Isolates Of Mycobacterium Abscessus Research Articles

Novel external quality assurance scheme for drug susceptibility testing of non-tuberculous mycobacteria: a multicentre pilot study.

Our aim was to conduct a multicentre study involving laboratories participating in the European TB Reference Laboratory Network aiming to develop a pilot external quality assessment (EQA) scheme for drug susceptibility testing (DST) of non-tuberculous mycobacteria (NTM). The study comprised a survey using a structured questionnaire followed by a pilot EQA round using identical panels of 10 Mycobacterium avium (MAV) and Mycobacterium abscessus (MAB) isolates. EQA results were received from 16 laboratories utilizing the broth microdilution method. Consensus modal MIC values were determined, and essential and categorical agreement rates were calculated. Twenty-four out of 31 laboratories (77.4%) reported DST for NTM routinely. Essential agreement ranged from 78.8% (amikacin) to 96.2% (linezolid) for MAV and from 76.0% (amikacin) to 100% (doxycycline) for MAB. Categorical agreement ranged from 56.8% (moxifloxacin) to 100% (clarithromycin) for MAV and from 53.6% (linezolid) to 100% (doxycycline) for MAB. Our results show that interlaboratory reproducibility of DST for NTM is insufficient, highlighting the need for expanding EQA schemes. As EQAs for Mycobacterium tuberculosis complex have led to more reliable and reproducible DST, we propose to follow a similar approach for clinically relevant NTM.

A bedaquiline/clofazimine combination regimen might add activity to the treatment of clinically relevant non-tuberculous mycobacteria.

Non-tuberculous mycobacteria (NTM) infections are hard to treat. New antimicrobial drugs and smarter combination regimens are needed. Our aim was to determine the in vitro activity of bedaquiline against NTM and assess its synergy with established antimycobacterials. We determined MICs of bedaquiline for clinically relevant NTM species and Mycobacterium tuberculosis by broth microdilution for 30 isolates. Synergy testing was performed using the chequerboard method for 22 reference strains and clinical isolates of Mycobacterium abscessus (MAB) and Mycobacterium avium complex (MAC). Time-kill kinetics (TK) assays with resistance monitoring of bedaquiline alone and combined with clofazimine were performed for MAB CIP 104536 and M. avium ATCC 700898; bedaquiline/clarithromycin combinations were evaluated against M. avium ATCC 700898. Interactions were assessed for TK experiments based on Bliss independence. Bedaquiline had modest activity against tested NTM, with MICs between <0.007 and 1 mg/L. Bedaquiline showed no interaction with tested drugs against MAB or MAC. Lowest mean fractional inhibitory concentration index (FICI) values were 0.79 with clofazimine for MAB and 0.97 with clofazimine and 0.82 with clarithromycin for MAC. In TK assays, bedaquiline showed a bacteriostatic effect. Clofazimine extended the bacteriostatic activity of bedaquiline against MAB and yielded a slight bactericidal effect against M. avium. The bedaquiline/clofazimine combination slowed emergence of bedaquiline resistance for M. avium but promoted it for MAB. Relative to Bliss independence, bedaquiline/clofazimine showed synergistic interaction over time for MAB and no interaction for M. avium and bedaquiline/clarithromycin showed antagonistic interaction for M. avium. Following these in vitro data, a bedaquiline/clofazimine combination might add activity to MAB and MAC treatment. The bedaquiline/clarithromycin combination might have lower activity compared with bedaquiline alone for MAC treatment.

In Vitro Susceptibility of Mycobacterium abscessus and Mycobacterium fortuitum Isolates to 30 Antibiotics.

Objective Nontuberculous mycobacteria (NTM) cause various diseases in humans and animals. Recently, the prevalence of NTM-related disease has been on the rise, becoming an emerging public health problem. The aim of this study was to determine the antibiotic susceptibility profiles of clinical isolates of Mycobacterium abscessus and Mycobacterium fortuitum. Methods. We performed susceptibility tests on 37 clinical NTM isolates to 30 antibiotics with the microdilution method recommended by the Clinical and Laboratory Standards Institute. Results Both M. abscessus and M. fortuitum were highly resistant to antitubercular drugs such as isoniazid, rifampin, ethambutol, clofazimine, ethionamide, and rifabutin. M. abscessus showed the lowest resistant rates to cefoxitin (10%), azithromycin (10%), amikacin (10%), and clarithromycin (20%) and very high resistant to sulfamethoxazole, vancomycin, oxacillin, clindamycin, and all fluoroquinolones. M. fortuitum showed low resistance to tigecycline (0%), tetracycline (0%), cefmetazole (12%), imipenem (12%), linezolid (18%), and the aminoglycosides amikacin (0%), tobramycin (0%), neomycin (0%), and gentamycin (24%). ConclusionAmikacin, cefoxitin, and azithromycin have the highest in vitro activity against M. abscessus. Isolates of M. fortuitum need to be individually evaluated for drug susceptibility before choosing an effective antimicrobial regimen for treatment of infections.

