Using Reduced Inoculum Densities of Mycobacterium tuberculosis in MGIT Pyrazinamide Susceptibility Testing to Prevent False-Resistant Results and Improve Accuracy: A Multicenter Evaluation.

The primary platform used for pyrazinamide (PZA) susceptibility testing of Mycobacterium tuberculosis is the MGIT culture system (Becton Dickinson). Since false-resistant results have been associated with the use of this system, we conducted a multicenter evaluation to determine the effect of using a reduced cell density inoculum on the rate of false resistance. Two reduced inoculum densities were compared with that prescribed by the manufacturer (designated as "BD" method). The reduced inoculum methods (designated as "A" and "C") were identical to the manufacturer's protocol in all aspects with the exception of the cell density of the inoculum. Twenty genetically and phenotypically characterized M. tuberculosis isolates were tested in duplicate by ten independent laboratories using the three inoculum methods. False-resistant results declined from 21.1% using the standard "BD" method to 5.7% using the intermediate ("A") inoculum and further declined to 2.8% using the most dilute ("C") inoculum method. The percentages of the resistant results that were false-resistant declined from 55.2% for the "BD" test to 28.8% and 16.0% for the "A" and "C" tests, respectively. These results represent compelling evidence that the occurrence of false-resistant MGIT PZA susceptibility test results can be mitigated through the use of reduced inoculum densities.

Mycobacterium orygis Lymphadenitis in New York, USA.

We report a case of lymphadenitis caused by Mycobacterium orygis in an immunocompetent person in Stony Brook, New York, USA. Initial real-time PCR assay failed to provide a final subspecies identification within the M. tuberculosis complex, but whole-genome sequencing characterized the isolate as M. orygis.

Performance of the G4 Xpert® MTB/RIF assay for the detection of Mycobacterium tuberculosis and rifampin resistance: a retrospective case-control study of analytical and clinical samples from high- and low-tuberculosis prevalence settings.

BACKGROUND: The Xpert® MTB/RIF (Xpert) assay is a rapid PCR-based assay for the detection of Mycobacterium tuberculosis complex DNA (MTBc) and mutations associated with rifampin resistance (RIF). An updated version introduced in 2011, the G4 Xpert, included modifications to probe B and updated analytic software. METHODS: An analytical study was performed to assess Xpert detection of mutations associated with rifampin resistance in rifampin-susceptible and -resistant isolates. A clinical study was performed in which specimens from US and non-US persons suspected of tuberculosis (TB) were tested to determine Xpert performance characteristics. All specimens underwent smear microscopy, mycobacterial culture, conventional drug-susceptibility testing and Xpert testing; DNA from isolates with discordant rifampin resistance results was sequenced. RESULTS: Among 191 laboratory-prepared isolates in the analytical study, Xpert sensitivity for detection of rifampin resistance associated mutations was 97.7% and specificity was 90.8%, which increased to 99.0% after DNA sequencing analysis of the discordant samples. Of the 1,096 subjects in the four clinical studies, 49% were from the US. Overall, Xpert detected MTBc in 439 of 468 culture-positive specimens for a sensitivity of 93.8% (95% confidence interval [CI]: 91.2%-95.7%) and did not detect MTBc in 620 of 628 culture-negative specimens for a specificity of 98.7% (95% CI: 97.5%-99.4%). Sensitivity was 99.7% among smear-positive cases, and 76.1% among smear-negative cases. Non-determinate MTBc detection and false-positive RIF resistance results were low (1.2 and 0.9%, respectively). CONCLUSIONS: The updated Xpert assay retained the high sensitivity and specificity of the previous assay versions and demonstrated low rates of non-determinate and RIF resistance false positive results.

Draft Genome Sequence of Branchiibius sp. NY16-3462-2, Isolated from a Mixed Clinical Sample.

