Evaluation of Various Culture Media for Detection of Rapidly Growing Mycobacteria from Patients with Cystic Fibrosis

Emergence of Mycobacterium gordonae in heater-cooler units: a five-year prospective surveillance of devices frequently subjected to chloramine-T booster disinfection

BACKGROUND

Worldwide, the detection of Mycobacterium chimaera in LivaNova heater-cooler units (HCUs) has led to their replacement with other HCUs, although non-tuberculous mycobacteria (NTM) have been reported also for HCUs produced by other manufacturers. In almost all hospitals of our region, LivaNova HCUs have been replaced with Maquet HCU40s, regularly disinfected with chloramine-T.

AIM

To report the results of the surveillance over a 63-month operation period of the Maquet devices, and to provide a trend in NTM positivity over time.

METHODS

Twenty-nine Maquet devices (HCU40 and HU35) were monitored by two culture methods and propidium monoazide polymerase chain reaction (PMA-PCR) method. The trend in NTM positivity rate was evaluated through the Locally Estimated Scatterplot Smoothing regression and then modelled over time through segmented logistic regression.

FINDINGS

The data acquired during the study period demonstrate a remarkable increase in the positivity rate, especially after the third year (maximum slope change at 1280 days). Non-tuberculous mycobacteria were isolated in 150 water samples (37.2%); 100% and 62% of HCU40 and HU35 devices, respectively, were colonized with non-tuberculous mycobacteria. The most frequently detected species were Mycobacterium gordonae (73%) followed by Mycobacterium chelonae (41%) and Mycobacterium paragordonae (11%).

CONCLUSION

Preventive strategies by disinfection with chloramine-T did not effectively reduce non-tuberculous mycobacteria colonization of Maquet devices. Although, to date, no cases of postoperative invasive infections linked to Maquet devices have been reported, our microbiological results emphasize the need for (1) designing changes to increase safety of devices and (2) researching and developing new disinfection protocols including alternative molecules.

Multicenter study of the performance of NTM Elite agar for the detection of nontuberculous mycobacteria from patients with cystic fibrosis

The performance of a novel selective agar was evaluated against the performance of conventional mycobacterial cultures, i.e., a combination of the mycobacterial growth indicator tube (MGIT) with Löwenstein-Jensen (LJ), for the detection of nontuberculous mycobacteria (NTM) in sputum samples from people with cystic fibrosis (pwCF). Two hundred eighty-three sputum samples (231 fresh sputum and 52 spiked sputum) from 143 pwCF were collected. They were inoculated without prior decontamination on NTM Elite agar (30°C ± 2°C for 28 days) and inoculated on both MGIT and LJ (35°C-37°C for 6-8 weeks) after N-acetyl-L-cysteine-2% sodium hydroxide decontamination. NTM were identified by Matrix-Assisted Laser Desorption Ionization/Time of Flight Mass Spectrometry and/or PCR, and whole-genome sequencing. A total of 67 NTM were recovered overall by the combination of all culture media. NTM Elite agar allowed the recovery of 65 NTM (97%), compared to 22 for the conventional MGIT and LJ media combination (32.8%), including 22 NTM for MGIT (32.8%) and 3 NTM with the LJ medium (4.5%). For Mycobacterium abscessus complex, the sensitivity of NTM Elite agar was 95% compared with a sensitivity of 30% for the conventional MGIT and LJ media combination. Overall, 17.3% of cultures on NTM Elite agar were contaminated with other micro-organisms vs 46.3% on MGIT and 77% on LJ. This study shows that the novel selective agar (NTM Elite agar) significantly outperforms the conventional MGIT and LJ media combination in terms of sensitivity, selectivity, and ease of culture, without the requirement of an L3 laboratory.IMPORTANCENontuberculous mycobacteria (NTM) are significant pulmonary pathogens in patients with pre-existing structural lung conditions such as cystic fibrosis, bronchiectasis, or chronic obstructive pulmonary disease. Mycobacterium avium complex and Mycobacterium abscessus complex (MABSC) are the most frequently isolated organisms. Compared to the recommended culture method for NTM, which combines solid and liquid culture media, NTM Elite agar enables a faster/easier diagnosis and speeds up identification and susceptibility testing as the final reading is at 28 days instead of 6-8 weeks for the conventional mycobacterial cultures. In addition, for the NTM Elite agar, no decontamination stage before inoculation is necessary, unlike the conventional mycobacterial cultures. NTM Elite agar is derived from a formulation of medium adapted to rapidly growing mycobacteria (RGM). The medium enables the growth of RGM while suppressing other flora. It is supported with published clinical data showing the benefits of this medium.

