A novel gene, erm(41), confers inducible macrolide resistance to clinical isolates of Mycobacterium abscessus but is absent from Mycobacterium chelonae

Nontuberculous mycobacteria in cystic fibrosis and non-cystic fibrosis bronchiectasis

Increasing numbers of cystic fibrosis (CF) and non-CF bronchiectasis patients are affected by pulmonary nontuberculous mycobacteria (NTM) infection worldwide. Two species of NTM account for up to 95% of the pulmonary NTM infections: Mycobacterium avium complex (MAC) and Mycobacterium abscessus complex (MABSC). Diagnosis of pulmonary NTM infection is based on criteria specified in the 2007 American Thoracic Society/Infectious Disease Society of America (ATS/IDSA) guidelines. While many initial positive cultures do not progress to active NTM disease, even a single positive NTM sputum culture obtained from higher risk groups such as classic CF or older women with bronchiectasis and very low body mass index should be closely monitored for progressive disease. Macrolides remain the most effective agents available against MAC and MABSC. Infection with MABSC may be associated with worse clinical outcomes, as more than half of MABSC isolates have inducible macrolide resistance conferred by an active erm(41) gene. Of growing concern in CF is that MABSC is becoming more common than MAC, seems to target younger patients with classic CF, and is more difficult to manage, often requiring prolonged courses of intravenous antibiotics. Recurrence rates of NTM after initial successful treatment remain high, likely due to nonmodifiable risk factors raising the question of whether secondary prophylaxis is feasible. More rapid and readily available methods for detecting inducible macrolide resistance and better in vitro susceptibility testing methods for other drugs that correlate with clinical responses are needed. This is crucial to identify more effective regimens of existing drugs and for development of novel drugs for NTM infection.

Bacterial phospholipases C as vaccine candidate antigens against cystic fibrosis respiratory pathogens: the Mycobacterium abscessus model

BACKGROUND

Vaccine strategies represent one of the fighting answers against multiresistant bacteria in a number of clinical settings like cystic fibrosis (CF). Mycobacterium abscessus, an emerging CF pathogen, raises difficult therapeutic problems due to its intrinsic antibiotic multiresistance.

METHODS

By reverse vaccinology, we identified M. abscessus phospholipase C (MA-PLC) as a potential vaccine target. We deciphered here the protective response generated by vaccination with plasmid DNA encoding the MA-PLC formulated with a tetra functional block copolymer 704, in CF (ΔF508) mice. Protection was tested against aerosolized smooth and rough (hypervirulent) variants of M. abscessus.

RESULTS

MA-PLC DNA vaccination (days 0, 21, 42) elicited a strong antibody response. A significant protective effect was obtained against aerosolized M. abscessus (S variant) in ΔF508 mice, but not in wild-type FVB littermates; similar results were observed when: (i) challenging mice with the "hypervirulent" R variant, and; (ii) immunizing mice with purified MA-PLC protein. High IgG titers against MA-PLC protein were measured in CF patients with M. abscessus infection; interestingly, significant titers were also detected in CF patients positive for Pseudomonas aeruginosa versus P. aeruginosa-negative controls.

CONCLUSIONS

MA-PLC DNA- and PLC protein-vaccinated mice cleared more rapidly M. abscessus than β-galactosidase DNA- or PBS- vaccinated mice in the context of CF. PLCs could constitute interesting vaccine targets against common PLC-producing CF pathogens like P. aeruginosa.

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.

Aminoglycoside-modifying enzymes determine the innate susceptibility to aminoglycoside antibiotics in rapidly growing mycobacteria

OBJECTIVES

Infections caused by the rapidly growing mycobacterium (RGM) Mycobacterium abscessus are notoriously difficult to treat due to the innate resistance of M. abscessus to most clinically available antimicrobials. Aminoglycoside antibiotics (AGA) are a cornerstone of antimicrobial chemotherapy against M. abscessus infections, although little is known about intrinsic drug resistance mechanisms. We investigated the role of chromosomally encoded putative aminoglycoside-modifying enzymes (AME) in AGA susceptibility in M. abscessus.

METHODS

Clinical isolates of M. abscessus were tested for susceptibility to a series of AGA with different substituents at positions 2', 3' and 4' of ring 1 in MIC assays. Cell-free extracts of M. abscessus type strain ATCC 19977 and Mycobacterium smegmatis strains SZ380 [aac(2')-Id(+)], EP10 [aac(2')-Id(-)] and SZ461 [aac(2')-Id(+), rrs A1408G] were investigated for AGA acetylation activity using thin-layer chromatography (TLC). Cell-free ribosome translation assays were performed to directly study drug-target interaction.

RESULTS

Cell-free translation assays demonstrated that ribosomes of M. abscessus and M. smegmatis show comparable susceptibility to all tested AGA. MIC assays for M. abscessus and M. smegmatis, however, consistently showed the lowest MIC values for 2'-hydroxy-AGA as compared with 2'-amino-AGA, indicating that an aminoglycoside-2'-acetyltransferase, Aac(2'), contributes to innate AGA susceptibility. TLC experiments confirmed enzymatic activity consistent with Aac(2'). Using M. smegmatis as a model for RGM, acetyltransferase activity was shown to be up-regulated in response to AGA-induced inhibition of protein synthesis.

CONCLUSIONS

Our findings point to AME as important determinants of AGA susceptibility in M. abscessus.

Absence of a functional erm gene in isolates of Mycobacterium immunogenum and the Mycobacterium mucogenicum group, based on in vitro clarithromycin susceptibility

Macrolide resistance has been linked to the presence of a functional erythromycin ribosomal methylase (erm) gene in most species of pathogenic rapidly growing mycobacteria (RGM). For these Mycobacterium isolates, extended incubation in clarithromycin is necessary to determine macrolide susceptibility. In contrast, the absence of a detectable erm gene in isolates of M. chelonae, M. senegalense, and M. peregrinum and a nonfunctional erm gene in M. abscessus subsp. massiliense and 15% to 20% of M. abscessus subsp. abscessus isolates renders these species intrinsically macrolide susceptible. Not all RGM species have been screened for the presence of an erm gene, including the Mycobacterium mucogenicum group (M. mucogenicum, M. phocaicum, and M. aubagnense) and Mycobacterium immunogenum. A total of 356 isolates of these two pathogenic RGM taxa from two reference laboratories (A.R.U.P. Reference Laboratories and the Mycobacteria/Nocardia Laboratory at the University of Texas Health Science Center at Tyler) underwent clarithromycin susceptibility testing with readings at 3 to 5 days and 14 days. Only 13 of the 356 isolates had resistant clarithromycin MICs at initial extended MIC readings, and repeat values on all available isolates were ≤2 μg/ml. These studies suggest that these two additional RGM groups do not harbor functional erm genes and, like M. chelonae, do not require extended clarithromycin susceptibility testing. We propose to the Clinical Laboratory and Standards Institute that isolates belonging to these above-mentioned six rapidly growing mycobacterial groups based on molecular identification with no known functional erm genes undergo only 3 to 5 days of susceptibility testing (to exclude mutational resistance).

