S315T Mutation Research Articles

Molecular patterns of multidrug resistance of Mycobacterium tuberculosis in Georgia

BackgroundTuberculosis (TB) infections caused by multidrug-resistant Mycobacterium tuberculosis (MDR MTB) remain a significant public health concern worldwide. Georgia has a high prevalence of MDR MTB. The genetic mechanisms underlying the emergence of MDR MTB strains in this region are poorly understood and need to be determined for developing better strategies for TB control. This study investigated the frequency of major drug resistance mutations across rpoB, katG and inhA loci of Georgian MDR MTB strains and explored differences between new and previously treated patients. MethodsA total of 634 MTB strains were examined for which an MDR phenotype had been previously determined by the proportions method. The GenoType®MTBDRplus system was applied to screen the strains for the presence of rpoB (S531L, H526D, H526Y, and D516V), katG (S315T) and inhA promoter region (C15T and T8C) mutations. The target loci were amplified by PCR and then hybridized with the respective site-specific and wild type (control) probes. ResultsOut of the 634 isolates tested considered by phenotypic testing to be resistant to RIF and INH, this resistance was confirmed by the GenoType®MTBDRplus assay in 575 (90.7%) isolates. RIF resistance was seen in 589 (92.9%) and INH resistance was seen in 584 (92.1%); 67.2% and 84.3% of MDR strains harbored respectively rpoB S531L and katG S315T mutations (generally known as having low or no fitness cost in MTB). The inhA C15T mutation was detected in 22.6% of the strains, whereas rpoB H526D, rpoB H526Y, rpoB D516V and inhA T8C were revealed at a markedly lower frequency (⩽5.2%). The specific mutations responsible for the RIF resistance of 110 isolates (17.4%) could not be detected as no corresponding mutant probe was indicated in the assay. There was no specific association of the presence of mutations with the gender/age groups. All types of prevailing mutations had higher levels in new cases. ConclusionsA great majority of the Georgian MDR MTB strains have a strong preference for the drug resistance mutations carrying no or low fitness cost. Thus, it can be suggested that MDR MTB strains with such mutations will continue to arise in Georgia at a high frequency even in the absence of antibiotic pressure.

Detección de la mutación S315T en el gen katg como estrategia para identificación de Mycobacterium tuberculosis resistente a isoniacida en un laboratorio de referencia

The emergence of strains of Mycobacterium tuberculosis resistant to drugs is a public health problem. To characterize the resistance to isoniazid (INH) in M. tuberculosis. Phenotypic and genotypic methods were used to determine the contribution of mutations at 315 codon of katG gene to the phenotypic expression of resistance. The analysis of susceptibility to antibiotics was performed by the proportional method of Canetti and nitrate reductase method.Genotypic analysis of INH resistance was performed by PCR-RFLP. 193 strains of M. tuberculosis from patients with respiratory symptoms were analyzed. Nineteen (9.8%) strains resistant to INH were identified, of which 12 (63.2%) showed resistance to other drugs. Genotypic analysis allowed to detect the mutation S315T in the katG gene in 15 of 17 strains phenotypically resistant to INH, showing a sensitivity of 88.24%, 100% specificity, 100% positive predictive value, 92% negative predictive value and high concordance with phenotypic methods (kappa = 0.85 (p < 0.01). The S315T mutation in the katG gene is the predominant mechanism of INH resistance in our circulating strains. This feature could be used as a rapid diagnostic tool with potential to detect at least 88% of isoniazid resistant strains, with great impact on the therapeutic management of patients.

