Mycobacterium abscessus biofilms produce an extracellular matrix and have a distinct mycolic acid profile

Exposure of Mycobacteriodes abscessus clones to mucin affects bacterial phenotype

In the past 20 years infections caused by Mycobacterioides abscessus have become increasingly common in patients with chronic lung conditions. The microorganisms are also resistant to a number of antibiotic classes, making treatment challenging. To begin understanding how the bacterium adapts to the lung environment, pure colonies of M. abscessus strain 19,977 were grown in 7H9 broth with or without mucin over 30-day intervals for 6 months and analyzed for colony morphology, 7 day-growth curves, the ability to form biofilms after 14 days, and the susceptibility to antibiotics determined using previous published methods. In presence of mucin by month 3 the non-replicating stage of growth occurred by day 3, compared to earlier months. Similar characteristics were seen in colonies grown in absence of mucin by month 5. During biofilm formation, the amount of protein in the matrix started to decrease at month 3 between day 7 and day 14, with progressive overall biomass decreased in month 6. Mucin exposed clones had less of this decrease between day 7 and day 14 compared to clones naïve to mucin. The number of bacteria in the biofilms were similar in all 6 months in 7H9 medium and 7H9 with mucin. Some of the strains increased the amount of carbohydrates in the biofilm matrix overtime while others exported more DNA, the matrix containing large amounts of it. The presence of mucin was associated with increased antibiotic resistance to amikacin, 5-fold increase of MIC in 7 out of 8 strains evaluated. Some of the colonies transitioned from smooth to rough morphotypes, again indicating the influence of different environments. Overall, M. abscessus phenotype changes overtime influenced by mucin, an important component in the host lung environment. Bacteria clones arrested growth, produced different biofilms compositions, increased the resistance to antibiotics, and some changed the cell wall surfaces. These observations have direct implications in virulence and the response of the pathogen to treatment.

Heme alters biofilm formation in Mycobacterium abscessus

Mycobacterium abscessus (Mabs) is commonly found in the cystic fibrosis (CF) lung. During infection, Mabs can form biofilms in the lung which reduce both the ability of the immune response to clear infection and the effectiveness of antibiotic therapy. In the CF lung, heme and hemoglobin levels are increased and may provide both iron and heme to Mabs cells. In this work, we show that exogenous heme altered Mabs biofilm formation and measured the effects of exogenous heme on protein level and metabolism in Mabs. Our findings suggest that heme impacts iron homeostasis in Mabs and affects other aspects of its metabolism, highlighting the potential role of heme as a critical nutrient for Mabs growth and biofilm formation.IMPORTANCEMycobacterium abscessus (Mabs) is commonly found in the cystic fibrosis (CF) lung, where Mabs can form biofilms that can reduce the efficacy of antibiotics. During infection, the CF lung can have more than 10 times the extracellular heme than that of a healthy lung. We have found that extracellular heme can change the way Mabs cells grow and form biofilms, which may have implications for pathogenesis.

Biofilm formation and polar lipid biosynthesis in Mycobacterium abscessus are inhibited by naphthylmethylpiperazine