β-Lactamase inhibition by avibactam in Mycobacterium abscessus

OBJECTIVES

Two β-lactams, cefoxitin and imipenem, are part of the reference treatment for pulmonary infections with Mycobacterium abscessus. M. abscessus has recently been shown to produce a broad-spectrum β-lactamase, BlaMab, indicating that the combination of β-lactams with a BlaMab inhibitor may improve treatment efficacy. The objectives of this study were to evaluate the impact of BlaMab production on the efficacy of β-lactams in vitro and to assess the benefit of BlaMab inhibition on the activity of β-lactams intracellularly and in an animal model.

METHODS

We analysed the mechanism and kinetics of BlaMab inactivation by avibactam, a non-β-lactam β-lactamase inhibitor currently in Phase III of development, in combination with ceftazidime for the treatment of serious infections due to Gram-negative bacteria. We then deleted the gene encoding BlaMab to assess the extent of BlaMab inhibition by avibactam based on a comparison of the impact of chemical and genetic inactivation. Finally, the efficacy of amoxicillin in combination with avibactam was evaluated in cultured human macrophages and in a zebrafish model of M. abscessus infection.

RESULTS

We showed that avibactam efficiently inactivated BlaMab via the reversible formation of a covalent adduct. An inhibition of BlaMab by avibactam was observed in both infected macrophages and zebrafish.

CONCLUSIONS

Our data identify avibactam as the first efficient inhibitor of BlaMab and strongly suggest that β-lactamase inhibition should be evaluated to provide improved therapeutic options for M. abscessus infections.

Antibiotic treatment for nontuberculous mycobacteria lung infection in people with cystic fibrosis

BACKGROUND

Nontuberculous mycobacteria are mycobacteria, other than those in the Mycobacterium tuberculosis complex, and are commonly found in the environment. Nontuberculous mycobacteria species (most commonly Mycobacterium avium complex and Mycobacterium abscessus) are isolated from the respiratory tract of approximately 5% to 20% of individuals with cystic fibrosis; they can cause lung disease in people with cystic fibrosis leading to more a rapid decline in lung function and even death in certain circumstances. Although there are guidelines for the antimicrobial treatment of nontuberculous mycobacteria lung disease, these recommendations are not specific for people with cystic fibrosis and it is not clear which antibiotic regimen may be the most effective in the treatment of these patients.

OBJECTIVES

The objective of our review was to compare antibiotic treatment to no antibiotic treatment, or to compare different combinations of antibiotic treatment, for nontuberculous mycobacteria lung infections in people with cystic fibrosis. The primary objective was to assess the effect of treatment on lung function and pulmonary exacerbations and to quantify adverse events. The secondary objectives were to assess treatment effects on the amount of bacteria in the sputum, quality of life, mortality, nutritional parameters, hospitalizations and use of oral antibiotics.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis Trials Register, compiled from electronic database searches and hand searching of journals and conference abstract books. Date of last search: 13 November 2014.We also searched a register of ongoing trials and the reference lists of relevant articles and reviews. Date of last search: 24 September 2014.

SELECTION CRITERIA

Any randomized controlled trials comparing nontuberculous mycobacteria antibiotics to no antibiotic treatment, as well as one nontuberculous mycobacteria antibiotic regimen compared to another nontuberculous mycobacteria antibiotic regimen, in individuals with cystic fibrosis.  

DATA COLLECTION AND ANALYSIS

Data were not collected because no completed trials were identified by the searches.

MAIN RESULTS

No completed trials were identified by the searches, but one ongoing trial was identified, which may be eligible for inclusion in this review when completed.

AUTHORS' CONCLUSIONS

This review did not find any evidence for the effectiveness of different antimicrobial treatment for nontuberculous mycobacteria lung disease in people with cystic fibrosis. Until such evidence becomes available, it is reasonable for clinicians to follow the American Thoracic Society guidelines for the diagnosis and treatment of nodular or bronchiectatic pulmonary disease due to Mycobacterium avium complex or Mycobacterium abscessus in patients with cystic fibrosis.

Management of Mycobacterium abscessus post abdominoplasty

Atypical mycobacterium is the source of a recent outbreak of cosmetic surgery infections [1]. Such an infection is difficult to eradicate and presents unique challenges in its management after esthetic surgery. Delays in appropriate treatment are frequent because of difficulty in diagnosis and unfamiliarity with this type of infection. We present cases of our management of Mycobacterial abscessus abdominoplasty infections following cosmetic surgery in the Dominican Republic. Rapid initial recognition of this problem and the frequent need for surgical treatment of atypical mycobacterium abdominoplasty infection may aid in the treatment of this rare but increasingly encountered infection.

LEVEL OF EVIDENCE V

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266.

Whole-genome sequencing and epidemiological analysis do not provide evidence for cross-transmission of mycobacterium abscessus in a cohort of pediatric cystic fibrosis patients

We have not been able to demonstrate cross-transmission of Mycobacterium abscessus within our hospital, except between siblings who had intense contact in the home environment. The role of the environment in the acquisition of M. abscessus infection requires further investigation.

Background. Mycobacterium abscessus has emerged as a major pathogen in cystic fibrosis (CF) patients and has been associated with poor clinical outcomes, particularly following lung transplant. We investigated the acquisition of this bacterium in a cohort of pediatric CF patients.

Methods. Demographic and patient location data were used to uncover epidemiological links between patients with genetically related strains of M. abscessus that had been previously typed by variable-number tandem repeat profiling. Whole-genome sequencing was applied to 27 M. abscessus isolates from the 20 patients in this cohort to provide definitive data on the genetic relatedness of strains.

Results. Whole-genome sequencing data demonstrated that M. abscessus isolates from 16 patients were unrelated, differing by at least 34 single-nucleotide polymorphisms (SNPs) from any other isolate, suggesting that independent acquisition events have occurred. Only 2 clusters of very closely related (<25 SNPs) isolates from different patients were seen. The first cluster contained 8 isolates, differing by a maximum of 17 SNPs, from a sibling pair who had intense exposure to each other both inside and outside the hospital. The second cluster contained 3 isolates, differing by a maximum of 24 SNPs, from 2 individuals with no apparent epidemiological links.

Conclusions. We have not demonstrated cross-transmission of M. abscessus within our hospital, except between 1 sibling pair. Alternative routes of acquisition of M. abscessus infection, in particular the environment, require further investigation.