Here, we report the release of a draft genome assembly of a Gram-positive cocci Branchiibius sp. NY16-3462-2 with a high-GC content, sequenced from a mixed clinical sample containing Mycobacterium tuberculosis This genome is the first publicly available sequence from a representative of the genus Branchiibius.

Rapid prediction of inducible clarithromycin resistance in Mycobacterium abscessus.

We have developed a single tube TaqMan(®) real-time PCR assay that differentiates the full-length and truncated erm(41) gene to predict inducible resistance to clarithromycin in Mycobacterium abscessus. A study of 87 clinical isolates found this assay to be 90.8% concordant to conventional drug susceptibility testing results for the prediction of inducible clarithromycin drug resistance.

Whole Genome Sequencing Investigation of a Tuberculosis Outbreak in Port-au-Prince, Haiti Caused by a Strain with a "Low-Level" rpoB Mutation L511P - Insights into a Mechanism of Resistance Escalation.

The World Health Organization recommends diagnosing Multidrug-Resistant Tuberculosis (MDR-TB) in high burden countries by detection of mutations in Rifampin (RIF) Resistance Determining Region of Mycobacterium tuberculosis rpoB gene with rapid molecular tests GeneXpert MTB/RIF and Hain MTBDRplus. Such mutations are found in >95% of Mycobacterium tuberculosis strains resistant to RIF by conventional culture-based drug susceptibility testing (DST). However routine diagnostic screening with molecular tests uncovered specific "low level" rpoB mutations conferring resistance to RIF below the critical concentration of 1 µg/ml in some phenotypically susceptible strains. Cases with discrepant phenotypic (susceptible) and genotypic (resistant) results for resistance to RIF account for at least 10% of resistant diagnoses by molecular tests and urgently require new guidelines to inform therapeutic decision making. Eight strains with a "low level" rpoB mutation L511P were isolated by GHESKIO laboratory between 2008 and 2012 from 6 HIV-negative and 2 HIV-positive patients during routine molecular testing. Five isolates with a single L511P mutation and two isolates with double mutation L511P&M515T had MICs for RIF between 0.125 and 0.5 µg/ml and tested susceptible in culture-based DST. The eighth isolate carried a double mutation L511P&D516C and was phenotypically resistant to RIF. All eight strains shared the same spoligotype SIT 53 commonly found in Haiti but classic epidemiological investigation failed to uncover direct contacts between the patients. Whole Genome Sequencing (WGS) revealed that L511P cluster isolates resulted from a clonal expansion of an ancestral strain resistant to Isoniazid and to a very low level of RIF. Under the selective pressure of RIF-based therapy the strain acquired mutation in the M306 codon of embB followed by secondary mutations in rpoB and escalation of resistance level. This scenario highlights the importance of subcritical resistance to RIF for both clinical management of patients and public health and provides support for introducing rpoB mutations as proxy for MICs into laboratory diagnosis of RIF resistance. This study illustrates that WGS is a promising multi-purpose genotyping tool for high-burden settings as it provides both "gold standard" sequencing results for prediction of drug susceptibility and a high-resolution data for epidemiological investigation in a single assay.

Detection of Mycobacterium avium complex DNA directly in clinical respiratory specimens: opportunities for improved turn-around time and cost savings.

We developed, evaluated, and implemented a Taqman multiplex real-time polymerase chain reaction (PCR) assay for the detection of Mycobacterium avium complex (MAC), targeting the 16S-23S rRNA internal transcribed spacer, which we have combined with an existing Mycobacterium tuberculosis complex assay for use directly in clinical respiratory specimens. Evaluation of the performance of this assay for MAC detection included 464 clinical respiratory specimens tested prospectively. This real-time PCR assay was found overall to have a sensitivity of 71.1%, a specificity of 99.5%, a positive predictive value of 98.0%, and a negative predictive value of 90.2% for MAC. The assay provides results prior to the availability of cultured material and identification, most within 24 h of specimen receipt, and may reduce the need to culture MAC-PCR-positive specimens when susceptibility testing is not requested. Additionally, we have found significant cost savings of approximately $21.00 per specimen and staff time reductions of 3.75 h per specimen with implementation of this assay.

