Rapidly Growing Mycobacteria Species Research Articles

Characteristics and management of periprosthetic joint infections caused by rapidly growing mycobacteria: a retrospective study and a review of the literature.

Background: Periprosthetic joint infection (PJI) following total joint arthroplasty is a serious complication associated with significant morbidity. While Gram-positive cocci are the predominant causative organisms, PJIs caused by rapidly growing mycobacteria (RGM) have been reported, albeit at a lower frequency. This study aimed to investigate the characteristics and management of PJI caused by RGM. Methods: A retrospective review was conducted using an institutional PJI database to identify patients diagnosed with PJI due to RGM from January2010 to December2021. Clinical data, including demographics, symptoms, comorbidity information, laboratory parameters, surgical procedures, medical treatment and outcomes, were collected and analyzed. Results: A total of eight patients were identified with PJI caused by RGM during the study period. The median age was 66years old, and most cases occurred in patients with total knee arthroplasty (). The isolated RGM species included Mycobacteriumabscessus (threecases), M.fortuitum (threecases), and one case each of M.immunogenum and M.mageritense. Surgical debridement was performed in all cases, with six patients undergoing two-stage revision and two patients requiring amputation. Combination antimicrobial therapy was administered based on antimicrobial susceptibility testing, and the median duration of treatment was 7.5months. Adverse events related to therapy occurred in 75 % of cases. No relapses were observed during the median follow-up period of 39.6months. Conclusions: PJI caused by RGM is a rare complication of total joint arthroplasty. Surgical debridement and combination antimicrobial therapy are the mainstays of treatment. Although clinical cure rates are high, amputation may be required in severe cases.

Emergence of Inducible Macrolide Resistance in Mycobacterium chelonae Due to Broad-Host-Range Plasmid and Chromosomal Variants of the Novel 23S rRNA Methylase Gene, erm(55).

Macrolides are a mainstay of therapy for infections due to nontuberculous mycobacteria (NTM). Among rapidly growing mycobacteria (RGM), inducible macrolide resistance is associated with four chromosomal 23S rRNA methylase (erm) genes. Beginning in 2018, we detected high-level inducible clarithromycin resistance (MICs of ≥16μg/mL) in clinical isolates of Mycobacterium chelonae, an RGM species not previously known to contain erm genes. Using whole-genome sequencing, we identified a novel plasmid-mediated erm gene. This gene, designated erm(55)P, exhibits <65% amino acid identity to previously described RGM erm genes. Two additional chromosomal erm(55) alleles, with sequence identities of 81% to 86% to erm(55)P, were also identified and designated erm(55)C and erm(55)T. The erm(55)T is part of a transposon. The erm(55)P allele variant is located on a putative 137-kb conjugative plasmid, pMchErm55. Evaluation of 133 consecutive isolates from 2020 to 2022 revealed 5 (3.8%) with erm(55). The erm(55)P gene was also identified in public data sets of two emerging pathogenic pigmented RGM species: Mycobacterium iranicum and Mycobacterium obuense, dating back to 2008. In both species, the gene appeared to be present on plasmids homologous to pMchErm55. Plasmid-mediated macrolide resistance, not described previously for any NTM species, appears to have spread to multiple RGM species. This has important implications for antimicrobial susceptibility guidelines and treatment of RGM infections. Further spread could present serious consequences for treatment of other macrolide-susceptible RGM. Additional studies are needed to determine the transmissibility of pMchErm55 and the distribution of erm(55) among other RGM species.

Development of a nucleic acid chromatography assay for the detection of commonly isolated rapidly growing mycobacteria.

Introduction. Non-tuberculosis mycobacterium infections are increasing worldwide, including those caused by rapidly growing mycobacteria (RGM).Gap Statement. The identification of the aetiological agent in the context of infections is essential for the adoption of an adequate therapeutic approach. However, the methods for the rapid distinction of different RGM species are less than optimal.Aim. To develop a nucleic acid chromatography kit to identify clinically common RGM.Methodology. We tried to develop a nucleic acid chromatography kit designed to detect four RGM species (including three subspecies) i.e. Mycobacterium abscessus subsp. abscessus, Mycobacterium abscessus subsp. bolletii (detected as M. abscessus/bolletii) Mycobacterium abscessus subsp. massiliense, Mycobacterium fortuitum, Mycobacterium chelonae and Mycobacterium peregrinum. The amplified target genes for each species/subspecies using multiplex PCR were analysed using a nucleic acid chromatography assay.Results. Among the 159 mycobacterial type strains and 70 RGM clinical isolates tested, the developed assay correctly identified all relevant RGM without any cross-reactivity or false-negatives. The limits of detection for each species were approximately 0.2 pg µl-1.Conclusion. The rapid and simple nucleic acid chromatography method developed here, which does not involve heat denaturation, may contribute to the rapid identification and treatment of RGM infections.

