Recent studies have identified genes involved in high-altitude adaptation in Tibetans. Genetic variants/haplotypes within regions containing three of these genes (EPAS1, EGLN1, and PPARA) are associated with relatively decreased hemoglobin levels observed in Tibetans at high altitude, providing corroborative evidence for genetic adaptation to this extreme environment. The mechanisms that afford adaptation to high-altitude hypoxia, however, remain unclear. Considering the strong metabolic demands imposed by hypoxia, we hypothesized that a shift in fuel preference to glucose oxidation and glycolysis at the expense of fatty acid oxidation would improve adaptation to decreased oxygen availability. Correlations between serum free fatty acids and lactate concentrations in Tibetan groups living at high altitude and putatively selected haplotypes provide insight into this hypothesis. An EPAS1 haplotype that exhibits a signal of positive selection is significantly associated with increased lactate concentration, the product of anaerobic glycolysis. Furthermore, the putatively advantageous PPARA haplotype is correlated with serum free fatty acid levels, suggesting a possible decrease in the activity of fatty acid oxidation. Although further studies are required to assess the molecular mechanisms underlying these patterns, these associations suggest that genetic adaptation to high altitude involves alteration in energy utilization pathways.
Iron overload is associated with increased diabetes risk. We therefore investigated the effect of iron on adiponectin, an insulin-sensitizing adipokine that is decreased in diabetic patients. In humans, normal-range serum ferritin levels were inversely associated with adiponectin, independent of inflammation. Ferritin was increased and adiponectin was decreased in type 2 diabetic and in obese diabetic subjects compared with those in equally obese individuals without metabolic syndrome. Mice fed a high-iron diet and cultured adipocytes treated with iron exhibited decreased adiponectin mRNA and protein. We found that iron negatively regulated adiponectin transcription via FOXO1-mediated repression. Further, loss of the adipocyte iron export channel, ferroportin, in mice resulted in adipocyte iron loading, decreased adiponectin, and insulin resistance. Conversely, organismal iron overload and increased adipocyte ferroportin expression because of hemochromatosis are associated with decreased adipocyte iron, increased adiponectin, improved glucose tolerance, and increased insulin sensitivity. Phlebotomy of humans with impaired glucose tolerance and ferritin values in the highest quartile of normal increased adiponectin and improved glucose tolerance. These findings demonstrate a causal role for iron as a risk factor for metabolic syndrome and a role for adipocytes in modulating metabolism through adiponectin in response to iron stores.
Excess fatty acids and carbohydrates have both been implicated in the pathogenesis of type 2 diabetes, and both can reproduce essential features of the disease including insulin resistance and beta cell failure. It has been proposed that both nutrients may regulate metabolism through a common fuel sensing mechanism, namely hexosamine synthesis. We have previously shown that transgenic over-expression of the rate-limiting enzyme for hexosamine synthesis, glutamine:fructose-6-phosphate amidotransferase (GFA), targeted to muscle and fat, leads to insulin resistance mediated by increased O-linked glycosylation of nuclear and cytosolic proteins. We report here that hexosamine-induced insulin resistance is not additive with that induced by high fat feeding. In control mice fed a high fat diet, glucose disposal rates during euglycemic hyperinsulinemia were decreased by 37% (p < 0.02) compared to mice on a low fat diet. Transgenic mice overexpressing GFA and fed a low fat diet exhibited a 51% decrease in glucose disposal compared to controls on a low fat diet (p < 0.001), but no further decrease was evident in the transgenic mice fed a high fat diet. Decreased glucose disposal rates were mirrored by increases in skeletal muscle levels of the principal end product of the hexosamine pathway, UDP-N-acetyl glucosamine. Serum leptin levels, which are modulated both by feeding and hexosamine flux, also show no additivity in their stimulation by GFA overexpression and high fat feeding. These data are consistent with a shared nutrient sensing pathway for high fat and carbohydrate fluxes and a common pathway by which glucose and lipids induce insulin resistance.
Insulin resistance; Hexosamine synthesis; N-Acetylglucosamine; O-Linked glycosylation
Excess tissue iron levels are a risk factor for diabetes, but the mechanisms underlying the association are incompletely understood. We previously published that mice and humans with a form of hereditary iron overload, hemochromatosis, exhibit loss of β-cell mass. This effect by itself is not sufficient, however, to fully explain the diabetes risk phenotype associated with all forms of iron overload.
