Minimum inhibitory concentrations of azithromycin in clinical isolates of Mycobacterium avium complex in Japan

The latest guidelines include azithromycin as a preferred regimen for treating Mycobacterium avium complex (MAC) pulmonary disease. However, serially collected susceptibility data on clinical MAC isolates are limited, and no breakpoints have been determined. We investigated the minimum inhibitory concentrations (MICs) of azithromycin and clarithromycin for all MAC strains isolated in 2021 from a single center in Japan, excluding duplicates. The MICs were determined using a panel based on the microbroth dilution method, according to the latest Clinical and Laboratory Standards Institute recommendations. The MICs were determined for 318 MAC strains. Although there was a significant positive correlation between the MICs of azithromycin and clarithromycin, the MICs of azithromycin tended to be higher than those of clarithromycin. Among the cases in which the strains were isolated, 18 patients initiated treatment, including azithromycin treatment, after sample collection. Some patients infected with stains with relatively high azithromycin MICs achieved a microbiological cure with azithromycin-containing regimens. This study revealed a higher MIC distribution for azithromycin than clarithromycin, raising questions about the current practice of estimating azithromycin susceptibility based on the clarithromycin susceptibility test result. However, this was a single-center study that included only a limited number of cases treated with azithromycin. Therefore, further multicenter studies that include a greater number of cases treated with azithromycin are warranted to verify the distribution of azithromycin MICs and examine the correlation between azithromycin MICs and treatment effectiveness.IMPORTANCEThe macrolides serve as key drugs in the treatment of pulmonary Mycobacterium avium complex infection, and the administration of macrolide should be guided by susceptibility test results. Azithromycin is recommended as a preferred choice among macrolides, surpassing clarithromycin; however, drug susceptibility testing is often not conducted, and clarithromycin susceptibility is used as a surrogate. This study represents the first investigation into the minimum inhibitory concentration of azithromycin on a scale of several hundred clinical isolates, revealing an overall tendency for higher minimum inhibitory concentrations compared with clarithromycin. The results raise questions about the appropriateness of using clarithromycin susceptibility test outcomes for determining the administration of azithromycin. This study highlights the need for future discussions on the clinical breakpoints of azithromycin, based on large-scale clinical research correlating azithromycin susceptibility with treatment outcomes.

Role of MIC levels and 23S rRNA mutation sites to clarithromycin in 14-day clarithromycin bismuth quadruple therapy for Helicobacter pylori eradication: A prospective trial in Beijing

Background

Rising clarithromycin resistance undermines Helicobacter pylori (H. pylori) treatment efficacy. We aimed to determine clarithromycin's minimum inhibitory concentration (MIC) levels and identify specific mutation sites in the 23S ribosomal subunit (23S rRNA) that predict treatment outcomes in a 14-day regimen of clarithromycin bismuth quadruple therapy (amoxicillin 1g, clarithromycin 500 mg, rabeprazole 10 mg, and colloidal bismuth pectin 200 mg).

Materials and methods

We included adult H. pylori patients who hadn't previously undergone clarithromycin-based treatment, either as initial or rescue therapy. Exclusions were made for penicillin allergy, recent use of related medications, severe illnesses, or inability to cooperate. Patients underwent a 14-day clarithromycin bismuth quadruple therapy. Gastric mucosa specimens were obtained during endoscopy before eradication. MIC against amoxicillin and clarithromycin was determined using the E-test method. The receiver operating characteristic (ROC) curve helped to find the optimal clarithromycin resistance MIC breakpoint. Genetic sequences of H. pylori 23S rRNA were identified through Sanger Sequencing. (ChiCTR2200061476).

Results

Out of 196 patients recruited, 92 met the inclusion criteria for the per-protocol (PP) population. The overall intention-to-treat (ITT) eradication rate was 80.00 % (84/105), while the modified intention-to-treat (MITT) and PP eradication rates were 90.32 % (84/93) and 91.30 % (84/92) respectively. No amoxicillin resistance was observed, but clarithromycin resistance rates were 36.19 % (38/105), 35.48 % (33/93), and 34.78 % (33/92) in the ITT, MITT, and PP populations respectively. Compared with the traditional clarithromycin resistance breakpoint of 0.25 μg/mL, a MIC threshold of 12 μg/mL predicted better eradication. Among 173 mutations on 152 sites in the 23S rRNA gene, only the 2143A > G mutation could predict eradication outcomes (p < 0.000).

Conclusions

Interpretation of elevated MIC values is crucial in susceptibility testing, rather than a binary "susceptible" or "resistant" classification. The 2143A > G mutation has limited specificity in predicting eradication outcomes, necessitating further investigation into additional mutation sites associated with clarithromycin resistance.

Development of a rapid detection method for the macrolide resistance gene in Mycobacterium avium using the amplification refractory mutation system-loop-mediated isothermal amplification method