Comparison of the in vitro activity of linezolid, tedizolid, sutezolid, and delpazolid against rapidly growing mycobacteria isolated in Beijing, China

BackgroundThe natural resistance of rapidly growing mycobacteria (RGM) to multiple antibiotics renders the treatment of the infections caused less successful. The objective of this study was to evaluate the in vitro susceptibilities of four oxazolidinones against different RGM species. MethodsThe microplate alamarBlue assay was performed to identify the minimum inhibitory concentrations (MICs) of four oxazolidinones – delpazolid, sutezolid, tedizolid, and linezolid – for 32 reference strains and 115 clinical strains of different RGM species. The MIC breakpoint concentration was defined as 16 μg/ml for linezolid. Next, the gene fragments associated with oxazolidinone resistance were amplified and sequenced, and mutations were defined in contrast with the sequences of the reference strains. ResultsTedizolid showed the strongest inhibitory activity against the Mycobacterium abscessus isolates. Delpazolid exhibited better antimicrobial activity against the Mycobacterium fortuitum isolates when compared to linezolid, with 4-fold lower MIC values. The protein alignment and structure-based analysis showed that there might be no correlation between oxazolidinone resistance and mutations in the rplC, rplD, and 23S rRNA genes in the tested RGM. ConclusionsTedizolid had the strongest inhibitory activity against M. abscessus in vitro, while delpazolid presented the best inhibitory activity against M. fortuitum. This provides important insights into the potential clinical application of oxazolidinones to treat RGM infections.

Nationwide surveillance of antimicrobial susceptibility of 509 rapidly growing mycobacteria strains isolated from clinical specimens in Japan

This study aimed to identify effective treatments against rapidly growing mycobacteria (RGM) infections by investigating the minimum inhibitory concentrations (MIC) of 24 antimicrobial agents and their molecular mechanisms of resistance. In total, 509 clinical RGM isolates were identified by analyzing the sequences of three housekeeping genes (hsp65, rpoB, and sodA), and their susceptibilities to 24 antimicrobial agents were tested. We also performed sequencing analysis of antimicrobial resistance genes (rrl, rrs, gyrA, and gyrB). To identify Mycobacteroides abscessus group subspecies, we performed PCR-based typing and determined the sequevar of erm(41). We identified 15 RGM species, most of which were susceptible to amikacin and linezolid. Among these species, arbekacin and sitafloxacin had the lowest MIC among the same class of antimicrobials. The MIC of rifabutin for M. abscessus subsp. abscessus (MAB) was lower than that for M. abscessus subsp. massiliense (MMA). The proportion of MAB isolates with MIC ≤ 2 mg/L for rifabutin was significantly higher than that of MMA [MAB: 50/178 (28.1%) vs. MMA: 23/130 (17.7%); p = 0.041]. In summary, our study revealed the antimicrobial susceptibility profile of 15 RGM species isolated in Japan and indicated that arbekacin, sitafloxacin, and rifabutin may be possible therapeutic options for RGM infections.