Analysis of drug-susceptibility patterns and gene sequences associated with clarithromycin and amikacin resistance in serial Mycobacterium abscessus isolates from clinical specimens from Northeast Thailand.

Mycobacterium abscessus is an important infectious agent highly associated with drug resistance and treatment failure. We investigated the drug resistance situation of M. abscessus in Northeast Thailand and the possible genetic basis for this. Sixty-eight M. abscessus clinical isolates were obtained from 26 patients at Srinagarind Hospital during 2012–2016. Drug susceptibility tests and sequencing of erm(41), rrl and rrs genes were performed. Mycobacterium abscessus was resistant to 11/15 antibiotics (nearly 100% resistance in each case). Partial susceptibility to four antibiotics was found (amikacin, tigecycline, clarithromycin and linezolid). Non-massiliense subspecies were significantly associated with clarithromycin resistance (p<0.0001) whereas massiliense subspecies were associated with tigecycline resistance (p = 0.028). Inducible clarithromycin resistance was seen in 22/68 (32.35%) isolates: 21 of these isolates (95.45%) belonged to non-massiliense subspecies and resistance was explicable by the T28C mutation in erm(41). Inducible clarithromycin resistance was found in one isolate of the massiliense subspecies. Acquired clarithromycin resistance explicable by the A2271G/C mutation of rrl was seen in only 7/16 (43.75%) of strains. Inducible and acquired resistance mechanisms can be interchangeable during the course of infection. Rrs mutations were not associated with amikacin resistance in our study. Antibiotic resistance in subspecies of M. abscessus was reported from Northeast Thailand. Known resistance-associated mutations cannot explain all of the resistance patterns observed.

Outbreak of Tattoo-associated Nontuberculous Mycobacterial Skin Infections.

On 29 April 2015, the Florida Department of Health in Miami-Dade County (DOH Miami-Dade) was notified by a local dermatologist of 3 patients with suspected nontuberculous mycobacterial (NTM) infection after receiving tattoos at a local tattoo studio. DOH Miami-Dade conducted interviews and offered testing, described below, to tattoo studio clients reporting rashes. Culture of clinical isolates and identification were performed at the Florida Bureau of Public Health Laboratories. Characterization of NTM was performed by the Centers for Disease Control and Prevention and the US Food and Drug Administration (FDA), respectively. Whole-genome sequencing (WGS) and single-nucleotide polymorphism (SNP) analyses were used to construct a phylogeny among 21 Mycobacterium isolates at the FDA. Thirty-eight of 226 interviewed clients were identified as outbreak-associated cases. Multivariate logistic regression revealed that individuals who reported gray tattoo ink in their tattoos were 8.2 times as likely to report a rash (95% confidence interval, 3.1-22.1). Multiple NTM species were identified in clinical and environmental specimens. Phylogenetic results from environmental samples and skin biopsies indicated that 2 Mycobacterium fortuitum isolates (graywash ink and a skin biopsy) and 11 Mycobacterium abscessus isolates (5 from the implicated bottle of graywash tattoo ink, 2 from tap water, and 4 from skin biopsies) were indistinguishable. In addition, Mycobacterium chelonae was isolated from 5 unopened bottles of graywash ink provided by 2 other tattoo studios in Miami-Dade County. WGS and SNP analyses identified the tap water and the bottle of graywash tattoo ink as the sources of the NTM infections.

Determination of MIC Distribution and Mechanisms of Decreased Susceptibility to Bedaquiline among Clinical Isolates of Mycobacterium abscessus.

