Therapy of refractory nontuberculous mycobacterial lung disease:

Lung transplantation for cystic fibrosis: results, indications, complications, and controversies

Survival in patients with cystic fibrosis (CF) has improved dramatically over the past 30 to 40 years, with mean survival now approximately 40 years. Nonetheless, progressive respiratory insufficiency remains the major cause of mortality in CF patients, and lung transplantation (LT) is eventually required. Timing of listing for LT is critical, because up to 25 to 41% of CF patients have died while awaiting LT. Globally, approximately 16.4% of lung transplants are performed in adults with CF. Survival rates for LT recipients with CF are superior to other indications, yet LT is associated with substantial morbidity and mortality (∼50% at 5-year survival rates). Myriad complications of LT include allograft failure (acute or chronic), opportunistic infections, and complications of chronic immunosuppressive medications (including malignancy). Determining which patients are candidates for LT is difficult, and survival benefit remains uncertain. In this review, we discuss when LT should be considered, criteria for identifying candidates, contraindications to LT, results post-LT, and specific complications that may be associated with LT. Infectious complications that may complicate CF (particularly Burkholderia cepacia spp., opportunistic fungi, and nontuberculous mycobacteria) are discussed.

Risk factors for recurrence after successful treatment of Mycobacterium avium complex lung disease

This study analyzed the recurrence rate and risk factors for recurrence of Mycobacterium avium complex (MAC) lung disease in patients successfully treated for this disease. The medical records of 158 patients successfully treated for MAC lung disease at a tertiary referral center in South Korea between March 2000 and December 2009 were retrospectively analyzed. Recurrence was recorded, and factors associated with recurrence were analyzed. The mean age of the 158 patients was 60.7 ± 11.1 years. The etiologic agent was Mycobacterium avium in 77 patients (48.7%) and Mycobacterium intracellulare in 81 patients (51.3%). Radiographic features included nodular bronchiectatic disease in 95 (60.1%), fibrocavitary disease in 49 (31.0%), and an unclassifiable form in 14 (8.9%) patients. Almost all (98.7%, 156/158) patients had been previously treated with a macrolide-containing regimen, and 68 (43.0%) patients had received treatment with an aminoglycoside. During a median follow-up of 43.8 months after completion of therapy, 50 patients (31.6%) experienced recurrence, at a median of 11.9 months after treatment completion. Multivariate analysis showed that only the nodular bronchiectatic form of the disease (hazard ratio, 2.39; 95% confidence interval, 1.19 to 4.81) was independently associated with an increased risk of recurrence. Recurrence after successful treatment is frequent in patients with MAC lung disease. The recurrence rate was significantly higher in patients with the nodular bronchiectatic form than in those with the fibrocavitary form or an unclassifiable form of the disease.

Intermittent antibiotic therapy for nodular bronchiectatic Mycobacterium avium complex lung disease

RATIONALE

Although intermittent, three-times-weekly therapy is recommended for the initial treatment of noncavitary nodular bronchiectatic Mycobacterium avium complex (MAC) lung disease, supporting data are limited.

OBJECTIVES

To evaluate the clinical efficacy of intermittent therapy compared with daily therapy for nodular bronchiectatic MAC lung disease.

METHODS

A retrospective cohort study of 217 patients with treatment-naive noncavitary nodular bronchiectatic MAC lung disease. All patients received either daily (n = 99) or intermittent therapy (n = 118) that included clarithromycin or azithromycin, rifampin, and ethambutol.

MEASUREMENTS AND MAIN RESULTS

Modification of the initial antibiotic therapy occurred more frequently in the daily therapy group than in the intermittent therapy group (46 vs. 21%; P < 0.001); in particular, ethambutol was more frequently discontinued in the daily therapy group than in the intermittent therapy group (24 vs. 1%; P ≤ 0.001). However, the rates of symptomatic improvement, radiographic improvement, and sputum culture conversion were not different between the two groups (daily therapy vs. intermittent therapy: 75 vs. 82%, P = 0.181; 68 vs. 73%, P = 0.402; 76 vs. 67%, P = 0.154, respectively). In addition, the adjusted proportion of sputum culture conversion was similar between the daily therapy (71.3%; 95% confidence interval, 59.1-81.1%) and the intermittent therapy groups (73.6%; 95% confidence interval, 62.9-82.2%; P = 0.785).