Geographical distribution and regional differences in 532 clinical isolates of rapidly growing mycobacterial species in Japan

Infectious diseases caused by nontuberculous mycobacteria (NTM) are increasingly becoming a major global problem. Additionally, Mycobacteroides abscessus subsp. abscessus (MAB) infections are refractory to macrolides. This study was conducted to investigate the epidemiology of rapidly growing mycobacteria (RGM) species isolated from clinical specimens in Japan and assess differences in the regional distribution of lower respiratory specimens (LRS)- and non-lower respiratory specimens (NLRS)-derived species. 532 strains (427 LRS, 92 NLRS and 15 unknown specimens) were isolated in nine areas of Japan. We collected 418 specimens from Bio Medical Laboratories (BML), Inc., and 114 specimens from 45 hospitals in Japan. Their epidemiological differences were examined according to the specimen type, region, and climate. Fifteen species were identified. The proportion of M. abscessus group (MAG) strains was significantly lower in NLRS than in LRS (35.9% vs. 68.4%). The proportion of MAG strains was higher in northern Japan than in other regions (83.7% vs. 60.5%). Variations in strain abundance among RGM species was evident in regions with a mean annual temperature below 15 °C. We conclude that the proportions of MAG strains differed between NLRS and LRS in Japan. In addition, the mean annual temperature likely influenced the distribution of RGM species.

Sulfonamides complexed with metals as mycobacterial biofilms inhibitors

Rapidly growing mycobacteria (RGM) are found in non-sterile water and often associated with severe post-surgical infections and affect immunocompromised patients. In addition, RGM can prevent the host's immune response and have the ability to adhere to and form biofilms on biological and synthetic substrates, making pharmacological treatment difficult because conventional antimicrobials are ineffective against biofilms. Thus, there is an urgent need for new antimicrobial compounds that can overcome these problems. In this context, sulfonamides complexed with Au, Cd, Ag, Cu, and Hg have shown excellent activity against various microorganisms. Considering the importance of combating RGM-associated infections, this study aimed to evaluate the activity of sulfonamide metal complexes against RGM biofilm. The sulfonamides were tested individually for their ability to inhibit mycobacterial formation and destroy the preformed biofilm of standard RGM strains, such as Mycobacterium abscessus, M. fortuitum, and M. massiliense. All sulfonamides complexed with metals could reduce, at subinhibitory concentrations, the adhesion and biofilm formation of three RGM species in polystyrene tubes. It is plausible that the anti-biofilm capacity of the compounds is due to the inhibition of c-di-GMP synthesis, which is an important signal for RGM biofilm formation. Hence, the impacts and scientific contribution of this study are based on the discovery of a potential new therapeutic option against RGM-associated biofilm infections. Sulfonamides complexed with metals have proven to be a useful and promising tool to reduce microbial adhesion on inert surfaces, stimulating the improvement of methodologies to insert compounds as new antibacterial and coating agents for medical and hospital materials.

Profiles of Extrapulmonary Nontuberculous Mycobacteria Infections and Predictors for Species: A Multicenter Retrospective Study.

Extrapulmonary nontuberculous mycobacteria (NTM) infections contribute to morbidity and mortality worldwide. However, studies about extrapulmonary NTM infections have been limited. Therefore, we aim to describe the diversity of extrapulmonary NTM infections and identify predictors for species. Information regarding diversity of NTM isolates, antimicrobial susceptibility testing, treatment regimens, and outcomes were collected from four tertiary care centers in South Korea. Comparisons were made between patients with rapidly growing mycobacteria (RGM) and slowly growing mycobacteria (SGM) infections. A total of 117 patients (46 males vs. 71 females) were included. Skin and soft tissue infections (SSTIs) predominated (34.2%), followed by bone and joint infections (28.2%). In SSTIs, RGM species were predominantly identified (26/28, 92.9%), whereas SGM species were mainly identified in bone and joint infections (18/26, 69.2%), and the difference of isolated sites was verified by a post hoc test (p < 0.001). Multivariable regression analysis revealed that male sex (vs. female sex; OR 5.30, CI 1.35–24.26, p = 0.020) and bone and joint infections (vs. SSTIs; OR 18.10, CI 3.28–157.07, p = 0.002) were predictors of SGM infections, whereas the opposite was observed for RGM infections. Bone and joint infections and male sex were predictors for SGM infections, whereas SSTIs and female sex were predictors for RGM infections.

