Abscessus Isolates Research Articles

Population Genomics of Mycobacterium abscessus from U.S. Cystic Fibrosis Care Centers.

Rationale:Mycobacterium abscessus is a significant threat to individuals with cystic fibrosis (CF) because of innate drug resistance and potential transmission between patients. Recent studies described global dominant circulating clones of M. abscessus, but detailed genomic surveys have not yet been described for the United States. Objectives: We examined the genetic diversity of respiratory M. abscessus isolates from U.S. patients with CF and evaluated the potential for transmission events within CF Care Centers. Methods: Whole-genome sequencing was performed on 558 M. abscessus isolates from 266 patients with CF attending 48 CF Care Centers in 28 U.S. states as part of a nationwide surveillance program. U.S. isolates were also compared with 64 isolate genomes from 13 previous studies to evaluate the prevalence of recently described dominant circulating clones. Results: More than half of study patients with CF and M. abscessus had isolates within four dominant clones; two clones of M. abscessus subspecies (subsp.) abscessus (MAB) and two clones of M. abscessus subsp. massiliense (MMAS). Acquired drug resistance mutations for aminoglycosides and macrolides were rare in the isolate population, and they were not significantly enriched in dominant clones compared with unclustered isolates. For a subset of 55 patients, there was no relationship between dominant clones and diagnosis of active lung disease (P = 1.0). Twenty-nine clusters of genetically similar MAB isolates and eight clusters of genetically similar MMAS isolates were identified. Overall, 28 of 204 (14%) patients with MAB and 15 of 64 (23%) patients with MMAS had genetically isolates similar to those of at least one other patient at the same CF Care Center. Genetically similar isolates were also found between 60 of 204 (29%) patients with MAB and 19 of 64 (30%) patients with MMAS from different geographic locations. Conclusions: Our study reveals the predominant genotypes of M. abscessus and frequency of shared strains between patients in U.S. CF Care Centers. Integrated epidemiological and environmental studies would help to explain the widespread presence of dominant clones in the United States, including the potential for broad distribution in the environment. Single site studies using systematic, evidence-based approaches will be needed to establish the contributions of health care-associated transmission versus shared environmental exposures.

Mycobacterium abscessus Strain Morphotype Determines Phage Susceptibility, the Repertoire of Therapeutically Useful Phages, and Phage Resistance.

Mycobacterium abscessus is an opportunistic pathogen whose treatment is confounded by widespread multidrug resistance. The therapeutic use of bacteriophages against Mycobacterium abscessus infections offers a potential alternative approach, although the spectrum of phage susceptibilities among M. abscessus isolates is not known. We determined the phage infection profiles of 82 M. abscessus recent clinical isolates and find that colony morphotype-rough or smooth-is a key indicator of phage susceptibility. None of the smooth strains are efficiently killed by any phages, whereas 80% of rough strains are infected and efficiently killed by at least one phage. The repertoire of phages available for potential therapy of rough morphotype infections includes those with relatively broad host ranges, host range mutants of Mycobacterium smegmatis phages, and lytically propagated viruses derived from integrated prophages. The rough colony morphotype results from indels in the glycopeptidolipid synthesis genes mps1 and mps2, negating reversion to smooth as a common route to phage resistance. Resistance is thus rare, and although mutations in polyketide synthesis, uvrD2, and rpoZ can confer resistance, these likely also impair survival in vivo The expanded therapeutic repertoire and the resistance profiles show that small cocktails or single phages could be suitable for controlling infections with rough strains.IMPORTANCEMycobacterium abscessus infections in cystic fibrosis patients are challenging to treat due to widespread antibiotic resistance. The therapeutic use of lytic bacteriophages presents a new potential strategy, but the great variation among clinical M. abscessus isolates demands determination of phage susceptibility prior to therapy. Elucidation of the variation in phage infection and factors determining it, expansion of the suite of therapeutic phage candidates, and a greater understanding of phage resistance mechanisms substantially advances the potential for broad implementation of new therapeutic options for M. abscessus infections.