ABSTRACTChemotherapeutic options against Mycobacterium abscessus infections are very limited. Bedaquiline, a new antituberculosis (anti-TB) drug, is effective for the treatment of multidrug-resistant TB. However, few data are available on bedaquiline for treatment of M. abscessus infections. In this study, we determined the profile for in vitro susceptibility of M. abscessus clinical isolates to bedaquiline and investigated the potential molecular mechanisms of decreased susceptibility. A total of 197 M. abscessus clinical isolates were collected from sputum and bronchoalveolar fluid of patients with lung infections. Standard broth microdilution test revealed that bedaquiline exhibited high in vitro killing activity against M. abscessus isolates, with a MIC50 of 0.062 and a MIC90 of 0.125 mg/liter. Whole-genome sequencing data showed that no nonsynonymous mutation occurred in atpE, the gene encoding the bedaquiline-targeted protein. However, of 6 strains with decreased susceptibility of bedaquiline (MIC = 0.5 to 1 mg/liter), 3 strains had nonsynonymous mutations in mab_4384, the gene encoding the repressor of efflux pump MmpS5/MmpL5. Quantitative reverse transcription-PCR (qRT-PCR) analysis showed that the expression of MmpS5/MmpL5 in the group with decreased susceptibility to bedaquiline was significantly higher than in those with medium MICs (MIC = 0.125 to 0.5 mg/liter) or in the low-MIC group (MIC ≤ 0.062 mg/liter). Two isolates with increased MICs did not show overexpression of MmpS5/MmpL5, which could not be explained by known molecular mechanisms. This is the first report showing the association of MmpS5/MmpL5 with decreased bedaquiline susceptibility in M. abscessus clinical isolates and suggesting the presence of other, yet-to-be identified mechanisms for decreased bedaquiline susceptibility in M. abscessus.

In Vitro Activity of Clofazimine against Nontuberculous Mycobacteria Isolated in Beijing, China.

Due to the natural resistance of nontuberculous mycobacteria (NTM) to many antibiotics, the treatment of diseases caused by NTM is often long-term but unsuccessful. The main goal of this study was to evaluate the in vitro susceptibilities to clofazimine of 209 isolates consisting of different NTM species isolated in Beijing, China. Furthermore, 47 reference strains were also tested, including 30 rapidly growing mycobacterium (RGM) species and 17 slowly growing mycobacterium (SGM) species. The potential molecular mechanism contributing to clofazimine resistance of NTM was investigated as well. Clofazimine exhibited excellent activity against both reference strains and clinical isolates of different SGM species, and most of the strains had MICs far below 1 μg/ml. Although the majority of the clinical isolates of Mycobacterium abscessus and Mycobacterium fortuitum had MICs higher than 2 μg/ml, 17 out of the 30 reference strains of different RGM species had MICs below 1 μg/ml in vitro According to the MIC distributions, the tentative epidemiological cutoff (ECOFF) values for Mycobacterium kansasii, Mycobacterium avium, and Mycobacterium intracellulare were defined at 0.5 μg/ml, 1 μg/ml, and 2 μg/ml, respectively. Intriguingly, single-direction cross-resistance between bedaquiline- and clofazimine (Cfz)-resistant isolates was observed among the tested NTM species. This study demonstrates that clofazimine had strong activity against most SGM species in vitro, as well as some RGM species. The data provide important insights into the possible clinical application of Cfz to treat NTM infections.

WS02.6 Improving antibiotic activity against Mycobacterium abscessus isolates by inducing bacterial disaggregation and oxygen availability

WS02.6 Improving antibiotic activity against Mycobacterium abscessus isolates by inducing bacterial disaggregation and oxygen availability

Activities of Dual Combinations of Antibiotics Against Multidrug-Resistant Nontuberculous Mycobacteria Recovered from Patients with Cystic Fibrosis.