Impact of Isoniazid Resistance-Conferring Mutations on the Clinical Presentation of Isoniazid Monoresistant Tuberculosis

BackgroundSpecific isoniazid (INH) resistance conferring mutations have been shown to impact the likelihood of tuberculosis (TB) transmission. However, their role in the clinical presentation and outcomes of TB has not been evaluated.MethodsWe included all cases of culture-confirmed, INH monoresistant tuberculosis reported to the San Francisco Department of Public Health Tuberculosis Control Section from October 1992 through October 2005. For cases with stored culture isolates, we used polymerase chain reaction (PCR) testing and gene sequencing to identify INH resistance-conferring mutations, and compared genotypic and phenotypic characteristics.ResultsAmong 101 consecutive cases of INH monoresistant TB in San Francisco 19 (19%) had isolates with a katG mutation other than S315T; 38 (38%) had isolates with the katG S315T mutation, 29 (29%) had isolates with a inhA-15;c-t promoter mutation, and 15 (15%) had isolates with other mutations. The katG S315T mutation was independently associated with high-level INH resistance (risk ratio [RR] 1.56, 95% confidence interval [CI] 1.07–2.27), and the inhA-15;c-t promoter mutation was inversely associated with high-level INH resistance (RR 0.43, 95% CI 0.21–0.89). However, specific INH resistance-conferring mutations were not associated with the clinical severity or outcomes of INH monoresistant TB cases.ConclusionThese data suggest that INH resistance-conferring mutations do not impact the clinical presentation of TB.

Molecular analysis of isoniazid-resistant Mycobacterium tuberculosis isolates in Uruguay [Short communication

The incidence of tuberculosis (TB) is increasing in high-risk populations in Uruguay, possibly owing to emerging resistance. Mycobacterial interspersed repetitive units (MIRU) genotyping and katG sequence analysis of isoniazid (INH) resistance-associated mutations were performed in 45 INH-resistant Mycobacterium tuberculosis isolates in Uruguayan patients. The genotype distribution among INH-resistant isolates shares features of that of neighbouring countries, with a predominance of Latin American and Mediterranean, T and Haarlem genotypes, although the S genotype was particularly frequent among our isolates. Forty-four per cent of INH-resistant strains harboured the S315T mutation in katG; we found novel katG mutations (W321X, G269T, P232R and G221Wfs1) that could explain INH resistance.

Evaluation of the AdvanSure MDR-TB GenoBlot Assay for Detection of Rifampin and Isoniazid ResistantMycobacterium tuberculosisComplex in Respiratory Specimens

Background: We evaluated the performance of the AdvanSure MDR-TB GenoBlot Assay kit (AdvanSure MDR-TB, LG Life Science, Korea) to detect mutations related to rifampin (RFP)and isoniazid (INH)-resistant Mycobacterium tuberculosis complex in respiratory specimens. Methods: From February 2010 to June 2010, a total of 542 M. tuberculosis clinical isolates were collected from pulmonary tuberculosis patients in six university hospitals across Korea. We analyzed the conventional drug susceptibility testing (DST) and compared the results with those of the AdvanSure MDR-TB. Results: Compared with the conventional DST, the overall agreement rates, sensitivity, and specificity were 98.2% (532/542), 84.6% (33/39), and 99.2% (499/503), respectively, for RFP resistance and 96.1% (521/542), 79.7% (59/74), 98.7% (462/468), respectively, for INH resistance. The three common rpoB mutations were rpoB S531L (53.8%), rpoB D516V (15.4%) and rpoB H526R (7.7%) in RFP-resistant strains. For INH resistance, the katG S315T mutation (58.1%) was the most common, followed by inhA C-15T (23.0%) and katG S315N (4.1%). Conclusion: The AdvanSure MDR-TB showed high concordance with the conventional DST and would be helpful for early detection of RFP and INH resistance, although it requires improved sensitivity. (Korean J Clin Microbiol 2012;15:117-124)

Impaired fitness of Mycobacterium tuberculosis resistant isolates in a cell culture model of murine macrophages

We analysed the ability of Mycobacterium tuberculosis clinical isolates to penetrate and grow inside murine macrophages as a surrogate of fitness. Thirty-five drug-resistant and 10 drug-susceptible M. tuberculosis isolates were studied in a murine macrophage model from the J774.2 cell line in a 6 day protocol, performing semi-quantitative counts in Middlebrook 7H11 medium. The mycobacterial penetration index (MPI) after infection and the mycobacterial growth ratio (MGR) inside the macrophages were determined to evaluate the fitness of isolates. Isolates with the katG S315T mutation and multidrug-resistant (MDR) isolates had a significantly lower MGR compared with drug-susceptible isolates. The MPI of the isolates with the katG S315T mutation showed a significant decrease compared with the MPI of those without this mutation. A trend to significantly lower values was also observed on comparing the MPI of the MDR isolates with that of the drug-susceptible isolates and the isolates resistant to isoniazid. The isoniazid-resistant and MDR isolates with mutations in the katG gene showed decreased multiplication inside murine macrophages, suggesting a lower fitness of M. tuberculosis with these resistance patterns.