RESEARCH DESIGN AND METHODS
We therefore examined glucose and fatty acid metabolism and hepatic glucose production in vivo and in vitro in a mouse model of hemochromatosis in which the gene most often mutated in the human disease, HFE, has been deleted (Hfe−/−).
Although Hfe−/− mice exhibit increased glucose uptake in skeletal muscle, glucose oxidation is decreased and the ratio of fatty acid to glucose oxidation is increased. On a high-fat diet, the Hfe−/− mice exhibit increased fatty acid oxidation and are hypermetabolic. The decreased glucose oxidation in skeletal muscle is due to decreased pyruvate dehydrogenase (PDH) enzyme activity related, in turn, to increased expression of PDH kinase 4 (pdk4). Increased substrate recycling to liver contributes to elevated hepatic glucose production in the Hfe−/− mice.
Increased hepatic glucose production and metabolic inflexibility, both of which are characteristics of type 2 diabetes, may contribute to the risk of diabetes with excessive tissue iron.
Mycobacterium cosmeticum; catheter infection; rapidly growing mycobacteria; letter
Impaired insulin signaling via phosphatidylinositol 3-kinase/Akt to endothelial nitric oxide synthase (eNOS) in the vasculature has been postulated to lead to arterial dysfunction and hypertension in obesity and other insulin resistant states. To investigate this, we compared insulin signaling in the vasculature, endothelial function, and systemic blood pressure in mice fed a high-fat (HF) diet to mice with genetic ablation of insulin receptors in all vascular tissues (TTr-IR−/−) or mice with genetic ablation of Akt1 (Akt1−/−). HF mice developed obesity, impaired glucose tolerance, and elevated free fatty acids that was associated with endothelial dysfunction and hypertension. Basal and insulin-mediated phosphorylation of extracellular signal-regulated kinase 1/2 and Akt in the vasculature was preserved, but basal and insulin-stimulated eNOS phosphorylation was abolished in vessels from HF versus lean mice. In contrast, basal vascular eNOS phosphorylation, endothelial function, and blood pressure were normal despite absent insulin-mediated eNOS phosphorylation in TTr-IR−/− mice and absent insulin-mediated eNOS phosphorylation via Akt1 in Akt1−/− mice. In cultured endothelial cells, 6 hours of incubation with palmitate attenuated basal and insulin-stimulated eNOS phosphorylation and NO production despite normal activation of extracellular signal-regulated kinase and Akt. Moreover, incubation of isolated arteries with palmitate impaired endothelium-dependent but not vascular smooth muscle function. Collectively, these results indicate that lower arterial eNOS phosphorylation, hypertension, and vascular dysfunction following HF feeding do not result from defective upstream signaling via Akt, but from free fatty acid–mediated impairment of eNOS phosphorylation.
arterial insulin signaling; hypertension; endothelial dysfunction; mice; diabetes
Diet-induced obesity is associated with increased myocardial fatty acid (FA) utilization, insulin resistance, and cardiac dysfunction. The study was designed to test the hypothesis that impaired glucose utilization accounts for initial changes in FA metabolism.
Methods and results
Ten-week-old C57BL6J mice were fed a high-fat diet (HFD, 45% calories from fat) or normal chow (4% calories from fat). Cardiac function and substrate metabolism in isolated working hearts, glucose uptake in isolated cardiomyocytes, mitochondrial function, insulin-stimulated protein kinase B (Akt/PKB) and Akt substrate (AS-160) phosphorylation, glucose transporter 4 (GLUT4) translocation, pyruvate dehydrogenase (PDH) activity, and mRNA levels for metabolic genes were determined after 2 or 5 weeks of HFD. Two weeks of HFD reduced basal rates of glycolysis and glucose oxidation and prevented insulin stimulation of glycolysis in hearts and reduced insulin-stimulated glucose uptake in cardiomyocytes. Insulin-stimulated Akt/PKB and AS-160 phosphorylation were preserved, and PDH activity was unchanged. GLUT4 content was reduced by 55% and GLUT4 translocation was significantly attenuated. HFD increased FA oxidation rates and myocardial oxygen consumption (MVO2), which could not be accounted for by mitochondrial uncoupling or by increased expression of peroxisome proliferator activated receptor-α (PPAR-α) target genes, which increased only after 5 weeks of HFD.