Recent progress towards understanding genetic variation in the Mycobacterium abscessus complex

Mycobacterium abscessus is an emerging cause of respiratory disease and soft tissue infections. Whole genome sequencing and other molecular approaches are enhancing our understanding of outbreaks, antibiotic resistance mechanisms, and virulence properties, and of the phylogeny of the M. abscessus complex. Infection models are providing further insights into factors such as colony phenotype that impact host-pathogen interactions. This paper reviews recent developments in our understanding of genetic variation in M. abscessus and the potential relevance for disease and treatment.

The treatment of rapidly growing mycobacterial infections

Rapidly growing mycobacteria (RGM) include a diverse group of species. We address the treatment of the most commonly isolated RGM-M abscessus complex, M fortuitum, and M chelonae. The M abscessus complex is composed of 3 closely related species: M abscessus senso stricto (hereafter M abscessus), M massiliense, and M bolletii. Most studies address treatment of M abscessus complex, which accounts for 80% of lung disease caused by RGM and is the second most common RGM to cause extrapulmonary disease (after M fortuitum). The M abscessus complex represent the most drug-resistant nontuberculous mycobacteria and are the most difficult to treat.

Mycobacterium abscessus subsp abscessus lung disease: 'trouble ahead, trouble behind…'

Mycobacterium abscessus subsp abscessus is the most common respiratory pathogen among the rapidly growing non-tuberculous mycobacteria (NTM) and is also the most feared due to its well-deserved reputation for being refractory to antibiotic therapy. M. abscessus subsp abscessus has multiple innate antibiotic resistance mechanisms, but the most important one described so far is an inducible erythromycin methylase (erm) gene. M. abscessus subsp abscessus isolates may appear macrolide susceptible on initial in vitro testing but become macrolide resistant after exposure to macrolide. It is therefore very important to test clinically significant M. abscessus subsp abscessus isolates for erm gene activity. Remarkably, controversy still exists about the taxonomy and nomenclature of M. abscessus subspecies including subsp abscessus, subsp massiliense and subsp bolletii. Identification of these subspecies is not moot as M. abscessus subsp massiliense does not have an active erm gene resulting in both in vitro and in vivo susceptibility to macrolide. It is imperative from the clinician's perspective that mycobacterial laboratories correctly and rapidly identify M. abscessus to the subspecies level. Unfortunately, there are no reliably or predictably effective treatment regimens for M. abscessus subsp abscessus and better, more effective antimicrobial agents are badly needed. Surgical resection of involved lung tissue as an adjunct to antibiotic therapy is beneficial in selected patients but cannot be broadly applied. Overall, M. abscessus subsp abscessus remains a formidable respiratory mycobacterial pathogen, one that we are only beginning to understand microbiologically and one that as yet consistently evades our best efforts at successful therapeutic outcomes.

‘trouble ahead, trouble behind, and you know that notion just crossed my mind’.

Casey Jones, Grateful Dead (1970)

Structural and functional characterization of an arylamineN-acetyltransferase from the pathogenMycobacterium abscessus: differences from other mycobacterial isoforms and implications for selective inhibition

Mycobacterium abscessusis the most pathogenic rapid-growing mycobacterium and is one of the most resistant organisms to chemotherapeutic agents. However, structural and functional studies ofM. abscessusproteins that could modify/inactivate antibiotics remain nonexistent. Here, the structural and functional characterization of an arylamineN-acetyltransferase (NAT) fromM. abscessus[(MYCAB)NAT1] are reported. This novel prokaryotic NAT displays significantN-acetyltransferase activity towards aromatic substrates, including antibiotics such as isoniazid andp-aminosalicylate. The enzyme is endogenously expressed and functional in both the rough and smoothM. abscessusmorphotypes. The crystal structure of (MYCAB)NAT1 at 1.8 Å resolution reveals that it is more closely related toNocardia farcinicaNAT than to mycobacterial isoforms. In particular, structural and physicochemical differences from other mycobacterial NATs were found in the active site. Peculiarities of (MYCAB)NAT1 were further supported by kinetic and docking studies showing that the enzyme was poorly inhibited by the piperidinol inhibitor of mycobacterial NATs. This study describes the first structure of an antibiotic-modifying enzyme fromM. abscessusand provides bases to better understand the substrate/inhibitor-binding specificities among mycobacterial NATs and to identify/optimize specific inhibitors. These data should also contribute to the understanding of the mechanisms that are responsible for the pathogenicity and extensive chemotherapeutic resistance ofM. abscessus.

Risk factors for microbiologic failure among Taiwanese adults with Mycobacterium abscessus complex pulmonary disease

BACKGROUND

The Mycobacterium abscessus complex is a common cause of pulmonary nontuberculous mycobacteria infections in Taiwan. We examined the risk factors associated with treatment outcome in Taiwanese adults with pulmonary disease caused by the M. abscessus complex.

METHODS

We retrospectively reviewed the records of all patients from a southern Taiwan medical center from 2006 to 2012 who had respiratory specimens identified as M. abscessus complex and met the American Thoracic Society criteria for pulmonary disease.

RESULTS

Of the 106 included patients, females (58.5%) and nonsmokers (79.2%) predominated. The mean age of patients was 64.8 years. Sixty-three patients (59.4%) had pre-existing lung disease. Previous mycobacterial pulmonary disease (34.9%) was the most common underlying disorder. Chest radiography indicated that bronchiectasis was common (47.2%) and that cavitations were less common (14.2%). Fifty-six patients received antibiotic treatment. Clinicians were more likely to prescribe antibiotics if the initial sputum acid-fast staining was positive (p < 0.001). Treatment outcome was analyzed in 26 patients who were treated for more than 3 months; three of these patients (11.5%) had clinical failure and 18 (69.2%) experienced sputum conversion. Patients with cavitary lesions were more likely to experience microbiologic failure (p = 0.02). Nine patients had positive cultures after antibiotic treatment for > 1 year. Previous mycobacterial pulmonary disease (p = 0.011) and cavitary lesion (p = 0.034) are risk factors for persistence of M. abscessus complex.

CONCLUSION

With antimicrobial therapy, previous mycobacterial disease, and cavitary lesion are associated with microbiologic failure in Taiwanese adults with M. abscessus complex pulmonary disease.