Patients with cystic fibrosis (CF) are at risk for recurrent pulmonary infections due to increased viscosity of airway secretions, leading to persistent colonization with pathogenic bacteria, including nontuberculous mycobacteria (NTM). Extensive antibiotic use for treatment of infections has led to increasing antimicrobial resistance, which is a significant barrier to the treatment of NTMs. We examined the in vitro activity of several antibiotics against a selection of the most drug-resistant clinical isolates of Mycobacterium abscessus, Mycobacterium chelonae, and Mycobacterium avium complex recovered from CF patients at our institution, as well as paired combinations of antibiotics against a subset of M. abscessus strains, to determine whether they exhibit synergy in inhibiting bacterial growth. Most isolates displayed resistance to at least six of the nine antibiotics tested for which phenotypic interpretation is available, and elevated minimum inhibitory concentrations (MICs) were observed for many of the other drugs. The major exception was clofazimine, which had relatively low MICs for most isolates across all species. When synergy testing was performed by using paired combinations of drugs, clofazamine and clarithromycin exhibited 100% synergy for all combinations tested, as did amikacin, with the exception of one isolate. These results suggest that synergistic antibiotic combinations are capable of overcoming drug resistance in vitro, and laboratories might consider implementation of synergy testing in multidrug-resistant (MDR)-NTM organisms to guide treatment decisions in the setting of extensive antimicrobial resistance.

Mycobacterium abscessus l,d-Transpeptidases Are Susceptible to Inactivation by Carbapenems and Cephalosporins but Not Penicillins.

As a growing number of clinical isolates of Mycobacterium abscessus are resistant to most antibiotics, new treatment options that are effective against these drug-resistant strains are desperately needed. The majority of the linkages in the cell wall peptidoglycan of M. abscessus are synthesized by nonclassical transpeptidases, namely, the l,d-transpeptidases. Emerging evidence suggests that these enzymes represent a new molecular vulnerability in this pathogen. Recent studies have demonstrated that inhibition of these enzymes by the carbapenem class of β-lactams determines their activity against Mycobacterium tuberculosis Here, we studied the interactions of β-lactams with two l,d-transpeptidases in M. abscessus, namely, LdtMab1 and LdtMab2, and found that both the carbapenem and cephalosporin, but not penicillin, subclasses of β-lactams inhibit these enzymes. Contrary to the commonly held belief that combination therapy with β-lactams is redundant, doripenem and cefdinir exhibit synergy against both pansusceptible M. abscessus and clinical isolates that are resistant to most antibiotics, which suggests that dual-β-lactam therapy has potential for the treatment of M. abscessus Finally, we solved the first crystal structure of an M. abscessus l,d-transpeptidase, LdtMab2, and using substitutions of critical amino acids in the catalytic site and computational simulations, we describe the key molecular interactions between this enzyme and β-lactams, which provide an insight into the molecular basis for the relative efficacy of different β-lactams against M. abscessus.

Antibiotic resistance in Mycobacterium Abscessus and Mycobacterium Fortuitum isolates from Malaysian patients

Rapidly growing mycobacterial species (RGM) are increasingly being recognized as the cause of various superficial and deep infections in humans. Two of the species most frequently isolated from clinical specimens are Mycobacterium abscessus and Mycobacterium fortuitum. Both species are associated with antibiotic resistances that may complicate therapy. This paper describes the pattern of resistance to five antibiotics commonly prescribed for RGM infections, in M. abscessus and M. fortuitum isolated from Malaysian patients. The bacterial strains studied were examined with Etest strips to determine their minimum inhibitory concentrations (MICs) toward amikacin, ciprofloxacin, clarithromycin, imipenem, and linezolid. Among 51 M. abscessus isolates examined by the Etest, the overall MICs of ciprofloxacin, imipenem, amikacin, clarithromycin, and linezolid showed resistance rates of 33.3%, 31.4%, 2.0%, 5.9%, and 21.6%, to the five antibiotics, respectively. M. abscessus subspecies abscessus was more resistant than M. abscessus subsp. massilience to ciprofloxacin, imipenem, and linezolid but was more susceptible to clarithromycin and amikacin. M. fortuitum isolates were significantly less resistant than M. abscessus to ciprofloxacin (3.6%) and imipenem (7.1%) but more resistant to clarithromycin (42.9%) and linezolid (39.3%). A suitable combination therapy for Malaysian patients would be amikacin plus clarithromycin and ciprofloxacin, to cover infections by all three M. abscessus subspecies and M. fortuitum.