Rates of myocardial glucose utilization are altered early in the course of HFD because of reduced GLUT4 content and GLUT4 translocation despite normal insulin signalling to Akt/PKB and AS-160. The reciprocal increase in FA utilization is not due to PPAR-α-mediated signalling or mitochondrial uncoupling. Thus, the initial increase in myocardial FA utilization in response to HFD likely results from impaired glucose transport that precedes impaired insulin signalling.
Glucose transport; Glycolysis; Fatty acid metabolism; Insulin resistance; Mitochondria
Mycobacterium avium complex (MAC) and rapidly growing mycobacteria (RGM) such as M. abscessus, M. mucogenicum, M. chelonae, and M. fortuitum, implicated in health care-associated infections, are often isolated from potable water supplies as part of the microbial flora. To understand factors that influence growth in their environmental source, clinical RGM and slowly growing MAC isolates were grown as biofilm in a laboratory batch system. High and low nutrient levels were compared, as well as stainless steel and polycarbonate surfaces. Biofilm growth was measured after 72 h of incubation by enumeration of bacteria from disrupted biofilms and by direct quantitative image analysis of biofilm microcolony structure. RGM biofilm development was influenced more by nutrient level than by substrate material, though both affected biofilm growth for most of the isolates tested. Microcolony structure revealed that RGM develop several different biofilm structures under high-nutrient growth conditions, including pillars of various shapes (M. abscessus and M. fortuitum) and extensive cording (M. abscessus and M. chelonae). Although it is a slowly growing species in the laboratory, a clinical isolate of M. avium developed more culturable biofilm in potable water in 72 h than any of the 10 RGM examined. This indicates that M. avium is better adapted for growth in potable water systems than in laboratory incubation conditions and suggests some advantage that MAC has over RGM in low-nutrient environments.
Between March and May 2006, a Texas hospital identified five Mycobacterium mucogenicum bloodstream infections among hospitalized oncology patients using fluorescence high-performance liquid chromatography analysis of mycolic acids. Isolates from blood cultures were compared to 16 isolates from environmental sites or water associated with this ward. These isolates were further characterized by hsp65, 16S rRNA, and rpoB gene sequencing, hsp65 PCR restriction analysis, and molecular typing methods, including repetitive element PCR, random amplified polymorphic DNA PCR, and pulsed-field gel electrophoresis (PFGE) of large restriction fragments. Three of five patient isolates were confirmed as M. mucogenicum and were in a single cluster as determined by all identification and typing methods. The remaining two patient isolates were identified as different strains of Mycobacterium phocaicum by rpoB sequence analysis. One of these matched an environmental isolate from a swab of a hand shower in the patient's room, while none of the clinical isolates of M. mucogenicum matched environmental strains. Among the other 15 environmental isolates, 11 were identified as M. mucogenicum and 4 as M. phocaicum strains, all of which were unrelated by typing methods. Although the 16S rRNA gene sequences matched for all 14 M. mucogenicum isolates, there were two each of the hsp65 and rpoB sequevars, seven PCR typing patterns, and 12 PFGE patterns. Among the seven M. phocaicum isolates were three 16S rRNA sequevars, two hsp65 sequevars, two rpoB sequevars, six PCR typing patterns, and six PFGE patterns. This outbreak represents the first case of catheter-associated bacteremia caused by M. phocaicum and the first report of clinical isolates from a U.S. hospital. The investigation highlights important differences in the available typing methods for mycobacteria and demonstrates the genetic diversity of these organisms even within narrow confines of time and space.
Previous phenotyping of glucose homeostasis and insulin secretion in a mouse model of hereditary hemochromatosis (Hfe−/−) and iron overload suggested mitochondrial dysfunction. Mitochondria from Hfe−/− mouse liver exhibited decreased respiratory capacity and increased lipid peroxidation. Although the cytosol contained excess iron, Hfe−/− mitochondria contained normal iron but decreased copper, manganese, and zinc, associated with reduced activities of copper-dependent cytochrome c oxidase and manganese-dependent superoxide dismutase (MnSOD). The attenuation in MnSOD activity was due to substantial levels of unmetallated apoprotein. The oxidative damage in Hfe−/− mitochondria is due to diminished MnSOD activity, as manganese supplementation of Hfe−/− mice led to enhancement of MnSOD activity and suppressed lipid peroxidation. Manganese supplementation also resulted in improved insulin secretion and glucose tolerance associated with increased MnSOD activity and decreased lipid peroxidation in islets. These data suggest a novel mechanism of iron-induced cellular dysfunction, namely altered mitochondrial uptake of other metal ions.
