Different molecular methods for the identification of rarely isolated non-tuberculous mycobacteria and description of new hsp65 restriction fragment length polymorphism patterns

Whole-Genome Sequencing Analysis to Identify Infection with Multiple Species of Nontuberculous Mycobacteria

Mixed infection with multiple species of nontuberculous mycobacteria (NTM) is difficult to identify and to treat. Current conventional molecular-based methods for identifying mixed infections are limited due to low specificity. Here, we evaluated the utility of whole-genome sequencing (WGS) analysis to detect and identify mixed NTM infections. Analytical tools used included PubMLST, MetaPhlAn3, Kraken2, Mykrobe-Predictor and analysis of heterozygous SNP frequencies. The ability of each to identify mixed infections of NTM species was compared. Sensitivity was tested using 101 samples (sequence sets) including 100 in-silico simulated mixed samples with various proportions of known NTM species and one sample of known mixed NTM species from a public database. Single-species NTM control samples (155 WGS samples from public databases and 15 samples from simulated reads) were tested for specificity. Kraken2 exhibited 100% sensitivity and 98.23% specificity for detection and identification of mixed NTM species with accurate estimation of relative abundance of each species in the mixture. PubMLST (99% and 96.47%) and MetaPhlAn3 (95.04% and 83.52%) had slightly lower sensitivity and specificity. Mykrobe-Predictor had the lowest sensitivity (57.42%). Analysis of read frequencies supporting single nucleotide polymorphisms (SNPs) could not detect mixed NTM samples. Clinical NTM samples (n = 16), suspected on the basis of a 16S-23S rRNA gene sequence-based line-probe assay (LPA) to contain more than one NTM species, were investigated using WGS-analysis tools. This identified only a small proportion (37.5%, 6/16 samples) of the samples as mixed infections and exhibited only partial agreement with LPA results. LPAs seem to be inadequate for detecting mixed NTM species infection. This study demonstrated that WGS-analysis tools can be used for diagnosis of mixed infections with different species of NTM.

Disseminated Mycobacterium interjectum Infection with Bacteremia, Hepatic and Pulmonary Involvement Associated with a Long-Term Catheter Infection

We present a 49-year-old female with one year of intermittent fevers, chills, night sweats, and significant weight loss. Liver and lung biopsy showed evidence of a granulomatous process. Blood and liver biopsy cultures yielded growth of presumed Mycobacterium interjectum, thought to be related to a disseminated long-term central venous catheter infection. She successfully received one year of combined antimicrobial therapy after catheter removal without recurrence of disease. M. interjectum has been previously described as a cause of lymphadenitis in healthy children and associated with pulmonary disease in adults, although other localized infections have been reported. This is the first case described of a disseminated M. interjectum infection with bacteremia, hepatic and pulmonary involvement associated with a long-term catheter infection.

Identification of Species of Nontuberculous Mycobacteria Clinical Isolates from 8 Provinces of China

Pulmonary diseases caused by nontuberculous mycobacteria (NTM) are increasing in incidence and prevalence worldwide. In this study, we identified NTM species of the clinical isolates from 8 provinces in China, in order to preliminarily provide some basic scientific data in the different species and distribution of NTM related to pulmonary disease in China. A total of 523 clinical isolates from patients with tuberculosis (TB) diagnosed clinically from 2005 to 2012 were identified to the species using conventional and molecular methods, including multilocus PCR, rpoB and hsp65 PCR-PRA, hsp65, rpoB, and 16S-23S internal transcribed spacer region sequencing. The isolates were identified into 3 bacterium genera, including NTM, Gordonia bronchialis, and Nocardia farcinica, and, for the 488 NTM isolates, 27 species were identified. For all the 27 species of NTM which were found to cause pulmonary infections in humans, the most prevalent species was M. intracellulare, followed by M. avium and M. abscessus. And seven other species were for the first time identified in patients with TB in China. NTM species identification is very important for distinguishing between tuberculosis and NTM pulmonary diseases, and the species diversity drives the creation of diverse and integrated identification methods with higher accuracy and efficacy.