Antibiotic management of lung infections in cystic fibrosis. II. Nontuberculous mycobacteria, anaerobic bacteria, and fungi

Airway infections are a key component of cystic fibrosis (CF) lung disease. Whereas the approach to common pathogens such as Pseudomonas aeruginosa is guided by a significant body of evidence, other infections often pose a considerable challenge to treating physicians. In Part I of this series on the antibiotic management of difficult lung infections, we discussed bacterial organisms including methicillin-resistant Staphylococcus aureus, gram-negative bacterial infections, and treatment of multiple bacterial pathogens. Here, we summarize the approach to infections with nontuberculous mycobacteria, anaerobic bacteria, and fungi. Nontuberculous mycobacteria can significantly impact the course of lung disease in patients with CF, but differentiation between colonization and infection is difficult clinically as coinfection with other micro-organisms is common. Treatment consists of different classes of antibiotics, varies in intensity, and is best guided by a team of specialized clinicians and microbiologists. The ability of anaerobic bacteria to contribute to CF lung disease is less clear, even though clinical relevance has been reported in individual patients. Anaerobes detected in CF sputum are often resistant to multiple drugs, and treatment has not yet been shown to positively affect patient outcome. Fungi have gained significant interest as potential CF pathogens. Although the role of Candida is largely unclear, there is mounting evidence that Scedosporium species and Aspergillus fumigatus, beyond the classical presentation of allergic bronchopulmonary aspergillosis, can be relevant in patients with CF and treatment should be considered. At present, however there remains limited information on how best to select patients who could benefit from antifungal therapy.

Delivery of aerosolized liposomal amikacin as a novel approach for the treatment of nontuberculous mycobacteria in an experimental model of pulmonary infection

Pulmonary infections caused by nontuberculous mycobacteria (NTM) are an increasing problem in individuals with chronic lung conditions and current therapies are lacking. We investigated the activity of liposomal amikacin for inhalation (LAI) against NTM in vitro as well as in a murine model of respiratory infection. Macrophage monolayers were infected with three strains of Mycobacterium avium, two strains of Mycobacterium abscessus, and exposed to LAI or free amikacin for 4 days before enumerating bacterial survival. Respiratory infection was established in mice by intranasal inoculation with M. avium and allowing three weeks for the infection to progress. Three different regimens of inhaled LAI were compared to inhaled saline and parenterally administered free amikacin over a 28 day period. Bacteria recovered from the mice were analyzed for acquired resistance to amikacin. In vitro, liposomal amikacin for inhalation was more effective than free amikacin in eliminating both intracellular M. avium and M. abscessus. In vivo, inhaled LAI demonstrated similar effectiveness to a ∼25% higher total dose of parenterally administered amikacin at reducing M. avium in the lungs when compared to inhaled saline. Additionally, there was no acquired resistance to amikacin observed after the treatment regimen. The data suggest that LAI has the potential to be an effective therapy against NTM respiratory infections in humans.

Postsurgical wound infections due to rapidly growing mycobacteria in Swiss medical tourists following cosmetic surgery in Latin America between 2012 and 2014

Between October 2012 and August 2014, several Swiss patients developed severe soft tissue infections due to rapidly growing mycobacteria following cosmetic surgery in the Dominican Republic, Ecuador and Mexico. Infections were caused by Mycobacterium abscessus (n=5), Mycobacterium sp. JAN1 (n=1) and M. conceptionense (n=1). Similar cases may have remained unrecognised due to a lack of notification requirements. Microbiological work-up of medical tourists with infections following cosmetic surgery should include rapidly growing mycobacteria.

Mycobacterium abscessus infection in cystic fibrosis: molecular typing and clinical outcomes

Mycobacterium abscessus is a significant pathogen in the cystic fibrosis patient population. PCR amplification and sequencing can provide accurate subspecies identification, and can predict macrolide susceptibility, which is becoming increasingly important for patient management. Molecular techniques for further typing of isolates provide tools for the ongoing investigations into the clinical impact of particular M. abscessus strains. Whole-genome sequencing is likely to be the only technique that provides sufficient resolution for investigating transmission events between patients.

Genome sequencing of Mycobacterium abscessus isolates from patients in the united states and comparisons to globally diverse clinical strains

Nontuberculous mycobacterial infections caused by Mycobacterium abscessus are responsible for a range of disease manifestations from pulmonary to skin infections and are notoriously difficult to treat, due to innate resistance to many antibiotics. Previous population studies of clinical M. abscessus isolates utilized multilocus sequence typing or pulsed-field gel electrophoresis, but high-resolution examinations of genetic diversity at the whole-genome level have not been well characterized, particularly among clinical isolates derived in the United States. We performed whole-genome sequencing of 11 clinical M. abscessus isolates derived from eight U.S. patients with pulmonary nontuberculous mycobacterial infections, compared them to 30 globally diverse clinical isolates, and investigated intrapatient genomic diversity and evolution. Phylogenomic analyses revealed a cluster of closely related U.S. and Western European M. abscessus subsp. abscessus isolates that are genetically distinct from other European isolates and all Asian isolates. Large-scale variation analyses suggested genome content differences of 0.3 to 8.3%, relative to the reference strain ATCC 19977(T). Longitudinally sampled isolates showed very few single-nucleotide polymorphisms and correlated genomic deletion patterns, suggesting homogeneous infection populations. Our study explores the genomic diversity of clinical M. abscessus strains from multiple continents and provides insight into the genome plasticity of an opportunistic pathogen.

Whole-genome sequencing of clarithromycin resistant Helicobacter pylori characterizes unidentified variants of multidrug resistant efflux pump genes

BACKGROUND

Clarithromycin (CLR) is the key drug in eradication therapy of Helicobacter pylori (H. pylori) infection, and widespread use of CLR has led to an increase in primary CLR-resistant H. pylori. The known mechanism of CLR resistance has been established in A2146G and A2147G mutations in the 23S rRNA gene, but evidence of the involvement of other genetic mechanisms is lacking. Using the MiSeq platform, whole-genome sequencing of the 19 clinical strains and the reference strain ATCC26695 was performed to identify single nucleotide variants (SNVs) of multi-drug resistant efflux pump genes in the CLR-resistant phenotype.

RESULTS

Based on sequencing data of ATCC26695, over one million sequencing reads with over 50-fold coverage were sufficient to detect SNVs, but not indels in the bacterial genome. Sequencing reads of the clinical isolates ranged from 1.82 to 10.8 million, and average coverage ranged from 90.9- to 686.3-fold, which were acceptable criteria for detecting SNVs. Utilizing the conventional approach of allele-specific PCR, point mutations in the 23S rRNA gene were detected in 12 clinical resistant isolates, but not in 7 clinical susceptible isolates. All sequencing reads of CLR-resistant strains had a G mutation in an identical position of the 23S rRNA gene. In addition, genetic variants of four gene clusters (hp0605-hp0607, hp0971-hp0969, hp1327-hp1329, and hp1489-hp1487) of TolC homologues, which have been implicated in multi-drug resistance, were examined. Specific SNVs were dominantly found in resistant strains.

CONCLUSIONS

Gene clusters of TolC homologues are involved in CLR susceptibility profiles in individual H. pylori strains. Whole-genome sequencing has yielded novel understanding of genotype-phenotype relationships.

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.

Analysis of species and intra-species associations between the Mycobacterium abscessus complex strains using pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST)

PFGE and MLST showed that the strains of M. massiliense hsp65 II-1 were clearly separated from the strains of M. massiliense hsp65 I or II-2 as well as the strains of M. abscessus or M. bolletii; thus, M. massiliense hsp6 5II-1 might represent an additional subspecies of M. massiliense.