During pressure overload-induced hypertrophy, unloading-induced atrophy, and diabetes mellitus, the heart induces ‘fetal’ genes (e.g. myosin heavy chain β; mhcβ).
We propose that altered glucose homeostasis within the cardiomyocyte acts as a central mechanism for the regulation of gene expression in response to environmental stresses. The evidence is as follows.
Methods and Results
Forced glucose uptake both ex vivo and in vivo results in mhc isoform switching. Restricting dietary glucose prevents mhc isoform switching in hearts of both GLUT1-Tg mice and rats subjected to pressure overload-induced hypertrophy. Thus, glucose availability correlates with mhc isoform switching under all conditions investigated. A potential mechanism by which glucose affects gene expression is through O-linked glycosylation of specific transcription factors. Glutamine:fructose-6-phosphate amidotransferase (GFAT) catalyzes the flux generating step in UDP-N-acetylglucosamine biosynthesis, the rate determining metabolite in protein glycosylation. Ascending aortic constriction increased intracellular levels of UDP-N-acetylglucosamine, and the expression of gfat2, but not gfat1, in the rat heart.
Collectively, the results strongly suggest glucose-regulated gene expression in the heart, and the involvement of glucose metabolites in isoform switching of sarcomeric proteins characteristic for the fetal gene program.
Heart; Glucose Metabolism; Fetal Gene Program
From February to October 2003, Mycobacterium goodii wound infections were identified among three patients who received surgical implants at a Colorado hospital. This report summarizes the investigation of the first reported nosocomial outbreak of M. goodii. Increased awareness is needed about the potential for nontuberculous mycobacteria to cause postoperative wound infections.
Mycobacterium goodii; atypical mycobacteria; nosocomial infection; postoperative wound infection; implants; dispatch
We investigated mutations in the genes katG, inhA (regulatory and structural regions), and kasA and the oxyR-ahpC intergenic region of 97 isoniazid (INH)-resistant and 60 INH-susceptible Mycobacterium tuberculosis isolates obtained in two states in Brazil: São Paulo and Paraná. PCR-single-strand conformational polymorphism (PCR-SSCP) was evaluated for screening mutations in regions of prevalence, including codons 315 and 463 of katG, the regulatory region and codons 16 and 94 of inhA, kasA, and the oxyR-ahpC intergenic region. DNA sequencing of PCR amplicons was performed for all isolates with altered PCR-SSCP profiles. Mutations in katG were found in 83 (85.6%) of the 97 INH-resistant isolates, including mutations in codon 315 that occurred in 60 (61.9%) of the INH-resistant isolates and 23 previously unreported katG mutations. Mutations in the inhA promoter region occurred in 25 (25.8%) of the INH-resistant isolates; 6.2% of the isolates had inhA structural gene mutations, and 10.3% had mutations in the oxyR-ahpC intergenic region (one, nucleotide −48, previously unreported). Polymorphisms in the kasA gene occurred in both INH-resistant and INH-susceptible isolates. The most frequent polymorphism encoded a G269A substitution. Although KatG315 substitutions are predominant, novel mutations also appear to be responsible for INH resistance in the two states in Brazil. Since ca. 90.7% of the INH-resistant isolates had mutations identified by SSCP electrophoresis, this method may be a useful genotypic screen for INH resistance.