Mycobacteria mobility shift assay: a method for the rapid identification of Mycobacterium tuberculosis and nontuberculous mycobacteria

The identification of mycobacteria is essential because tuberculosis (TB) and mycobacteriosis are clinically indistinguishable and require different therapeutic regimens. The traditional phenotypic method is time consuming and may last up to 60 days. Indeed, rapid, affordable, specific and easy-to-perform identification methods are needed. We have previously described a polymerase chain reaction-based method called a mycobacteria mobility shift assay (MMSA) that was designed for Mycobacterium tuberculosis complex (MTC) and nontuberculous mycobacteria (NTM) species identification. The aim of this study was to assess the MMSA for the identification of MTC and NTM clinical isolates and to compare its performance with that of the PRA-hsp65 method. A total of 204 clinical isolates (102 NTM and 102 MTC) were identified by the MMSA and PRA-hsp65. For isolates for which these methods gave discordant results, definitive species identification was obtained by sequencing fragments of the 16S rRNA and hsp65 genes. Both methods correctly identified all MTC isolates. Among the NTM isolates, the MMSA alone assigned 94 (92.2%) to a complex or species, whereas the PRA-hsp65 method assigned 100% to a species. A 91.5% agreement was observed for the 94 NTM isolates identified by both methods. The MMSA provided correct identification for 96.8% of the NTM isolates compared with 94.7% for PRA-hsp65. The MMSA is a suitable auxiliary method for routine use for the rapid identification of mycobacteria.

Hsp65 phylogenetic assay for molecular diagnosis of nontuberculous mycobacteria isolated in Mexico

BACKGROUND AND AIMS

Nontuberculous mycobacteria (NTM) are mainly distributed as important emerging pathogens in patients with chronic or immunosuppressive diseases. Accurate identification of causative species is crucial for proper treatment and patient follow-up. However, several difficulties are associated with phenotypic and molecular diagnostic methods for precise identification at the species level due to shared metabolic and genetic characteristics. We undertook this study to evaluate the application of the phylogenetic method based on hsp65 gene into Telenti's PCR-restriction enzyme analysis (PRA) for molecular identification of NTM.

METHODS

The study population was comprised of 1646 Mycobacterium clinical isolates (AFB positive) collected from 2008-2011, of which 537 (32.6%) were MNT identified by PRA analysis. DNA sequencing of hsp65 in 53 isolates (10%) was performed. Sequence identification through NCBI-Basic Local Alignment Search Tool (BLAST) achieved correct identification in 23 isolates. Phylogenetic trees including hsp65 available GenBank sequences for all described genres of NTM and hsp65 obtained sequences were constructed using Mega 5.05 software. We compared sequence identification based on phylogenetic clustering and BLAST similarity search.

RESULTS

Phylogenetic clustering allowed more specific differentiation of closely related species and clearer identification in comparison with BLAST; 30 Mycobacterium species (this is the first report of isolation of some of these from clinical samples in Mexico) were identified in this way.

CONCLUSIONS

The proposed 440 bp hsp65 phylogenetic method allows a better identification tool to differentiate Mycobacterium species and is useful to complement diagnosis and epidemiological surveillance of NTM.

Mycobacterium interjectum Lung Infection

A 62-year-old male presented with productive cough, weight loss, and night sweats. CXR revealed a right upper lobe cavitary lesion. Evaluation was negative for Mycobacterium tuberculosis, and sputum revealed Mycobacterium avium intracellulare (MAI). Since his clinical course was atypical for MAI, further investigations were pursued which identified Mycobacterium interjectum in lung specimens, a very rarely described etiology of pulmonary disease. Appropriate therapy with rifampin, intravenous amikacin, trimethoprim/sulfamethoxazole (TMP/SMX), and ethambutol resulted in clinical and radiographic improvement. This is the third case described over a period of 20 years of destructive lung disease in an immunocompetent adult due to M. interjectum.

Molecular detection of nontuberculous mycobacteria: advantages and limits of a broad-range sequencing approach

The isolation of nontuberculous mycobacteria (NTM) from clinical specimens has become very common in recent years. Such organisms are typically environmental and occasionally pathogenic for humans and animals. Standard diagnosis of mycobacterial infections relies on direct examination and culture. However, molecular tools are now available which allow quicker and more accurate diagnosis. Detection of NTM can be performed directly from clinical samples, although identification is mostly carried out after isolation. Sequencing of genomic targets (such as 16S rRNA, ITS, rpoB or hsp65) allows accurate and rapid identification, but has some technical limitations. A brief summary of the molecular methods available for NTM identification and a discussion of the problems associated with the use of sequencing analysis together with a description of available algorithms for NTM identification are the major objectives of this review.