Rapid identification of M. abscessus and M. massiliense by MALDI-TOF mass spectrometry with a comparison to sequencing methods and antimicrobial susceptibility patterns

AIM

Development of the matrix-assisted laser desorption ionization-TOF (MALDI-TOF) mass spectrometry method to rapidly identify Mycobacteria abscessus and Mycobacteria massiliense from M. abscessus complex in clinical microbiology laboratories.

MATERIALS & METHODS

Of 128 M. abscessus complex clinical isolates, sequence analysis identified 64 as M. massiliense and 64 as M. abscessus. MALDI-TOF mass spectrometry with clustering analysis created a model to differentiate these two species. Multilocus sequence typing was used to confirm our model.

RESULTS

Using a model containing five signals, 100% species recognition was achieved for 50 strains of each species. The sequence type (ST) cluster of M. abscessus was distinct from the cluster of M. massiliense. ST1 was prevalent (59%) among M. abscessus isolates, and ST117 was common (41%) among M. massiliense isolates.

CONCLUSION

Molecular methods are more costly and time-consuming and may not be available in the clinical microbial laboratory. Subsequently, MALDI-TOF analysis could be a rapid identification method in the future.

Drug treatment of pulmonary nontuberculous mycobacterial disease in HIV-negative patients: the evidence

Pulmonary disease (PD) caused by nontuberculous mycobacteria is an emerging infection mainly in countries where the incidence of tuberculosis is in decline. It affects an elderly population, often with underlying chronic lung diseases, but its epidemiology shows significant regional variation. Guidelines and recommendations for treatment of these infections exist, but build strongly on expert opinion, as very few good quality clinical trials have been performed in this field. Only for the most frequent causative agents, the Mycobacterium avium complex, Mycobacterium kansasii and Mycobacterium abscessus, a reasonable number of trials and case series is now available. For the less frequent causative agents of pulmonary nontuberculous mycobacterial (NTM) disease (Mycobacterium xenopi, Mycobacterium malmoense, Mycobacterium fortuitum, Mycobacterium chelonae) data is mostly limited to a few very small case series. Within this review, we have collected and combined evidence from all available trials and case series. From the data of these trials and case series, we reconstruct a more evidence-based overview of possible drug treatment regimens and their outcomes.

Lack of antimicrobial bactericidal activity in Mycobacterium abscessus

Antibiotic therapy of infections caused by the emerging pathogen Mycobacterium abscessus is challenging due to the organism's natural resistance toward most clinically available antimicrobials. We investigated the bactericidal activity of antibiotics commonly administered in M. abscessus infections in order to better understand the poor therapeutic outcome. Time-kill curves were generated for clinical M. abscessus isolates, Mycobacterium smegmatis, and Escherichia coli by using antibiotics commonly categorized as bactericidal (amikacin and moxifloxacin) or bacteriostatic (tigecycline and linezolid). In addition, the impact of aminoglycoside-modifying enzymes on the mode of action of substrate and nonsubstrate aminoglycosides was studied by using M. smegmatis as a model organism. While amikacin and moxifloxacin were bactericidal against E. coli, none of the tested compounds showed bactericidal activity against M. abscessus. Further mechanistic investigations of the mode of action of aminoglycosides in M. smegmatis revealed that the bactericidal activity of tobramycin and gentamicin was restored by disruption of the chromosomal aac(2') gene in the mycobacterial genome. The lack of bactericidal antibiotics in currently recommended treatment regimens provides a reasonable explanation for the poor therapeutic outcome in M. abscessus infection. Our findings suggest that chromosomally encoded drug-modifying enzymes play an important role in the lack of aminoglycoside bactericidal activity against rapidly growing mycobacteria.

Rapid identification of strains belonging to the Mycobacterium abscessus group through erm(41) gene pyrosequencing

Mycobacterium abscessus and Mycobacterium massiliense lung infections have different clarithromycin susceptibilities, making proper identification important; however, standard multi-gene sequencing in clinical laboratories is laborious and time consuming. We developed a pyrosequencing-based method for rapid identification of strains belonging to the M. abscessus group by targeting erm(41). We examined 55 isolates from new pulmonary M. abscessus infections and identified 28 M. abscessus, 25 M. massiliense, and 2 Mycobacterium bolletii isolates. Multi-gene sequencing of 16S rRNA, hsp65, rpoB, and the 16S-23S ITS region was concordant with the results of erm(41) pyrosequencing; thus, the M. abscessus group can be identified by single-nucleotide polymorphisms in erm(41). The method also enables rapid identification of polymorphic, inducible clarithromycin-resistant sequevars (T28 or C28). Pyrosequencing of erm(41) is a rapid, reliable, high-throughput alternative method for identifying and characterizing M. abscessus species. Further testing of a diverse collection of isolates is necessary to demonstrate the discriminatory power of erm(41) sequencing to differentiating species with this highly divergent group.

Detection and assessment of clarithromycin inducible resistant strains among Korean Mycobacterium abscessus clinical strains: PCR methods

Background

Mycobacterium abscessus group belongs to a group of rapidly growing mycobacteria (RGM) and, following Mycobacterium avium complex, is the second most common pathogen responsible for lung disease caused by nontuberculous mycobacteria (NTM). Clarithromycin is known to be the key drug in the treatment of M. abscessus group disease, but a high failure rate of treatment response is reported due to clarithromycin inducible resistance.

Methods

Using the results from a clarithromycin susceptibility test we examined the proportion of clarithromycin inducible resistant M. abscessus (sensu stricto; hereafter referred to as M. abscessus) clinical strains. Also, we attempted to detect the clarithromycin resistant strains, using the amplification refractory mutation system‐PCR (ARMS‐PCR) and real‐time PCR methods for rapid detection of single‐nucleotide polymorphisms (SNPs) at position 28 (T or C) of the erm(41) gene of M. abscessus leading to resistance to clarithromycin.

Results

Of the 157 M. abscessus clinical strains, clarithromycin susceptible, resistant, and inducible resistant strains accounted for 10.83% (n = 17), 22.29% (n = 35), and 66.88% (n = 105), respectively. Clarithromycin resistant strains were able to separate from clarithromycin susceptible strains by ARMS‐PCR and real‐time PCR identical to DNA sequence analysis.

Conclusion

Most M. abscessus clinical strains in Korea are resistant to clarithromycin, and ARMS‐PCR and real‐time PCR are useful tools for the rapid detection of single‐nucleotide polymorphisms (SNPs) at position 28 of the erm(41) gene.

Clinical experience in 52 patients with tigecycline-containing regimens for salvage treatment of Mycobacterium abscessus and Mycobacterium chelonae infections

OBJECTIVES

We report the largest clinical experience using tigecycline-containing regimens for salvage treatment of patients with Mycobacterium abscessus and Mycobacterium chelonae.