CONCLUSIONS

These results suggest that intermittent three-times-weekly therapy with a macrolide, rifampin, and ethambutol is a reasonable initial treatment regimen for patients with noncavitary nodular bronchiectatic MAC lung disease. Clinical trial registered with www.clinicaltrials.gov (NCT 00970801).

Treatment outcomes of adjuvant resectional surgery for nontuberculous mycobacterial lung disease

Background

Outcomes of antibiotic treatment for lung disease caused by nontuberculous mycobacteria (NTM) are unsatisfactory. The role of adjunctive surgery in the treatment of NTM lung disease is still unclear.

Methods

We conducted a retrospective review of 70 patients who underwent pulmonary resection for NTM lung disease from March 2007 to February 2013. All patients received recommended antibiotic treatment before and after the surgery.

Results

A total of 70 patients underwent 74 operations. The median age of the patients was 50 years. Of the 70 patients, 45 (64%) had Mycobacterium avium complex infection (24 M. intracellulare and 21 M. avium) and 23 (33%) had M. abscessus complex infection (15 M. abscessus and 8 M. massiliense). Thirty-eight (54%) patients had the nodular bronchiectatic form and 28 (40%) had the fibrocavitary form of NTM lung disease. The indications for surgery were a poor response to drug therapy (n=52), remnant cavitary lesions and severe bronchiectasis (n=14), and hemoptysis (n=4). Preoperative sputum acid-fast bacilli staining results were positive in 44 (63%) patients, and sputum culture was positive in 54 (76%). The surgery included lobectomy or lobectomy plus segmentectomy (n=50, 68%), segmentectomy (n=11, 15%), pneumonectomy or completion pneumonectomy (n=8, 11%), bilobectomy or bilobectomy plus segmentectomy (n=4, 5%), and wedge resection (n=1, 1%). Postoperative complications occurred in 15 (21%) patients, including one postoperative death and bronchopleural fistula in 5 patients with the fibrocavitary form of the disease. A negative sputum culture was achieved and maintained in 57 (81%) patients.

Conclusions

Although adjuvant pulmonary resection is associated with a relatively high complication rate, this procedure may provide a high level of treatment success for selected patients with NTM lung disease, such as those with a poor response to antibiotic treatment alone.

Nontuberculous mycobacteria among patients with cystic fibrosis in the United States: screening practices and environmental risk

RATIONALE

Persons with cystic fibrosis (CF) are at greater risk of nontuberculous mycobacterial (NTM) infections than the general population. However, among patients with CF, geographic variation in prevalence is poorly understood.

OBJECTIVES

To describe the prevalence and screening practices of NTM among U.S. patients with CF.

METHODS

CF Patient Registry data from 2010-2011 were obtained to estimate the prevalence of NTM among patients with CF 12 years of age or older by state. Climatic data were also obtained and predictors of NTM infection analyzed using regression analysis. Geographic clustering and mycobacterial culture rates by state were also assessed.

MEASUREMENTS AND MAIN RESULTS

Among patients with CF 12 years of age or older, 58% had mycobacterial cultures; 14% were positive for NTM. Most states (n = 31) had a prevalence of 10-20%; seven states predominantly in the West and Southeast had a prevalence of 20% or greater, including Alaska, which cultured patients more frequently than any other state. Nearly 60% of positive cultures were for Mycobacterium avium complex, although this ranged by state, from 29% in Louisiana to 100% for Nebraska/Delaware. Significant (P < 0.002) spatial clustering of NTM was detected, centering in Wisconsin, Arizona, Florida, and Maryland. Higher saturated vapor pressure increased risk for NTM (odds ratio = 1.06; 95% confidence interval = 1.02-1.10). The proportion of patients cultured for mycobacteria varied greatly by state of residence (median = 46%; range = 9-73%).

CONCLUSIONS

NTM prevalence varies significantly among patients with CF by geographic area, and is largely influenced by environmental factors. However, NTM culture practices vary greatly, with some high-prevalence states screening less than 25% annually. Routine screening for all patients with CF is needed for timely detection.

Lack of adherence to evidence-based treatment guidelines for nontuberculous mycobacterial lung disease

RATIONALE

The 2007 American Thoracic Society (ATS) and Infectious Diseases Society of America (IDSA) recommend that patients with pulmonary nontuberculous mycobacterial (PNTM) disease caused by Mycobacterium avium complex (MAC) or M. abscessus be treated with a macrolide-based multidrug antibiotic regimen until sputum culture negative for 1 year. After 6 years, the degree of adherence to recommended guidelines among physicians remains unknown.