Association between 16S rRNA gene mutations and susceptibility to amikacin in Mycobacterium avium Complex and Mycobacterium abscessus clinical isolates

We evaluated the association between 16S rRNA gene (rrs) mutations and susceptibility in clinical isolates of amikacin-resistant nontuberculous mycobacteria (NTM) in NTM-pulmonary disease (PD) patients. Susceptibility was retested for 134 amikacin-resistant isolates (minimum inhibitory concentration [MIC] ≥ 64 µg/ml) from 86 patients. Amikacin resistance was reconfirmed in 102 NTM isolates from 62 patients with either Mycobacterium avium complex-PD (MAC-PD) (n = 54) or M. abscessus-PD (n = 8). MICs and rrs mutations were evaluated for 318 single colonies from these isolates. For the 54 MAC-PD patients, rrs mutations were present in 34 isolates (63%), comprising all 31 isolates with amikacin MICs ≥ 128 µg/ml, but only three of 23 isolates with an MIC = 64 µg/ml. For the eight M. abscessus-PD patients, all amikacin-resistant (MIC ≥ 64 µg/ml) isolates had rrs mutations. In amikacin-resistant isolates, the A1408G mutation (n = 29) was most common. Two novel mutations, C1496T and T1498A, were also identified. The culture conversion rate did not differ by amikacin MIC. Overall, all high-level and 13% (3/23) of low-level amikacin-resistant MAC isolates had rrs mutations whereas mutations were present in all amikacin-resistant M. abscessus isolates. These findings are valuable for managing MAC- and M. abscessus-PD and suggest the importance of phenotypic and genotypic susceptibility testing.

WS13.5 Molecular epidemiology of Mycobacterium abscessus isolates recovered from German cystic fibrosis patients

WS13.5 Molecular epidemiology of Mycobacterium abscessus isolates recovered from German cystic fibrosis patients

A real-time PCR assay for rapid identification of inducible and acquired clarithromycin resistance in Mycobacterium abscessus.

BackgroundMycobacterium abscessus is a rapidly growing mycobacteria involved in severe infections of the lung, skin, or soft tissue. Macrolides such as clarithromycin are the recommended first line drugs for treatment of M. abscessus infections. However, M. abscessus has dual mechanisms of resistance to macrolides, making treatment by macrolides difficult. A functional erm(41) gene confers for inducible resistance while acquired mutations on the 23S rRNA rrl gene confer for constitutive resistance.MethodsWe have developed a real-time PCR assay to detect both inducible and acquired resistance to clarithromycin, and compared the results to traditional erm(41) and rrl sequencing and phenotypic susceptibility testing using Sensititre™ plates.ResultsOf the total 126 M. abscessus isolates tested, truncated erm(41) was found in 23/126 (18.3%) of the samples, 27/126 (21.4%) had a T28C mutation in erm(41), and 2/126 (1.6%) had an acquired A2058C mutation in rrl. The phenotypic results correlated with the expected sequencing results in 121/126 samples (96%). Phenotypic testing compared to real-time PCR resolved 2 of these discrepancies by showing the existence of both erm(41) alleles in the isolates that sequencing missed. One culture was found to be mixed with two M. abscessus subsp. as per hsp65 sequencing and 2 isolates had discordance between molecular and phenotypic results. It was presumed that 3 isolates showed discrepancy between sequencing and real-time PCR, but one culture was mixed and other 2 detected both alleles by real-time PCR leading to 100% concordance when compared to sequencing.ConclusionIn conclusion, real-time PCR is more accurate for detection of both acquired and induced clarithromycin resistance, specifically when mixed genic profiles are present in a sample.

<p>Zinc Chelator N,N,N′,N′-Tetrakis(2-Pyridylmethyl)Ethylenediamine Reduces the Resistance of <em>Mycobacterium abscessus</em> to Imipenem</p>

PurposeImipenem is one of the very few effective options for treating Mycobacterium abscessus (M. abscessus) infections; the development of imipenem resistance is a major health concern.Materials and MethodsThe susceptibility of 194 clinical M. abscessus isolates to imipenem was determined. The ability of imipenem to synergize with N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), a zinc chelator and a metallo-β-lactamases (MBLs) inhibitor, to inhibit M. abscessus growth was also assessed.ResultsM. abscessus exhibited an elevated resistance to imipenem (MIC50 = 16 mg/L, MIC90 = 64 mg/L). A combination of TPEN and imipenem synergized to inhibit the growth of 100% of imipenem-resistant and 79.2% of imipenem-resistance intermediate isolates; no synergy was observed treating imipenem-sensitive isolates. A remarkable decrease in the MIC50 (from 16 to 4 mg/L) and MIC90 (from 64 to 8 mg/L) of imipenem was observed when it was combined with TPEN; the portion of imipenem-resistant isolates also decreased (from 48.4% to 0%). Consistent with these results demonstrating synergy, a time-kill assay showed the addition of TPEN significantly improved the bactericidal activity of imipenem toward M. abscessus. Similarly, EDTA (a potent MBLs inhibitor) promoted the anti-M. abscessus activity of imipenem in a disk assay, corroborating the effect of TPEN and supporting the role of MBLs in imipenem resistance exhibited by some isolates.ConclusionThese findings demonstrate that TPEN can reduce the resistance of M. abscessus to imipenem and suggest that the inhibition of MBLs activity is the underlying mechanism.