Mycobacterium abscessus is a biofilm-forming, non-tuberculous mycobacterium that is highly resistant to antibiotics. Bacterial efflux pumps contribute to biofilm formation, export of biofilm-associated lipids and antibiotic tolerance. The Resistance Nodulation Cell Division (RND) and ATP-Binding Cassette (ABC) families of efflux pumps export lipids to the mycobacterial cell surface. 1-(1-naphthyl methyl)-piperazine (NMP) is a chemosensitizer that causes membrane destabilization and is an inhibitor of RND efflux pumps. The effects of NMP on biofilm formation and lipid metabolism in M. abscessus biofilms have not been investigated. Plumbagin (PLU) is an inhibitor of ABC efflux pumps that has not been studied for its effects on antibiotic tolerance in M. abscessus biofilms. In this study, we report that the efflux pump inhibitors NMP and PLU inhibit biofilm formation by 50% at sub-MIC levels. We show that NMP inhibits the incorporation of the radiolabeled long-chain fatty acid 14C-palmitate into glycopeptidolipids in cell surface lipids of log-phase M. abscessus. NMP also inhibits the utilization of the radiolabel in the biosynthesis of phosphatidylethanolamine in the cell surface and cellular lipids of M. abscessus cells in log-phase and in biofilms. Incorporation of the radiolabel into cardiolipin in the cellular lipids of M. abscessus biofilms was inhibited by NMP. The incorporation of 14C-acetate into cell surface phosphatidylethanolamine in log-phase and biofilm cells was also inhibited by NMP. Triacylglycerol biosynthesis using 14C-palmitate and 14C-acetate in cellular lipids of log-phase and biofilm cells was increased several folds by NMP. Efflux pump activity in M. abscessus cells was inhibited by 97% and 68% by NMP and PLU respectively. NMP and PLU caused 5-fold decreases in the minimum inhibitory concentrations of ciprofloxacin and clarithromycin against M. abscessus. Our results demonstrate that NMP and PLU affect important physiological processes in M. abscessus associated with its pathogenesis.

Mycobacteroides abscessus Outbreak and Mitigation in a Cardiothoracic Transplant Population: The Problem with Tap Water

BACKGROUND

Hospital outbreaks caused by Mycobacteroides abscessus complex are a major cause for concern in vulnerable patients such as the cardiothoracic transplant population.

AIM

To describe the outbreak investigation and mitigation steps undertaken to address an increase in healthcare-associated Mycobacteroides abscessus (M. abscessus) complex cases in an inpatient cardiothoracic transplant population.

METHODS

We extracted clinical characteristics from patients with M. abscessus pre-outbreak (March 2018 - December 2020) and during the outbreak (January 2021 - June 2022) from the electronic medical record. A multidisciplinary team conducted the outbreak investigation and devised a mitigation strategy to implement at our institution.

FINDINGS

The baseline incidence of healthcare-associated M. abscessus was 0.11 cases per 10,000 patient-days; this increased to 0.24 cases per 10,000 patient-days during the outbreak. There were 1/9 (11%) cardiothoracic transplant patients in the pre-outbreak group compared to 7/12 (58%) during the outbreak, and respiratory specimen types compromised 6/9 (67%) of M. abscessus results in the pre-outbreak group compared to 10/12 (83%) during the outbreak. Among the clinical care activities involving water, a variety of water sources were utilized, including filtered and tap water. The incidence of healthcare-associated M. abscessus subsequently decreased to 0.06 cases per 10,000 patient-days after implementing an outbreak mitigation strategy of sterile water precautions.

CONCLUSION

Robust educational efforts from a multidisciplinary team on eliminating exposure to tap water were effective measures to reduce healthcare-associated M. abscessus incidence at our institution. NTM infection surveillance, targeted education, and water mitigation strategies may be beneficial preventative strategies for other lung transplant centres facing similar issues.

Mycobacteroides abscessus ability to interact with the host mucosal cells plays an important role in pathogenesis of the infection

Non-tuberculous mycobacteria (NTM) are opportunistic pathogens ubiquitous in the environment. Mycobacteroides abscessus is a relatively new pathogen associated with underlying lung chronic pathologies, accounting for most of the pulmonary infections linked to the rapidly growing mycobacteria group. This includes chronic obstructive pulmonary disease, bronchiectasis, or cystic fibrosis. Patient outcomes from M. abscessus infections are poor due to complicated treatments and other factors. Intrinsic drug resistance plays an important role. The M. abscessus toolbox of resistance is varied leading to complex strategies for treatment. Mechanisms include waxy cell walls, drug export mechanisms, and acquired resistance. Many studies have also shown the impact of extracellular DNA found in the biofilm matrix during early infection and its possible advantage in pathogenicity. In this review, we discuss the current knowledge of early infection focusing on biofilm formation, an environmental strategy, and which treatments prevent its formation improving current antibiotic treatment outcomes in preliminary studies.