Macrolide antibiotics such as clarithromycin (CLR) and azithromycin are the key drugs used in multidrug therapy for Mycobacterium avium complex (MAC) diseases. For these antibacterial drugs, drug susceptibility has been correlated with clinical response in MAC diseases. We have previously demonstrated the correlation between drug susceptibility and mutations in the 23S rRNA gene, which confers resistance to macrolides. Herein, we developed a rapid detection method using the amplification refractory mutation system (ARMS)-loop-mediated isothermal amplification (LAMP) technique to identify mutations in the 23S rRNA gene of M. avium. We examined the applicability of the ARMS-LAMP method to genomic DNA extracted from six genotypes of M. avium clinical isolates. The M. avium isolates were classified into 21 CLR-resistant and 9 CLR-susceptible strains based on the results of drug susceptibility tests; the 23S rRNA genes of these strains were sequenced and analyzed using the ARMS-LAMP method. Sequence analysis revealed that the 9 CLR-sensitive strains were wild-type strains, whereas the 21 CLR-resistant strains comprised 20 mutant-type strains and one wild-type strain. Using ARMS-LAMP, no amplification from genomic DNAs of the 10 wild-type strains was observed using the mutant-type mismatch primer sets (MTPSs); however, amplification from the 20 mutant-type strain DNAs was observed using the MTPSs. The rapid detection method developed by us integrates ARMS-LAMP with a real-time turbidimeter, which can help determine drug resistance in a few hours. In conclusion, ARMS-LAMP might be a new clinically beneficial technology for rapid detection of mutations.IMPORTANCEMultidrug therapy for pulmonary Mycobacterium avium complex disease is centered on the macrolide antibiotics clarithromycin and azithromycin, and resistance to macrolides is an important prognosticator for clinical aggravation. Therefore, it is important to develop a quick and easy method for detecting resistance to macrolides. Drug resistance is known to be correlated with mutations in macrolide resistance genes. We developed a rapid detection method using amplification refractory mutation system (ARMS)-loop-mediated isothermal amplification (LAMP) to identify a mutation in the 23S rRNA gene, which is a macrolide resistance gene. Furthermore, we examined the applicability of this method using M. avium clinical isolates. The rapid method developed by us for detection of the macrolide resistance gene by integrating ARMS-LAMP and a real-time turbidimeter can help in detection of drug resistance within a few hours. Since this method does not require expensive equipment or special techniques and shows high analytical speed, it would be very useful in clinical practice.

MGIT-seq for the Identification of Nontuberculous Mycobacteria and Drug Resistance: a Prospective Study

Because nontuberculous mycobacterial pulmonary disease is a considerable health burden, a simple and clinically applicable analytical protocol enabling the identification of subspecies and drug-resistant disease is required to determine the treatment strategy. We aimed to develop a simplified workflow consisting only of direct sequencing of mycobacterial growth indicator tube cultures (MGIT-seq). In total, 138 patients were prospectively enrolled between April 2021 and May 2022, and culture-positive MGIT broths were subjected to sequencing using MinION, a portable next-generation sequencer. Sequence analysis was conducted to identify species using core genome multilocus sequence typing and to predict macrolide and amikacin (AMK) resistance based on previously reported mutations in rrl, rrs, and erm(41). The results were compared to clinical tests for species identification and drug susceptibility. A total of 116 patients with positive MGIT cultures were included in the analysis. MGIT-seq yielded 99.1% accuracy in species-level identification and identified 98 isolates (84.5%) at the subspecies level. Macrolide and AMK resistance were detected in 19.4% and 1.9% of Mycobacterium avium complex (MAC) and Mycobacterium abscessus isolates. The predicted macrolide and AMK resistance was consistent with the results of conventional drug susceptibility tests, with specificities of 97.6% and 100.0%, respectively. Direct MGIT-seq has achieved comprehensive identification and drug resistance detection of nontuberculous mycobacteria, which could be applicable to determine the treatment strategy by a single test in clinical practice.

A Rapid Screening Assay for Clarithromycin-Resistant Mycobacterium avium Complex Using Melting Curve Analysis with Nonfluorescent Labeled Probes

Mycobacterium avium complex (MAC) thrives in various environments and mainly causes lung disease in humans. Because macrolide antibiotics such as clarithromycin or azithromycin are key drugs for MAC lung disease, the emergence of macrolide-resistant strains prevents the treatment of MAC. More than 95% of macrolide-resistant MAC strains are reported to have a point mutation in 23S rRNA domain V. This study successfully developed a melting curve assay using nonfluorescent labeled probes to detect the MAC mutation at positions 2058 to 2059 of the 23S rRNA gene (AA genotype, clarithromycin susceptible; TA, GA, AG, CA, AC, and AT genotypes, clarithromycin resistant). In the AA-specific probe assay, the melting peak of the DNA fragment of the AA genotype was higher than that of DNA fragments of other genotypes. Melting temperature (Tm) values of the AA genotype and the other genotypes were about 80°C and 77°C, respectively. DNA fragments of each genotype were identified correctly in six other genotype-specific probes (TA, GA, AG, CA, AC, and AT) assays. Using genomic DNA from six genotype strains of M. avium and four genotype strains of M. intracellulare, we confirmed that all genomic DNAs could be correctly identified as individual genotypes according to the highest Tm values among the same probe assays. These results indicate that this melting curve-based assay is able to determine MAC genotypes at positions 2058 to 2059 of the 23S rRNA gene. This simple method could contribute to the rapid detection of clarithromycin-resistant MAC strains and help to provide accurate drug therapy for MAC lung disease. IMPORTANCE Since macrolide antibiotics such as clarithromycin or azithromycin are key drugs in multidrug therapy for Mycobacterium avium complex (MAC) lung diseases, the rapid detection of macrolide-resistant MAC strains has important implications for the treatment of MAC. Previous studies have reported a correlation between drug susceptibility testing and the mutation of macrolide resistance genes. In this study, we developed a novel melting curve-based assay using nonfluorescent labeled probes to identify both clarithromycin-resistant M. avium and M. intracellulare with mutations in the 23S rRNA gene, which is the clarithromycin or azithromycin resistance gene. This assay contributed to not only the detection of MAC mutations but also the determination of all genotypes at positions 2058 to 2059 of the 23S rRNA gene. Furthermore, because nonfluorescent labeled probes are used, this assay is more easily and more immediately available than other methods.