Combined rpoB duplex PCR and hsp65 PCR restriction fragment length polymorphism with capillary electrophoresis as an effective algorithm for identification of mycobacterial species from clinical isolates

Background

Mycobacteria can be quickly and simply identified by PCR restriction-enzyme analysis (PRA), but misidentification can occur because of similarities in band sizes that are critical for discriminating among species. Capillary electrophoresis can provide computer-aided band discrimination. The aim of this research was to develop an algorithm for identifying mycobacteria by combined rpoB duplex PRA (DPRA) and hsp65 PRA with capillary electrophoresis.

Results

Three hundred and seventy-six acid-fast bacillus smear-positive BACTEC cultures, including 200 Mycobacterium tuberculosis complexes (MTC) and 176 non-tuberculous mycobacteria (NTM) were analyzed. With combined hsp65 and rpoB DPRA, the accuracy rate was 100% (200 isolates) for the MTC and 91.4% (161 isolates) for the NTM. Among the discordant results (8.6%) for the NTM, one isolate of Mycobacterial species and an isolate of M. flavescens were found as new sub-types in hsp65 PRA.

Conclusions

This effective and novel identification algorithm using combined rpoB DPRA and hsp65 PRA with capillary electrophoresis can rapidly identify mycobacteria and find new sub-types in hsp65 PRA. In addition, it is complementary to 16 S rDNA sequencing.

Point-of-use membrane filtration and hyperchlorination to prevent patient exposure to rapidly growing mycobacteria in the potable water supply of a skilled nursing facility

BACKGROUND

Healthcare-associated outbreaks and pseudo-outbreaks of rapidly growing mycobacteria (RGM) are frequently associated with contaminated tap water. A pseudo-outbreak of Mycobacterium chelonae-M. abscessus in patients undergoing bronchoscopy was identified by 2 acute care hospitals. RGM was identified in bronchoscopy specimens of 28 patients, 25 of whom resided in the same skilled nursing facility (SNF). An investigation ruled out bronchoscopy procedures, specimen collection, and scope reprocessing at the hospitals as sources of transmission.

OBJECTIVE

To identify the reservoir for RGM within the SNF and evaluate 2 water system treatments, hyperchlorination and point-of-use (POU) membrane filters, to reduce RGM.

DESIGN

A comparative in situ study of 2 water system treatments to prevent RGM transmission.

SETTING

An SNF specializing in care of patients requiring ventilator support.

METHODS

RGM and heterotrophic plate count (HPC) bacteria were examined in facility water before and after hyperchlorination and in a subsequent 24-week assessment of filtered water by colony enumeration on Middlebrook and R2A media.

RESULTS

Mycobacterium chelonae was consistently isolated from the SNF water supply. Hyperchlorination reduced RGM by 1.5 log(10) initially, but the population returned to original levels within 90 days. Concentration of HPC bacteria also decreased temporarily. RGM were reduced below detection level in filtered water, a 3-log(10) reduction. HPC bacteria were not recovered from newly installed filters, although low quantities were found in water from 2-week-old filters.

CONCLUSION

POU membrane filters may be a feasible prevention measure for healthcare facilities to limit exposure of sensitive individuals to RGM in potable water systems.

[Use of different PCR-based techniques integrated into a non-tuberculous identification algorithm]

INTRODUCTION

The aim of the present work was to demonstrate the utility of a non-tuberculous mycobacteria (NTM) identification algorithm, which integrates different PCR-based techniques and basic phenotypic features. Moreover, the algorithm for pattern restriction analysis of hsp65 (hsp65 PRA) interpretation has been updated.

METHODS

The workflow chosen consisted of the identification by a DNA hybridization probe method, followed by PCR-restriction enzyme analysis of hsp65 (hsp65 PRA) in those isolates that cannot be identified by hybridization probes. If necessary, 16S rRNA gene and hsp65 gene sequencing were used for speciation.

RESULTS

A total of 236 NTM were collected, in which 102 (43.2%) isolates were identified by DNA specific probes and 76 (32.2%) isolates were identified with hsp65 PRA. Partial sequencing of the 16S rRNA gene was used for species identification of the remaining 58 (24.5%) isolates. Fifty-three (22.4%) were identified using this method. Five isolates (2.1%) were submitted for partial sequencing of hsp65 gene and one isolate was identified with this method. Four strains (1.7%) could not be identified at species level. Three new PRA patterns were found. Seven isolates tested positive with the AccuProbe Mycobacterium avium complex identification test but did not test positive with the M. avium or Mycobacterium intracellulare specific probes. Five and two of these isolates were identified as M. intracellulare and Mycobacterium colombiense, respectively.

CONCLUSION

This approach allowed us to identify almost all NTM isolates found in this study, including some recently described species.