OBJECTIVE

To describe antibiotic treatment practices among physicians treating patients with PNTM in the United States.

METHODS

A nationally representative sample of 1,286 U.S. physicians was contacted in December 2011 through January 2012; 582 of the responding physicians were treating patients with PNTM and were eligible to participate. Physicians were asked to extract medical record data on the last four patients they treated in the past year with PNTM disease from either MAC or M. abscessus. Treatment patterns were assessed for all patients by NTM species and physician specialty, and compared with the 2007 recommended ATS/IDSA guidelines.

MAIN RESULTS

Questionnaires were completed by 349 physicians on 915 patients with PNTM, including 744 (81%) with MAC and 174 (19%) with M. abscessus; 3 patients were positive for both. Physicians treated 76 (44%) patients with M. abscessus and 411 (55%) patients with MAC. Only 13% of antibiotic regimens prescribed to patients with MAC met ATS/IDSA guidelines, 56% did not include a macrolide, and 16% were for macrolide monotherapy. Among patients with M. abscessus, 64% of regimens prescribed did not include a macrolide.

CONCLUSIONS

Adherence to the 2007 ATS/IDSA guidelines for treating PNTM disease is poor. Across all physician specialties evaluated, suboptimal or potentially harmful antibiotic regimens were commonly prescribed.

Highlight on advances in nontuberculous mycobacterial disease in North America

Nontuberculous mycobacteria (NTM) are ubiquitous in the environment and exist as an important cause of pulmonary infections in humans. Pulmonary involvement is the most common disease manifestation of NTM and the incidence of NTM is growing in North America. Susceptibility to NTM infection is incompletely understood; therefore preventative tools are not well defined. Treatment of pulmonary nontuberculous mycobacterial (NTM) infection is difficult and entails multiple antibiotics and an extended treatment course. Also, there is a considerable variation in treatment management that should be considered before initiating treatment. We highlight the new findings in the epidemiology diagnosis and treatment of mycobacterial infections. We debate new advances regarding NTM infection in cystic fibrosis patients and solid organ transplant recipients. Finally, we introduce a new epidemiologic model for NTM disease based on virulence-exposure-host factors.

Species identification of Mycobacterium abscessus subsp. abscessus and Mycobacterium abscessus subsp. bolletii using rpoB and hsp65, and susceptibility testing to eight antibiotics

OBJECTIVES

To separate Mycobacterium abscessus subsp. bolletii from Mycobacterium abscessus subsp. abscessus using species identification, and to investigate the in vitro activity of amikacin, cefoxitin, imipenem, levofloxacin, moxifloxacin, clarithromycin, azithromycin, and linezolid against Mycobacterium abscessus.

METHODS

Seventy M. abscessus isolates, previously identified by 16S rRNA sequencing, were further identified by comparative sequence analysis of rpoB and hsp65. Drug susceptibility testing was conducted using the microplate Alamar Blue assay in accordance with Clinical and Laboratory Standards Institute (CLSI) guidelines and interpreted using CLSI breakpoints.

RESULTS

Of the 70 strains, 45 (64%) were M. abscessus subsp. abscessus and 25 (36%) were M. abscessus subsp. bolletii. The majority of M. abscessus isolates were susceptible to azithromycin, amikacin, linezolid, and imipenem (M. abscessus subsp. abscessus: 93%, 98%, 93%, and 73%, respectively; M. abscessus subsp. bolletii: 96%, 96%, 80%, and 68%, respectively). Approximately half of the M. abscessus isolates were moderately susceptible to cefoxitin and moxifloxacin (M. abscessus subsp. abscessus 53% and 49%; M. abscessus subsp. bolletii 72% and 68%). Nearly all the M. abscessus isolates were resistant to levofloxacin (M. abscessus subsp. abscessus 96%, M. abscessus subsp. bolletii 100%). Inducible clarithromycin resistance was found in M. abscessus. After 14 days of incubation, 83% M. abscessus subsp. abscessus and 36% M. abscessus subsp. bolletii were resistant to clarithromycin.

CONCLUSIONS

Using rpoB and hsp65, M. abscessus subsp. bolletii could be distinguished from M. abscessus subsp. abscessus. Amikacin and azithromycin showed excellent activity against M. abscessus in vitro. Imipenem, linezolid, cefoxitin, and moxifloxacin also showed good activity. Levofloxacin was inactive against M. abscessus. Although clarithromycin showed excellent activity against M. abscessus on day 3, inducible resistance occurred, and after 14 days clarithromycin showed little activity against M. abscessus subsp. abscessus, but still had good activity against M. abscessus subsp. bolletii.