Transition metal homoeostasis is key to metabolism and drug tolerance of Mycobacterium abscessus

Antimicrobial resistance (AMR) is one of the major challenges humans are facing this century. Understanding the mechanisms behind the rise of AMR is therefore crucial to tackling this global threat. The presence of transition metals is one of the growth-limiting factors for both environmental and pathogenic bacteria, and the mechanisms that bacteria use to adapt to and survive under transition metal toxicity resemble those correlated with the rise of AMR. A deeper understanding of transition metal toxicity and its potential as an antimicrobial agent will expand our knowledge of AMR and assist the development of therapeutic strategies. In this study, we investigate the antimicrobial effect of two transition metal ions, namely cobalt (Co2+) and nickel (Ni2+), on the non-tuberculous environmental mycobacterium and the opportunistic human pathogen Mycobacterium abscessus. The minimum inhibitory concentrations of Co2+ and Ni2+ on M. abscessus were first quantified and their impact on the bacterial intracellular metallome was investigated. A multi-omics strategy that combines transcriptomics, bioenergetics, metabolomics, and phenotypic assays was designed to further investigate the mechanisms behind the effects of transition metals. We show that transition metals induced growth defect and changes in transcriptome and carbon metabolism in M. abscessus, while the induction of the glyoxylate shunt and the WhiB7 regulon in response to metal stresses could be the key response that led to higher AMR levels. Meanwhile, transition metal treatment alters the bacterial response to clinically relevant antibiotics and enhances the uptake of clarithromycin into bacterial cells, leading to increased efficacy. This work provides insights into the tolerance mechanisms of M. abscessus to transition metal toxicity and demonstrates the possibility of using transition metals to adjuvant the efficacy of currently using antimicrobials against M. abscessus infections.

Benzenesulfonohydrazide-tethered non-fused and fused heterocycles as potential anti-mycobacterial agents targeting enoyl acyl carrier protein reductase (InhA) with antibiofilm activity

Because resistant variants of the disease are always emerging, tuberculosis is a global issue that affects economies. New antitubercular medications should be developed, and this can be done by inhibiting druggable targets. Enoyl acyl carrier protein (ACP) reductase (InhA) is a crucial enzyme for the survival of Mycobacterium tuberculosis (MTB). In this study, a series of small molecules based on non-fused and fused heterocycles (pyridine, coumarin, quinoline, and indole) tethered with benzenesulfonohydrazide were prepared via an aza-Michael reaction exploiting a one-pot synthesis approach. The synthesized molecules (2-7) were evaluated for their activity against tubercle bacilli. Three analogues showed efficacy against tuberculosis, with compound 7 demonstrating a MIC value as low as 8 μg mL-1. Consequently, compounds 3 and 7 successfully hindered the growth of mycobacteria in human monocyte-derived macrophages (MDMs), demonstrating their ability to penetrate human professional phagocytes. Furthermore, they restricted the ability of mycobacteria to produce biofilms. In addition, the inhibitory effects of compounds 3 and 7 against InhA were assessed. Compound 7 exhibited the best efficacy, with an IC50 value of 0.91 μM. The findings showed that the sulfonamide and methyl ester's carbonyl functionalities were engaged in hydrogen bonding with the essential Ile194 and Tyr158 residues, respectively.

New coumarin linked thiazole derivatives as antimycobacterial agents: Design, synthesis, enoyl acyl carrier protein reductase (InhA) inhibition and molecular modeling