Exploring how structural changes to new Licarin A derivatives effects their bioactive properties against rapid growing mycobacteria and biofilm formation

Several species of rapidly growing mycobacteria (RGM) have been associated with biofilms in areas such as biomedical devices, water distribution systems, cosmetic surgery, and catheter-related blood infections. Biofilms which exhibit antimicrobial resistance such as those formed by the genus Mycobacterium pose a significant risk to health and are of particular interest to researchers. Licarin A (a neolignan found in numerous plant species e.g. nutmeg) has been reported to show a wide range of biological actions including anti-inflammatory, antioxidant, and antibacterial properties. The aim of this study was to prepare a set of Licarin A derivatives and investigate the impact of specific structural changes on its antimycobacterial ability, and its effect on the biofilm formation of RGM species. Initially, the phenolic sub-unit and alkenyl side chain of Licarin A were modified to create derivatives with a higher partition coefficient; as the activity of a compound against mycobacteria seems to be strongly influenced by its hydrophobicity. Further, polar groups were inserted into the side chain to change the hydrophilic-lipophilic profile of the molecules. Results showed variability in the susceptibility profile of mycobacteria against the Licarin A derivatives under analysis. A number of the derivatives showed significant inhibitory activity of planktonic growth of the three strains of mycobacteria used, with even lower MIC values than those observed with reference drugs and Licarin A itself. Cytotoxicity assays showed they also have low toxicity, confirming that structural modifications to the Licarin A have made improvements to its antimycobacterial properties.

1358. A Novel Rapidly Growing Mycobacteria (RGM) Species Causing Soft Tissue and Orthopedic Hardware Infection After Trauma

BackgroundThe widespread use of molecular techniques has resulted in increasing numbers of newly characterized rapidly growing mycobacteria (RGM). Many RGM cause soft tissue and orthopedic hardware infection, particularly after trauma. RGM species identification remains challenging with few genetic differences between species.MethodsWe describe a case involving RGM. We report results of matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry (Bruker Biotyper), sequencing of rpoB, erm(39), and 16S rRNA genes, and antibiotic susceptibility testing (AST). We review previous reports describing similar RGM infections.ResultsA 58-year-old male sustained multiple fractures and right thigh compartment syndrome after a motorcycle accident. He underwent fasciotomy and multi-stage surgical fixations. 3 months later, he had wound dehiscence, purulence and multiple fluid collections of his right leg and knee requiring surgical drainage and removal of orthopedic hardware. After 4 days, acid-fast bacilli grew on routine bacterial culture media. MALDI-TOF identified the isolate as Mycobacterium mageritense. In contrast, sequencing of 16S rRNA (100% identity) and erm(39) (> 99% identity) identified the isolate as Mycobacterium houstonense; erm(39) only had 80% similarity with Mycobacterium fortuitum. Sequencing of rpoB showed a 19 bp difference with the M. houstonense type strain, and showed similarity to M. fortuitum (97.64%) than M. houstonense (97.45%). AST demonstrated resistance to clarithromycin only. After initial treatment with imipenem, ciprofloxacin, and doxycycline, definite therapy with ciprofloxacin and doxycycline was successful. In the literature, we found one case each of M. mageritense and M. houstonense infection after trauma.ConclusionThis case highlights the importance of RGM other than M. fortuitum as a cause of soft tissue and orthopedic hardware infections, and illustrates the difficulty of identifying them to the species level. Sequencing of erm(39) and 16S rRNA gene identified the isolate as M. houstonense, but the larger difference (>2.5%) in rpoB sequence suggests a novel species. Further characterization is underway. Efforts to determine RGM species and antibiotic susceptibility give important insight into diagnosis and management.Disclosures All authors: No reported disclosures.

Rifamycin derivatives active against pathogenic rapidly-growing mycobacteria.

Infections due to rapidly growing mycobacteria (RGM), and in particular the RGM species Mycobacterium abscessus (Mab), are very difficult to treat and reports on novel therapeutic options are scarce. A hallmark of all pathogenic RGM species is their resistance to the four first-line drugs used to treat infections with Mycobacterium tuberculosis including rifampicin. This study demonstrates that modification of the rifampicin scaffold can restore rifampicin activity against the three most commonly isolated pathogenic RGM species including Mab. We also note that the structure-activity relationship for Mab is different as compared to the non-pathogenic RGM species Mycobacterium smegmatis.