Clinical Evaluation of Nontuberculous Mycobacteria (NTM) Elite Agar, a New Medium for the Isolation of NTM: a Multicenter Study

Nontuberculous mycobacteria (NTM) are gaining interest with the increased number of infected patients. NTM Elite agar is designed specifically for the isolation of NTM without the decontamination step. We assessed the clinical performance of this medium combined with Vitek mass spectrometry (MS) matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) technology for the isolation and identification of NTM in a prospective multicenter study, including 15 laboratories (24 hospitals). A total of 2,567 samples from patients with suspected NTM infection were analyzed (1,782 sputa, 434 bronchial aspirates, 200 bronchoalveolar lavage samples, 34 bronchial lavage samples, and 117 other samples). A total of 220 samples (8.6%) were positive with existing laboratory methods against 330 with NTM Elite agar (12.8%). Using the combination of both methods, 437 isolates of NTM were detected in 400 positive samples (15.6% of samples). In total, 140 samples of the standard procedures (SP) and 98 of the NTM Elite agar were contaminated. NTM Elite agar showed a higher performance for rapidly growing mycobacteria (RGM) species than SP (7% versus 3%, P < 0.001). A trend has been noted for the Mycobacterium avium complex (4% with SP versus 3% with NTM Elite agar, P = 0.06). The time to positivity was similar (P = 0.13) between groups. However, the time to positivity was significantly shorter for the RGM in subgroup analysis (7 days with NTM and 6 days with SP, P = 0.01). NTM Elite agar has been shown to be useful for the recovery of NTM species, especially for the RGM. Using NTM Elite agar + Vitek MS system in combination with SP increases the number of NTM isolated from clinical samples.

Nontuberculous Mycobacteria in Cystic Fibrosis in the Era of Cystic Fibrosis Transmembrane Regulator Modulators

Nontuberculous mycobacteria (NTM) are a group of mycobacteria which represent opportunistic pathogens that are of increasing concern in people with cystic fibrosis (pwCF). The acquisition has been traditionally though to be from environmental sources, though recent work has suggested clustered clonal infections do occur and transmission potential demonstrated among pwCF attending CF specialist centers. Guidelines for the screening, diagnosis, and identification of NTM and management of pwCF have been published. The emergence of CF-specific therapies, in particular cystic fibrosis transmembrane regulator (CFTR) modulator drugs, have led to significant improvement in the health and well-being of pwCF and may lead to challenges in sampling the lower respiratory tract including to screen for NTM. This review highlights the epidemiology, modes of acquisition, screening and diagnosis, therapeutic approaches in the context of improved clinical status for pwCF, and the clinical application of CFTR modulator therapies.

Methods of isolation and identification of nontuberculous mycobacteria from environmental samples: A scoping review

Nontuberculous mycobacteria (NTM) are ubiquitous in the environment. Some species of NTM are pathogenic and cause lung disease in susceptible persons. Epidemiologic studies of environmental NTM infection risk rely on both culture-dependent and culture-independent techniques for NTM isolation and identification. In this review, we summarized current methods used to isolate and identify NTM from the environment. We searched PubMed, Embase, Scopus, Web of Science: Core Collection, and Global Health (CAB Direct) for peer-reviewed studies from the last 12 years. We identified 1685 unique citations and 110 studies met our inclusion and exclusion criteria. Approximately half (55%) of the studies identified in this review used a combination of culture-independent and culture-dependent methods. The most common environmental substrate analyzed was water (n = 90). Identification of current, common methods for the isolation and identification of NTM from environmental samples may contribute to the development of standard methodological practices in the future. The choice of isolation method is based on the research question, environment, and species. A summary of common methods may contribute to the development of standard practices for isolation and identification of NTM from environmental samples, which may lead to more robust and comparable results.