Variability of Mycobacterium avium Complex Isolates Drug Susceptibility Testing by Broth Microdilution

Non-tuberculous mycobacteria are widely distributed in environments and are capable of infecting humans, particularly those with a compromised immune system. The most prevalent species that cause nontuberculous mycobacterial lung diseases are slow-growing bacteria from the Mycobacterium avium complex (MAC), mainly M. avium or M. intracellulare. The key treatment of MAC infections includes macrolides, ethambutol, and rifampicin; however, the therapy outcomes are unsatisfactory. Phenotypic drug susceptibility testing is a conditional recommendation prior to treatment, and critical concentrations for clarithromycin, amikacin, moxifloxacin, and linezolid have been established. In this review, data from studies on the determination of MIC of clinical isolates using the broth microdilution method were summarized. A significant variation in the MIC distributions from different studies was found. The main reasons could impact the findings: insufficient reproducibility of the phenotypic testing and variation in species lineages identified in different laboratories, which could have various intrinsic susceptibility to drugs. For most of the drugs analyzed, the MICs are too high, which could undermine the treatment efficiency. Further improvement of treatment outcomes demands the validation of microbiological resistance criteria together with the identification of molecular mechanisms of resistance.

Early-Phase Adverse Effects and Management of Liposomal Amikacin Inhalation for Refractory Mycobacterium avium Complex Lung Disease in Real-World Settings

Purpose

Amikacin liposome inhalation suspension (ALIS), which efficiently allows amikacin to reach the pulmonary periphery for effect while minimising systemic adverse effects, was recently approved for treating Mycobacterium avium complex (MAC) infections. The international Phase 3 open-label clinical trials showed promising results, contributing to sputum culture conversion, but few studies have examined the efficacy and adverse effects of ALIS using real-world data. We identified the clinical outcome and adverse effects of ALIS in the early phase of treatment, for more effective and safe use in clinical practice.

Patients and Methods

The study population consisted of patients with MAC lung disease (MAC-LD), introduced to ALIS therapy after July 2021 at Keio University Hospital due to poor response to multidrug therapy. The sputum smear/culture results, symptoms, adverse effects, and the serum amikacin concentrations of the early phase of ALIS inhalation therapy were examined.

Results

A total of 11 patients (9 women; median age 64.6 years) were included in this study. The median disease duration of MAC-LD was 13.7 years, and all patients exhibited a positive culture at the beginning of ALIS inhalation. Three of the six patients (50.0%) who were initially sputum-smear-positive were confirmed to have become sputum-smear-negative within one month, including one culture conversion. ALIS inhalation therapy caused some adverse effects in nine patients (81.8%); however, no serious systemic adverse effects were observed. The most common adverse effect was hoarseness (72.7%), which mostly occurred around 1 week after initiation. The medians of peak serum amikacin concentrations were 1.4 and 2.3 μg/mL for the first and third inhalations, respectively. Trough serum concentrations just before the third inhalation were <1.2 μg/mL in all patients.

Conclusion

ALIS therapy might be a treatment option for patients with refractory MAC infection with long disease duration and a poor response to guideline-based therapy.

Mycobacterioses Induced by Mycobacterium abscessus: Case Studies Indicating the Importance of Molecular Analysis for the Identification of Antibiotic Resistance

Mycobacterioses are less frequently occurring but serious diseases. In recent years, at a global level, the incidence of mycobacterioses induced by the rapidly growing species Mycobacterium abscessus (M. a.), which is considered to be the most resistant to antibiotics and most difficult to treat, has been on the rise. Correct identification to the level of the subspecies (M. a. abscessus, M. a. massiliense, and M. a. bolletii) and determination of its sensitivity to macrolides, which are the basis of combination therapy, are of principal importance for the management of the disease. We describe five cases of mycobacterioses caused by M. a., where the sequencing of select genes was performed to identify the individual subspecies and antibiotic resistance. The analysis of the rpoB gene showed two isolates each of M. a. abscessus and M. a. massiliense and one isolate of M. a. bolletii. The complete (full length) erm(41) gene responsible for the development of inducible resistance to macrolides was demonstrated in both M. a. abscessus and M. a. bolletii isolates. A partially deleted and non-functional erm(41) gene was demonstrated in M. a. massiliense isolates. The subsequent sequencing of the full length erm(41) gene products showed, however, the mutation (T28→C) in both isolates of M. a. abscessus, causing a loss of the function and preserved sensitivity to macrolides. The antibiotic sensitivity testing confirmed that both the isolates of M. a. abscessus and M. a. massiliense were sensitive to clarithromycin even after prolonged 14-day incubation. The inducible resistance to clarithromycin was maintained only in M. a. bolletii. Thus, the sequence analysis of the erm(41) gene can reliably identify the preservation of sensitivity to macrolides and serve as an important tool in the establishment of therapeutic regimens in cases of infections with M. abscessus.