Pentacyclic nitrofurans with in vivo efficacy and activity against nonreplicating Mycobacterium tuberculosis

The reductively activated nitroaromatic class of antimicrobials, which include nitroimidazole and the more metabolically labile nitrofuran antitubercular agents, have demonstrated some potential for development as therapeutics against dormant TB bacilli. In previous studies, the pharmacokinetic properties of nitrofuranyl isoxazolines were improved by incorporation of the outer ring elements of the antitubercular nitroimidazole OPC-67683. This successfully increased stability of the resulting pentacyclic nitrofuran lead compound Lee1106 (referred to herein as 9a). In the current study, we report the synthesis and antimicrobial properties of 9a and panel of 9a analogs, which were developed to increase oral bioavailability. These hybrid nitrofurans remained potent inhibitors of Mycobacterium tuberculosis with favorable selectivity indices (>150) and a narrow spectrum of activity. In vivo, the pentacyclic nitrofuran compounds showed long half-lives and high volumes of distribution. Based on pharmacokinetic testing and lack of toxicity in vivo,9a remained the series lead. 9a exerted a lengthy post antibiotic effect and was highly active against nonreplicating M. tuberculosis grown under hypoxia. 9a showed a low potential for cross resistance to current antitubercular agents, and a mechanism of activation distinct from pre-clinical tuberculosis candidates PA-824 and OPC-67683. Together these studies show that 9a is a nanomolar inhibitor of actively growing as well as nonreplicating M. tuberculosis.

Rapid detection and differentiation of mycobacterial species using a multiplex PCR system

INTRODUCTION

The early diagnosis of mycobacterial infections is a critical step for initiating treatment and curing the patient. Molecular analytical methods have led to considerable improvements in the speed and accuracy of mycobacteria detection.

METHODS

The purpose of this study was to evaluate a multiplex polymerase chain reaction system using mycobacterial strains as an auxiliary tool in the differential diagnosis of tuberculosis and diseases caused by nontuberculous mycobacteria (NTM) RESULTS: Forty mycobacterial strains isolated from pulmonary and extrapulmonary origin specimens from 37 patients diagnosed with tuberculosis were processed. Using phenotypic and biochemical characteristics of the 40 mycobacteria isolated in LJ medium, 57.5% (n=23) were characterized as the Mycobacterium tuberculosis complex (MTBC) and 20% (n=8) as nontuberculous mycobacteria (NTM), with 22.5% (n=9) of the results being inconclusive. When the results of the phenotypic and biochemical tests in 30 strains of mycobacteria were compared with the results of the multiplex PCR, there was 100% concordance in the identification of the MTBC and NTM species, respectively. A total of 32.5% (n=13) of the samples in multiplex PCR exhibited a molecular pattern consistent with NTM, thus disagreeing with the final diagnosis from the attending physician.

CONCLUSIONS

Multiplex PCR can be used as a differential method for determining TB infections caused by NTM a valuable tool in reducing the time necessary to make clinical diagnoses and begin treatment. It is also useful for identifying species that were previously not identifiable using conventional biochemical and phenotypic techniques.

Dynamics of immune effector mechanisms during infection with Mycobacterium avium in C57BL/6 mice

Opportunistic infections with non-tuberculous mycobacteria such as Mycobacterium avium are receiving renewed attention because of increased incidence and difficulties in treatment. As for other mycobacterial infections, a still poorly understood collaboration of different immune effector mechanisms is required to confer protective immunity. Here we have characterized the interplay of innate and adaptive immune effector mechanisms contributing to containment in a mouse infection model using virulent M. avium strain 104 in C57BL/6 mice. M. avium caused chronic infection in mice, as shown by sustained organ bacterial load. In the liver, bacteria were contained in granuloma-like structures that could be defined morphologically by expression of the antibacterial innate effector protein Lipocalin 2 in the adjoining hepatocytes and infiltrating neutrophils, possibly contributing to containment. Circulatory anti-mycobacterial antibodies steadily increased throughout infection and were primarily of the IgM isotype. Highest levels of interferon-γ were found in infected liver, spleen and serum of mice approximately 2 weeks post infection and coincided with a halt in organ bacterial growth. In contrast, expression of tumour necrosis factor was surprisingly low in spleen compared with liver. We did not detect interleukin-17 in infected organs or M. avium-specific T helper 17 cells, suggesting a minor role for T helper 17 cells in this model. A transient and relative decrease in regulatory T cell numbers was seen in spleens. This detailed characterization of M. avium infection in C57BL/6 mice may provide a basis for future studies aimed at gaining better insight into mechanisms leading to containment of infections with non-tuberculous mycobacteria.