In vitro efficacy of combinations of eight antimicrobial agents against Mycobacteroides abscessus complex

ObjectivesA standard treatment regimen against Mycobacteroides abscessus complex (MABC) infections has not yet been established, making MABC difficult to treat successfully. In this study, we sought to develop an active ingredient for the clinical treatment of MABC infections. MethodsWe screened 102 MABC strains isolated from clinical specimens using DNA sequence analysis with the housekeeping genes hsp65 and rpoB. Drug susceptibility testing was performed against two subspecies—Mycobacteroides abscessus subsp. abscessus (M. abscessus) and Mycobacteroides abscessus subsp. massiliense (M. massiliense)—using eight antimicrobial agents (clarithromycin, amikacin, doxycycline, imipenem, linezolid, moxifloxacin, faropenem, and rifampicin). The combined efficacy of the antimicrobial agents was investigated using a checkerboard method. ResultsWe identified 51 isolates as M. abscessus, 46 as M. massiliense, and five as others. Most of the M. abscessus isolates (83.0 %) exhibited inducible resistance to clarithromycin via the expression of the erm(41) gene. Combinations of imipenem with linezolid, moxifloxacin, and rifampicin exhibited additive effects against 81.0 %, 40.7 %, and 26.9 % of M. abscessus, respectively, and against 54.5 %, 69.2 %, and 30.8 % of M. massiliense, respectively. ConclusionsThese results demonstrated the potential efficacy of a regimen containing imipenem against M. abscessus and M. massiliense infections.

Antimicrobial Susceptibility of Mycobacterium abscessus Complex Clinical Isolates from a Chinese Tertiary Hospital.

IntroductionMycobacterium abscessus complex (MABC) is a group of important infectious agents that are highly associated with drug resistance, and antibiotic treatment is usually ineffective. This study investigated the characteristics of antimicrobial susceptibility of MABC isolates and the synergy between certain β-lactam combinations against MABC infection.MethodsWe collected 129 MABC isolates from patients with lower respiratory tract infections and categorized them into three subspecies. The minimum inhibitory concentrations (MICs) of 15 antimicrobials for the MABC isolates were determined using commercial Sensititre RAPMYCOI MIC plates and the broth microdilution method, as recommended in the CLSI (M24-A2). In addition, the MICs of imipenem, alone and with ceftazidime and/or avibactam, were assessed in vitro for all isolates. The erm(41) and rrl genes were also sequenced.ResultsThe MABC isolates exhibited >80% resistance to 11 of the 15 antimicrobials. Regarding the remaining four antimicrobials, the isolates were least resistant to tigecycline (12.4%) and amikacin (3.9%), and only partially resistant to two cefoxitin (39.5%) and imipenem (40.3%). Compared with M. massiliense isolates, M. abscessus and M. bolletii isolates were more resistant to amikacin and imipenem, whereas M. abscessus was significantly less resistant to tigecycline relative to M. massiliense and M. bolletii isolates. The clarithromycin inducible resistance rate was 68.4% and 74.3% among M. bolletii and M. abscessus isolates. Furthermore, 88.7% of the M. abscessus isolates carried a T at position 28 of erm(41), which is associated with inducible clarithromycin resistance. In addition, compared to imipenem with avibactam only, the MIC50 and MIC90values of imipenem after adding ceftazidime plus avibactam were decreased fourfold.ConclusionThe antimicrobial resistance rates and the characteristics of the erm(41) gene associated with inducible clarithromycin resistance were different among the three MABC subspecies. There was also synergy between imipenem and 100μg/mL ceftazidime against MABC isolates.

Genetic Evolution of Mycobacterium abscessus Conferring Clarithromycin Resistance during Long-Term Antibiotic Therapy.