Tuberculosis is a global serious problem that imposes major health, economic and social challenges worldwide. The search for new antitubercular drugs is extremely important which could be achieved via inhibition of different druggable targets. Mycobacterium tuberculosis enoyl acyl carrier protein reductase (InhA) enzyme is essential for the survival of M. tuberculosis. In this investigation, a series of coumarin based thiazole derivatives was synthesized relying on a molecular hybridization approach and was assessed against thewild typeMtb H37Rv and its mutant strain (ΔkatG) via inhibiting InhA enzyme. Among the synthesized derivatives, compounds 2b, 3i and 3j were the most potent against wild type M. tuberculosis with MIC values ranging from 6 to 8 μg/ mL and displayed low cytotoxicity towards mouse fibroblasts at concentrations 8-13 times higher than the MIC values. The three hybrids could also inhibit the growth of ΔkatGmutant strain which is resistant to isoniazid (INH). Compounds 2b and 3j were able to inhibit the growth of mycobacteria inside human macrophages, indicating their ability to penetrate human professional phagocytes. The two derivatives significantly suppress mycobacterial biofilm formation by 10-15 %. The promising target compounds were also assessed for their inhibitory effect against InhA and showed potent effectiveness with IC50 values of 0.737 and 1.494 µM, respectively. Molecular docking studies revealed that the tested compounds occupied the active site of InhA in contact with the NAD+ molecule. The 4-phenylcoumarin aromatic system showed binding interactions within the hydrophobic pocket of the active site. Furthermore, H-bond formation and π -π stacking interactions were also recorded for the promising derivatives.

Mycobacterial biofilms: Understanding the genetic factors playing significant role in pathogenesis, resistance and diagnosis

Even though the genus Mycobacterium is a diverse group consisting of a majority of environmental bacteria known as non-tuberculous mycobacteria (NTM), it also contains some of the deadliest pathogens (Mycobacterium tuberculosis) in history associated with chronic disease called tuberculosis (TB). Formation of biofilm is one of the unique strategies employed by mycobacteria to enhance their ability to survive in hostile conditions. Biofilm formation by Mycobacterium species is an emerging area of research with significant implications for understanding its pathogenesis and treatment of related infections, specifically TB. This review provides an overview of the biofilm-forming abilities of different species of Mycobacterium and the genetic factors influencing biofilm formation with a detailed focus on M. tuberculosis. Biofilm-mediated resistance is a significant challenge as it can limit antibiotic penetration and promote the survival of dormant mycobacterial cells. Key genetic factors promoting biofilm formation have been explored such as the mmpL genes involved in lipid transport and cell wall integrity as well as the groEL gene essential for mature biofilm formation. Additionally, biofilm-mediated antibiotic resistance and pathogenesis highlighting the specific niches, sites of infection along with the possible mechanisms of biofilm dissemination have been discussed. Furthermore, drug targets within mycobacterial biofilm and their role as potential biomarkers in the development of rapid diagnostic tools have been highlighted. The review summarises the current understanding of the complex nature of Mycobacterium biofilm and its clinical implications, paving the way for advancements in the field of disease diagnosis, management and treatment against its multi-drug resistant species.

Mycobacterium abscessus, a complex of three fast-growing subspecies sharing virulence traits with slow-growing mycobacteria

BACKGROUND

Mycobacterium abscessus belongs to the largest group of mycobacteria, the rapid-growing saprophytic mycobacteria, and is one of the most difficult-to-treat opportunistic pathogen. Several features pertain to the high adaptability of M. abscessus to the host. These include the capacity to survive and persist within amoebae, to transition from a smooth to a rough morphotype that occurs during the course of the disease and to express of a wide array of virulence factors.

OBJECTIVES

The main objective of this narrative review consists to report major assets of M. abscessus that contribute to the virulence of these rapid-growing saprophytic mycobacteria. Strikingly, many of these determinants, whether they are from a mycobacterial origin or acquired by horizontal gene transfer, are known virulence factors found in slow-growing and strict pathogens for humans and animals.

SOURCES

In the light of recent published work in the field we attempted to highlight major features characterizing M. abscessus pathogenicity and to explain why this led to the emergence of this mycobacterial species in patients with cystic fibrosis.

CONTENT

M. abscessus genome plasticity, the smooth-to-rough transition, and the expression of a panel of enzymes associated with virulence in other bacteria are key players in M. abscessus virulence. In addition, the very large repertoire of lipid transporters, known as mycobacterial membrane protein large and small (MmpL and MmpS respectively), deeply influences the pathogenicity of M. abscessus, as exemplified here for some of them.