A New Culture Method for the Detection of Non-Tuberculous Mycobacteria in Water Samples from Heater-Cooler Units and Extracorporeal Membrane Oxygenation Machines

The isolation of non-tuberculous mycobacteria (NTM) from cultures is particularly laborious due to the potential overgrowth of coexisting non-acid fast bacilli. To reduce the overgrowth of these non-mycobacterial organisms, a decontamination step with NaOH or cetylpyridinium chloride is highly recommended before plating the samples on the culture medium. However, due to their toxicity, decontamination solutions tend to decrease NTM recovery from clinical and environmental samples. Here, we tested an alternative method for NTM recovery based on the use of NTM Elite agar, a selective medium that does not require a decontamination step. Using NTM Elite agar, we were able to detect non-tuberculous mycobacteria in 27.7% (30/108) of water samples analyzed. The average time to NTM detection was 18 days, but some strains required longer to grow, perhaps due to the stressful environmental conditions (periodical disinfection of devices). NTM Elite agar's effectiveness in inhibiting background flora was proven by the isolation of NTM from samples with and without background flora, showing no statistically significant differences in detection rates for different total viable counts of background flora (p = 0.4989). In conclusion, our findings indicate that effective NTM recovery from HCU- and ECMO-derived water samples can be achieved via filtration and direct culture of the filters on NTM Elite agar. This simple procedure can speed up laboratory work and provide an improved method, successfully resulting in low contamination and high detection rate, in addition to being less time-consuming. Its sensitivity and lack of a decontamination step make this protocol particularly useful for monitoring the effectiveness of device disinfection in hospital settings, even in the presence of low NTM loads. Reading timeframes should probably be extended to 7 weeks (i.e., well beyond the standard 4 weeks advised by the manufacturer), in order to isolate even the slow-growing mycobacteria. However, an extended incubation period is not necessary for exclusion of M. chimaera contamination of the devices, as M. chimaera isolation times do not generally exceed 3 weeks.

A Comparison of Three Culture Media for the Detection of Rapid-Growing Nontuberculous Mycobacteria in Environmental Samples

Nontuberculous mycobacteria (NTM) are common in the environment and certain species can cause serious infections. Improved environmental surveillance methods are needed to combat the increased incidence of NTM disease. Recently, two methods were developed to improve NTM detection. The MYChrOme™ Culture Plate (patent-pending, Phigenics, LLC, Reno, NV, USA) is the first chromogenic medium for rapid-growing NTM detection in water samples. NTM Elite agar (Biomerieux, Marcy-l’Étoile, France), was developed for rapid-growing NTM detection in clinical samples. Fifty water samples (25 potable and 25 non-potable) with three technical replicates were analyzed by each method and Middlebrook 7H11 selective medium (7H11S) (ASTM E2563-07 method modified for water). The MYChrOme method was overall equivalent to or better than 7H11S medium and NTM Elite agar for the detection of rapid-growing NTM in potable water. All three methods detected similar amounts of NTM in non-potable water samples. The chromogenic property of MYChrOme allowed NTM colonies to be quickly identified and differentiated from other bacteria. Additional analysis is required for colony confirmation on 7H11S medium and NTM Elite agar. The use of innovative environmental NTM diagnostics, in addition to proper water management, can greatly reduce the risk of NTM disease.

Rapid growth atypical mycobacteria infection associated with growth hormone injections: a case report

Introduction

Infections caused by fast growing mycobacteria have increased markedly worldwide. They are normally associated with trauma, surgery or cosmetic interventions. Paraguay has a deficit in sanitary control including clinics, private practices, and aesthetic centres. This situation is accompanied by the easy access to drugs, which leads to the performance of exclusively medical aesthetic procedures by people without professional knowledge or training.

Case report

A 26-year-old female patient comes to a medical consultation with pain and bruising in the abdominal area with more than 3 months of progression, without fever or apparent cause. Later, she confessed to the application of subcutaneous injections of ‘growth hormones’ at the gym. Excisional biopsy of the lesions was carried out for anatomopathological and microbiological studies. In addition, the use of polymerase chain reaction analysis was indicated because of the strong suspicion of an atypical mycobacterial infection. The Ziehl-Neelsen staining was negative for BAAR, and the PAS-Hematoxylin negative for fungal elements. When performing the culture, the growth of atypical mycobacteria was observed on chocolate and blood agar medium culture. Through the polymerase chain reaction study, it was possible to identify the atypical mycobacterium as ‘Mycobacterium abscessus’.

Conclusion

The irresponsible application of medications by people without professional authorization or biosafety precautions can lead to the development atypical infections that are difficult to diagnose and treat. This situation could lead to serious complications and even death.