Objectives Clarithromycin is recommended as the core agent for treating M. abscessus infections, which usually calls for at least one year of treatment course, facilitating the development of resistance. This study aimed to identify the underlying mechanism of in vivo development of clarithromycin resistance in M. abscessus clinical isolates. Methods M. abscessus isolates from patients with lung infections during long-term antibiotic therapy were longitudinally collected and sequenced. PFGE DNA fingerprinting was used to confirm the genetic relationships of the isolates. Whole genome comparative analysis was performed to identify the genetic determinants that confer the clarithromycin resistance. Results Three pairs of initially clarithromycin-susceptible and subsequently clarithromycin-resistant M. abscessus isolates were obtained. We found that the clarithromycin-resistant isolates emerged relatively rapidly, after 4–16 months of antibiotic therapy. PFGE DNA fingerprinting showed that the clarithromycin-resistant isolates were identical to the initial clarithromycin-susceptible ones. Whole genome sequencing and bioinformatics analysis identified several genetic alternations in clarithromycin-resistant isolates, including genes encoding efflux pump/transporter, integral component of membrane, and the tetR and lysR family transcriptional regulators. Conclusion We identified genes likely encoding new factors contributing to clarithromycin-resistance phenotype of M. abscessus, which can be useful in prediction of clarithromycin resistance in M. abscessus.

Assessment of Clofazimine and TB47 Combination Activity against Mycobacterium abscessus Using a Bioluminescent Approach.

Mycobacterium abscessus is intrinsically resistant to most antimicrobial agents. The emerging infections caused by M. abscessus and the lack of effective treatment call for rapid attention. Here, we intended to construct a selectable marker-free autoluminescent M. abscessus strain (designated UAlMab) as a real-time reporter strain to facilitate the discovery of effective drugs and regimens for treating M. abscessus The UAlMab strain was constructed using the dif/Xer recombinase system. In vitro and in vivo activities of several drugs, including clofazimine and TB47, a recently reported cytochrome bc1 inhibitor, were assessed using UAlMab. Furthermore, the efficacy of multiple drug combinations, including the clofazimine and TB47 combination, were tested against 20 clinical M. abscessus isolates. The UAlMab strain enabled us to evaluate drug efficacy both in vitro and in live BALB/c mice in a real-time, noninvasive fashion. Importantly, although TB47 showed marginal activity either alone or in combination with clarithromycin, amikacin, or roxithromycin, the drug markedly potentiated the activity of clofazimine, both in vitro and in vivo This study demonstrates that the use of the UAlMab strain can significantly facilitate rapid evaluation of new drugs and regimens. The clofazimine and TB47 combination is effective against M. abscessus, and dual/triple electron transport chain (ETC) targeting can be an effective therapeutic approach for treating mycobacterial infections.

Efflux Pumps Contribute to Intrinsic Clarithromycin Resistance in Clinical, Mycobacterium abscessus Isolates.

PurposeThe emergence of clarithromycin resistance is a challenge in treating Mycobacterium abscessus infections. Known mechanisms that contribute to intrinsic clarithromycin resistance focus on rrl gene-related mutations, but resistant clinical isolates often exhibit an inconsistent rrl genotype.Patients and MethodsIn this study, 194 clinical Mycobacterium abscessus isolates were collected from patients with lung infections and the whole genome of each isolate was sequenced. A comprehensive examination of the molecular mechanisms underlying intrinsic clarithromycin resistance was performed, combining MIC determination, comparative genome sequence analysis and qRT-PCR.ResultsOf the 194 isolates, 13 (6.7%) were clarithromycin resistant; only seven of these harbored a rrl 2270/2271 mutation. The remaining six resistant isolates did not exhibit a specific resistance-associated mutation in the clarithromycin target-site genes, rrl, rplC, rplD and rplV, or in the rrl modification gene erm(41). qRT-PCR analysis showed that the increased expression of the efflux pump genes, MAB_2355c, MAB_1409c and MAB_1846, as well as their positive regulatory gene whiB7, consistently correlated with increased clarithromycin resistance. The presence of efflux pump inhibitors significantly decreased the MIC of clarithromycin for nonsusceptible isolates, especially the intrinsic resistant isolates that exhibited no rrl 2270/2271 mutation.ConclusionThese findings indicate that efflux pumps play a prominent role in the intrinsic resistance of M. abscessus to clarithromycin, complementing other known resistance mechanisms.