Mycobacterium heckeshornense peritonitis in a peritoneal dialysis patient: a case report and review of the literature

We report the first case of peritonitis attributed to Mycobacterium heckeshornense. This is a rare, non-tuberculous mycobacterium that has been reported as an aetiological agent in a growing number and widening spectrum of infections.

Evaluation of PCR–RFLP analysis targeting hsp65 and rpoB genes for the typing of mycobacterial isolates in Malaysia

In this study, PCR–RFLP analysis (PRA) targeting hsp65 and rpoB gene regions was evaluated for the identification of mycobacterial species isolated from Malaysian patients. Overall, the hsp65 PRA identified 92.2 % of 90 isolates compared to 85.6 % by the rpoB PRA. With 47 rapidly growing species, the hsp65 PRA identified fewer (89.4 %) species than the rpoB PRA (95.7 %), but with 23 slow-growing species the reverse was true (91.3 % identification by the hsp65 PRA but only 52.5 % by the rpoB PRA). There were 16 isolates with discordant PRA results, which were resolved by 16S rRNA and hsp65 gene sequence analysis. The findings in this study suggest that the hsp65 PRA is more useful than the rpoB PRA for the identification of Mycobacterium species, particularly with the slow-growing members of the genus. In addition, this study reports 5 and 12 novel restriction patterns for inclusion in the hsp65 and rpoB PRA algorithms, respectively.

Revival and emended description of 'Mycobacterium paraffinicum' Davis, Chase and Raymond 1956 as Mycobacterium paraffinicum sp. nov., nom. rev

The omission of the name 'Mycobacterium paraffinicum' from the Approved Lists of Bacterial Names was due to phenotypic confusion surrounding a close relationship with Mycobacterium scrofulaceum. Correspondingly, 'M. paraffinicum' strains grew slowly in > 7 days, stained acid-alcohol-fast and produced yellow-pigmented, smooth, waxy colonies in the dark at an optimal temperature of 35°C. However, 'M. paraffinicum' strains demonstrated no activity for urease, nicotinamidase or pyrazinamidase and lacked growth at 42°C, unlike M. scrofulaceum. The mycolic acid pattern, as determined by HPLC, clustered 'M. paraffinicum' with M. scrofulaceum, Mycobacterium avium and Mycobacterium parascrofulaceum. Strains were fully susceptible to linezolid, rifabutin, clarithromycin and amikacin. Examination of the historical reference strain of 'M. paraffinicum', ATCC 12670, and five additional isolates using comparative studies with 16S rRNA, hsp65 and rpoB gene and concatenated sequences showed that they formed a tight taxonomic group that was distinct from similar non-tuberculous mycobacteria. Multilocus enzyme electrophoresis (MEE) analysis confirmed a close association of the five additional isolates with the reference strain of 'M. paraffinicum' with a genetic distance of 0.12 and showed that all six strains were distinct from other closely related species. These genetic results provided unambiguous evidence of the uniqueness of this slowly growing, scotochromogenic species and supported the revival of the name as Mycobacterium paraffinicum (ex Davis, Chase and Raymond 1956) sp. nov., nom. rev. We propose the previously deposited reference strain ATCC 12670(T) =DSM 44181(T) =NCIMB 10420(T), located in collections worldwide, as the type strain.

Mycobacterium heckeshornense tenosynovitis

We describe the first case of tenosynovitis due to Mycobacterium heckeshornense, a mycobacterium characterized in 2000 and only incriminated in a few previous cases of infections. Molecular identification of this pathogen included 16S rRNA and hsp65 gene sequencing. M. heckeshornense may cause a wide spectrum of human infectious diseases and may be underestimated due to its phenotypic relatedness with Mycobacterium xenopi.

First case of Mycobacterium heckeshornense lymphadenitis

Mycobacterium heckeshornense is a slow-growing nontuberculous mycobacterium first characterized in 2000. It is reported to cause lung disease and tenosynovitis. We report a case of isolated massive axillary lymphadenopathy in an elderly woman, where histology showed necrotizing granulomata and M. heckeshornense was isolated as the causative organism.