Nontuberculous Mycobacteria in Humans, Animals, and Water in Zambia: A Systematic Review

Nontuberculous mycobacteria (NTM) are environmental opportunistic pathogens of humans and animals that are emerging with a serious public health impact particularly in individuals with Acquired Immunodeficiency Syndromes. Recent scientific evidence is shifting from NTMs being known as traditional environmental organisms to serious pathogenic organisms in both animals and humans. In humans, factors attributable to this rise have been linked mainly to Human Immunodeficiency Virus and Acquired Immunodeficiency Syndrome pandemic. In recent years there has been an increase in multidrug resistant Tuberculosis in Zambia and it is thought that NTMs could possibly be the cause. This study was therefore formulated to review available information on the prevalence of NTM in humans, animals and the environment, species distribution, zoonotic potential and public health importance in Zambia. This review was conducted in accordance with PRISMA guidelines. A literature search was done in PubMed and Google scholar using predefined search terms such as ‘nontuberculous mycobacteria’, ‘atypical mycobacteria’, ‘mycobacteria other than mycobacterium tuberculosis’ and ‘Zambia’, in combination with Boolean operators (AND, OR). This particular systematic review draws findings based on literature search between 2000 and 2020. Through literature search 243 papers were identified, 23 duplicates were identified and removed and 206 articles were excluded as they did not meet the inclusion criteria. The full text of the remaining 14 articles were considered for this review. The overall prevalence of NTM in humans was 24.39%, in water 21.5%, in animals 16.05% of which the prevalence in cattle was 14.81% and Kafue Lechwe 1.23%. Mycobacterium intracellulare was the most common isolated nontuberculous mycobacteria in humans and cattle while Mycobacterium gordonae was the most common in water, and Mycobacterium stomatepiae sp Nov in Kafue Lechwe. Nontuberculous mycobacteria are an emerging public health threat in Zambia both in humans and animals and this calls for the need for molecular information on the zoonotic transmission of nontuberculous mycobacteria. Increased awareness of nontuberculous mycobacteria diseases among clinicians and laboratory personnel is crucial for patient management and an essential step for facilitating the identification of nontuberculous mycobacteria species in laboratories.

16S and 23S rRNA Gene Mutation Independent Multidrug Resistance of Non-Tuberculous Mycobacteria Isolated from South Korean Soil

Non-tuberculous mycobacteria (NTM) are ubiquitous microorganisms that have the potential to cause disease in both humans and animals. Recently, NTM infections have rapidly increased in South Korea, especially in urbanized areas. However, the distribution of species and the antibiotic resistance profile of NTM in environmental sources have not yet been investigated. Therefore, we analyzed the distribution of species and the antibiotic resistance profile of NTM in soil within urban areas of South Korea. A total of 132 isolates of NTM were isolated from soil samples from 1 municipal animal shelter and 4 urban area parks. Among the 132 isolates, 105 isolates were identified as slowly growing mycobacteria (SGM) and 27 isolates as rapidly growing mycobacteria (RGM) based on the sequences of the rpoB and hsp65 genes. The antibiotic resistance patterns of NTM isolates differed from species to species. Additionally, a mutation in the rrs gene found in this study was not associated with aminoglycoside resistance. In conclusion, our results showed that NTM isolates from South Korean soil exhibit multidrug resistance to streptomycin, amikacin, azithromycin, ethambutol, isoniazid, and imipenem. These results suggest that NTM may pose a public threat.

Macrolide resistant Mycobacterium avium complex pulmonary disease following clarithromycin and ethambutol combination therapy

RATIONALE

Whether two-drug therapy (clarithromycin and ethambutol) for Mycobacterium avium complex (MAC) pulmonary disease contributes to the development of macrolide-resistant MAC is unclear.

OBJECTIVE

To compare the incidence of macrolide-resistant MAC between patients treated with two-drug therapy (clarithromycin and ethambutol) and the standard three-drug therapy (clarithromycin, ethambutol, and rifampicin) for MAC pulmonary disease.

METHODS

We retrospectively reviewed 147 patients with treatment-naive MAC pulmonary disease who had received two-drug therapy (n = 47) or three-drug therapy (n = 100) between 1997 and 2016 at National Hospital Organization, Tenryu Hospital, Hamamatsu, Japan. The risk of development of macrolide-resistant MAC was evaluated by calculating the cumulative incidence rate using Gray's test.

RESULTS

The median follow-up period was 74.5 months. During the follow-up period, one of the 47 patients (2.1%) in the two-drug group developed macrolide-resistant MAC, compared to 12 of the 100 patients (12.0%) in the three-drug group. The cumulative incidence rate of macrolide-resistant MAC was lower in the two-drug group than in the three-drug group (0.0023; 95% confidence interval, 0.002 to 0.107 versus 0.200; 95% confidence interval, 0.100 to 0.324, p = 0.0593).

CONCLUSIONS

These results suggest that two-drug treatment with clarithromycin and ethambutol for MAC pulmonary disease does not lead to a higher incidence of resistance acquisition to clarithromycin than the standard three-drug treatment.

Antimicrobial Susceptibility of Clinical and Environmental Mycobacterium chimaera Isolates

Mycobacterium chimaera is a slow-growing nontuberculous Mycobacterium species belonging to the Mycobacterium avium complex (MAC). It has been identified globally as the cause of a large outbreak of cardiovascular infections following open heart surgery, but it can also cause respiratory infections in individuals with underlying structural pulmonary disease. Invasive M. chimaera infections are associated with poor clinical responses, and the optimal antibiotic treatment regimen for these infections is not known. In this study, the drug susceptibility profiles of clinical and environmental M. chimaera isolates for antimicrobial agents that are commonly considered for treatment of MAC infections were determined. All M. chimaera isolates were susceptible to clarithromycin, with a median MIC of 2 μg/ml, while 98% (85/87 isolates) were susceptible to amikacin. Twenty-five percent of isolates (22/87 isolates) had intermediate susceptibility and 52% (46/87 isolates) were resistant to moxifloxacin. Similarly, 39% of isolates (34/87 isolates) had intermediate susceptibility and 39% (34/87 isolates) were resistant to linezolid. MIC breakpoints derived from the literature were used to determine resistance to rifampin (16/87 isolates [18%]), ethambutol (10/87 isolates [11%]), rifabutin (2/87 isolates [2%]), and streptomycin (1/87 isolates [1%]). In conclusion, our results showed that clarithromycin, amikacin, rifabutin, and streptomycin had the best activity against M. chimaera isolates, while susceptibility rates were lower for rifampin and ethambutol. In contrast, there was a high prevalence of isolates that were not susceptible to moxifloxacin or linezolid. While factors in addition to antibiotic susceptibility may determine the outcomes of treatment of M. chimaera infections, our results should inform the selection of antimicrobials as part of the overall therapeutic strategy.