The goal of this study was to apply temperature-mediated heteroduplex analysis using denaturing high-performance liquid chromatography to identify pyrazinamide (PZA) resistance in Mycobacterium tuberculosis isolates and simultaneously differentiate between M. tuberculosis and Mycobacterium bovis. Features that contributed to an optimal assay included the use of two different reference probes for the pncA gene targets from wild-type M. tuberculosis and wild-type M. bovis, optimization of the column temperature, increasing the starting concentration of the elution buffer, and reducing the rate of elution buffer increase (slope). A total of 69 strains were studied, including 48 wild-type M. tuberculosis strains (13 were PZA-resistant strains) and 21 M. bovis strains (8 were BCG strains). In all isolates tested, wild-type M. tuberculosis generated a single-peak pattern when mixed with the M. tuberculosis probe and a double-peak pattern with the M. bovis probe. In contrast, all M. bovis isolates generated a double-peak pattern when mixed with the M. tuberculosis probe and a single-peak pattern with the M. bovis probe. PZA-resistant mutant M. tuberculosis isolates generated characteristic patterns that were easily distinguishable from both wild-type M. tuberculosis and M. bovis isolates. Chromatographic patterns generated by the two reference probes allowed the rapid detection of PZA resistance with the simultaneous ability to distinguish between M. tuberculosis and M. bovis. This approach may allow the detection of drug resistance-associated mutations, with potential application to clinical and epidemiological aspects of tuberculosis control.
Ethionamide (ETH) is a structural analog of the antituberculosis drug isoniazid (INH). Both of these drugs target InhA, an enzyme involved in mycolic acid biosynthesis. INH requires catalase-peroxidase (KatG) activation, and mutations in katG are a major INH resistance mechanism. Recently an enzyme (EthA) capable of activating ETH has been identified. We sequenced the entire ethA structural gene of 41 ETH-resistant Mycobacterium tuberculosis isolates. We also sequenced two regions of inhA and all or part of katG. The MICs of ETH and INH were determined in order to associate the mutations identified with a resistance phenotype. Fifteen isolates were found to possess ethA mutations, for all of which the ETH MICs were ≥50 μg/ml. The ethA mutations were all different, previously unreported, and distributed throughout the gene. In eight of the isolates, a missense mutation in the inhA structural gene occurred. The ETH MICs for seven of the InhA mutants were ≥100 μg/ml, and these isolates were also resistant to ≥8 μg of INH per ml. Only a single point mutation in the inhA promoter was identified in 14 isolates. A katG mutation occurred in 15 isolates, for which the INH MICs for all but 1 were ≥32 μg/ml. As expected, we found no association between katG mutation and the level of ETH resistance. Mutations within the ethA and inhA structural genes were associated with relatively high levels of ETH resistance. Approximately 76% of isolates resistant to ≥50 μg of ETH per ml had such mutations.
The presence of mutations in specific regions of the katG, inhA, and ahpC genes was analyzed with 69 Mycobacterium tuberculosis isoniazid-resistant isolates from three Brazilian states. Point mutations in codon 315 of the katG gene were observed in 87.1, 60.9, and 60% of the isolates from Rio Grande do Sul, Rio de Janeiro, and São Paulo, respectively. Mutations in the inhA gene were identified only in one isolate from RJ State, and the ahpC promoter region revealed mutations in distinct positions in 12.9, 21.7, and 6.7% of the isolates from RS, RJ and SP, respectively.
The present update on the global distribution of Mycobacterium tuberculosis complex spoligotypes provides both the octal and binary descriptions of the spoligotypes for M. tuberculosis complex, including Mycobacterium bovis, from >90 countries (13,008 patterns grouped into 813 shared types containing 11,708 isolates and 1,300 orphan patterns). A number of potential indices were developed to summarize the information on the biogeographical specificity of a given shared type, as well as its geographical spreading (matching code and spreading index, respectively). To facilitate the analysis of hundreds of spoligotypes each made up of a binary succession of 43 bits of information, a number of major and minor visual rules were also defined. A total of six major rules (A to F) with the precise description of the extra missing spacers (minor rules) were used to define 36 major clades (or families) of M. tuberculosis. Some major clades identified were the East African-Indian (EAI) clade, the Beijing clade, the Haarlem clade, the Latin American and Mediterranean (LAM) clade, the Central Asian (CAS) clade, a European clade of IS6110 low banders (X; highly prevalent in the United States and United Kingdom), and a widespread yet poorly defined clade (T). When the visual rules defined above were used for an automated labeling of the 813 shared types to define nine superfamilies of strains (Mycobacterium africanum, Beijing, M. bovis, EAI, CAS, T, Haarlem, X, and LAM), 96.9% of the shared types received a label, showing the potential for automated labeling of M. tuberculosis families in well-defined phylogeographical families. Intercontinental matches of shared types among eight continents and subcontinents (Africa, North America, Central America, South America, Europe, the Middle East and Central Asia, and the Far East) are analyzed and discussed.