Correlation between genotypic and phenotypic testing for resistance to rifampin in Mycobacterium tuberculosis clinical isolates in Haiti: investigation of cases with discrepant susceptibility results.

The World Health Organization has recommended use of molecular-based tests MTBDRplus and GeneXpert MTB/RIF to diagnose multidrug-resistant tuberculosis in developing and high-burden countries. Both tests are based on detection of mutations in the Rifampin (RIF) Resistance-Determining Region of DNA-dependent RNA Polymerase gene (rpoB). Such mutations are found in 95-98% of Mycobacterium tuberculosis strains determined to be RIF-resistant by the "gold standard" culture-based drug susceptibility testing (DST). We report the phenotypic and genotypic characterization of 153 consecutive clinical Mycobacterium tuberculosis strains diagnosed as RIF-resistant by molecular tests in our laboratory in Port-au-Prince, Haiti. 133 isolates (86.9%) were resistant to both RIF and Isoniazid and 4 isolates (2.6%) were RIF mono-resistant in MGIT SIRE liquid culture-based DST. However the remaining 16 isolates (10.5%) tested RIF-sensitive by the assay. Five strains with discordant genotypic and phenotypic susceptibility results had RIF minimal inhibitory concentration (MIC) close to the cut-off value of 1 µg/ml used in phenotypic susceptibility assays and were confirmed as resistant by DST on solid media. Nine strains had sub-critical RIF MICs ranging from 0.063 to 0.5 µg/ml. Finally two strains were pan-susceptible and harbored a silent rpoB mutation. Our data indicate that not only detection of the presence but also identification of the nature of rpoB mutation is needed to accurately diagnose resistance to RIF in Mycobacterium tuberculosis. Observed clinical significance of low-level resistance to RIF supports the re-evaluation of the present critical concentration of the drug used in culture-based DST assays.

Use of Luminex MagPlex magnetic microspheres for high-throughput spoligotyping of Mycobacterium tuberculosis isolates in Port-au-Prince, Haiti.

Genotyping of Mycobacterium tuberculosis strains became indispensable for understanding tuberculosis transmission dynamics and designing measures to combat the disease. Unfortunately, typing involves sophisticated laboratory analysis, is expensive, and requires a high level of technical expertise, which limited its use in the resource-poor countries where the majority of tuberculosis cases occur. Spoligotyping is a PCR-based M. tuberculosis complex genotyping method with advantages of technical simplicity, numerical output, and high reproducibility. It is based on the presence or absence of 43 distinct "spacers" separating insertion elements in the direct repeat region of the M. tuberculosis genome. The spoligotyping assay involves reverse hybridization of PCR products to the capture spacers attached to nitrocellulose membranes or to microspheres. Here we report modification of the classic 43-spacer method using the new generation of Luminex multiplexing technology with magnetic microspheres. The method was successfully established and validated on strains with known spoligotypes in our laboratory in Haiti. The distribution of spoligotypes determined in a collection of 758 recent M. tuberculosis isolates was in accordance with previous data for Haitian isolates in the SITWITWEB international database, which were obtained with the traditional membrane-based method. In the present form, spoligotyping may be suitable as a high-throughput, first-line tool for genotyping of Mycobacterium tuberculosis in countries with limited resources.

Outbreak of Mycobacterium chelonae infection associated with tattoo ink.