Long-term Outcome of Pulmonary Resection for Nontuberculous Mycobacterial Pulmonary Disease

Background

Pulmonary resection along with multiple antimicrobial therapy has produced favorable outcomes at a few centers. However, little is known regarding the risk factors for long-term survival and microbiological recurrence after pulmonary resection for nontuberculous mycobacterial pulmonary disease (NTMPD). We evaluated the long-term outcomes of pulmonary resection, including microbiological recurrence and survival.

Methods

This retrospective cohort study included 125 patients (median age, 60 years) with NTMPD treated by pulmonary resection at two referral centers between January 1994 and August 2015.

Results

Postoperative complications occurred in 27 patients (22%). The complication rate after pneumonectomy was significantly higher than those after other types of pulmonary resection (odds ratio, 4.1; 95% confidence interval [CI], 1.6-10.3; P = .005). The median follow-up period was 7.1 years. While 19 patients experienced microbiological recurrence, 26 died. Multivariate analysis revealed pneumonectomy (adjusted hazard ratio [aHR], 0.12; 95% CI, .007-.66; P = .0098) and cavitary lesions after surgery (aHR, 6.73; 95% CI, 1.68-22.7; P = .0095) to be predictors of microbiological recurrence and old age (aHR, 1.06; 95% CI, 1.01-1.13; P = .016), low body mass index (BMI; aHR for every 1-kg/m2 increase, 0.72; 95% CI, .60-.85; P < .0001), pneumonectomy (aHR, 4.38; 95% CI, 1.78-11.3; P = .014), and remnant cavitary lesions (aHR, 3.53; 95% CI, 1.35-9.57; P = .011) to be predictors of poor prognosis.

Conclusions

Patients who could benefit from pulmonary resection should be carefully selected considering age, BMI, remnant lesions after surgery, and type of pulmonary resection.

Drug Susceptibility Profiling and Genetic Determinants of Drug Resistance in Mycobacterium kansasii

Very few studies have examined drug susceptibility of Mycobacterium kansasii, and they involve a limited number of strains. The purpose of this study was to determine drug susceptibility profiles of M. kansasii isolates representing a spectrum of species genotypes (subtypes) with two different methodologies, i.e., broth microdilution and Etest assays. To confirm drug resistance, drug target genes were sequenced. A collection of 85 M. kansasii isolates, including representatives of eight different subtypes (I to VI, I/II, and IIB) from eight countries, was used. Drug susceptibility against 13 and 8 antimycobacterial agents was tested by using broth microdilution and Etest, respectively. For drug-resistant or high-MIC isolates, eight structural genes (rrl, katG, inhA, embB, rrs, rpsL, gyrA, and gyrB) and one regulatory region (embCA) were PCR amplified and sequenced in the search for resistance-associated mutations. All isolates tested were susceptible to rifampin (RIF), amikacin (AMK), co-trimoxazole (SXT), rifabutin (RFB), moxifloxacin (MXF), and linezolid (LZD) according to the microdilution method. Resistance to ethambutol (EMB), ciprofloxacin (CIP), and clarithromycin (CLR) was found in 83 (97.7%), 17 (20%), and 1 (1.2%) isolate, respectively. The calculated concordance between the Etest and dilution method was 22.6% for AMK, 4.8% for streptomycin (STR), 3.2% for CLR, and 1.6% for RIF. For EMB, INH, and SXT, not even a single MIC value determined by one method equaled that by the second method. The only mutations disclosed were A2266C transversion at the rrl gene (CLR-resistant strain) and A128G transition at the rpsL gene (strain with STR MIC of >64 mg/liter). In conclusion, eight drugs, including RIF, CLR, AMK, SXT, RFB, MXF, LZD, and ethionamide (ETO), showed high in vitro activity against M. kansasii isolates. Discrepancies of the results between the reference microdilution method and Etest preclude the use of the latter for drug susceptibility determination in M. kansasii Drug resistance in M. kansasii may have different genetic determinants than resistance to the same drugs in M. tuberculosis.

A Laboratory-based Analysis of Nontuberculous Mycobacterial Lung Disease in Japan from 2012 to 2013

RATIONALE

Since 2010, mycobacterial examination results have been used widely to survey nontuberculous mycobacteria (NTM) lung disease.

OBJECTIVES

To reveal the clinical and epidemiological status of NTM lung disease in Japan.

METHODS

All data on the isolation and identification of mycobacteria in 2012 and 2013 were obtained from three dominant commercial laboratories in Japan. Pulmonary NTM disease was defined on the basis of bacteriological diagnostic criteria issued by the American Thoracic Society/Infectious Diseases Society of America. The coverage population was estimated using the ratio between national tuberculosis registration data and laboratory results for each of the eight regions of Japan.

