]. These mutations may be favored because mutations at this location appear to decrease INH activation without abolishing catalase-peroxidase activity and, therefore, without diminishing the virulence or transmissibility of M. tuberculosis strains [17]. The region of the genome within which katG lies appears to be relatively unstable and therefore susceptible to aforementioned alterations, possibly because of the presence of repetitive DNA sequences.…”

“…tuberculosis may compensate for katG mutations by overexpressing the ahpC gene, that encodes alkyl-hydroperoxide reductase, protein involved in cellular regulation of oxidative stress capable of detoxifying damaging organic peroxides [17,36]. Five different nucleotide alterations have been identified in the promoter region of ahpC which lead to overexpression of this protein in INH resistant isolates: −48(G→A), −51(G→A), −54(C→T), −74(G→A) and −81(C→T) [37].…”

“…InhA promoter mutations are more frequently seen, about 8% to 20%, and are present at positions −24(G-T), −16(A-G), or −8(T-G/A) and −15(C-T) [41]. This inhA promoter gene region regulates the expression of the enoyl acyl carrier protein reductase and those mutations may increase the level of protein expression [17,30,41,42]. The overexpression of inhA, due to mutations in the inhA promoter region, leads to low level INH resistance and is accompanied by cross-resistance to the second-line anti-TB drug ethionamide (ETH) which has structural similarity to that of isoniazid [43].…”

“…Consequently, more than 450,000 MDR-TB cases are estimated to occur globally each year [13] and a global surveillance of M. tuberculosis drug resistance has been proposed to guide appropriate treatment policies [14]. In the last years, studies have shown that certain emerging M. tuberculosis strains, like Beijing/W and Haarlem strain families, induce more severe forms of TB, manifest higher failure/relapse than others, and are strongly associated with drug resistance [15][16][17]. The present occurrences of these strains in developed countries emphasize TB burden even in countries with good TB control programs, and broaden the horizon for the elimination of this disease.…”