Identification of non-tuberculous mycobacteria from the Central Public Health Laboratory from Mato Grosso do Sul and analysis of clinical relevance

Non-tuberculous mycobacteria isolated at the Central Public Health Laboratory from Mato Grosso do Sul in 2003 and 2004 were identified by conventional phenotypic methods (TI) and by PCR-Restriction Enzyme Analysis (PRA) using the hsp65 gene as target (PRA-hsp65). With 15 of the 32 analysed isolates, results of both methods were concordant, being 8 Mycobacterium avium, 3 M. fortutium, 1 M. kansasii, 1 M. flavescens, 1 M. peregrinum and 1 Nocardia brasiliensis. TI of 12 isolates was inconclusive. Novel PRA-hsp65 patterns were observed with 11 isolates. Medical data were evaluated for inference of clinical relevance of these isolates.

Characterization of "Mycobacterium paraffinicum" associated with a pseudo-outbreak

We describe the first "Mycobacterium paraffinicum" (unofficial taxon) pseudo-outbreak in a tertiary-care medical center. Fifteen clinical nontuberculous mycobacterium isolates from 10 patients were initially identified by biochemical tests and high-performance liquid chromatography as Mycobacterium scrofulaceum. However, further testing by molecular analysis revealed "M. paraffinicum." Epidemiological and environmental investigation determined that the ice machine was the source of the pseudo-outbreak.

Reliable identification of mycobacterial species by PCR-restriction enzyme analysis (PRA)-hsp65 in a reference laboratory and elaboration of a sequence-based extended algorithm of PRA-hsp65 patterns

BACKGROUND

Identification of nontuberculous mycobacteria (NTM) based on phenotypic tests is time-consuming, labor-intensive, expensive and often provides erroneous or inconclusive results. In the molecular method referred to as PRA-hsp65, a fragment of the hsp65 gene is amplified by PCR and then analyzed by restriction digest; this rapid approach offers the promise of accurate, cost-effective species identification. The aim of this study was to determine whether species identification of NTM using PRA-hsp65 is sufficiently reliable to serve as the routine methodology in a reference laboratory.

RESULTS

A total of 434 NTM isolates were obtained from 5019 cultures submitted to the Institute Adolpho Lutz, Sao Paulo Brazil, between January 2000 and January 2001. Species identification was performed for all isolates using conventional phenotypic methods and PRA-hsp65. For isolates for which these methods gave discordant results, definitive species identification was obtained by sequencing a 441 bp fragment of hsp65. Phenotypic evaluation and PRA-hsp65 were concordant for 321 (74%) isolates. These assignments were presumed to be correct. For the remaining 113 discordant isolates, definitive identification was based on sequencing a 441 bp fragment of hsp65. PRA-hsp65 identified 30 isolates with hsp65 alleles representing 13 previously unreported PRA-hsp65 patterns. Overall, species identification by PRA-hsp65 was significantly more accurate than by phenotype methods (392 (90.3%) vs. 338 (77.9%), respectively; p < .0001, Fisher's test). Among the 333 isolates representing the most common pathogenic species, PRA-hsp65 provided an incorrect result for only 1.2%.

CONCLUSION

PRA-hsp65 is a rapid and highly reliable method and deserves consideration by any clinical microbiology laboratory charged with performing species identification of NTM.

Differentiation of Mycobacterium species by analysis of the heat-shock protein 65 gene (hsp65)

The nucleotide sequences (604 bp) of partial heat-shock protein genes (hsp65) from 161 Mycobacterium strains containing 56 reference Mycobacterium species and 105 clinical isolates were determined and compared. hsp65 sequence analysis showed a higher degree of divergence between Mycobacterium species than did 16S rRNA gene analysis. Generally, the topology of the phylogenetic tree based on the hsp65 DNA sequences was similar to that of the 16S rRNA gene, thus revealing natural relationships among Mycobacterium species. When a direct sequencing protocol targeting 422 bp sequences was applied to 70 non-tuberculous mycobacterium (NTM) clinical isolates, all NTMs were clearly identified. In addition, an XhoI PCR restriction fragment length polymorphism analysis method for the differentiation of Mycobacterium tuberculosis complex from NTM strains was developed during this study. The results obtained suggest that 604 bp hsp65 sequences are useful for the phylogenetic analysis and species identification of mycobacteria.

A mutation in the 65,000Dalton heat shock protein gene, commonly used for molecular identification of non-tuberculous mycobacteria, leads to the misidentification of Mycobacterium malmoense as Mycobacterium marinum

We describe a case of a Mycobacterium isolated from a patient with cervical lymphadenitis which was initially identified by hsp65 RFLP as Mycobacterium marinum. Sequence analysis of the hsp65 DNA fragment and the 16S rDNA signature sequence, however, led to the identification of Mycobacterium malmoense. A point mutation in one of the restriction sites had shifted the M. malmoense typical RFLP pattern to the M. marinum specific RFLP pattern. As a consequence, care should be taken when identifying mycobacteria with the use of one molecular technique, only.