IMPLICATIONS

All these traits largely contribute to make M. abscessus a unique mycobacterium regarding to its pathophysiological processes, ranging from the early colonization steps to the establishment of severe and chronic pulmonary diseases.

Formative evaluation and structural analysis of non-tuberculosis mycobacterial biofilm using material pieces

Non-tuberculosis mycobacteria (NTM) can form biofilms on diverse artificial surfaces. In the present study, we induced NTM biofilm formation on materials used in various medical devices, evaluated the total amount of biofilm, and observed the ultrastructure by scanning electron microscopy.

A laboratory perspective on Mycobacterium abscessus biofilm culture, characterization and drug activity testing

Mycobacterium abscessus is an emerging opportunistic pathogen causing severe pulmonary infections in patients with underlying lung disease and cystic fibrosis in particular. The rising prevalence of M. abscessus infections poses an alarming threat, as the success rates of available treatment options are limited. Central to this challenge is the absence of preclinical in vitro models that accurately mimic in vivo conditions and that can reliably predict treatment outcomes in patients. M. abscessus is notorious for its association with biofilm formation within the lung. Bacteria in biofilms are more recalcitrant to antibiotic treatment compared to planktonic bacteria, which likely contributes to the lack of correlation between preclinical drug activity testing (typically performed on planktonic bacteria) and treatment outcome. In recent years, there has been a growing interest in M. abscessus biofilm research. However, the absence of standardized methods for biofilm culture, biofilm characterization and drug activity testing has led to a wide spectrum of, sometimes inconsistent, findings across various studies. Factors such as strain selection, culture medium, and incubation time hugely impact biofilm development, phenotypical characteristics and antibiotic susceptibility. Additionally, a broad range of techniques are used to study M. abscessus biofilms, including quantification of colony-forming units, crystal violet staining and fluorescence microscopy. Yet, limitations of these techniques and the selected readouts for analysis affect study outcomes. Currently, research on the activity of conventional antibiotics, such as clarithromycin and amikacin, against M. abscessus biofilms yield ambiguous results, underscoring the substantial impact of experimental conditions on drug activity assessment. Beyond traditional drug activity testing, the exploration of novel anti-biofilm compounds and the improvement of in vitro biofilm models are ongoing. In this review, we outline the laboratory models, experimental variables and techniques that are used to study M. abscessus biofilms. We elaborate on the current insights of M. abscessus biofilm characteristics and describe the present understanding of the activity of traditional antibiotics, as well as potential novel compounds, against M. abscessus biofilms. Ultimately, this work contributes to the advancement of fundamental knowledge and practical applications of accurate preclinical M. abscessus models, thereby facilitating progress towards improved therapies for M. abscessus infections.

Anti-biofilm potential of human senescence marker protein 30 against Mycobacterium smegmatis

Human senescence marker protein 30 (huSMP30) has been characterized as a multifaceted protein consisting of various enzymatic and cellular functions. It catalyzes the interconversion of L-gulonate and L-gulono-γ-lactone in the ascorbate biosynthesis pathway. Therefore, we hypothesized that it could be a potential anti-biofilm agent against pathogenic bacteria due to its lactonase activity. In order to corroborate this, the huSMP30 was recombinantly expressed, purified, and analyzed for its ability to inhibit Mycobacterium smegmatis biofilm formation, which showed a concentration-dependent inhibition as compared to the untreated control group. Further, in silico analysis was performed to redesign the huSMP30 with enhanced lactonase activity. Molecular docking analysis of the huSMP30 and lactone substrates facilitated the selection of three single amino acid substitutions (E18H, N154Q, and D204V), which were created using a PCR-based site-directed mutagenesis reaction. These mutant proteins and the wild-type huSMP30 were purified, and the effects on the enzymatic activity and biofilm formation were studied. The mutants E18H and D204V showed non-significant effects on specific lactonase activity, catalytic efficiency, and anti-biofilm property; however, the mutant N154Q showed significant improvement in the specific lactonase activity, catalytic efficiency, and inhibition in the biofilm formation. The protein stability analysis revealed that the wild-type huSMP30 and its designed mutants were stable at 37 °C for up to 4 days. In conclusion, the anti-biofilm property of the huSMP30 has been established, and an engineered version, N154Q, inhibits biofilm formation with greater efficiency. Human SMP30 is a versatile protein with multiple cellular and enzymatic functions, however, its anti-biofilm potential has not been explored. Our work presents the method to produce soluble and active huSMP30 in the E. coli expression system and establishes its role as an anti-biofilm agent against Mycobacterium smegmatis owing to its lactonase activity. Our results provide support for the future advancement of huSMP30 as a potential anti-biofilm agent targeting pathogenic Mycobacterium species.