BACKGROUND: In January 2012, on the basis of an initial report from a dermatologist, we began to investigate an outbreak of tattoo-associated Mycobacterium chelonae skin and soft-tissue infections in Rochester, New York. The main goals were to identify the extent, cause, and form of transmission of the outbreak and to prevent further cases of infection. METHODS: We analyzed data from structured interviews with the patients, histopathological testing of skin-biopsy specimens, acid-fast bacilli smears, and microbial cultures and antimicrobial susceptibility testing. We also performed DNA sequencing, pulsed-field gel electrophoresis (PFGE), cultures of the ink and ingredients used in the preparation and packaging of the ink, assessment of source water and faucets at tattoo parlors, and investigation of the ink manufacturer. RESULTS: Between October and December 2011, a persistent, raised, erythematous rash in the tattoo area developed in 19 persons (13 men and 6 women) within 3 weeks after they received a tattoo from a single artist who used premixed gray ink; the highest occurrence of tattooing and rash onset was in November (accounting for 15 and 12 patients, respectively). The average age of the patients was 35 years (range, 18 to 48). Skin-biopsy specimens, obtained from 17 patients, showed abnormalities in all 17, with M. chelonae isolated from 14 and confirmed by means of DNA sequencing. PFGE analysis showed indistinguishable patterns in 11 clinical isolates and one of three unopened bottles of premixed ink. Eighteen of the 19 patients were treated with appropriate antibiotics, and their condition improved. CONCLUSIONS: The premixed ink was the common source of infection in this outbreak. These findings led to a recall by the manufacturer.

Multidrug-resistant tuberculosis in Port-au-Prince, Haiti.

OBJECTIVE: To determine the prevalence of multidrug-resistant tuberculosis (MDR-TB) among patients with new smear-positive pulmonary TB in Port-au-Prince, Haiti. METHODS: Sputum samples were cultured from 1 006 patients newly diagnosed with TB in 2008. The core region of the rpoB gene that is associated with resistance to rifampin was sequenced. All isolates with rpoB mutations were sent to the New York State reference laboratory for conventional drug susceptibility testing (DST). All isolates were also tested with the GenoType MTBDRplus line-probe assay. RESULTS: Mycobacterium tuberculosis was isolated from 906 patients. Twenty-six (2.9%) of the isolates had missense mutations or deletions in rpoB and were resistant to rifampin by DST. All 26 were also resistant to isoniazid and classified as MDR-TB. Forty-six control isolates without rpoB mutations were found to be rifampin sensitive by DST. The GenoType MTBDRplus line-probe assay correctly identified 26 MDR-TB strains. It misclassified one pansusceptible isolate as rifampin resistant. CONCLUSIONS: This study shows an MDR-TB prevalence of 2.9% in newly diagnosed TB patients in Haiti and suggests that rpoB sequencing and hybridization assays are good screening tools for early detection of MDR-TB.

Multidrug-resistant tuberculosis in Port-au-Prince, Haiti / Tuberculosis multirresistente en Puerto Príncipe, Haití

OBJECTIVE: To determine the prevalence of multidrug-resistant tuberculosis (MDR-TB) among patients with new smear-positive pulmonary TB in Port-au-Prince, Haiti. METHODS: Sputum samples were cultured from 1 006 patients newly diagnosed with TB in 2008. The core region of the rpoB gene that is associated with resistance to rifampin was sequenced. All isolates with rpoB mutations were sent to the New York State reference laboratory for conventional drug susceptibility testing (DST). All isolates were also tested with the GenoType MTBDRplus line-probe assay. RESULTS: Mycobacterium tuberculosis was isolated from 906 patients. Twenty-six (2.9 percent) of the isolates had missense mutations or deletions in rpoB and were resistant to rifampin by DST. All 26 were also resistant to isoniazid and classified as MDR-TB. Forty-six control isolates without rpoB mutations were found to be rifampin sensitive by DST. The GenoType MTBDRplus line-probe assay correctly identified 26 MDR-TB strains. It misclassified one pansusceptible isolate as rifampin resistant. CONCLUSIONS: This study shows an MDR-TB prevalence of 2.9 percent in newly diagnosed TB patients in Haiti and suggests that rpoB sequencing and hybridization assays are good screening tools for early detection of MDR-TB.