PATIENTS AND METHODS

Data were collected from 52 patients on emergency/compassionate use (n = 38) or two open-label studies (n = 7 patients each). Based on information that was available, 46 (88.5%) of the subjects received antibiotic therapy prior to treatment with tigecycline. Treatment groups were evaluated based on length of tigecycline therapy (<1 and ≥1 month). ClinicalTrials.gov identifiers: Study 205, NCT00600600 and Study 310, NCT00205816.

RESULTS

The most commonly used concomitant antimicrobials were macrolides, amikacin and linezolid. Pulmonary disease was the most common presentation (36/52; 69.2%), and 58.3% of these patients had underlying cystic fibrosis. The majority were M. abscessus complex (n = 30) or M. chelonae/abscessus (n = 4). With therapy ≥1 month (mean, 255.0 ± 265.7 days), 10/15 patients (66.7%) with cystic fibrosis and 16/26 (61.5%) overall were considered improved. Skin/soft-tissue/bone infections were the most common extrapulmonary infections. With therapy ≥1 month (mean, 143 ± 123 days), 9/12 patients (75.0%) were considered improved. Nine of the 16 cases reported as failures regardless of site of infection occurred in patients who stopped treatment due to adverse events. There were eight deaths; none was related to tigecycline.

CONCLUSIONS

Tigecycline given for ≥1 month as part of a multidrug regimen resulted in improvement in >60% of patients with M. abscessus and M. chelonae infections, including those with underlying cystic fibrosis, despite failure of prior antibiotic therapy. Adverse events were reported in >90% of cases, the most common being nausea and vomiting.

Rapid molecular detection of inducible macrolide resistance in Mycobacterium chelonae and M. abscessus strains: a replacement for 14-day susceptibility testing?

The erm(41) gene causes inducible macrolide resistance in Mycobacterium abscessus but not Mycobacterium chelonae. erm(41) sequencing of 285 M. abscessus and 45 M. chelonae isolates was compared to 14-day susceptibility; agreement percentages were 98.9% and 100%, respectively. Extended incubation may not be necessary for M. chelonae, and the erm(41) genotype is a useful adjunct for M. abscessus.

Erm(41)-dependent inducible resistance to azithromycin and clarithromycin in clinical isolates of Mycobacterium abscessus

OBJECTIVES

The ribosomal methylase Erm(41) confers inducible resistance to macrolides in Mycobacterium abscessus. The aim of this work was to systematically study and compare drug susceptibility to clarithromycin and azithromycin in M. abscessus and Mycobacterium chelonae clinical isolates with a particular focus on inducible drug resistance.

METHODS

Clinical isolates of M. abscessus subsp. abscessus (n = 21), M. abscessus subsp. bolletii (n = 16), M. abscessus subsp. massiliense (n = 10) and M. chelonae (n = 22) were characterized regarding their erm(41) and rrl genotypes and subjected to drug susceptibility testing (DST) for clarithromycin and azithromycin. Microdilution DST was performed in cation-adjusted Mueller-Hinton broth (pH 7.4) with readings at days 3, 7 and 12 and with pre-incubation at subinhibitory macrolide concentrations for erm(41) induction. In addition, the influence of variations in pH and growth medium on DST results was examined.

RESULTS

MICs of azithromycin were consistently higher than those of clarithromycin. In strains with an inducible erm(41) gene, high median MICs of ≥256 mg/L on day 12 were observed for both clarithromycin and azithromycin. Inducible resistance was at least as pronounced for azithromycin as for clarithromycin.

CONCLUSIONS

Our findings do not support the suggestion of a preferential use of azithromycin over clarithromycin in order to limit inducible macrolide resistance. Both compounds provoked a comparable resistance phenotype in M. abscessus. Caution is needed when using either azithromycin or clarithromycin for treatment of M. abscessus infections.

Nontuberculous mycobacteria in guadeloupe, martinique, and French Guiana from 1994 to 2012

Nontuberculous mycobacteria (NTM) are ubiquitous environmental organisms able to cause severe opportunistic human infections. Their distribution patterns are subject to geographical variations. This study describes their isolation frequencies from clinical specimen in the three French overseas departments of the Americas, namely, Guadeloupe, Martinique, and French Guiana during 1994-2012. A total of 651 strains from as many patients (one isolate per species per patient) were analysed regarding regional isolation patterns and potential pattern changes over time. The Mycobacterium avium complex was the most common group of NTM in Guadeloupe and French Guiana. In Martinique it was the second most common after the rapidly growing mycobacteria. M. fortuitum was the most commonly isolated species in all three departments. Some species (M. kansasii, M. xenopi, and M. terrae complex) displayed a clear regional preference. Furthermore a change in isolation frequency was observed for M. intracellulare (increase) and M. kansasii (decrease) in Guadeloupe. In conclusion, marked regional differences in isolation frequencies of NTM species were observed in the study area. Results are discussed in context of variables such as study populations, risk factors, methodology employed, isolation from pulmonary versus sterile isolation sites (blood, urine, and CSF), and in vitro drug-susceptibility patterns.

The drug resistance profile of Mycobacterium abscessus group strains from Korea

Background

Bacteria of the Mycobacterium abscessus group are the second most common pathogens responsible for lung disease caused by nontuberculous mycobacteria in Korea. There is still a lack of studies investigating the genetic mechanisms involved in M. abscessus resistance to antibiotics other than clarithromycin. This study investigated the characteristics of drug resistance exhibited by M. abscessus clinical isolates from Korea.

Methods

We performed drug susceptibility testing for a total of 404 M. abscessus clinical strains. Subspecies were differentiated by molecular biological methods and examined for mutations in drug resistance-related genes.

Results

Of the 404 strains examined, 202 (50.00%), 199 (49.26%), and 3 (0.74%) strains were identified as M. abscessus, M. massiliense, and M. bolletii, respectively. Of the 152 clarithromycin-resistant strains, 6 possessed rrl mutations, while 4 of the 30 amikacin-resistant strains contained rrs mutations, and 5 of the 114 quinolone-resistant strains had gyr mutations. All mutant strains had high minimal inhibitory concentration values for the antibiotics.

Conclusions

Our results showed the distribution of the strains with mutations in drug resistance-related genes was low in the M. abscessus group. Furthermore, we performed drug susceptibility testing and sequence analyses to determine the characteristics of these genes in the M. abscessus group.