Identification of Mycobacterium abscessus species and subspecies using the Cas12a/sgRNA-based nucleic acid detection platform.

The rapidly growing mycobacterium Mycobacterium abscessus is a clinically important organism causing pulmonary and skin diseases. The M. abscessus complex is comprised of three subspecies: M. abscessus subsp. abscessus, M. abscessus subsp. massiliense, and M. abscessus subsp. bolletii. Here, we aimed to develop a Cas12a/sgRNA-based nucleic acid detection platform to identify M. abscessus species and subspecies. By designing specific sgRNA probes targeting rpoB and erm(41), we demonstrated that M. abscessus could be differentiated from other major mycobacterial species and identified at the subspecies level. Using this platform, a total of 38 clinical M. abscessus isolates were identified, 18 as M. abscessus subsp. abscessus and 20 as M. abscessus subsp. massiliense. We concluded that the Cas12a/sgRNA-based nucleic acid detection platform provides an easy-to-use, quick, and cost-effective approach for identification of M. abscessus species and subspecies.

Non-tuberculous mycobacteria profiles and their anti-mycobacterial resistance at a major medical center in Lebanon

Infection with non-tuberculosis mycobacteria (NTM) has been on the rise globally causing a wide spectrum of respiratory and extrapulmonary infections in humans. Studies on these pathogens from the Middle-East including Lebanon are scarce. This retrospective study addresses the approach used for investigation, speciation and antimicrobial resistance (AMR) profiles of recovered NTM isolates from respiratory sources at a major tertiary care center in Lebanon during two periods (2003-2007 and 2013-2017). Processing of specimens, culture and differentiation of recovered NTM isolates from Mycobacterium tuberculosis were done in-house according to standard procedures. Upon request, speciation and AMR testing were performed using molecular and broth dilution methods, respectively, at Mayo Medical Laboratories (Rochester, Minnesota, USA). Among 108 NTM analyzed isolates, 8 species were revealed during the two periods: M. simiae (51% vs 61%), M. avium complex (MAC) (6 % vs 12%) M. fortuitum (12% vs 5%), M. gordonae (6% vs 5%), M. abscessus (6% vs 7%), M. immunogenum (12% vs 0%), M. szulgai (4% vs 0%) and M. peregrinum (0% vs 2%). M. simiae isolates showed high susceptibility (93%-96%) to amikacin and clarithromycin, but high resistance to rifampin, ethambutol, ciprofloxacin, rifabutin, linezolid, trimethoprim/sulfamethoxazole and moxifloxacin. MAC isolates were only susceptible to clarithromycin (86%). M. abscessus isolates were uniformly susceptible to amikacin (100%). The revelaed different NTM species, with predominance of M.simiae and various AMR profiles provide a current epidemiologic database and help guiding the selection of appropriate empirical therapy once the clinical relevance is established.

Outcomes in Lung Transplant Recipients With Mycobacterium abscessus Infection: A 15-Year Experience From a Large Tertiary Care Center

BackgroundMycobacterium abscessus (M abscessus) infection is a serious complication post–lung transplant (LTx). We examined determinants of outcomes in LTx recipients infected with M abscessus. MethodsElectronic records of all patients who underwent LTx in a single transplant center between 2000 and 2015 were screened for isolation of M abscessus before or after LTx. ResultsTwenty-six cases of M abscessus isolation were identified. Twenty-four had M abscessus isolation post-LTx. Two had M abscessus isolated from a surgical site, while the others were pulmonary isolates. Out of these 22 with pulmonary isolates, 12 had clinical disease. In 73% of patients, treatment had to be temporarily held or switched due to intolerance and toxicity. There was a statistically significant worsening in survival in those who developed clinical disease compared to matched controls. Among the 12 patients with clinical pulmonary disease, use of clofazimine was significantly associated with a favorable outcome. Six patients had M abscessus isolation pretransplant. Four developed M abscessus recurrence at a median of 2 months post-LTx. Two recurrences were surgical site infections, and 2 were pulmonary infections. ConclusionM abscessus infection is difficult to treat as tolerance to medications used is poor. M abscessus pneumonia is associated with worse survival post-LTx. Use of clofazimine is associated with 1-year infection-free survival.

Cross-transmission Is Not the Source of New Mycobacterium abscessus Infections in a Multicenter Cohort of Cystic Fibrosis Patients.