OBJETIVO: Determinar la prevalencia de tuberculosis (TB) multirresistente en pacientes con TB pulmonar nueva con baciloscopia positiva en Puerto Príncipe, Haití. MÉTODOS: Se cultivaron muestras de esputo de 1 006 pacientes con diagnóstico reciente de tuberculosis efectuado durante el 2008. Se secuenció la región nuclear del gen rpoB, que se asocia con la resistencia a la rifampicina. Todos los aislados con mutaciones de rpoB se enviaron al laboratorio de referencia del estado de Nueva York para llevar a cabo un antibiograma convencional. Todos los aislados se estudiaron también con el ensayo de sonda lineal GenoType MTBDRplus. RESULTADOS: Se aisló Mycobacterium tuberculosis de 906 pacientes. Veintiséis (2,9 por ciento) de los aislados presentaban mutaciones de sentido erróneo o deleciones en rpoB y fueron resistentes a la rifampicina en el antibiograma. Los 26 aislados fueron resistentes también a la isoniacida y se clasificaron como TB multirresistente. Cuarenta y seis aislados de control sin mutaciones de rpoB resultaron sensibles a la rifampicina en el antibiograma. El ensayo de sonda lineal GenoType MTBDRplus identificó correctamente a las 26 cepas de TB multirresistente y clasificó de manera errónea un aislado sensible a múltiples fármacos como resistente a la rifampicina. CONCLUSIONES: Este estudio revela una prevalencia de TB multirresistente de 2,9 por ciento en los pacientes con TB recién diagnosticada en Haití e indica que los ensayos de secuenciación e hibridación de rpoB son estudios de detección sistemática adecuados para la detección temprana de la TB multirresistente.

Evaluation of a single-tube multiplex real-time PCR for differentiation of members of the Mycobacterium tuberculosis complex in clinical specimens.

Members of the Mycobacterium tuberculosis complex (MTBC) differ in virulence attributes, drug resistance patterns, and host preferences. The rapid differentiation of these species to determine zoonotic or human sources of tuberculosis disease or to direct treatment can benefit both public health and patient management. Commercially available assays cannot differentiate these species, and published assays have not been evaluated directly on clinical specimens. A real-time PCR assay for the differentiation of M. tuberculosis, M. bovis, M. bovis BCG, M. africanum, M. microti, and M. canettii was developed. The presence or absence of regions of difference (RD) between the genomes of members of the MTBC allowed for the design of a single-tube five-plex real-time PCR assay to differentiate these species. This assay assesses the presence of RD1, RD4, RD9, RD12, and a region exterior to RD9 which is present in all MTBC members. To evaluate the performance of this assay, 192 clinical specimens positive for MTBC by real-time PCR were tested, resulting in a 94% correlation of the real-time PCR with the identification results obtained with cultured material. Additionally, 727 Bactec MGIT 960-positive cultures were tested, resulting in a 97% concordance between the methods. This real-time PCR is an inexpensive and rapid (2.5-h) method performed in a closed-format system and requiring minimal hands-on time that can be implemented in a clinical laboratory and used directly on clinical specimens.

Combined real-time PCR and rpoB gene pyrosequencing for rapid identification of Mycobacterium tuberculosis and determination of rifampin resistance directly in clinical specimens.