Identification of Mycobacterium species by secA1 sequences

We describe a novel molecular method for the differentiation and identification of 29 mycobacterial species. The target is the secA1 gene that codes for the essential protein SecA1, a key component of the major pathway of protein secretion across the cytoplasmic membrane. A 700-bp region of the secA1 gene was amplified and sequenced from 47 American Type Culture Collection strains of 29 Mycobacterium species as well as from 59 clinical isolates. Sequence variability in the amplified segment of the secA1 gene allowed the differentiation of all species except for the members of the Mycobacterium tuberculosis (MTB) complex, which had identical sequences. A range of 83.3 to 100% interspecies similarity was observed. All species could also be differentiated by their amino acid sequences as deduced from the sequenced region of the secA1 gene, with the exception of the MTB complex. Partial sequences of secA1 from clinical isolates belonging to nine frequently isolated species of mycobacteria revealed a very high intraspecies similarity at the DNA level (typically >99%; range, 96.0 to 100%); all clinical isolates were correctly identified. Comparison of the deduced 233-amino-acid sequences among clinical isolates of the same species showed between 99.6 and 100% similarity. To our knowledge, this is the first time a secretion-related gene has been used for the identification of the species within a bacterial genus.

Mycobacteria in drinking water distribution systems: ecology and significance for human health

In contrast to the notorious pathogens Mycobacterium tuberculosis and M. leprae, the majority of the mycobacterial species described to date are generally not considered as obligate human pathogens. The natural reservoirs of these non-primary pathogenic mycobacteria include aquatic and terrestrial environments. Under certain circumstances, e.g., skin lesions, pulmonary or immune dysfunctions and chronic diseases, these environmental mycobacteria (EM) may cause disease. EM such as M. avium, M. kansasii, and M. xenopi have frequently been isolated from drinking water and hospital water distribution systems. Biofilm formation, amoeba-associated lifestyle, and resistance to chlorine have been recognized as important factors that contribute to the survival, colonization and persistence of EM in water distribution systems. Although the presence of EM in tap water has been linked to nosocomial infections and pseudo-infections, it remains unclear if these EM provide a health risk for immunocompromised people, in particular AIDS patients. In this regard, control strategies based on maintenance of an effective disinfectant residual and low concentration of nutrients have been proposed to keep EM numbers to a minimum in water distribution systems.

A new method for species identification and differentiation of Mycobacterium chelonae complex based on amplified hsp65 restriction analysis (AHSPRA)

Members of the Mycobacterium chelonae complex (MCC), namely M. chelonae, Mycobacterium abscessus and Mycobacterium immunogenum, have been implicated in nosocomial infections and occupational respiratory illnesses like hypersensitivity pneumonitis (HP) associated with contaminated metalworking fluid (MWF) exposures. Close relationship among these member species makes their differentiation cumbersome using the existing methods. Here we report a simple and rapid method for unambiguous identification and differentiation of the three-member species of the MCC group with PCR-restriction analysis targeting a 667-bp segment of a variable region of the 65-kDa-heat shock protein (hsp65) gene. This assay, described as Amplified hsp65 Restriction Analysis (AHSPRA), can discriminate all the three individual species using a one-step restriction digestion using either BbvI or Eco0109I. The enzyme NarI can differentiate M. immunogenum from the other two MCC species (M. chelonae and M. abscessus). The developed method was validated using several non-MCC reference species of other rapidly growing mycobacteria (RGM) and MCC field isolates from MWF samples. Direct cell-lysis was used instead of the conventional DNA template preparation, which improved the rapidity, simplicity and adaptability of the developed method. The results suggest that the developed method can unambiguously differentiate species of the M. chelonae complex from other RGM species and from one another.

The genetics of nontuberculous mycobacterial infection

The molecular aetiology of familial susceptibility to disseminated mycobacterial disease, usually involving weakly pathogenic strains of mycobacteria, has now been elucidated in more than 30 families. Mutations have been identified in five genes in the interleukin-12-dependent interferon-gamma pathway, highlighting the importance of this pathway in human mycobacterial immunity. Knowledge derived from the study of these rare patients contributes to our understanding of the immune response to common mycobacterial pathogens such as Mycobacterium tuberculosis and Mycobacterium leprae, which remain major public health problems globally. This knowledge can be applied to the rational development of novel therapies and vaccines for these important mycobacterial diseases.