Antimicrobial susceptibility testing of rapidly growing mycobacteria isolated in Japan

BackgroundDifficult-to-treat infections caused by rapidly growing mycobacteria (RGM) are increasingly observed in clinical settings. However, studies on antimicrobial susceptibilities and effective treatments against RGM in Japan are limited.MethodsWe conducted susceptibility testing of potential antimicrobial agents, including tigecycline and tebipenem, against RGM. Clinical RGM isolates were collected from a university hospital in Japan between December 2010 and August 2013. They were identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and the sequencing of 16S rRNA, rpoB, and hsp65 genes. The samples were utilized for susceptibility testing using 16 antimicrobials, with frozen broth microdilution panels.ResultsForty-two isolates were obtained: 13, Mycobacterium abscessus complex; 12, Mycobacterium chelonae; 9, Mycobacterium fortuitum; and 8, M. fortuitum group species other than M. fortuitum. Different antimicrobial susceptibility patterns were observed between RGM species. Clarithromycin-susceptible strain rates were determined to be 0, 62, and 100% for M. fortuitum, M. abscessus complex, and M. chelonae, respectively. M. abscessus complex (100%) and >80% M. chelonae isolates were non-susceptible, while 100% M. fortuitum group isolates were susceptible to moxifloxacin. Linezolid showed good activity against 77% M. abscessus complex, 89% M. fortuitum, and 100% M. chelonae isolates. Regardless of species, all tested isolates were inhibited by tigecycline at very low minimal inhibitory concentrations (MICs) of ≤0.5 μg/mL. MICs of tebipenem, an oral carbapenem, were ≤4 μg/mL against all M. fortuitum group isolates.ConclusionsOur study demonstrates the importance of correct identification and antimicrobial susceptibility testing, including the testing of potential new agents, in the management of RGM infections.

Multilocus enzyme electrophoresis analysis of rapidly-growing mycobacteria: an alternative tool for identification and typing.

Rapidly growing mycobacteria (RGM) have emerged as important pathogens in clinical settings, associated with esthetic procedures and postsurgical infections, pulmonary infections among cystic fibrosis patients, and other structural pulmonary diseases. Microorganisms belonging to Mycobacterium abscessus-Mycobacterium chelonae and to Mycobacterium fortuitum groups have frequently been associated with outbreaks and various epidemics. In the present study, RGM strains were characterized in order to investigate molecular markers based on proteomic analysis. Multilocus enzyme electrophoresis (MLEE) was used for species identification and clonal analysis of RGM recovered from postsurgical wound infections during an epidemic. The study included 30M. abscessus subsp. bolletii clinical isolates, most belonging to the BRA100 clone (epidemic in Rio de Janeiro city), as well as 16 RGM ATCC reference strains. Molecular typing allowed the detection of diversity in the studied population and revealed species-specific isoenzymatic patterns. Additionally, the clonal relationship among M. abscessus subsp. bolletii outbreak isolates, as examined using MLEE, was markedly consistent. Isoenzymatic characterization was found to be a useful molecular tool to identify RGM species and to determine the relatedness among closely related M. abscessus subsp. bolletii isolates. This may be considered a powerful approach for epidemiological studies on RGM.

86 Molecular typing of rapidly growing mycobacteria (RGM) in patients with cystic fibrosis (CF)

Objectives To perform molecular typing of clinical strains of RGM isolated from the lower respiratory tract of CF patients with persistent, transient and intermittent infections. Secondary, to assess whether chronic infections are sustained by the same bacterial species, over time. Methods Twenty-three patients, out of the 793 followed at the Regional Reference Centre for Cystic Fibrosis of Milan, have a persistent RGM infection, and 19 show an intermittent infection. From October 2013 to October 2014, 65 strains were isolated and typed by gene sequencing of the rpo B gene. The gene sequences obtained were compared to those already present in the GenBank database to discriminate subspecies of RGM. Results Molecular typing of 46 strains (at two different follow-up times: T1, T2), isolated from 23 patients with chronic RGM colonization, reveals that chronic infection are sustained, in 100% of cases, by MAC (61% M. abscessus sensu stricto, 26% M. bolletii and 13% M. massiliense ), and species identified at T1 is the same identified at T2. In 19 patients, the intermittent infection is sustained by different species of RGM: 37% M. chelonae, 26% M. abscessus sensu stricto, 26% M. bolletii, 5.5% M. fortuitum and 5.5% M. massiliense. Conclusion The chronic infections are sustained by MAC, with a higher prevalence of M. abscessus sensu stricto, and that species acquired at T1 persists over time. Intermittent infections are sustained by M. chelonae, M. fortuitum and MAC. Further correlation studies between the clinical course of the pulmonary disease and the presence of MAC different subspecies are recommended in order to create appropriate therapeutic schemes.