Chemical susceptibility testing of non-tuberculous mycobacterium strains and other aquatic bacteria: Results of a study for the development of a more sensitive and simple method for the detection of NTM in environmental samples

The methods employed to detect non-tuberculous mycobacteria on environmental samples are essentially those classically used in clinical microbiology, which envisage a decontamination step to reduce the overgrowth of non-mycobacterial organisms before plating them on the culture medium. The aim of this study was to propose alternative culture techniques to improve non-tuberculous mycobacteria detection in environmental samples. We used artificially contaminated samples to compare the membrane filter washing procedure against direct plating of membrane filters on culture media in relation to M.chimaera and M.chelonae recovery efficiency. Moreover, we compared the efficacy of NTM Elite agar in inhibiting the growth of aquatic bacteria with that of cetylpyridinium chloride and N-acetyl-L-cysteine sodium hydroxide decontamination treatments. The washing procedure yielded a low release of both mycobacterium strains (6.6% for Mycobacterium chimaera and 7.5% for Mycobacterium chelonae) from the membrane filters; on the contrary, direct plating of membrane filters led to a 100% cell recovery. Water sample pretreatment with N-acetyl-L-cysteine sodium hydroxide (1%), despite achieving complete suppression of non-acid fast bacilli, caused a reduction in mycobacteria growth. Decontamination with cetylpyridinium chloride (0.005%) was found to be ineffective against Methylobacterium spp. and Burkholderia multivorans. NTM Elite agar was ineffective against B. multivorans, but it inhibited the growth of all other aquatic bacteria. Our results indicate that NTM Elite agar provides a valid alternative method of recovering non-tuberculous mycobacteria from environmental samples. It does not involve a decontamination step and provides greater recovery efficiency by skipping the washing step and directly plating the filters on the media.

Evaluation of Three Culture Media for Isolation of Burkholderia cepacia Complex from Respiratory Samples of Patients with Cystic Fibrosis

Burkholderia cepacia complex (BCC) is a significant pathogen causing respiratory disease in individuals with cystic fibrosis (CF). Diagnosis is typically achieved by isolation of BCC on selective culture media following culture of sputum or other respiratory samples. The aim of this study was to compare the efficacy of three commercially available selective media for the isolation of BCC. The three media comprised Burkholderia cepacia selective agar (BCSA; bioMérieux), BD Cepacia medium (BD: Becton–Dickinson) and MAST Cepacia medium (MAST laboratories). Each medium was challenged with 270 respiratory samples from individuals with CF as well as an international collection of BCC (n = 26) and 14 other isolates of Burkholderia species at a range of inocula. The international collection was also used to artificially “spike” 26 respiratory samples. From a total of 34 respiratory samples containing BCC, 97% were recovered on BD and 94% were detected on MAST and BCSA. All three media were effective for isolation of BCC. BCSA was much more selective than the other two media (p < 0.0001) meaning that fewer isolates required processing to exclude the presence of BCC.

Decontamination Strategies Used for AFB Culture Significantly Reduce the Viability of Mycobacterium abscessus Complex in Sputum Samples from Patients with Cystic Fibrosis

Nontuberculous mycobacteria are important respiratory pathogens in patients with cystic fibrosis (CF). For diagnosis, international guidelines recommend culture of sputum that has been decontaminated via chemical treatment. Fifty-six sputum samples from 32 patients known to be previously colonized or infected with NTM were subdivided, and the aliquots were subjected to six different decontamination strategies, followed by quantitative culture for NTM. Thirty sputum samples contained Mycobacterium abscessus complex (MABSC) and 11 contained Mycobacterium avium complex (MAC). Decontamination strategies included treatment with N-acetyl L-cysteine with 2% sodium hydroxide (NALC-NaOH), 4% NaOH, 1% chlorhexidine, 0.5 N sulfuric acid, 5% oxalic acid, double decontamination with NALC-NaOH, followed by 5% oxalic acid, and saline (0.85%) as a control. The samples were also cultured directly with no treatment. Treatment with NALC-NaOH resulted in an average reduction in colony count of 87% for MABSC when compared with direct culture. NaOH at 4% caused a 98.3% average reduction in colony count. All treatments that included NaOH resulted in colony counts that were statistically lower than those obtained from direct culture or the saline-treated control (p < 0.05). Standard treatments using sulfuric or oxalic acids were less deleterious, but still resulted in an average reduction in colony count of at least 30%. The viability of MAC was much less affected by most decontamination treatments. In conclusion, the viability of MABSC was severely compromised by standard decontamination regimens. This supports recent evidence showing that optimal recovery of MABSC is achieved by culture on an appropriate selective agar without decontamination of sputum samples.