Evaluation of the GenoType® NTM DR for Subspecies Identification and Determination of Drug Resistance in Clinical M. abscessus Isolates

Introduction: A new line probe assay, the GenoType® NTM DR, has been developed for subspecies identification and detection of resistance to macrolides and aminoglycosides in clinical Mycobacterium abscessus isolates. We studied the performance of the test compared to DNA sequencing and phenotypic drug susceptibility testing (pDST). Methods: 48 clinical M. abscessus isolates collected between 2015 and 2016 were identified to the subspecies level and analysed for erm (41) genotype, rrl and rrs gene mutations by Sanger sequencing. Broth micro dilution was performed for pDST of Clarithromycin and Amikacin. The results were compared to those of the GenoType® NTM DR assay. Discordant results were further analysed by repeat pDST and whole genome sequencing (WGS). Results: 35 isolates were identified as M. abscessus subsp. abscessus , 6 as M. abscessus subsp. bolletii , and 7 as M. abscessus subsp. massiliense based on rpoB sequences. Concordance of GenoType® NTM DR results with Sanger sequencing was 92% for subspecies identification and 100% for erm (41), rrl, and rrs genotypes, respectively. GenoType® NTM DR and pDST results matched in 98% for Clarithromycin resistance and in 96% for Amikacin resistance when repeat pDST results were taken into account. Conclusion: The new GenoType® NTM DR assay is a valuable test for subspecies identification of M. abscessus isolates and detection of defined mutations conferring resistance to Amikacin and Clarithromycin. Discrepancies between the line probe assay and pDST mainly relate to variations in phenotypic test results.

Global spread of aggressive mycobacteria

Emerging Infections Many mycobacteria, in addition to those causing leprosy and tuberculosis, are capable of infecting humans. Some can be particularly dangerous in patients suffering from immunosuppression or chronic disease, such as cystic fibrosis (CF). Bryant et al. observed clusters of near-identical isolates of drug-resistant Mycobacterium abscessus in patients reporting to CF clinics. The similarity of the isolates suggests transmission between patients, rather than environmental acquisition. Although this bacterium is renowned for its environmental resilience, the mechanism for its long-distance transmission among the global CF patient community remains a puzzle. Science , this issue p. [751][1] [1]: /lookup/doi/10.1126/science.aaf8156

The impact of protein extraction protocols on the performance of currently available MALDI-TOF mass spectrometry for identification of mycobacterial clinical isolates cultured in liquid media

BackgroundProtein extraction step is particularly important for identification of mycobacterial isolates by MALDI-TOF mass spectrometry (MS) because of its thick and solid cell wall. This study compared the performance of MALDI-TOF MS for identification of mycobacterial clinical isolates cultured in liquid media between heating-based protocol and non-heating protocol. MethodsClinical mycobacterial isolates cultured in liquid media were prospectively analyzed. Reference identification was real-time PCR and restriction fragment length polymorphism. The specimens prepared by heating protocol and non-heating protocol were tested using MALDI Biotyper (Bruker Daltonics, Bremen, Germany) and Vitek MS (bioMérieux, Marcy l'Etoile, France), respectively. ResultsAmong the 206 clinical specimens prepared by heating method, identification rates were 90.3% and 60.7% in MALDI Biotyper and Vitek MS, respectively. Identification accuracy of MALDI Biotyper and Vitek MS was 100% for the isolates of Mycobacterium tuberculosis complex (MTBC), Mycobacterium avium, Mycobacterium intracellulare, Mycobacterium abscessus and Mycobacterium fortuitum. Among the 121 clinical specimens prepared by non-heating method, identification rate for MALDI Biotyper and Vitek MS were 61.2% and 69.4%, respectively. Identification accuracy of MALDI Biotyper/Vitek MS were 92.9%/94.1% for MTBC, 92.9%/100% for M. avium, 90%/100% for M. intracellulare, 100%/100% for M. abscessus and 100%/100% for M. fortuitum. ConclusionsThe performance of MALDI-TOF MS for identification of mycobacterial clinical isolates is affected by protein extraction protocol. For best performance, protein extraction protocol should be chosen considering the MALDI-TOF MS system. In the present study, heating protocol with MALDI Biotyper system showed reliable identification results for mycobacterial clinical isolates.