The genome sequence of 'Mycobacterium massiliense' strain CIP 108297 suggests the independent taxonomic status of the Mycobacterium abscessus complex at the subspecies level

Members of the Mycobacterium abscessus complex are rapidly growing mycobacteria that are emerging as human pathogens. The M. abscessus complex was previously composed of three species, namely M. abscessus sensu stricto, 'M. massiliense', and 'M. bolletii'. In 2011, 'M. massiliense' and 'M. bolletii' were united and reclassified as a single subspecies within M. abscessus: M. abscessus subsp. bolletii. However, the placement of 'M. massiliense' within the boundary of M. abscessus subsp. bolletii remains highly controversial with regard to clinical aspects. In this study, we revisited the taxonomic status of members of the M. abscessus complex based on comparative analysis of the whole-genome sequences of 53 strains. The genome sequence of the previous type strain of 'Mycobacterium massiliense' (CIP 108297) was determined using next-generation sequencing. The genome tree based on average nucleotide identity (ANI) values supported the differentiation of 'M. bolletii' and 'M. massiliense' at the subspecies level. The genome tree also clearly illustrated that 'M. bolletii' and 'M. massiliense' form a distinct phylogenetic clade within the radiation of the M. abscessus complex. The genomic distances observed in this study suggest that the current M. abscessus subsp. bolletii taxon should be divided into two subspecies, M. abscessus subsp. massiliense subsp. nov. and M. abscessus subsp. bolletii, to correspondingly accommodate the previously known 'M. massiliense' and 'M. bolletii' strains.

In vitro activity of cefoxitin and imipenem against Mycobacterium abscessus complex

The in vitro activity of cefoxitin and imipenem was compared for 43 strains of the Mycobacterium abscessus complex, mostly isolated from cystic fibrosis patients. The MICs of imipenem were lower than those of cefoxitin, although the number of imipenem-resistant strains was higher according to the CLSI breakpoints. Strain comparisons indicated that the MICs of cefoxitin were significantly higher for Mycobacterium bolletii than for M. abscessus. The MICs of both β-lactams were higher for the rough morphotype than for the smooth morphotype. The clinical impact of the in vitro difference between the activity of imipenem and that of cefoxitin remains to be determined.

Characterization of rough and smooth morphotypes of Mycobacterium abscessus isolates from clinical specimens

Mycobacterium abscessus, which consists of the two subspecies M. abscessus subspecies abscessus and M. abscessus subspecies bolletii, can produce rough or smooth colony morphologies. Here we analyzed 50 M. abscessus isolates cultured from the respiratory specimens of 34 patients, 28 (82%) of whom had cystic fibrosis (CF), with respect to their colony morphologies and antibiotic susceptibilities. The overall proportions of occurrences of the two morphotypes were similar, with specimens from 50% of the patients showing a rough and 38% showing a smooth morphotype. A total of 12% of the specimens from the patients showed both morphotypes simultaneously. At the subspecies level, the proportions of rough and smooth morphotypes differed substantially; 88% of rough morphotypes belonged to M. abscessus subspecies abscessus, and 85% of smooth morphotypes belonged M. abscessus subspecies bolletii. Inducible clarithromycin resistance due to the Erm(41) methylase, as well as high-level resistance to clarithromycin due to mutations within the rrl gene, occurred independently of the morphotype. The MIC50s of amikacin and cefoxitin were identical for the two morphotypes, whereas the MIC50s of tigecycline were 0.25 μg/ml for the rough morphotype and 2.0 μg/ml for the smooth morphotype. Our results show that the smooth morphotype was more dominant in respiratory specimens from CF patients than previously thought. With respect to resistance, colony morphology did not affect the susceptibility of Mycobacterium abscessus to the first-line antibiotics clarithromycin, amikacin, and cefoxitin.

Comparison of the Bruker Biotyper and Vitek MS matrix-assisted laser desorption ionization-time of flight mass spectrometry systems for identification of mycobacteria using simplified protein extraction protocols

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has recently been described as a fast and inexpensive method for the identification of mycobacteria. Although mycobacteria require extraction prior to MALDI-TOF MS analysis, previously published protocols have been relatively complex, involving significant hands-on time and materials not often found in the clinical laboratory. In this study, we tested two simplified protein extraction protocols developed at the University of Washington (UW) and by bioMérieux (BMX) for use with two different mass spectrometry platforms (the Bruker MALDI Biotyper and the bioMérieux Vitek MS, respectively). Both extraction protocols included vortexing with silica beads in the presence of ethanol. The commercial Bruker database was also augmented with an in-house database composed of 123 clinical Mycobacterium strains. A total of 198 clinical strains, representing 18 Mycobacterium species, were correctly identified to the species level 94.9% of the time when extracted using the UW protocol and compared to the augmented database. The BMX protocol and Vitek MS system resulted in correct species-level identifications for 94.4% of these strains. In contrast, only 79.3% of the strains were identified to the species level by the nonaugmented Bruker database, although the use of a lower identification score threshold (≥1.7) increased the identification rate to 93.9%, with two misidentifications that were unlikely to be clinically relevant. The two simplified protein extraction protocols described in this study are easy to use for identifying commonly encountered Mycobacterium species.

Characterization of broad-spectrum Mycobacterium abscessus class A β-lactamase

OBJECTIVES

Imipenem and cefoxitin are used to treat Mycobacterium abscessus infections and have moderate activity against this fast-growing mycobacterium (MIC₅₀ of 16 and 32 mg/L, respectively). M. abscessus is highly resistant to most other β-lactams, although the underlying mechanisms have not been explored. Here, we characterized M. abscessus class A β-lactamase (Bla(Mab)) and investigated its role in β-lactam resistance.

METHODS

Hydrolysis kinetic parameters of purified Bla(Mab) were determined by spectrophotometry for various β-lactams and compared with those of related BlaC from Mycobacterium tuberculosis. MICs of β-lactams were determined for M. abscessus CIP104536 and for Escherichia coli producing Bla(Mab) and BlaC.

RESULTS

Bla(Mab) had a broad hydrolysis spectrum, similar to that of BlaC, but with overall higher catalytic efficiencies, except for cefoxitin. As expected from its in vivo efficacy, cefoxitin was very slowly hydrolysed by Bla(Mab) (k(cat)/K(m) = 6.7 M(-1) s(-1)). Bla(Mab) hydrolysed imipenem more efficiently (k(cat)/K(m) = 3.0 × 10(4) M(-1) s(-1)), indicating that the in vivo activity of this drug might be improved by combination with a β-lactamase inhibitor. β-Lactamase inhibitors clavulanate, tazobactam and sulbactam did not inhibit Bla(Mab). This enzyme efficiently hydrolysed clavulanate, in contrast to BlaC, which is irreversibly acylated by this inhibitor. Bla(Mab) and BlaC were functional in E. coli and the resistance profiles mediated by these enzymes were in agreement with the kinetic parameters.

CONCLUSIONS

M. abscessus produces a clavulanate-insensitive broad-spectrum β-lactamase that limits the in vivo efficacy of β-lactams.