Evaluation of a new culture medium for isolation of nontuberculous mycobacteria from environmental water samples

Nontuberculous mycobacteria (NTM) are waterborne pathogens commonly found in building water systems where they are a primary concern to vulnerable patient populations and can cause severe disease. The recovery of NTM from environmental samples can be a laborious undertaking and current pre-treatment methods and selective media lack sensitivity. We explored the use of the highly selective Rapidly Growing Mycobacteria (RGM) medium for culturing NTM from environmental water samples compared to existing methods. In total, 223 environmental water samples, including potable and non-potable water, were cultured for NTM using three culture media. In addition to direct culture on RGM medium, each sample was cultured on Middlebrook 7H10 medium and Mitchison 7H11 medium after pre-treatment with 0.2M KCl-HCl. Additionally, 33 distinct species of NTM were inoculated onto RGM medium and 7H10 medium in parallel to directly compare their growth. The use of RGM medium alone without pre-treatment provided a sensitivity (91%) comparable to that offered by culture on both 7H10 and 7H11 with acid pretreatment (combined sensitivity; 86%) with significantly less overgrowth and interference from other organisms on RGM medium. The average concentration of NTM observed on RGM medium alone was comparable to or greater than the NTM concentration on either medium alone or combined. Thirty-three species were examined in parallel and all tested strains of 27 of these species successfully grew on RGM medium, including 19 of 21 from the CDC’s healthcare-associated infections species list. RGM medium was successful at recovering environmental NTM without a pre-treatment, greatly reducing labor and materials required to process samples. Simplification of culture processing for environmental NTM will allow for a better assessment of their presence in building water systems and the potential for reduced exposure of susceptible populations.

Is prolonged incubation required for optimal recovery of Burkholderia cepacia complex in sputum from cystic fibrosis patients? Data versus dogma

Cystic fibrosis (CF) expert groups globally recommend using selective medium for isolation of Burkholderia cepacia complex (BCC) from respiratory specimens of CF patients. However, there is no consensus available for optimal duration of incubation and recommendations are variable. The purpose of our study was to compare the difference in recovery of BCC in CF samples at 48 hours versus 7 days when inoculated on Burkholderia cepacia selective agar. A total of 307 consecutive clinical respiratory specimens from our local CF unit were studied prospectively (August 2017 to December 2017). All specimens were inoculated on Burkholderia cepacia medium, containing polymyxin B, gentamicin and ticarcillin. In our laboratory, these plates are routinely incubated for 48 hours as per the manufacturer's recommendation. However, for this study all plates with no growth at 48 hours were further incubated for total of 7 days at 35°C in O₂. Plates were read daily to look for any growth. Microbial identification was performed using MALDI-TOF Vitek MS (database V3.0). Of the 307 CF respiratory specimens cultured, 177 (58%) were from paediatric and 130 (42%) were from adult patients; 155 (50%) specimens were sputum, 148 (48%) were cough swabs and four (1%) were bronchoalveolar lavage (BAL). All specimens from adults were sputum except one BAL. Thirteen (4%) cultures from eight adult and five paediatric specimens grew BCC. The majority (294, 96%) of specimens had no growth when incubated for 7 days. All 13 positive isolates recovered within 48 hours and there were no additional positive isolates found beyond 48 hours of incubation. We conclude from our analysis that prolonged incubation is not warranted for recovery of BCC in CF specimens if selective medium containing gentamicin and polymyxin is used. By adopting this approach of non-extended incubation, the burden of work on laboratory personnel can be significantly reduced and much faster turnaround time for CF cultures achieved. Our study confirms the results of recently published data on this point and challenges the prevailing dogma of utility of extended incubation for BCC isolation. For devising consensus statements for microbiology laboratories on this issue, CF societies and expert groups should consider reviewing data from the recent studies.