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).

Rapidly growing mycobacteria among pediatric hematopoietic cell transplant patients traced to the hospital water supply.

Rapidly growing mycobacteria (RGM) have a predilection for those with immunocompromised states. We report increased isolation of RGM among pediatric hematopoietic cell transplant patients that was traced to the hospital water supply. Cases of RGM-positive patients were differentiated based on whether they were community-acquired or nosocomial, colonized or infected based on predefined criteria. Medical records of all RGM-positive patients were reviewed and data extracted. Infection control outbreak measures were instituted and an environmental investigation was conducted. Between July 2011 and April 2012, 16 RGM isolates were identified among 15 hematopoietic cell transplant patients, compared with none in the preceding year. After environmental samples were initially grown on media for heterotrophic counts and further speciated, RGM species were identified in the hospital water supply. This outbreak of RGM was traced to an environmental source and was successfully controlled through institution of infection control measures.

Improved identification of rapidly growing mycobacteria by a 16S-23S internal transcribed spacer region PCR and capillary gel electrophoresis.

The identification of rapidly growing mycobacteria (RGM) remains problematic because of evolving taxonomy, limitations of current phenotypic methods and absence of a universal gene target for reliable speciation. This study evaluated a novel method of identification of RGM by amplification of the mycobacterial 16S–23S rRNA internal transcribed spacer (ITS) followed by resolution of amplified fragments by capillary gel electrophoresis (CGE). Nineteen American Type Culture Collection (ATCC) Mycobacterium strains and 178 clinical isolates of RGM (12 species) were studied. All RGM ATCC strains generated unique electropherograms with no overlap with slowly growing mycobacteria species, including M. tuberculosis. A total of 47 electropherograms for the 178 clinical isolates were observed allowing the speciation of 175/178 (98.3%) isolates, including the differentiation of the closely related species, M. massiliense (M. abscessus subspecies bolletii) and M. abscessus (M. abscessus sensu stricto). ITS fragment size ranged from 332 to 534 bp and 33.7% of clinical isolates generated electropherograms with two distinct peaks, while the remainder where characterized with a single peak. Unique peaks (fragment lengths) were identified for 11/12 (92%) RGM species with only M. moriokaense having an indistinguishable electropherogram from a rarely encountered CGE subtype of M. fortuitum. We conclude that amplification of the 16S–23S ITS gene region followed by resolution of fragments by CGE is a simple, rapid, accurate and reproducible method for species identification and characterization of the RGM.

Diversity, Community Composition, and Dynamics of Nonpigmented and Late-Pigmenting Rapidly Growing Mycobacteria in an Urban Tap Water Production and Distribution System

Nonpigmented and late-pigmenting rapidly growing mycobacteria (RGM) have been reported to commonly colonize water production and distribution systems. However, there is little information about the nature and distribution of RGM species within the different parts of such complex networks or about their clustering into specific RGM species communities. We conducted a large-scale survey between 2007 and 2009 in the Parisian urban tap water production and distribution system. We analyzed 1,418 water samples from 36 sites, covering all production units, water storage tanks, and distribution units; RGM isolates were identified by using rpoB gene sequencing. We detected 18 RGM species and putative new species, with most isolates being Mycobacterium chelonae and Mycobacterium llatzerense. Using hierarchical clustering and principal-component analysis, we found that RGM were organized into various communities correlating with water origin (groundwater or surface water) and location within the distribution network. Water treatment plants were more specifically associated with species of the Mycobacterium septicum group. On average, M. chelonae dominated network sites fed by surface water, and M. llatzerense dominated those fed by groundwater. Overall, the M. chelonae prevalence index increased along the distribution network and was associated with a correlative decrease in the prevalence index of M. llatzerense, suggesting competitive or niche exclusion between these two dominant species. Our data describe the great diversity and complexity of RGM species living in the interconnected environments that constitute the water production and distribution system of a large city and highlight the prevalence index of the potentially pathogenic species M. chelonae in the distribution network.