Determinants of Multidrug-Resistant Tuberculosis Clusters, California, USA, 2004–2007

Laboratory and epidemiologic evidence suggests that pathogen-specific factors may affect multidrug-resistant (MDR) tuberculosis (TB) transmission and pathogenesis. To identify demographic and clinical characteristics of MDR TB case clustering and to estimate the effect of specific isoniazid resistance-conferring mutations and strain lineage on genotypic clustering, we conducted a population-based cohort study of all MDR TB cases reported in California from January 1, 2004, through December 31, 2007. Of 8,899 incident culture-positive cases for which drug susceptibility information was available, 141 (2%) were MDR. Of 123 (87%) strains with genotype data, 25 (20%) were aggregated in 8 clusters; 113 (92%) of all MDR TB cases and 21 (84%) of clustered MDR TB cases occurred among foreign-born patients. In multivariate analysis, the katG S315T mutation (odds ratio 11.2, 95% confidence interval 2.2-Yen; p = 0.004), but not strain lineage, was independently associated with case clustering.

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

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.

Rapid genotypic assays to identify drug-resistant Mycobacterium tuberculosis in South Africa

Molecular assays to detect drug resistance in Mycobacterium tuberculosis are more rapid than standard drug susceptibility testing. To evaluate the efficacy of such assays in this setting, the GenoType MTBDRplus assay (HAIN Lifescience) and multiplex allele-specific PCR assays were carried out. The GenoType MTBDRplus assay was evaluated for the detection of rifampicin and isoniazid resistance in 223 M. tuberculosis isolates of known phenotypic drug sensitivity. The presence of KatG S315T and inhA C-15T mutations that confer isoniazid resistance was determined using multiplex allele-specific PCR assays. The relationship between isolate lineage and resistance determinant was investigated by spoligotyping and mycobacterial interspersed repetitive unit-variable number tandem repeat analysis. The GenoType MTBDRplus assay detected multidrug-resistant, isoniazid-monoresistant and rifampicin-monoresistant isolates with sensitivities of 91.5%, 56.1% and 70%, respectively. Multiplex allele-specific PCR detected isoniazid resistance in 91.5% of the MDR isolates and 53.7% of the isoniazid-monoresistant isolates. The W-Beijing lineage was overrepresented in the MDR subgroup of strains (odds ratio, 3.29; 95% confidence interval, 1.76-6.16). A proportion of isoniazid resistance, particularly in isoniazid-monoresistant isolates of lineage X3, is due to resistance determinants other than KatG S315T and inhA C-15T. The fact that these isolates will be indicated as drug susceptible highlights the need for determining local patterns of resistance mutations to provide users with information regarding the capabilities of rapid genotypic assays.

Molecular snapshot of drug-resistant and drug-susceptible Mycobacterium tuberculosis strains circulating in Bulgaria

We report results of the first study on the molecular basis of drug resistance in Mycobacterium tuberculosis strains currently circulating in Bulgaria. The study panel consisted of 133 (including 37 drug-resistant) isolates recovered from newly diagnosed, adult pulmonary TB patients from different regions of Bulgaria in 2005–2006. Three types of the rpoB mutations were found in 20 of 27 RIF-resistant isolates; rpoB S531L was the most frequent. Eleven (48%) of 23 INH-resistant isolates had katG S315T mutation. inhA −15C > T mutation was detected in one INH-resistant isolate (that also had katG315 mutation) and three INH-susceptible isolates. A mutation in embB306 was found in 7 of 11 EMB-resistant isolates. Comparison with spoligotyping and 24-VNTR locus typing data suggested that emergence and spread of drug-resistant and MDR-TB in Bulgaria are not associated with any specific spoligotype or MIRU-VNTR genotype.