MEASUREMENTS AND MAIN RESULTS

A total of 113,313 mycobacterial specimens from 4,710 institutes were collected, and specimens from 26,059 patients tested positive for NTM cultures at least once. Among patients with positive cultures, 7,167 (27.5%) satisfied the American Thoracic Society/Infectious Diseases Society of America criteria for NTM lung disease, resulting in a 2-year prevalence rate of 24.0 per 100,000. Mycobacterium avium complex (MAC) was the most commonly isolated species (93.3%), and 29.0% of the patients from whom MAC was isolated satisfied the criteria for NTM lung disease. Individuals older than 70 years of age accounted for the majority of cases, and 65.5% of cases involved females. After MAC, Mycobacterium kansasii and Mycobacterium abscessus exhibited the highest (43.6%) and second-highest (37.1%) incidence per isolation, respectively. The prevalence of M. kansasii was highest in the Kinki region (P < 0.05), and M. abscessus had the greatest prevalence in the Kyushu-Okinawa region (P < 0.005). The proportion of Mycobacterium intracellulare in MAC cases was higher in the southwestern part of Japan than in other regions. The period prevalence was highest in the southwestern part of Japan, and the standardized prevalence ratio was highest in central regions. Evaluations of clarithromycin susceptibility revealed a clear binomial distribution.

CONCLUSIONS

This investigation is the first laboratory-based study in which a large number of NTM isolated from clinical samples in Japan have been assessed. Although the calculated prevalence of NTM disease might be underestimated, the approach may prove useful for monitoring relative epidemiological data for NTM lung disease.

Evaluation of the new GenoType NTM-DR kit for the molecular detection of antimicrobial resistance in non-tuberculous mycobacteria

Objectives

Non-tuberculous mycobacteria (NTM) are emerging pathogens causing difficult-to-treat infections. We tested a new assay (GenoType NTM-DR) that detects natural and acquired resistance mechanisms to macrolides and aminoglycosides in frequently isolated NTM species.

Methods

Performance was assessed on 102 isolates including reference strains [16 Mycobacterium avium , 10 Mycobacterium intracellulare , 8 Mycobacterium chimaera , 15 Mycobacterium chelonae and 53 Mycobacterium abscessus (including subsp. abscessus isolates, 18 with a t28 in erm(41) and 10 with a c28, 13 subsp. bolletii isolates and 12 subsp. massiliense isolates)]. Genotypes were determined by PCR sequencing of erm(41) and rrl for clarithromycin resistance and of the 1400-1480 rrs region for aminoglycoside resistance. Phenotypes were determined by MIC microdilution.

Results

GenoType NTM-DR yielded results concordant with Sanger sequencing for 100/102 (98%) isolates. The erm(41) genotypic pattern was accurately identified for M. abscessus isolates . Mutations in rrl were detected in 15 isolates (7 M. avium complex, 5 M. abscessus and 3 M. chelonae ) with acquired clarithromycin resistance harbouring rrl mutations (a2057c, a2058g, a2058t or a2059c). Mutations in rrs were detected in five isolates with amikacin resistance harbouring the rrs mutation a1408g. In two isolates, the NTM-DR test revealed an rrl mutation (initial sequencing being WT), which was confirmed by re-sequencing. The test results were concordant with phenotypic susceptibility testing in 96/102 (94.1%) isolates, with four clarithromycin-resistant and two amikacin-resistant isolates not harbouring mutations.

Conclusions

The GenoType NTM-DR test is efficient in detecting mutations predictive of antimicrobial resistance in M. avium complex, M. abscessus and M. chelonae.

The efficacy, safety, and feasibility of inhaled amikacin for the treatment of difficult-to-treat non-tuberculous mycobacterial lung diseases

Background

In multidrug regimens, including an intravenous aminoglycoside (e.g. amikacin [AMK]) is recommended for difficult-to-treat non-tuberculous mycobacterial (NTM) lung diseases. We aimed to evaluate the efficacy, safety, and feasibility of inhaled AMK therapy in patients with difficult-to-treat NTM lung diseases in a retrospective chart review.

Methods

The study population consisted of patients with NTM lung diseases who received combination therapy, including inhaled AMK therapy, at Keio University Hospital (Tokyo, Japan), from January 2014 through May 2016. A total of 26 cases, consisting of 23 Mycobacterium avium complex (MAC) and three Mycobacterium abscessus complex (MABC) infections cases, were included in this study. The efficacy, safety, and feasibility of inhaled AMK therapy were retrospectively investigated. The Research Ethics Committee of Keio University Hospital approved this study, and informed consent was obtained from all patients.

Results

All 26 patients were culture-positive at enrolment. Twenty-three of the 26 patients (88.5%), including 21/23 MAC patients (91.3%) and 2/3 MABC patients (66.7%), were administered inhaled AMK therapy for >3 months. The proportion of patients who had clinical symptoms, including, cough and sputum, declined after inhalation AMK therapy. Ten of the 23 patients (43.5%) who received AMK inhalation, including 8/21 MAC (38.1%) and 2/2 MABC patients (100%), showed sputum conversion, defined as at least three consecutive negative sputum cultures. Seven of the 23 patients, including, 5/21 MAC and 2/2 MABC patients, showed improvements in high-resolution computed tomography imaging of the chest. In addition, the serum AMK trough levels before the second inhalation were <1.2 μg/mL in all 26 patients, with no occurrence of severe adverse events, such as renal toxicity. One patient (3.8%) experienced auditory toxicity, in the form of tinnitus. However, this symptom was reversible, after temporary interruption of AMK, the patient was able to safely resume the therapy.

Conclusions

Inhaled AMK therapy is an effective and feasible therapy for difficult-to-treat NTM lung disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-017-2665-5) contains supplementary material, which is available to authorized users.