We present a short summary of recent observations on the global distribution of the major clades of the Mycobacterium tuberculosis complex, the causative agent of tuberculosis. This global distribution was defined by data-mining of an international spoligotyping database, SpolDB3. This database contains 11,708 patterns from as many clinical isolates originating from more than 90 countries. The 11,708 spoligotypes were clustered into 813 shared types. A total of 1,300 orphan patterns (clinical isolates showing a unique spoligotype) were also detected.
Mycobacterium tuberculosis; spoligotyping
Mycobacterium tuberculosis complex isolates from cerebrospinal fluid of 67 meningitis patients were obtained from six fever hospitals in Egypt. One M. bovis and 66 M. tuberculosis isolates were identified by PCR-restriction fragment length polymorphism (RFLP) analysis of oxyR. Among the M. tuberculosis isolates, 53 unique strain types (with 3 to 16 copies of IS6110) were found by RFLP analyses. Nine clusters (eight with two isolates each and one with six isolates) were also found. Thirty-six spoligotypes, including at least 10 that have been previously reported from other countries, were also observed. Forty-one (62.1%) of the isolates were in spoligotype clusters, and 22 (33%) of the isolates were in RFLP clusters. Fifty-one of the isolates were susceptible in vitro to all of the antituberculosis drugs tested, 11 were monoresistant to capreomycin, rifampin, isoniazid (INH), pyrazinamide, or streptomycin (STR), 4 were resistant to STR and INH, and 1 was resistant to STR, INH, and ethambutol.
PCR products containing sequence polymorphisms were prepared from six mycobacterial genes, denatured, mixed with reference PCR products, and reannealed; the mixtures were then examined with a denaturing high-performance liquid chromatography system (WAVE) equipped with a temperature-controlled alkalated polystyrene divinyl benzene column. Mismatching of bases in heteroduplexes of the PCR products causes elution patterns of the DNA from the column to be altered. The six mycobacterial genes studied were oxyR, in which a specific polymorphism (G1031A) is found only in certain species of the Mycobacterium tuberculosis complex, and five genes in which mutations associated with antituberculosis drug resistance have been found. The resistance genes (with affected drug and PCR product sizes given parenthetically) were rpoB (rifampin; 258 bp), katG (isoniazid; 205 bp), pncA (pyrazinamide; 579 bp); rpsL (streptomycin; 196 bp), and embB (ethambutol; 185 bp). Elution patterns of heteroduplexes of all 20 polymorphisms studied shifted detectably at column temperatures ranging from 65.3 to 68°C and elution times of 3.5 to 6 min. These results show that temperature-mediated heteroduplex analysis is a potentially useful genotypic screen for mutations associated with antituberculosis drug resistance and for the G1031A polymorphism in oxyR. The method may allow users to detect novel as well as heterogeneous mutations without using expensive kits or detection labels.
To investigate the role of insulin signaling on postnatal cardiac development, physiology, and cardiac metabolism, we generated mice with a cardiomyocyte-selective insulin receptor knockout (CIRKO) using cre/loxP recombination. Hearts of CIRKO mice were reduced in size by 20–30% due to reduced cardiomyocyte size and had persistent expression of the fetal β-myosin heavy chain isoform. In CIRKO hearts, glucose transporter 1 (GLUT1) expression was reduced by about 50%, but there was a twofold increase in GLUT4 expression as well as increased rates of cardiac glucose uptake in vivo and increased glycolysis in isolated working hearts. Fatty acid oxidation rates were diminished as a result of reduced expression of enzymes that catalyze mitochondrial β-oxidation. Although basal rates of glucose oxidation were reduced, insulin unexpectedly stimulated glucose oxidation and glycogenolysis in CIRKO hearts. Cardiac performance in vivo and in isolated hearts was mildly impaired. Thus, insulin signaling plays an important developmental role in regulating postnatal cardiac size, myosin isoform expression, and the switching of cardiac substrate utilization from glucose to fatty acids. Insulin may also modulate cardiac myocyte metabolism through paracrine mechanisms by activating insulin receptors in other cell types within the heart.
We evaluated 25 Mycobacterium tuberculosis isolates from patients at a major Egyptian reference hospital in Assiut, Egypt, who had been treated for at least 1 year for tuberculosis. Typing patterns (IS6110) were diverse, and multidrug resistance was found among 11 (44%) of the isolates. Mutations associated with antimicrobial drug resistance were found in rpoB, katG, rpsL, and embB in the resistant isolates.