Prognostic factors and radiographic outcomes of nontuberculous mycobacterial lung disease in rheumatoid arthritis

OBJECTIVE

The aims of our study were to retrospectively review patients with rheumatoid arthritis (RA) with nontuberculous mycobacterial (NTM) lung disease, to assess the prognostic factors, and to analyze the time to disease deterioration according to the antirheumatic drugs received during the NTM lung disease followup period.

METHODS

We retrospectively analyzed medical records of 98 HIV-negative RA patients with NTM lung disease treated at our institution, and investigated potential risk factors of mortality with Cox regression analysis. Time to radiologic deterioration was evaluated if antirheumatic drugs were not changed during observational periods and computed tomography was performed once each year.

RESULTS

Mean patient age was 67.6 years, and median followup period was 4.4 years. NTM species included Mycobacterium avium complex (83.7%), M. kansasii (6.1%), M. gordonae (6.1%), and others (4.1%). Radiographic features included nodular/bronchiectatic (NB) disease (57.1%), fibrocavitary (FC) disease (14.3%), FC+NB disease (16.3%), and other types (12.2%). Initial management included observation in 74 (75.5%) patients. Negative prognostic factors of mortality were C-reactive protein (CRP) ≥ 1.0 mg/dl and radiographic features of FC, FC+NB, or other disease types. Median time to radiologic deterioration was 3.6 years. Erythrocyte sedimentation rate (ESR) > 50 mm/h was a negative prognostic factor of radiologic deterioration.

CONCLUSION

The most frequent NTM species was M. avium complex. CRP and radiographic features were prognostic factors for all-cause mortality, and ESR was a prognostic factor of radiologic deterioration. Further studies are warranted focusing on time to disease deterioration according to antirheumatic drug received during NTM followup.

Treatment of refractory Mycobacterium avium complex lung disease with a moxifloxacin-containing regimen

Moxifloxacin (MXF) has in vitro and in vivo activity against Mycobacterium avium complex (MAC) in experimental models. However, no data are available concerning its treatment effect in patients with MAC lung disease. The aim of this study was to evaluate the clinical efficacy of an MXF-containing regimen for the treatment of refractory MAC lung disease. Patients with MAC lung disease who were diagnosed between January 2002 and December 2011 were identified from our hospital database. We identified 41 patients who received MXF for ≥ 4 weeks for the treatment of refractory MAC lung disease. A total of 41 patients were treated with an MXF-containing regimen because of a persistent positive culture after at least 6 months of clarithromycin-based standardized antibiotic therapy. The median duration of antibiotic therapy before MXF administration was 410 days (interquartile range [IQR], 324 to 683 days). All patients had culture-positive sputum when MXF treatment was initiated. The median duration of MXF administration was 332 days (IQR, 146 to 547 days). The overall treatment success rate was 29% (12/41), and the median time to sputum conversion was 91 days (IQR, 45 to 190 days). A positive sputum acid-fast-bacillus smear at the start of treatment with MXF-containing regimens was an independent predictor of an unfavorable microbiological response. Our results indicate that MXF may improve treatment outcomes in about one-third of patients with persistently culture-positive MAC lung disease who fail to respond to clarithromycin-based standardized antibiotic treatment. Prospective studies are required to assess the clinical efficacy of MXF treatment for refractory MAC lung disease.

Mycobacterium avium-intracellulare otomastoiditis in a young AIDS patient: case report and review of the literature