Mycobacterium kansasii Subtype I Is Associated With Clarithromycin Resistance in China

Mycobacterium kansasii is the second most common cause of slowly growing non-tuberculous mycobacteria diseases in China. The aim of the present study was to analyze M. kansasii subtypes isolated from patients in China, and to explore the antimicrobial susceptibility of the differentiation among these diverse subtypes. A total of 78 M. kansasii strains from 16 provinces of China were enrolled in this study. Amikacin (AMK) was the most highly active against M. kansasii strains, and only 4 isolates (5.1%) exhibited in vitro resistance to AMK. The percentage of levofloxacin (LFX) resistant strains among the 78 M. kansasii isolates was 39.7% (31/78), which was significantly higher than that of moxifloxacin (16.7%, P = 0.001) and gatifloxacin (19.2%, P = 0.005). By using PCR-restriction fragment analysis of the hsp65 gene (PRA), all the isolates were classified as four different subtypes. Of these four subtypes, M. kansasii subtype I was the most frequent genotype in China, accounting for 71.8% (56/78) of M. kansasii isolates. Resistance to clarithromycin (CLA) was noted in 26.8% (15/56) of subtype I isolates, which was significant higher than that of other subtypes (4.5%, P = 0.031). DNA sequencing revealed that the presence of mutations in 23S rRNA was associated with 56.2% (9/16) of CLA-resistant M. kansasii isolates. In conclusion, our data demonstrate that AMK is the most active agent against M. kansasii in vitro, while the high proportion of CLA resistance is noted in M. kansasii isolates. In addition, the predominant subtype I is associated with CLA resistance in China.

Pneumothorax associated with nontuberculous mycobacteria: A retrospective study of 69 patients

The incidence of nontuberculous mycobacterial pulmonary disease (NTMPD) is increasing worldwide. Secondary spontaneous pneumothorax occurs as a complication of underlying lung disease and is associated with higher morbidity, mortality, and recurrence than primary spontaneous pneumothorax. We here investigated the clinical features and long-term outcomes of pneumothorax associated with NTMPD.We conducted a retrospective study on consecutive adult patients with pneumothorax associated with NTMPD at Fukujuji Hospital and Keio University Hospital from January 1992 to December 2013. We reviewed the medical records of 69 such patients to obtain clinical characteristics, radiological findings, and long-term outcomes, including pneumothorax recurrence and mortality.The median age of the patients was 68 years; 34 patients were women. The median body mass index was 16.8 kg/m. Underlying pulmonary diseases mainly included chronic obstructive pulmonary disease and pulmonary tuberculosis. On computed tomography, nodules and bronchiectasis were observed in 46 (98%) and 45 (96%) patients, respectively. Consolidation, pleural thickening, interlobular septal thickening, and cavities were most common, and observed in 40 (85%), 40 (85%), 37 (79%), and 36 (77%) patients, respectively. Regarding pneumothorax treatment outcomes, complete and incomplete lung expansion were observed in 49 patients (71%) and 15 patients (22%), respectively. The survival rate after pneumothorax was 48% at 5 years. By the end of the follow-up, 33 patients had died, and the median survival was 4.4 years with a median follow-up period of 1.7 years. The rate of absence of recurrence after the first pneumothorax was 59% at 3 years. By the end of the follow-up, 18 patients had experienced pneumothorax recurrence. Furthermore, 12/18 patients (66%) with recurrent pneumothorax died during the study period. Twenty-three patients (70%) died because of NTMPD progression. Low body mass index (BMI) was a negative prognostic factor for pneumothorax associated with NTMPD in multivariate analysis (HR 0.79, 95% CI 0.64-0.96; P = 0.018)Patients with pneumothorax associated with NTMPD have advanced disease, a high rate of pneumothorax recurrence, and poor prognosis, regardless of the pneumothorax treatment used. Further improvements in early diagnosis of NTMPD and appropriate management in both NTMPD and NTMPD-associated pneumothorax are needed.

PCR-Based Rapid Identification System Using Bridged Nucleic Acids for Detection of Clarithromycin-Resistant Mycobacterium avium-M. intracellulare Complex Isolates

The nontuberculous mycobacteria (NTM) cause miscellaneous disorders in humans, especially in the lungs, which present with a variety of radiological features. To date, knowledge of the pathogenic role of the Mycobacterium avium-intracellulare complex (MAC) in the human lung and the definitive criteria for initiating multidrug therapy are still lacking. However, there is little doubt that clarithromycin is the most efficacious drug among the various treatment regimens for lung NTM. In this study, with the use of a bridged nucleic acid (BNA) probe a detection system based on a real-time PCR (BNA-PCR) for the identification of the point mutations at position 2058 or 2059 in domain V of the 23S rRNA gene responsible for clarithromycin resistance was developed and has been assessed using MAC isolates from clinical samples. Out of 199 respiratory specimens, the drug susceptibility test demonstrated 12 strains resistant to clarithromycin, while the BNA-PCR showed 8 strains carrying the point mutation at position 2058 or 2059 of the 23S rRNA gene. This system revealed that there were mycobacterial strains resistant to clarithromycin which do not carry previously identified resistance genes. This paper documents a novel system for detecting clarithromycin-resistant strains and demonstrates that although these mutations are tacitly assumed to account for >90% of the reported resistant mutants, there is a significant fraction of resistant mutants that do not harbor these mutations. Therefore, unknown mechanisms affecting clarithromycin resistance remain to be elucidated.