We examined the correlation of mutations in the pyrazinamidase (PZase) gene (pncA) with the pyrazinamide (PZA) resistance phenotype with 60 Mycobacterium tuberculosis isolates. PZase activity was determined by the method of Wayne (L. G. Wayne, Am. Rev. Respir. Dis. 109:147–151, 1974), and the entire pncA nucleotide sequence, including the 74 bp upstream of the start codon, was determined. PZA susceptibility testing was performed by the method of proportions on modified Middlebrook and Cohn 7H10 medium. The PZA MICs were ≥100 μg/ml for 37 isolates, 34 of which had alterations in the pncA gene. These mutations included missense substitutions for 24 isolates, nonsense substitutions for 3 isolates, frameshifts by deletion for 4 isolates, a three-codon insertion for 1 isolate, and putative regulatory mutations for 2 isolates. Among 21 isolates for which PZA MICs were <100 μg/ml, 3 had the same mutation (Thr47→Ala) and 18 had the wild-type sequence. For the three Thr47→Ala mutants PZA MICs were 12.5 μg/ml by the method of proportions on 7H10 agar; two of these were resistant to 100 μg of PZA per ml and the third was resistant to 800 μg of PZA per ml by the BACTEC method. In all, 30 different pncA mutations were found among the 37 pncA mutants. No PZase activity was detected in 35 of 37 strains that were resistant to ≥100 μg of PZA per ml or in 34 of 37 pncA mutants. Reduced PZase activity was found in the three mutants with the Thr47→Ala mutation. This study demonstrates that mutations in the pncA gene may serve as a reliable indicator of resistance to ≥100 μg of PZA per ml.
We evaluated a recently described linear signal amplification method for sensitivity and specificity in detecting mutations associated with resistance to rifampin (RIF) and isoniazid (INH) in Mycobacterium tuberculosis. The assay utilizes the thermostable flap endonuclease Cleavase VIII, derived from Archaeoglobus fulgidus, which cleaves a structure formed by the hybridization of two overlapping oligonucleotide probes to a target nucleic acid strand. This method, termed the Invader assay, can discriminate single-base differences. Nine pairs of probes, encompassing five mutations in rpoB and katG that are associated with resistance to either RIF or INH, as well as the corresponding wild-type (drug-susceptible) alleles, were tested using amplified DNA. Fluorescent-labeled cleavage products, ranging from 4 to 13 nucleotides in length, depending on the genotype of the test sample, were separated by denaturing polyacrylamide (20 to 24%) gel electrophoresis and then detected by scanning. All nine alleles could be identified and differentiated on the basis of product size. Multiple mutations at a specific rpoB nucleotide in target PCR products could be identified, as could mutants that were present at ≥0.5% of the total population of target sequences. The Invader assay is a sensitive screen for some mutations associated with antituberculosis drug resistance in amplified gene regions.
We developed a scheme for the rapid identification of Mycobacterium species based upon PCR amplification of polymorphic genetic regions with fluorescent primers followed by restriction and analysis by fluorescence capillary electrophoresis. Mycobacterium species were identified by restriction enzyme analysis of a 439-bp segment of the 65-kDa heat shock protein gene (labeled [both strands] at the 5′ end with 4,7,2′,7′-tetrachloro-6-carboxyfluorescein) using HaeIII and BstEII and of a 475-bp hypervariable region of the 16S rRNA gene (labeled [both strands] at the 5′ end with 6-carboxyfluorescein) using HaeIII and CfoI. Samples were analyzed on an automated fluorescence capillary electrophoresis instrument, and labeled fragments were sized by comparison with an internal standard. DNA templates were prepared with pure cultures of type strains. In all, we analyzed 180 strains, representing 22 Mycobacterium species, and obtained distinctive restriction fragment length polymorphism (RFLP) patterns for 19 species. Three members of the Mycobacterium tuberculosis complex had a common RFLP pattern. A computerized algorithm which eliminates subjectivity from pattern interpretation and which is capable of identifying the species within a sample was developed. The convenience and short preparatory time of this assay make it comparable to conventional methodologies such as high-performance liquid chromatography and hybridization assays for identification of mycobacteria.