Detection of mutations in the gyrA and gyrB genes associated with fluoroquinolone-resistance among clinical isolates of Mycobacterium abscessus in China

To determine molecular mutations in gyrA and gyrB genes and their association with fluoroquinone-resistance among Mycobacterium abscessus isolates from China. Antimicrobial susceptibility profile of Mycobacterium abscessus isolates was evaluated for resistance to levofloxacin (LFX) and moxifloxacin (MFX). The quinolone resistant determing regions (QRDR) of gyrA and gyrB genes of all the isolates was sequenced and analyzed. A total 70 Mycobacterium abscessus isolates were analyzed, including 45 (64%) M. abscessus subsp. abscessus and 25 (36%) M. abscessus subsp. massiliense. Analysis of antimicrobial susceptibility profile showed 97% (n=68) of isolates were resistance to LFX and 14.3% (n=10) of isolates were resistance to MFX. All the MFX-resistant strains were resistant to LFX. Cross-resistance to LFX and MFX was noted in 14.3% (n=10) of isolates. Sequencing analysis revealed that the Ser83Ala substitution in the gyrA gene and Lys447Arg and Ser464Asn substitutions in the gyrB gene were found in all the isolates from both M. abscessus subsp. abscessus and M. abscessus subsp. massiliense. No mutation was found to be associated with cross-resistance of M. abscessus to LFX and MFX in the entire gyrA and gyrB gene. Our data suggest that there is no clear correlation between the type of mutation in the gene gyrA and gyrB, and the MIC levels of LFX and MFX for resistant M. abscessus strains.

Susceptibility testing of Mycobacterium abscessus by isothermal microcalorimetry

We evaluated a new method for susceptibility testing of a rapidly growing mycobacterium using real-time measurement of heat (microcalorimetry). MICs of 2 clinical Mycobacterium abscessus isolates were determined by microbroth dilution and E-test. For microcalorimetry, Middlebrook-7H10 agar+10% oleic acid–albumin–dextrose–catalase, containing amikacin, clarithromycin, linezolid, and ciprofloxacin was inoculated with ~105CFU/mL. Heat production was measured at 37°C for 72h. Minimal heat inhibition concentration (MHIC) was defined as the lowest antibiotic concentration inhibiting growth-related heat production. Growth of M. abscessus was detected after a median of 16.5h (range, 8.5–26.9h). Heat detection was proportionally delayed with increasing concentration of antibiotics. MHICs for the tested strains were 16 to >16mg/L for amikacin, >8mg/L for clarithromycin, 4 to >16mg/L for ciprofloxacin, 24 to >32mg/L for linezolid. MHICs were in agreement within two 2-fold dilutions with conventional MICs. Microcalorimetry may accelerate antimicrobial susceptibility testing in mycobacteria and provide additional real-time information on the drug effect.

Utility of sequencing the erm(41) gene in isolates of Mycobacterium abscessus subsp. abscessus with low and intermediate clarithromycin MICs.

The erm(41) gene confers inducible macrolide resistance in Mycobacterium abscessus subsp. abscessus, calling into question the usefulness of macrolides for treating M. abscessus subsp. abscessus infections. With an extended incubation (14 days), isolates with MICs of ≥8 μg/ml are considered macrolide resistant by current CLSI guidelines. Our goals were to determine the incidence of macrolide susceptibility in U.S. isolates, the validity of currently accepted MIC breakpoints, and the erm(41) sequences associated with susceptibility. Of 349 isolates (excluding those with 23S rRNA gene mutations), 85 (24%) had clarithromycin MICs of ≤8 μg/ml. Sequencing of the erm(41) genes from these isolates, as well as from isolates with MICs of ≥16 μg/ml, including ATCC 19977T, revealed 10 sequevars. The sequence in ATCC 19977T was designated sequevar (type) 1; most macrolide-resistant isolates were of this type. Seven sequevars contained isolates with MICs of >16 μg/ml. The T28C substitution in erm(41), previously associated with macrolide susceptibility, was identified in 62 isolates (18%) comprising three sequevars, with MICs of ≤2 (80%), 4 (10%), and 8 (10%) μg/ml. No other nucleotide substitution was associated with macrolide susceptibility. We recommend that clarithromycin susceptibility breakpoints for M. abscessus subsp. abscessus be changed from ≤2 to ≤4 μg/ml and that isolates with an MIC of 8 μg/ml have repeat MIC testing or erm sequencing performed. Our studies suggest that macrolides are useful for treating approximately 20% of U.S. isolates of M. abscessus subsp. abscessus. Sequencing of the erm gene of M. abscessus subsp. abscessus will predict inducible macrolide susceptibility.