Silencing essential gene expression in Mycobacterium abscessus during infection

IMPORTANCE

Mycobacterium abscessus represents the most common rapidly growing mycobacterial pathogen in cystic fibrosis and is extremely difficult to eradicate. Essential genes are required for growth, often participate in pathogenesis, and encode valid drug targets for further chemotherapeutic developments. However, assessing the function of essential genes in M. abscessus remains challenging due to the limited spectrum of efficient genetic tools. Herein, we generated a Tet-OFF-based system allowing to knock down the expression of mmpL3, encoding the mycolic acid transporter in mycobacteria. Using this conditional mutant, we confirm the essentiality of mmpL3 in planktonic cultures, in biofilms, and during infection in zebrafish embryos. Thus, in this study, we developed a robust and reliable method to silence the expression of any M. abscessus gene during host infection.

A Loss of Function in LprG-Rv1410c Homologues Attenuates Growth during Biofilm Formation in Mycobacterium smegmatis

MmpL (mycobacterial membrane protein large) proteins are integral membrane proteins that have been implicated in the biosynthesis and/or transport of mycobacterial cell wall lipids. Given the cellular location of these proteins, however, it is unclear how cell wall lipids are transported beyond the inner membrane. Moreover, given that mycobacteria grow at the poles, we also do not understand how new cell wall is added in a highly localized and presumably coordinated manner. Here, we examine the relationship between two lipid transport pathways associated with the proteins MmpL11 and LprG-Rv1410c. The lipoprotein LprG has been shown to interact with proteins involved in cell wall processes including MmpL11, which is required in biofilms for the surface localization of certain lipids. Here we report that deletion of mmpL11 (MSMEG_0241) or the lprG-rv1410c operon homologues MSMEG_3070-3069 in Mycobacterium smegmatis produced similar biofilm defects that were distinct from that of the previously reported mmpL11 transposon insertion mutant. Analysis of pellicle biofilms, bacterial growth, lipid profiles, and gene expression revealed that the biofilm phenotypes could not be directly explained by changes in the synthesis or localization of biofilm-related lipids or the expression of biofilm-related genes. Instead, the shared biofilm phenotype between ΔMSMEG_3070-3069 and ΔmmpL11 may be related to their modest growth defect, while the origins of the distinct mmpL11::Tn biofilm defect remain unclear. Our findings suggest that the mechanisms that drive pellicle biofilm formation in M. smegmatis are not connected to crosstalk between the LprG-Rv1410c and MmpL11 pathways and that any functional interaction between these proteins does not relate directly to their lipid transport function.

Comparative proteomic investigation unravels the pathobiology of Mycobacterium fortuitum biofilm