Identification and characterization of the genetic changes responsible for the characteristic smooth-to-rough morphotype alterations of clinically persistent Mycobacterium abscessus

Mycobacterium abscessus is an emerging pathogen that is increasingly recognized as a relevant cause of human lung infection in cystic fibrosis patients. This highly antibiotic-resistant mycobacterium is an exception within the rapidly growing mycobacteria, which are mainly saprophytic and non-pathogenic organisms. M. abscessus manifests as either a smooth (S) or a rough (R) colony morphotype, which is of clinical importance as R morphotypes are associated with more severe and persistent infections. To better understand the molecular mechanisms behind the S/R alterations, we analysed S and R variants of three isogenic M. abscessus S/R pairs using an unbiased approach involving genome and transcriptome analyses, transcriptional fusions and integrating constructs. This revealed different small insertions, deletions (indels) or single nucleotide polymorphisms within the non-ribosomal peptide synthase gene cluster mps1-mps2-gap or mmpl4b in the three R variants, consistent with the transcriptional differences identified within this genomic locus that is implicated in the synthesis and transport of Glyco-Peptido-Lipids (GPL). In contrast to previous reports, the identification of clearly defined genetic lesions responsible for the loss of GPL-production or transport makes a frequent switching back-and-forth between smooth and rough morphologies in M. abscessus highly unlikely, which is important for our understanding of persistent M. abscessus infections.

Insertion site and distribution of a genomic island conferring DNA phosphorothioation in the Mycobacterium abscessus complex

Nearly half of US clinical isolates of the emerging pathogen Mycobacterium abscessus were reported to exhibit smeared DNA during PFGE. This DNA degradation (Dnd) phenotype results from DNA phosphorothioation, a sulfur modification found in other bacteria and conferred by dnd genes located on mobile elements. Putative dnd genes are located on a 19.6 kbp genomic island (GI) in the M. abscessus type strain ATCC 19977. We confirmed that ATCC 19977(T) is Dnd-positive by PFGE and we developed a PCR assay to predict Dnd phenotype. Dnd-positive strains generated an amplicon from dndC whereas Dnd-negative strains generated a bridge amplicon that spanned the GI insertion site, indicating they lacked the entire 'Dnd-GI'. Comparative analyses of sequences from the bridge amplicon with ATCC 19977(T) revealed the Dnd-GI is flanked by 22 bp repeats in M. abscessus sensu stricto and inserted downstream of a tRNA-Ala gene and between inverted repeats. Regions flanking the Dnd-GI were highly conserved within the M. abscessus complex. Bioinformatics studies suggest the Dnd-GI inserted independently into a strain of Mycobacterium massiliense and that other species of mycobacteria also have dnd genes, supporting reports that the Dnd phenotype is common among actinomycetes. Within the M. abscessus complex, Dnd-positive clinical isolates were primarily M. abscessus sensu stricto, and tandem repeat typing indicated these isolates were highly related, confirming previous PFGE studies and revealing a widespread family of strains with significance in human disease.

Draft Genome Sequence of Mycobacterium massiliense Strain M159, Showing Phenotypic Resistance to β-Lactam and Tetracycline Antibiotics

Mycobacterium massiliense is a nontuberculous mycobacterium associated with human infections. We report here the draft genome sequence of M. massiliense strain M159, isolated from the bronchial aspirate of a patient who had a pulmonary infection. This strain showed genotypic and in vitro resistance to a number of tetracyclines and beta-lactam antibiotics.

In vitro activity of amikacin against isolates of Mycobacterium avium complex with proposed MIC breakpoints and finding of a 16S rRNA gene mutation in treated isolates

Amikacin is a major drug used for the treatment of Mycobacterium avium complex (MAC) disease, but standard laboratory guidelines for susceptibility testing are not available. This study presents in vitro amikacin MICs for 462 consecutive clinical isolates of the MAC using a broth microdilution assay. Approximately 50% of isolates had amikacin MICs of 8 μg/ml, and 86% had MICs of ≤16 μg/ml. Of the eight isolates (1.7%) with MICs of 64 μg/ml, five had an MIC of 32 μg/ml on repeat testing. Ten isolates (2.1%) had an initial amikacin MIC of >64 μg/ml, of which seven (1.5%) had MICs of >64 μg/ml on repeat testing. These seven isolates had a 16S rRNA gene A1408G mutation and included M. avium, Mycobacterium intracellulare, and Mycobacterium chimaera. Clinical data were available for five of these seven isolates, all of which had received prolonged (>6 months) prior therapy, with four that were known to be treated with amikacin. The 16S mutation was not detected in isolates with MICs of ≤64 μg/ml. We recommend primary testing of amikacin against isolates of the MAC and propose MIC guidelines for breakpoints that are identical to the CLSI guidelines for Mycobacterium abscessus: ≤16 μg/ml for susceptible, 32 μg/ml for intermediate, and ≥64 μg/ml for resistant. If considered and approved by the CLSI, this will be only the second drug recommended for primary susceptibility testing against the MAC and should facilitate its use for both intravenous and inhaled drug therapies.

Matrix-assisted laser desorption ionization-time of flight mass spectrometry can accurately differentiate between Mycobacterium masilliense (M. abscessus subspecies bolletti) and M. abscessus (sensu stricto)

Among 36 Mycobacterium masilliense and 22 M. abscessus isolates identified by erm(41) PCR and sequencing analysis of rpoB and 23S rRNA genes, the rate of accurate differentiation between these two subspecies was 100% by cluster analysis of spectra generated by Bruker Biotyper matrix-assisted laser desorption ionization-time of flight mass spectrometry.

New rapid scheme for distinguishing the subspecies of the Mycobacterium abscessus group and identifying Mycobacterium massiliense isolates with inducible clarithromycin resistance

Mycobacterium abscessus (M. abscessus sensu lato, or the M. abscessus group) comprises three closely related taxa whose taxonomic statuses are under revision, i.e., M. abscessus sensu stricto, Mycobacterium bolletii, and Mycobacterium massiliense. We describe here a simple, robust, and cost-effective PCR-based method for distinguishing among M. abscessus, M. massiliense, and M. bolletii. Based on the M. abscessus ATCC 19977(T) genome, regions that discriminated between M. abscessus and M. massiliense were identified through array-based comparative genomic hybridization. A typing scheme using PCR primers designed for four of these locations was applied to 46 well-characterized clinical isolates comprising 29 M. abscessus, 15 M. massiliense, and 2 M. bolletii isolates previously identified by multitarget sequencing. Interestingly, 2 isolates unequivocally identified as M. massiliense were shown to have a full-length erm(41) gene instead of the expected gene deletion and showed inducible clarithromycin resistance after 14 days. We propose using this PCR-based typing scheme combined with erm(41) PCR for straightforward identification of M. abscessus, M. massiliense, and M. bolletii and the assessment of inducible clarithromycin resistance. This method can be easily integrated into a routine workflow to provide subspecies-level identification within 24 h after isolation of the M. abscessus group.