Docking Simulations and QM/MM Studies between Isoniazid Prodrug, Catalase‐Peroxidase (KatG) and S315T Mutant from Mycobacterium tuberculosis

Isoniazid (INH), an antibiotic used to treat tuberculosis (TB), is a prodrug requiring activation by the Mycobacterium tuberculosis KatG (mtKatG). In the present work, theoretical calculations were carried out to locate the most energetically‐favorable INH–KatG interaction modes using the experimental structure of a wild type and mutant mtKatG active site. The S315T mutation significantly affects the ability of the enzyme to convert INH to isonicotinic acid in vitro. The results showed that significant changes occur in the INH binding pattern when serine is replaced by threonine.

Impact of Bacterial Genetics on the Transmission of Isoniazid-Resistant Mycobacterium tuberculosis

Understanding the ecology of drug-resistant pathogens is essential for devising rational programs to preserve the effective lifespan of antimicrobial agents and to abrogate epidemics of drug-resistant organisms. Mathematical models predict that strain fitness is an important determinant of multidrug-resistant Mycobacterium tuberculosis transmission, but the effects of strain diversity have been largely overlooked. Here we compared the impact of resistance mutations on the transmission of isoniazid-resistant M. tuberculosis in San Francisco during a 9-y period. Strains with a KatG S315T or inhA promoter mutation were more likely to spread than strains with other mutations. The impact of these mutations on the transmission of isoniazid-resistant strains was comparable to the effect of other clinical determinants of transmission. Associations were apparent between specific drug resistance mutations and the main M. tuberculosis lineages. Our results show that in addition to host and environmental factors, strain genetic diversity can influence the transmission dynamics of drug-resistant bacteria.

Rapid detection of specific gene mutations associated with isoniazid or rifampicin resistance in Mycobacterium tuberculosis clinical isolates using non-fluorescent low-density DNA microarrays

A new, fast 'low cost and density' DNA microarray (LCD array), designed for the detection of mutations that confer isoniazid or rifampicin resistance in Mycobacterium tuberculosis isolates, has been developed and was evaluated using 46 resistant clinical isolates from Barcelona. LCD chips are pre-structured polymer supports using a non-fluorescent detection principle based on the precipitation of a clearly visible dark substrate. One LCD chip consists of eight identical microarrays, designed to detect mutations within the 90 bp rpoB region, codon 315 in the katG gene and the mabA-inhA regulatory region. A total of 22 strains with a katG 315 mutation, 19 strains with alterations in the mabA-inhA regulatory region and 16 strains with mutations in the rpoB region, characterized previously, were studied. The identification of S315T and S315N mutations using the LCD was 100% concordant with the sequencing data. A strain with the S315R mutation, which is not tiled on the LCD array, was detected by the absence of hybridization using the wild-type probe. Of 19 strains with low-level isoniazid resistance related to the mabA-inhA regulatory region, 18 were identified correctly. The detection of mutations in the rpoB region was 93.8% concordant with the sequencing data. One mabA-inhA and rpoB mutated strain showed a cross-hybridization. The LCD array protocol takes 45 min (15 min 'hands-on' time) after prior PCR amplification. Only minimal laboratory equipment is required. LCD arrays provide a rapid and economical method to characterize mutations in codon 315 of the katG gene, in the mabA-inhA regulatory region and in the rpoB gene.

Characterization of the S315G mutant of Mycobacterium tuberculosis catalase‐peroxidase KatG