Current Opinions in the Treatment of Pulmonary Nontuberculous Mycobacteria in Non-Cystic Fibrosis Patients: Mycobacterium abscessus Group, Mycobacterium avium Complex, and Mycobacterium kansasii

Treatment of pulmonary infections caused by Mycobacterium avium complex (MAC) and Mycobacterium kansasii involves multidrug oral therapy with a macrolide (azithromycin or clarithromycin), ethambutol, and a rifamycin (rifampin or rifabutin). Patients with M. kansasii rapidly respond to a regimen of intermittent (three times weekly) or daily administration of this three-drug regimen. Patients with MAC respond more slowly and often require adjustment of the multidrug regimen because of drug intolerance. The usual treatment for patients with MAC nodular disease takes 15–18 months, with a goal of 12 months of negative cultures. Recent studies support the use of a three-times weekly oral treatment regimen for patients with macrolide-susceptible nodular MAC disease. Patients with upper lobe fibro-cavitary MAC, macrolide-resistant MAC, or severe nodular bronchiectatic disease are usually treated with a daily multidrug regimen supplemented with an injectable antibiotic (amikacin or streptomycin) or, most recently, inhaled preparations of amikacin. Patients with cavitary changes and/or those with macrolide-resistant isolates are often associated with poor treatment response and may require surgical resection in addition to their drug therapy. In contrast to patients with lung disease due to MAC and M. kansasii, the presence of a functional erythromycin ribosomal methylase (erm) gene in the majority of isolates of Mycobacterium abscessus (M. abscessus subsp. abscessus) blocks the activity of macrolides and precludes an effective oral drug regimen for most of these patients. Treatment regimens for macrolide-resistant M. abscessus require long-term intravenous access and parenteral drug combinations of amikacin, cefoxitin, imipenem, and/or tigecycline. Because of the inconvenience of dosing cefoxitin, a regimen of imipenem and amikacin may be preferred. Cure with these agents is infrequent because of the long-term toxicity and expense of these agents. Other treatment options are currently dismal. The role of newer antimicrobials such as tedizolid and bedaquiline has not been evaluated. Approximately 15 % of isolates of subsp. abscessus and all isolates of subsp. massiliense (infrequent in the USA) have a nonfunctional erm gene and are macrolide susceptible, making an oral macrolide an important treatment component and increasing the likelihood of long-term cure of the infection.

In vitro bactericidal assay of linezolid on multidrug-resistant tuberculosis and nontuberculous mycobacteria

Objective To investigate the mycobactericidal efficacy of linezolid on multidrug-resistant tuberculosis (MDR-TB)and nontuberculous mycobacteria (NTM) in vitro. Methods Seven hundred and sixty-two Mycobacterium tuberculosis and 20 NTM isolates from Hangzhou were identified by using hsp65 gene sequencing from March to June, 2013. Seventy MDR-TB isolates, which were screened by using proportion method, and twenty NTM isolates were tested the MIC to linezolid，and the differences of MICs to linezolid between MDR-TB and NTM werw analyzed in vitro. Results All 70 MDR-TB isolates were inhibited at concentrations of ≤1 mg/L by linezolid, MIC50 was 0.5 mg/L and MIC90 1 mg/L. Of all 8 isolates inhibited at concentration of 1 mg/L，there were 6 isolates resistant to isoniazid, rifampin, streptomycin and ethambutol, suggesting this resistance pattern may reduce sensitivity to linezolid. Among the NTM isolates, 18 Mycobacterium intracellulare isolates, whose MICs to linezolid at 8-16 mg/L, were non-resistant isolates, while 2 Mycobacterium abscessus isolates displaying MICs＞32 mg/L, were resistant to linezolid. Conclusions Linezolid showed great activity to MDR-TB and there were no linezolid-resistant MDR-TB isolates identified in this study. However, MICs of MDR-TB against linezolid increased with their resistant numbers to first-line agents. This study also showed that different NTM species have varied sensitivity to linezolid. （Chin J Lab Med,2014,37:535-538） Key words: Mycobacterium tuberculosis; Nontuberculous mycobacteria; Drug resistance, multiple, bacterial

160 Molecular profiling demonstrates clustering of Mycobacterium abscessus isolates in CF patients from a single centre

160 Molecular profiling demonstrates clustering of Mycobacterium abscessus isolates in CF patients from a single centre