Mycobacterium avium-intracellulare (MAI) complex is a common opportunistic infection that generally occurs in patients with a CD4 cell count less than 75. Current recommendations for prophylaxis include using a macrolide once a week, while treatment usually requires a multidrug regimen. Disseminated MAI infections often occur in patients who are not compliant with prophylaxis or their highly active antiretroviral therapy (HAART). Many manifestations of MAI infection are well documented in human immunodeficiency virus (HIV) patients, including pulmonary and cutaneous manifestations, but other unusual manifestations such as pericarditis, pleurisy, peritonitis, brain abscess, otitis media, and mastoiditis are sporadically reported in the infectious diseases literature. This case report is of a 22-year-old female who contracted HIV at a young age and who was subsequently noncompliant with HAART, MAI prophylaxis, and prior treatment for disseminated MAI infection. Unsurprisingly, the patient developed recurrent disseminated MAI infection. The patient’s presentation was atypical, as she developed severe otomastoiditis and posterior reversible encephalopathy syndrome. The posterior reversible encephalopathy syndrome was thought to be due to the disseminated MAI infection or to immune reconstitution inflammatory syndrome. The infection was confirmed to be secondary to MAI by culture of the mastoid bone. Microbiological analysis of the MAI strain cultured showed resistance to several first-line antibiotics used for prophylaxis against and treatment of MAI. This was likely due to the patient’s chronic noncompliance. Otomastoiditis secondary to MAI is extremely rare in adults and has been reported in only four case reports and one case series previously. Improved clinician education in the diagnosis, treatment, and, most important, prevention of MAI and other opportunistic infections is needed. Greater HIV screening, appropriate HAART medication administration, and availability of infectious disease specialists is needed in at-risk populations to help prevent such serious infections. Patient education and greater access to care should serve to prevent medication nonadherence and to enhance affordability of HAART and prophylactic antibiotics.

Clinical characteristics and prevalence of pneumothorax in patients with pulmonary Mycobacterium avium complex disease

Pneumothorax in patients with pulmonary Mycobacterium avium complex (MAC) disease is considered to be a rare complication, and little is known about its clinical course. In this study, we aimed to define the clinical features, outcome, and prevalence of pneumothorax in patients with pulmonary MAC disease. A retrospective review of medical records identified eight men and ten women (mean age, 75 years) with active pulmonary MAC disease complicated by pneumothorax between 2003 and 2010 in our institution. None of the patients was positive for HIV infection. Pneumothorax occurred in the right lung in 12 patients and in the left in six. All but one patient had MAC disease in both lungs, and 12 patients had widespread lesions covering a total area larger than one lung field. Seven of the 18 patients (39 %) were forced to undergo surgery following unsuccessful thoracic drainage. Five patients experienced recurrence during the study period and two others eventually developed chronic pneumothorax. The complication rate of pneumothorax was calculated on the bases of the total number of patients with active pulmonary MAC disease during the same period. The overall complication rate of pneumothorax was as high as 2.4 % (18 of 746 patients with MAC disease). In conclusion, the incidence of pneumothorax in patients with active pulmonary MAC disease was unexpectedly high, especially in patients who were elderly and had advanced MAC disease. This condition is often difficult to treat and can recur easily.

Macrolide treatment for Mycobacterium abscessus and Mycobacterium massiliense infection and inducible resistance

RATIONALE

Macrolides, such as clarithromycin (CLR) and azithromycin (AZM), are frequently the only oral antibiotics that are active against Mycobacterium abscessus and M. massiliense infections.

OBJECTIVES

To compare the activity of CLR and AZM in experimental models.

METHODS

We compared the treatment efficacies of CLR and AZM and determined the correlation between efficacy and induced erythromycin ribosome methyltransferase gene (erm)(41) expression in experimental models of M. abscessus and M. massiliense infections.

MEASUREMENTS AND MAIN RESULTS

In all tested M. abscessus isolates, a high level of inducible CLR resistance developed (minimal inhibitory concentration [MIC] on Day 3 versus Day 14; P < 0.001). Whereas the AZM MIC increased on Day 14 (P < 0.01 versus Day 3), the level was significantly lower than the CLR MIC on Day 14 (P < 0.001). However, the MICs of CLR and AZM for the M. massiliense isolates did not change. Compared with CLR, AZM presented greater antibiotic activity against M. abscessus in vitro, ex vivo, and in vivo (P < 0.05), whereas both macrolides were comparably effective against M. massiliense. In M. abscessus infection, the level of erm(41) expression was higher after exposure to CLR than after exposure to AZM (P < 0.001). Experiments using an erm(41)-knockout M. abscessus mutant and an M. massiliense transformant expressing M. abscessus erm(41) confirmed that erm(41) was responsible for inducible CLR resistance.

CONCLUSIONS

CLR induces greater erm(41) expression and thus higher macrolide resistance than AZM in M. abscessus infection. AZM may be more effective against M. abscessus, whereas both macrolides appear to be equally effective against M. massiliense.