Synergistic activities of tigecycline with clarithromycin or amikacin against rapidly growing mycobacteria in Taiwan

The occurrence of diseases caused by rapidly growing mycobacteria (RGM) is increasing in Taiwan. In this study, the in vitro antimicrobial activities of tigecycline, minocycline, tetracycline and doxycycline were evaluated against 160 clinical RGM isolates, including 34 Mycobacterium abscessus sensu stricto (s.s.), 44 Mycobacterium massiliense, 1 Mycobacterium bolletii, 58 Mycobacterium fortuitum and 23 Mycobacterium chelonae. Clarithromycin and amikacin were tested alone as well as for synergistic effect with tigecycline. Both amikacin and tigecycline showed excellent activities against the RGM. More than 85% of each of the five RGM species isolates showed susceptibility to the two drugs. The MIC50 and MIC90 values (drug concentrations at which 50% and 90%, respectively, of the tested isolates did not show any visible growth) of amikacin were 1–4mg/L and 2–8mg/L, respectively, whilst those of tigecycline were 0.125–1mg/L and 0.5–2.0mg/L. Clarithromycin had only moderate activity, with ≥42.9% but ≤87.5% of each RGM species isolates showing susceptibility. The other three drugs had limited or no antimicrobial activity, with <40% of each RGM species isolates showing susceptibility. Combined with clarithromycin, tigecycline had synergistic activity against 92.9%, 68.8%, 100%, 35.7% and 46.2% of M. abscessus s.s., M. massiliense, M. bolletii, M. fortuitum and M. chelonae isolates, respectively. However, tigecycline combined with amikacin had synergistic activity against <25% but antagonistic activity against >18% of each RGM species. Thus, tigecycline alone may be an alternative for treating RGM diseases in patients who are intolerant to cefoxitin, imipenem or amikacin. However, it should be used with caution or not used in combination with amikacin for RGM diseases.

Clinical and laboratory aspects of the diagnosis and management of cutaneous and subcutaneous infections caused by rapidly growing mycobacteria

Rapidly growing mycobacteria (RGM) are known to cause pulmonary, extra-pulmonary, systemic/disseminated, and cutaneous and subcutaneous infections. The erroneous detection of RGM that is based solely on microscopy, solid and liquid cultures, Bactec systems, and species-specific polymerase chain reaction (PCR) may produce misleading results. Thus, inappropriate therapeutic measures may be used in dermatologic settings, leading to increased numbers of skin deformity cases or recurrent infections. Molecular tools such as the sequence analyses of 16S rRNA, rpoB and hsp65 or PCR restriction enzyme analyses, and the alternate gene sequencing of the superoxide dismutase (SOD) gene, dnaJ, the 16S-23S rRNA internal transcribed spacers (ITS), secA, recA1, dnaK, and the 32-kDa protein gene have shown promising results in the detection of RGM species. PCR restriction enzyme analyses (PRA) work better than conventional methods at identifying species that are closely related. Recently introduced molecular tools such as matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), pyrosequencing, DNA chip technology, and Beacon probes-combined PCR probes have shown comparable results in the detection of various species of RGM. Closely related RGM species (e.g., Mycobacterium fortuitum, M. chelonae, and M. abscessus) must be clearly differentiated using accurate molecular techniques because their therapeutic responses are species-specific. Hence, this paper reviews the following aspects of RGM: (i) its sources, predisposing factors, clinical manifestations, and concomitant fungal infections; (ii) the risks of misdiagnoses in the management of RGM infections in dermatological settings; (iii) the diagnoses and outcomes of treatment responses in common and uncommon infections in immunocompromised and immunocompetent patients; (iv) conventional versus current molecular methods for the detection of RGM; (v) the basic principles of a promising MALDI-TOF MS, sampling protocol for cutaneous or subcutaneous lesions and its potential for the precise differentiation of M. fortuitum, M. chelonae, and M. abscessus; and (vi) improvements in RGM infection management as described in the recent 2011 Clinical and Laboratory Standards Institute (CLSI) guidelines, including interpretation criteria of molecular methods and antimicrobial drug panels and their break points [minimum inhibitory concentrations (MICs)], which have been highlighted for the initiation of antimicrobial therapy.