KatG(S315T) is the most common mutant found in clinical isolates of Mycobacterium tuberculosis resistant to the antibiotic Isoniazid (INH). Resistance due to the S315T mutation has been assigned to a decrease in the enzyme's affinity for the drug likely due to a decrease in the dimensions of a substrate access channel caused by the methyl group of the Thr 315 side chain. The main goal of the present study was to examine the effect of reducing the size of the side chain at residue 315 in this crucial region of the enzyme. Site-directed mutagenesis was used to prepare KatG(S315G). The overexpressed enzyme was characterized using optical and EPR spectroscopy. Catalase and peroxidase activities were reduced by nearly 2 fold and 10 fold, respectively, compared with the WT enzyme. Titration of KatG(S315G) with INH showed an approximately two-fold increase in affinity compared to WT KatG, while the rate of INH activation by KatG(S315G) was approximately 60% of that observed for the WT enzyme. Low temperature (10 K) EPR data showed the presence of mostly 5-c HS (high spin) and QS (quantum spin) heme spin states in the resting enzyme, more similar to KatG(S315T) than to WT enzyme. INH binding produced a transition from 6-c QS to 5-c QS and HS heme, also similar to the behavior of KatG (S315T). In addition, a small amount of 6-c low spin heme (due to the coordination of -OH group) was detected. The results are consistent with the hypothesis that a substrate access channel plays an important role in the binding of INH and its activation by KatG and that residue 315 plays a critical role in determining heme iron structure. Supported by NIH Grant # AI060014

Resonance Raman spectroscopy of Compound II and its decay in Mycobacterium tuberculosis catalase-peroxidase KatG and its isoniazid resistant mutant S315T

The reaction of Mycobacterium tuberculosis KatG and the mutant KatG(S315T) with two different organic peroxides is studied using resonance Raman spectroscopy. For the first time, an intermediate is observed in a catalase-peroxidase with vibrations that are characteristic of Compound II. The observation of this intermediate is consistent with photoreduction of Compound I and is in agreement with the formation of Compound I during the catalytic cycle of KatG. The same intermediate is detected in KatG(S315T), a mutant associated with resistance to isoniazid (INH), but with a lower yield, indicating that the organic peroxides cannot react with the heme iron in KatG(S315T) as efficiently as in wild-type KatG. Our results are consistent with catalytic competence of the S315T mutant and support the model that the S315T mutation confers antibiotic resistance by modifying the interaction between the enzyme and the drug.

Genotypic Diversity among Isoniazid-Resistant Isolates of Mycobacterium tuberculosis from Rashid Hospital in Dubai, United Arab Emirates

Objective: To perform molecular fingerprinting for strain relatedness among isoniazid-resistant Mycobacterium tuberculosis isolates recovered from tuberculosis (TB) patients in the United Arab Emirates (UAE). Materials and Methods: Thirty-two consecutive isoniazid-resistant M. tuberculosis strains isolated from TB patients (4 natives and 28 expatriates) at Rashid Hospital, Dubai, UAE were analyzed. The typing was carried out by touchdown double-repetitive-element PCR (DRE-PCR). The status of R463 or L463 polymorphism and the presence of S315T mutation in the katG gene were also determined for isolates exhibiting cluster pattern in DRE-PCR. Results: All the 32 isolates (28 from expatriate patients and 4 from UAE nationals) exhibited 21 distinct patterns in DRE-PCR with 20 of 32 isolates exhibiting unique patterns and the remaining 12 exhibiting cluster ‘A’ pattern. All the isolates (19 of 19) yielding two or more DNA fragments in DRE-PCR were unique strains. The genotypic heterogeneity among 10 of the 12 cluster isolates was suggested by the varying susceptibility of these isolates to anti-TB drugs, presence of R463 or L463 polymorphism in the katG gene and the presence or absence of S315T mutation in the katG gene. Conclusion: The genotypic diversity among isoniazid-resistant M. tuberculosis isolates mostly recovered from expatriate patients indicates that most expatriates were infected with a unique strain imported, most likely, from their country of origin and that their latent infection was reactivated in UAE.