Background Mycobacterium abscessus is an extensively drug–resistant pathogen that causes pulmonary disease, particularly in cystic fibrosis (CF) patients. Identifying direct patient-to-patient transmission of M. abscessus is critically important in directing an infection control policy for the management of risk in CF patients. A variety of clinical labs have used molecular epidemiology to investigate transmission. However, there is still conflicting evidence as to how M. abscessus is acquired and whether cross-transmission occurs. Recently, labs have applied whole-genome sequencing (WGS) to investigate this further and, in this study, we investigated whether WGS can reliably identify cross-transmission in M. abscessus.MethodsWe retrospectively sequenced the whole genomes of 145 M. abscessus isolates from 62 patients, seen at 4 hospitals in 2 countries over 16 years.ResultsWe have shown that a comparison of a fixed number of core single nucleotide variants alone cannot be used to infer cross-transmission in M. abscessus but does provide enough information to replace multiple existing molecular assays. We detected 1 episode of possible direct patient-to-patient transmission in a sibling pair. We found that patients acquired unique M. abscessus strains even after spending considerable time on the same wards with other M. abscessus–positive patients.ConclusionsThis novel analysis has demonstrated that the majority of patients in this study have not acquired M. abscessus through direct patient-to-patient transmission or a common reservoir. Tracking transmission using WGS will only realize its full potential with proper environmental screening, as well as patient sampling.

Detection and molecular characterisation of amikacin-resistant Mycobacterium abscessus isolated from patients with pulmonary disease.

The aim of this study was to investigate the molecular mechanisms conferring amikacin (AMK) resistance in Mycobacterium abscessus clinical isolates. A total of 194M. abscessus clinical isolates were collected from patients with pulmonary disease during the period 2012-2017. AMK susceptibility was determined by the broth microdilution method. Whole-genome data were used for identification of mutations in resistance-associated genes. Quantitative reverse transcription PCR (qRT-PCR) was performed to measure the gene transcriptional level. AMK showed high in vitro killing activity against M. abscessus, with an MIC50 of 8mg/L and an MIC90 of 16mg/L. Five isolates (2.6%) were resistant to AMK (MIC>1024mg/L), of which four (80.0%) harboured a resistance-associated rrs mutation A1408G. qRT-PCR analysis showed that most of the AMK-resistant isolates (4/5; 80.0%) overexpressed the transcriptional regulator gene whiB7 and the multidrug-efflux transporter gene tap. However, overexpression of the aminoglycoside-modifying enzyme gene eis2 was only observed in one (20.0%) AMK-resistant isolate. The AMK resistance rate in M. abscessus clinical isolates in this study was low (2.6%). The A1408G mutation in rrs and overexpression of WhiB7 and Tap were the predominant mechanisms of AMK resistance in M. abscessus.

Cutaneous nontuberculous mycobacteria infections: A retrospective case series of 78 patients from the Texas Gulf Coast region

The incidence of cutaneous nontuberculous mycobacteria (NTM) infections is increasing. These infections are a diagnostic and therapeutic challenge. We investigated the clinical features, diagnosis, and management of cutaneous NTM infections. A retrospective case series studied 78 patients from a Gulf Coast tertiary referral center diagnosed with cutaneous NTM infection by culture or stain of a skin biopsy specimen. A history of trauma, procedure, or environmental exposure was common. The mean time between the initial evaluation and diagnosis was 12weeks. Only 15% of acid-fast bacillus-positive cultures had a positive acid-fast bacillus smear, and only 43% of those accompanied by skin biopsy specimen had a positive Fite stain. Immunosuppressed patients were more likely to have a positive Fite stain. Treatment included surgery and multiple antibiotics. Immunosuppressed patients and Mycobacterium abscessus group infections were more likely to have persistent disease. M chelonae and M abscessus isolates were indistinguishable and therefore were reported together. Five cases were not confirmed by culture. Even with clinical suspicion, the diagnosis of NTM infection can be difficult. Results of acid-fast bacillus smears and special stains are frequently negative. Antibiotic resistance is common. Multidrug treatment is often required, and surgical therapy may be needed.

Amikacin exposure and susceptibility of macrolide-resistant Mycobacterium abscessus.