Revised guidelines for Australian laboratories performing mycobacteriology testing

Mycobacteriology laboratories play a key role in tuberculosis (TB) control by providing phenotypic and molecular diagnostics, by performing molecular typing to aid contact tracing, and by supporting research and similar laboratories in Australia's neighbouring countries where TB is prevalent. The National Tuberculosis Advisory Committee (NTAC) published a set of laboratory guidelines in 2006 aiming to document the infrastructure, equipment, staffing and work practices required for safe high-quality work in Australian mycobacteriology laboratories. These revised guidelines have the same aims and have been through a similar extensive consultative peer-review process involving the Mycobacterium Reference Laboratory (MRL) network, the Mycobacterium Special Interest Group (SIG) of the Australian Society for Microbiology (ASM), and other relevant national bodies. This revised document contains several significant changes reflecting the publication of new biosafety guidelines and tuberculosis standards by various national and international organisations, technology developments - such as the MPT64-based immunochromatographic tests (ICTs) and the Xpert MTB/RIF assay, and updated work practices in mycobacteriology laboratories. The biosafety recommendations affirm the latest Australian/New Zealand Standard 2243.3: 2010 and promote a biorisk assessment approach that, in addition to the risk categorisation of the organism, also considers the characteristics of the procedure being performed. Using this biorisk assessment approach, limited manipulations, such as Ziehl-Neelsen (ZN) microscopy, MPT64 ICTs, and culture inactivation/DNA extraction for molecular testing, may be performed on a positive TB culture in a PC2 laboratory with additional features and work practices. Other significant changes include recommendations on the integration of MPT64 ICTs and novel molecular tests into TB laboratory workflows to provide rapid accurate results that improve the care of TB patients. This revised document supersedes the original 2006 publication. NTAC will periodically review these guidelines and provide updates as new laboratory technologies become available.

Detection of β-alanyl aminopeptidase as a biomarker for Pseudomonas aeruginosa in the sputum of patients with cystic fibrosis using exogenous volatile organic compound evolution

A novel, rapid and sensitive analytical method has been developed and applied to 105 sputum samples from patients with cystic fibrosis, including 5 samples from post-lung transplant patients. This new method is specifically targeted to measure β-alanyl aminopeptidase activity which is characteristic of some important Gram-negative pathogens. Of relevance to this study are Pseudomonas aeruginosa and pathogens of the Burkholderia cepacia complex both of which are commonly associated with respiratory infections as well as increased morbidity and mortality in adult cystic fibrosis patients. The analytical method involves the addition of a novel enzyme substrate (i.e. 3-amino-N-(3-fluorophenyl)propanamide) that interacts with β-alanyl aminopeptidase to generate an exogenous volatile organic compound 3-fluoroaniline (LOD 0.02 μg mL⁻¹; LOQ 0.06 μg mL⁻¹). 3-Fluoroaniline was determined at 20 times above its calculated limit of quantification in the sputum samples by HS-SPME-GC-MS and then the results compared with standard culture methods and bacterial identification using MALDI-TOF-MS. Detection of 3-fluoroaniline was possible after only 8 h incubation of the sputum samples with a 95% success rate; this increased to 100% at 24 h which was well within the typical routine timeframe of 48 h. To our knowledge, this is the first demonstration of detection of P. aeruginosa by use of a custom-designed substrate to liberate a detectable and unique VOC. The very high negative predictive value (100% in this study) means such an assay could be appropriate as a screening technique for patients who are not yet colonized by this pathogen.

A novel, rapid and sensitive analytical method has been developed and applied to 105 sputum samples from patients with cystic fibrosis, including 5 samples from post-lung transplant patients.

Evaluation of a novel rapidly-growing mycobacteria medium for isolation of Mycobacterium abscessus complex from respiratory specimens from patients with bronchiectasis

This single center study assessed the performance of a novel solid rapidly-growing mycobacteria (RGM) medium for the recovery of nontuberculous mycobacteria (NTM), especially Mycobacterium abscessus complex, in patients with underlying bronchiectasis. A total of 297 mycobacterial sputa from 116 patients were plated directly on RGM medium and, following decontamination, onto an agar biplate [Middlebrook 7H11 and Mitchison (selective) agar] and into broth media (VersaTrek). The recovery of M. abscessus complex was increased by approximately 12% by implementation of the RGM medium. Contamination was reduced to 2% from 48% and 95% on routine solid media and broth cultures respectively. Our study corroborated previous studies in that recovery of M. abscessus complex was enhanced and contamination was virtually eliminated without the need for specimen decontamination when utilizing RGM medium.

An evaluation of methods for the isolation of nontuberculous mycobacteria from patients with cystic fibrosis, bronchiectasis and patients assessed for lung transplantation

BACKGROUND

RGM medium is an agar-based, selective culture medium designed for the isolation of nontuberculous mycobacteria (NTM) from the sputum of patients with cystic fibrosis (CF). We evaluated RGM medium for the detection of NTM in patients with CF (405 samples), bronchiectasis (323 samples) and other lung diseases necessitating lung transplantation (274 samples).