Mycobacterium tuberculosis KatG(S315T) Catalase−Peroxidase Retains All Active Site Properties for Proper Catalytic Function

Mycobacterium tuberculosis (Mtb) KatG is a catalase-peroxidase that is thought to activate the antituberculosis drug isoniazid (INH). The local environment of Mtb KatG and its most prevalent INH-resistant mutant, KatG(S315T), is investigated with the exogenous ligands CO and NO in the absence and presence of INH by using resonance Raman, FTIR, and transient absorption spectroscopy. The Fe-His stretching vibration is detected at 244 cm(-)(1) in the ferrous forms of both the wild-type enzyme and KatG(S315T). The ferrous-CO complex of both enzymes exhibits nu(CO), nu(Fe-CO), and delta(Fe-C-O) vibrations at 1925, 525, and 586 cm(-)(1), respectively, indicating a positive electrostatic environment for the CO complex, which is probably weakly hydrogen-bonded to a distal residue. The CO geometry is nonlinear as indicated by the unusually high intensity of the Fe-C-O bending vibration. The nu(Fe(III)-NO) and delta(Fe(III)-N-O) vibrations are detected at 596 and 571 cm(-)(1), respectively, in the ferric forms of wild-type and mutant enzyme and are indicative of a nonlinear binding geometry in support of the CO data. Although the presence of INH does not affect the vibrational frequencies of the CO- and NO-bound forms of either enzyme, it seems to perturb slightly their Raman intensities. Our results suggest a minimal, if any, perturbation of the distal heme pocket in the S315T mutant. Instead, the S315T mutation seems to induce small changes in the KatG conformation/dynamics of the ligand access channel as indicated by CO rebinding kinetics in flash photolysis experiments. The implications of these findings for the catalytic mechanism and mechanism of INH resistance in KatG(S315T) are discussed.

Oxidative stress increases susceptibility of Mycobacterium tuberculosis to isoniazid.

Isoniazid is a first-line antibiotic used in the treatment of infections caused by Mycobacterium tuberculosis. Isoniazid is a prodrug requiring oxidative activation by the catalase-peroxidase hemoprotein, KatG. Resistance to isoniazid can be obtained by point mutations in the katG gene, with one of the most common being a threonine-for-serine substitution at position 315 (S315T). The S315T mutation is found in more than 50% of isoniazid-resistant clinical isolates and results in an approximately 200-fold increase in the MIC of isoniazid compared to that for M. tuberculosis H37Rv. In the present study we investigated the hypothesis that superoxide plays a role in KatG-mediated isoniazid activation. Plumbagin and clofazimine, compounds capable of generating superoxide anion, resulted in a lower MIC of isoniazid for M. tuberculosis H37Rv and a strain carrying the S315T mutation. These agents did not cause as great of an increase in isoniazid susceptibility in the mutant strain when the susceptibilities were assessed by using the inhibitory concentration that causes a 50% decrease in growth. These results provide evidence that superoxide can play a role in isoniazid activation. Since clofazimine alone has antitubercular activity, the observation of synergism between clofazimine and isoniazid raises the interesting possibility of using both drugs in combination to treat M. tuberculosis infections.

Variations in the Occurrence of the S315T Mutation Within thekatGGene in Isoniazid-Resistant ClinicalMycobacterium tuberculosisIsolates from Kuwait

The worldwide threat of drug-resistant tuberculosis (TB) to human health has led to the development of molecular methods for rapidly determining the resistance of clinical Mycobacterium tuberculosis isolates to the two front-line antituberculous drugs, isoniazid and rifampin. The prevalence of the S315T mutation within the katG gene, which confers clinically significant resistance to isoniazid, was determined in isoniazid-resistant clinical M. tuberculosis isolates recovered from TB patients in Kuwait. A total of 67 isoniazid-resistant and 18 susceptible clinical M. tuberculosis isolates were tested. The mutation S315T was found in 46 (69%) of the 67 resistant strains, whereas none of the susceptible strains contained this mutation. The prevalence of this mutation was highest (32 of 40, 80%) in isolates recovered from patients of South Asian origin and lowest in isolates from patients of Middle Eastern origin (8 of 18, 44%). The genotyping performed on isolates carrying the S315T mutation showed that the isolates belong to several different types as they exhibited unique DNA banding patterns. The results point to a varying prevalence of the S315T mutation within the katG gene in clinical M. tuberculosis isolates recovered from patients of different ethnic groupings within the same country. The results also suggest that detection of the S315T mutation in the katG gene may be used as a rapid screening method for identifying isoniazid-resistant clinical M. tuberculosis isolates recovered from majority of patients in some ethnic groupings.