Mycobacterium abscessus is associated with antibiotic resistance and poor treatment outcomes. We described within-patient changes in M. abscessus resistance to clarithromycin and amikacin.Patients with amikacin exposure and a >50-month interval between M. abscessus isolates were identified. Antimicrobial susceptibility testing was performed on the first and last isolates by broth microdilution, and genetic markers of resistance were identified.16 patients were identified with a median amikacin exposure of 2.3 years (range 0.6–8.6 years). 15 patients also received macrolides (median 7.2 years, range 1.3–10.7 years). All initial isolates were resistant to clarithromycin (minimum inhibitory concentration (MIC) ≥8 µg·mL−1). Two patients had later susceptible isolates, which were of a different subspecies (M. abscessus subsp. massiliense) than the initial isolates (M. abscessus subsp. abscessus). All initial isolates were susceptible or intermediately resistant to amikacin, and only one patient had a resistant final isolate (MIC >64 µg·mL−1), accompanied by an A→G mutation at position 1408 of the 16S ribosomal RNA. Forced expiratory volume in 1 s decreased significantly over the study period, while smear quantity and the proportions of patients with elevated C-reactive protein or cavitary lesions all increased significantly.Despite prolonged, mostly inhaled amikacin exposure, development of amikacin resistance was uncommon in this patient population; however, disease progression continued.

In Vitro Synergism of Rifabutin with Clarithromycin, Imipenem, and Tigecycline against the Mycobacterium abscessus Complex.

Infections caused by the difficult-to-treat bacterium Mycobacterium abscessus are increasing in frequency. Rifabutin, in contrast to rifampin, appears to be active in vitro against M. abscessus, especially against clarithromycin-resistant strains. However, explorations for potential synergy between rifabutin and available antimicrobials are currently limited. In vitro synergism between rifabutin and 10 antimicrobials was evaluated in 31 mycobacterial strains by the checkerboard method. The fractional inhibitory concentration index (FICI) was calculated for each rifabutin-based combination. The colony morphology was recorded. Molecular methods for determination of the M. abscessus subspecies and analysis of macrolide resistance were performed by sequencing of the secA1, rpoB, hsp65, erm(41), and rrl genes. Rifabutin yielded an MIC50 of 16 mg/liter (range, 2 to 32 mg/liter) against 26 clinical M. abscessus isolates (comprising 13 M. abscessus subsp. abscessus and 13 M. abscessus subsp. massiliense isolates) and 5 reference strains, including M. abscessus subsp. abscessus ATCC 19977, M. abscessus subsp. bolletii BCRC 16915, M. abscessus subsp. massiliense BCRC 16916, M. chelonae ATCC 35752, and M. peregrinum ATCC 700686. Significant synergism, classified by an FICI of ≤0.5, was demonstrated for the combinations of rifabutin and imipenem in 100% of M. abscessus subsp. abscessus and 69% of M. abscessus subsp. massiliense isolates, and significant synergism for rifabutin and tigecycline was demonstrated in 77% of M. abscessus subsp. abscessus and 69% of M. abscessus subsp. massiliense isolates. Among the 6 clarithromycin-resistant (MICs ≥ 8 mg/liter) M. abscessus subsp. abscessus isolates, the combination of rifabutin and clarithromycin was 100% synergistic. Rifabutin showed promising in vitro synergism with first-line anti-M. abscessus agents, especially for macrolide-resistant M. abscessus subsp. abscessus isolates.

Investigating transmission of Mycobacterium abscessus amongst children in an Australian cystic fibrosis centre

BackgroundMycobacterium abscessus is an emerging pathogen in cystic fibrosis (CF) lung disease. Hospital transmission of M. abscessus has been described. This paper details the investigation into possible cross-transmission of M. abscessus locally at our paediatric hospital CF centre, and the subsequent infection control response. MethodsWhole genome sequencing (WGS) of M. abscessus respiratory isolates with epidemiological linkage analysis using hospital electronic medical records. Results6.7% (22/328) of CF patients had M. abscessus isolated from respiratory specimens.WGS revealed a cluster of three patients with genomically related isolates that differed by <7 single nucleotide polymorphisms (SNPs), suggesting a shared recent ancestor and probable cross-transmission.Epidemiological investigation revealed multiple potential crossovers between patients with genomically similar M. abscessus isolates. ConclusionsCross-infection of NTM occurs in CF hospital patients. Hospital infection control practices should be upgraded to reflect this. Consensus is needed between centres.