METHODS

In total, 1002 respiratory samples from 676 patients were included in the study. Direct culture on RGM medium, with incubation at two temperatures (30 °C and 37 °C), was compared with conventional culture of decontaminated samples for acid-fast bacilli (AFB) using both a solid medium (Löwenstein-Jensen medium) and a liquid medium (the Mycobacterial Growth Indicator Tube; MGIT).

RESULTS

For all three patient groups, significantly more isolates of NTM were recovered using RGM medium incubated at 30 °C than by any other method (sensitivity: 94.6% vs. 22.4% for conventional AFB culture; P < 0.0001). Significantly more isolates of Mycobacterium abscessus complex were isolated on RGM at 30 °C than by AFB culture (sensitivity: 96.1% vs. 58.8%; P < 0.0001). The recovery of Mycobacterium avium complex was also greater using RGM medium at 30 °C compared to AFB culture (sensitivity: 83% vs. 70.2%), although this difference was not statistically significant and a combination of methods was necessary for optimal recovery (P = 0.21).

CONCLUSIONS

In the largest study of RGM medium to date, we reaffirm its utility for isolation of NTM from patients with CF. Furthermore; we show that it also provides an effective tool for culture of respiratory samples from patients with bronchiectasis and other lung diseases.

Performance of RGM Medium for Isolation of Nontuberculous Mycobacteria from Respiratory Specimens from Non-Cystic Fibrosis Patients

A new selective medium for rapidly growing mycobacteria (RGM medium) was evaluated on respiratory specimens from non-cystic fibrosis patients and compared to the mycobacterial growth indicator tube (MGIT) system and Middlebrook 7H11 agar for the isolation of all nontuberculous mycobacteria (NTM). A total of 203 mucolyzed respiratory specimens collected from 163 patients were inoculated on RGM medium and incubated at both 30°C (RGM30) and 35°C (RGM35) over a 28-day period. N-Acetyl-l-cysteine-sodium hydroxide (NALC-NaOH)-decontaminated specimens were inoculated into MGIT and Middlebrook 7H11 agar and incubated at 35°C for 42 days. NTM were identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) or gene sequencing. A total of 133 NTM isolates were recovered overall from 101 (49.8%) specimens collected from 85 (52.1%) patients by a combination of all culture methods. The sensitivity of RGM30 for the recovery of NTM was significantly higher than that of either the MGIT system (76.7% versus 59.4%; P = 0.01) or Middlebrook 7H11 agar (76.7% versus 47.4%; P = 0.0001) alone, but it was not significantly different from that of an acid-fast bacillus culture (AFC) which includes both MGIT and Middlebrook 7H11 agar (76.7% versus 63.9%; P = 0.0647). RGM35 had significantly lower sensitivity than the MGIT system (49.6% versus 59.4%; P = 0.0367) and AFC (49.6% versus 63.9%; P = 0.0023). RGM medium was highly effective at inhibiting the growth of nonmycobacterial organisms in the respiratory specimens, with breakthrough contamination rates of 5.4% and 4.4% for RGM30 and RGM35, respectively.

Comparison of the RGM medium and the mycobacterial growth indicator tube automated system for isolation of non-tuberculous mycobacteria from sputum samples of cystic fibrosis patients in Belgium

Purpose

Pulmonary infections due to non-tuberculous mycobacteria (NTM) are an emerging issue in the cystic fibrosis (CF) population. Due to bacterial and fungal overgrowth, isolation of mycobacteria from the sputum samples of these patients remains challenging. RGM medium, a novel agar-based culture medium was evaluated for the isolation of NTM from sputum samples of CF patients.

Methodology

Sputum samples were inoculated onto RGM medium and conventional Mycobacterial Growth Indicator Tube (MGIT™, Becton Dickinson, USA). Agar plates were incubated at 35 °C and growth was recorded once a week during 42 days. We compared the yield of the two media.

Results

217 samples were obtained from 124 CF patients. 20 samples (13 patients) had a positive culture for NTM. 79/217 (36.4%) MGIT had to be discontinued due to contamination compared to 18/217 (8.3%) for RGM. We reported equivalent NTM detection performances for RGM and MGIT (P = 0.579): these media enabled the isolation of 15 and 12 NTM strains respectively.

Conclusion

RGM medium increases the proportion of interpretable results and the number of NTM cultured. Taking into account the non-inferiority compared to conventional methods and ease of use of RGM medium, we estimate that this test can replace current approaches for the screening of NTM among people with CF. Additionally, RGM provides semi-quantitative results (number of colonies) and information on the morphology of colonies, which may be clinically relevant information.