Our laboratory has developed a rapid, sensitive, and specific molecular approach for detection in clinical specimens, within 48 h of receipt, of both Mycobacterium tuberculosis complex (MTBC) DNA and mutations within the 81-bp core region of the rpoB gene that are associated with rifampin (RIF) resistance. This approach, which combines an initial real-time PCR with internal inhibition assessment and a pyrosequencing assay, was validated for direct use with clinical specimens. To assess the suitability of real-time PCR for use with respiratory, nonrespiratory, acid-fast bacillus (AFB)-positive and AFB-negative specimens, we evaluated specimens received in our laboratory between 11 October 2007 and 30 June 2009. With culture used as the "gold standard," the sensitivity, specificity, and positive and negative predictive values were determined for 1,316 specimens to be as follows: for respiratory specimens, 94.7%, 99.9%, 99.6%, and 98.6%, respectively; for nonrespiratory specimens, 88.5%, 100.0%, 100.0%, and 96.9%, respectively; for AFB-positive specimens, 99.6%, 100.0%, 100.0%, and 97.7%, respectively; and for AFB-negative specimens, 75.4%, 99.9%, 98.0%, and 98.4%, respectively. PCR inhibition was determined to be minimal in this assay, occurring in 0.2% of tests. The rpoB gene pyrosequencing assay was evaluated in a similar prospective study, in which 148 clinical specimens positive for MTBC DNA by real-time PCR were tested. The final results revealed that the results of direct testing of clinical specimens by the pyrosequencing assay were 98.6% concordant with the results of conventional testing for susceptibility to RIF in liquid culture and that our assay displayed adequate sensitivity for 96.6% of the clinical specimens tested. Used together, these assays provide reliable results that aid with the initial management of patients with suspected tuberculosis prior to the availability of the results for cultured material, and they also provide the ability to predict RIF resistance in Mycobacterium tuberculosis-positive specimens in as little as 48 h from the time of clinical specimen receipt.

The Emb proteins of mycobacteria direct arabinosylation of lipoarabinomannan and arabinogalactan via an N-terminal recognition region and a C-terminal synthetic region.

The arabinans of the mycobacterial cell wall are key structural and immunological polymers in the context of arabinogalactan (AG) and lipoarabinomannan (LAM) respectively. The three homologous membrane proteins EmbA, EmbB and EmbC are known to be involved in the synthesis of arabinan but their biochemical functions are not understood. Herein we show, that synthesis of LAM, but not AG, ceases after inactivation of embC in Mycobacterium smegmatis by insertional mutagenesis. LAM synthesis is restored upon complementation with the embC wild-type gene. Previously we have shown that the synthesis of the arabinan of AG is affected by embA or embB disruption. Thus the Emb proteins are capable of differential recognition of the galactan or mannan acceptors prior to appropriate arabinosylation. In addition, a combination of genetic and biochemical approaches have allowed us to assign some specific functions to the regions of emb gene products. Complementation of the embCmacr; mutant with a hybrid gene encoding the N-terminus of EmbC and the C-terminus of EmbB resulted in LAM with a lower molecular weight than the wild-type LAM. Structural studies involving enzyme digestion, chromatography and mass spectrometry analyses revealed that the arabinan of the 'LAM' formed in the hybrid was of AG kind rather than LAM type of arabinan.

Emerging therapeutic targets in tuberculosis: post-genomic era.

Every minute, somewhere in the world four people die from tuberculosis (TB), yet it has been nearly 40 years since a novel drug was introduced to treat this disease. The ever increasing number of TB cases together with the advent of multi-drug resistant (MDR) TB, has stimulated the search for novel anti-TB agents. An array of novel drug targets is provided by the mycobacterial cell wall, whose integrity is essential for bacterial viability. Over the years researchers have identified potential drug targets that are associated with the synthesis of various cell wall constituents. This classic approach, together with the unravelling of the Mycobacterium tuberculosis genome sequence, has placed TB drug research in an unprecedented position. An entire new set of genetic and bioinformatic tools for probing potential drug targets is now available. As therapies using first-line drugs like isoniazid (INH) or rifampin in combination with second-line drugs, like ethambutol (EMB) still continues, a number of substituted fluoroquinolones are being considered as the new generation of anti-TB drugs for their favourable pharmacokinetic profile and excellent oral bioavailability. In this review, the future of anti-TB drugs is discussed with reflection on the structure and biosynthesis of cell wall constituents that are potential drug targets. The importance and relevance of the M. tuberculosis genome sequence for the development of novel anti-TB drugs, have also been underscored.