Antimicrobial susceptibility and molecular characterization of Mycobacterium intracellulare in China

Mycobacterium avium complex (MAC) is the most common non-tuberculosis mycobacterial pathogen isolated from respiratory samples, mainly including two species, Mycobacterium avium (M. avium) and Mycobacterium intracellulare (M. intracellulare). Although these two species belong to the same group, M. avium and M. intracellulare reveal significantly differences in pathogenicity and biology. Nevertheless, little is known regarding the drug resistant details profile of M. avium or M. intracellulare instead of MAC. Here, we examined the antimicrobial susceptibility profiles of 52 clinical M. intracellulare isolates against fourteen antimicrobial agents, which are widely selected for the treatment of nontuberculous mycobacteria (NTM) infection. The drug susceptibility test revealed that clarithromycin (47/52, 90.4%), rifampicin (41/52, 78.8%) and capreomycin (40/52, 76.9%) revealed highly antimicrobial activities against M. intracellulare isolates in vitro. Furthermore, all clarithromycin resistant isolates harbored mutations in the 23S rRNA gene, and the percentage of amikacin resistant ones with mutation in the rrs gene is 62.5% (10/16). The Hunter-Gaston Discriminatory Index (HGDI) value for the 16-loci Variable Number of Tandem Repeat (VNTR) typing of M. intracellulare isolates was 0.994, and M. intracellulare resistance to moxifloxacin was significantly more commonly found in clustered strains than in nonclustered strains (χ(2)=5.551, P=0.040). In conclusion, our data demonstrated that clarithromycin and capreomycin revealed highly antimicrobial activities against M. intracellulare isolates, and clarithromycin and amikacin resistance could be detected more readily and rapidly using molecular scanning of corresponding drug target than conventional drug susceptibility testing. We also found that infection by clustered strains was significantly associated with resistance to moxifloxacin.

Diseases caused by nontuberculous mycobacteria in Asia

 The isolation rate of nontuberculous mycobacteria (NTM) species and the prevalence of NTM-associated diseases are on the rise in Asian, as well as in Western countries; however, the species distribution of NTM isolates and the types of diseases caused by NTM species vary from region to region. In this review, we present an update on the epidemiology of NTM in Asia. We demonstrate that the distribution of NTM species varies within Asia and differs from that in North America and Europe. In addition, the clinical manifestations of NTM diseases include respiratory tract infections, disseminated infections, skin and soft tissue infections, lymphadenitis, empyema, ocular infections, CNS infections and genitourinary infections. Finally, the rate of adaptive resistance of anti-NTM antimicrobial agents remains high and may be associated with a poor outcome for patients with NTM diseases.

Molecular Typing of Mycobacterium intracellulare Using Pulsed-Field Gel Electrophoresis, Variable-Number Tandem-Repeat Analysis, Mycobacteria Interspersed Repetitive-Unit-Variable-Number Tandem Repeat Typing, and Multilocus Sequence Typing: Molecular Characterization and Comparison of Each Typing Methods

OBJECTIVES

Mycobacterium intracellulare is the major causative agent of nontuberculous mycobacteria-related pulmonary infections. The strain typing of M. intracellulare is important for the treatment and control of its infections. We compared the discrimination capacity and effective value of four different molecular typing methods.

METHODS

Antibiotic susceptibility testing, hsp65 and rpoB sequencing, pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), mycobacteria interspersed repetitive-unit-variable-number tandem-repeat analysis (MIRU-VNTR), and VNTR assay targeting 44 M. intracellulare isolates obtained from patients with pulmonary infections were performed.

RESULTS

All the antibiotic susceptibility patterns had no association with the molecular and sequence types tested in this study; however, the molecular and sequence types were related with each other. PFGE gave best results for discriminatory capacity, followed by VNTR, MLST, and MIRU-VNTR.

CONCLUSION

The high discriminatory power of PFGE, VNTR, and MLST is enough for differentiating between reinfection and relapse, as well as for other molecular epidemiological usages. The MLST could be regarded as a representative classification method, because it showed the clearest relation with the sequence types.

Pulmonary disease caused by nontuberculous mycobacteria

The propensity of various nontuberculous mycobacteria to cause lung disease varies widely and is conditioned by host factors; infection is believed to occur from environmental sources. Nontuberculous mycobacteria pulmonary disease (PNTM) is increasing worldwide and Mycobacterium avium complex is the most common cause. PNTM usually occurs in one of three prototypical forms: hypersensitivity pneumonitis, cavitary tuberculosis-like disease or nodular bronchiectasis. PNTM has been linked in some patients to genetic variants of the cystic fibrosis transmembrane conductance regulator gene and a distinct patient phenotype. Interactions between PNTM and other comorbidities are also increasingly appreciated. Guidelines for diagnosis, emphasizing chest imaging and microbiology, have been published; speciation using molecular techniques is critical for accuracy and for treatment decisions. Clinical trials are lacking to inform treatment for many species and experience with M. avium complex and several others species serves as a guide instead. Use of multiple drugs for a period of at least 12 months following sputum conversion is the norm for most species. In vitro drug susceptibility results for many drugs may not correlate with clinical outcomes and such testing should be done on a selective basis.

Rapid molecular detection of macrolide resistance in the Mycobacterium avium complex: are we there yet?

Macrolides are an important tool in the treatment of Mycobacterium avium complex infections. Here, we evaluate the use of 23S rRNA gene sequencing for the rapid detection of macrolide resistance. Routine sequencing of the 23S rRNA gene is highly specific for macrolide resistance but lacks in sensitivity.

Taking a rational approach in the treatment of avian mycobacteriosis

Treatment for avian mycobacteriosis is still in its infancy and based on extrapolations from human medicine. The optimum drug choice, dose, or length of treatment has yet to be determined for most exotic animal species. Treatment should include multiple drugs for extended periods of time with appropriate monitoring of both drug levels and overall animal health. Risk to owners and handlers needs to be minimized through appropriate identification of the species of mycobacteri causing disease. More research is necessary on the pharmacokinetics of these drugs in other animal species and antibiotic resistance. Currently, euthanasia remains the most common action in the face of active mycobacteriosis.