Practice Guidelines for Clinical Microbiology Laboratories: Mycobacteria

Mycobacteria are the causative organisms for diseases such as tuberculosis (TB), leprosy, Buruli ulcer, and pulmonary nontuberculous mycobacterial disease, to name the most important ones. In 2015, globally, almost 10 million people developed TB, and almost half a million patients suffered from its multidrug-resistant form. In 2016, a total of 9,287 new TB cases were reported in the United States. In 2015, there were 174,608 new case of leprosy worldwide. India, Brazil, and Indonesia reported the most leprosy cases. In 2015, the World Health Organization reported 2,037 new cases of Buruli ulcer, with most cases being reported in Africa. Pulmonary nontuberculous mycobacterial disease is an emerging public health challenge. The U.S. National Institutes of Health reported an increase from 20 to 47 cases/100,000 persons (or 8.2% per year) of pulmonary nontuberculous mycobacterial disease among adults aged 65 years or older throughout the United States, with 181,037 national annual cases estimated in 2014. This review describes contemporary methods for the laboratory diagnosis of mycobacterial diseases. Furthermore, the review considers the ever-changing health care delivery system and stresses the laboratory's need to adjust and embrace molecular technologies to provide shorter turnaround times and a higher quality of care for the patients who we serve.

Evaluation of RGM Medium for Isolation of Nontuberculous Mycobacteria from Respiratory Samples from Patients with Cystic Fibrosis in the United States

A novel selective agar (RGM medium) has been advocated for the isolation of rapidly growing mycobacteria from the sputa of cystic fibrosis (CF) patients. The aim of this study was to compare RGM medium to Burkholderia cepacia selective agar (BCSA) and a standard acid-fast bacillus (AFB) culture method for the isolation of nontuberculous mycobacteria (NTM) from patients with CF. The applicability of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) for the identification of NTM isolated on RGM medium was also assessed. Respiratory samples (n = 869) were collected from 487 CF patients and inoculated directly onto RGM medium and BCSA. Cultures were incubated at 30°C and examined for up to 28 days. A subset of 212 samples (from 172 patients) was also cultured by using a mycobacterial growth indicator tube (MGIT) and on Lowenstein-Jensen medium following dual decontamination. By using a combination of all methods, 98 mycobacteria were isolated from 869 samples (11.3%). The sensitivity of RGM medium (96.9%) was significantly higher than that of BCSA (35.7%) for the isolation of mycobacteria (P < 0.0001). The sensitivity of RGM medium was also superior to that of standard AFB culture for the isolation of mycobacteria (92.2% versus 47.1%; P < 0.0001). MALDI-TOF MS was effective for the identification of mycobacteria in RGM medium. RGM medium offers a simple and highly effective tool for the isolation of NTM from patients with CF. Extended incubation of RGM medium for 28 days facilitates the isolation of slow-growing species, including members of the Mycobacterium avium complex (MAVC).

Comparison of Mycobacterial Growth Indicator Tube with Culture on RGM Selective Agar for Detection of Mycobacteria in Sputum Samples from Patients with Cystic Fibrosis

Nontuberculous mycobacteria (NTM) are an important cause of pulmonary disease in patients with cystic fibrosis (CF). A new culture medium (RGM medium) for the isolation of rapidly growing mycobacteria from the sputum of cystic fibrosis patients has recently been reported. The aim of this study was to compare culture of sputum samples on RGM medium with culture using a standard automated liquid culture method. Sputum samples were obtained from 187 distinct patients with CF attending King's College Hospital, London, United Kingdom. Each sample was decontaminated with 3% oxalic acid and inoculated into a mycobacterial growth indicator tube (MGIT) that was monitored for 42 days using the Bactec MGIT 960 instrument. Each sample was also cultured, without decontamination, onto RGM medium, which was incubated for 10 days at 30°C. Mycobacteria were isolated from 28 patients (prevalence, 15%). Mycobacteria were detected in 24 samples (86%) using the MGIT and in 23 samples (82%) using RGM medium (P = 1.00). In this setting, RGM medium showed sensitivity equivalent to that of the MGIT for isolation of NTM from the sputum of patients with CF. RGM medium offers a simple, convenient tool that can be embedded into routine culture methods, allowing the culture of all sputum samples that are submitted from patients with CF.