Biofilm formation by Mycobacterium fortuitum causes serious threats to human health due to its increased contribution to nosocomial infections. In this study, the first comprehensive global proteome analysis of M. fortuitum was reported under planktonic and biofilm growth states. A label-free Q Exactive Quadrupole-Orbitrap tandem mass spectrometry analysis was performed on the protein lysates. The differentially abundant proteins were functionally characterized and re-annotated using Blast2GO and CELLO2GO. Comparative analysis of the proteins among two growth states provided insights into the phenotypic switch, and fundamental pathways associated with pathobiology of M. fortuitum biofilm, such as lipid biosynthesis and quorum-sensing. Interaction network generated by the STRING database revealed associations between proteins that endure M. fortuitum during biofilm growth state. Hypothetical proteins were also studied to determine their functional alliance with the biofilm phenotype. CARD, VFDB, and PATRIC analysis further showed that the proteins upregulated in M. fortuitum biofilm exhibited antibiotic resistance, pathogenesis, and virulence. Heatmap and correlation analysis provided the biomarkers associated with the planktonic and biofilm growth of M. fortuitum. Proteome data was validated by qPCR analysis. Overall, the study provides insights into previously unexplored biochemical pathways that can be targeted by novel inhibitors, either for shortened treatment duration or for eliminating biofilm of M. fortuitum and related nontuberculous mycobacterial pathogens. KEY POINTS: • Proteomic analyses of M. fortuitum reveals novel biofilm markers. • Acetyl-CoA acetyltransferase acts as the phenotype transition switch. • The study offers drug targets to combat M. fortuitum biofilm infections.

Mycobacterium abscessus Complex-Associated Chronic Meningitis: Time to Think Beyond Tuberculosis

Background

Mycobacterium abscessus complex (MabC) has emerged as an important cause of human infections, including meningitis. In the absence of correct microbiological identification, cases of MabC meningitis are treated with conventional anti-tubercular therapy, thereby worsening the outcome.

Objective

The current study was conducted to determine the clinical features, antimicrobial susceptibility, and outcome of patients with MabC meningitis.

Material and Methods

Cerebrospinal fluid specimens processed between 2011 and 2021 were subjected to smear, culture, MALDI TOF identification, hsp65 gene sequencing, and susceptibility testing using Sensititre™ RAPMYCOI plates along with a literature review.

Results

12 cases of MabC meningitis were identified between 2011 and 2021, 11 of which were M. abscessus subspecies abscessus on hsp65 gene sequencing. A pioneer case of meningitis with M. abscessus subspecies bolletii was also identified. The common predispositions were TB elsewhere, HIV positivity, and head injury. Two patients had dual infections, both MabC and TB. Ten patients succumbed to infection with a mean survival of 11 months. All isolates were susceptible to amikacin and tigecycline and subspecies bolletii had a higher minimum inhibitory concentration (MIC) than subspecies abscessus. A combined analysis with the available literature, reporting 19 more cases, revealed that the overall mortality of MabC meningitis was 61.3% (19/31) and that of shunt-associated/neurosurgical intervention-related MabC meningitis was 66.7% (12/20). To date, out of 20 MabC meningitis isolates in which subspecies identification was carried, 13 were M. abscessus, six were M. massiliense, and one was M. bolletii.

Conclusion

MabC is an important differential diagnosis of chronic meningitis. Prompt identification and speciation are imperative for targeted therapy, thus improving the overall patient outcome.

Investigating bacterial infections in Galleria mellonella larvae: Insights into pathogen dissemination and behavior

The insect Galleria mellonella is an alternative animal model widely used for studying bacterial infections. It presents a wide range of advantages, including its low cost, easy maintenance and lack of ethical constraints. Among other features, their innate immune system is very similar to that of mammals. In this study, we dissected several larvae infected with important human pathogens: Mycobacterium abscessus, Staphylococcus aureus and Pseudomonas aeruginosa. By observing the fat body, gut, trachea, and hemolymph under the microscope, we were able to describe where bacteria tend to disseminate. We also quantified the number of bacteria in the hemolymph throughout the infection course and found significant differences between the different pathogens. With this work, we aimed to better understand the behavior and dissemination of bacteria in the infected larvae.

Use of niosomes for the treatment of intracellular pathogens infecting the lungs

The delivery of drugs in an encapsulated environment is designed to precisely target specific tissues, avoiding a systemic circulation of the drug. Lungs are organs exposed to the environment with multiple defense barriers. However, many pathogens can still colonize and infect the airways bypassing the hostile environment of the lungs. In more complicated situations, some pathogens have developed strategies to multiply and survive within macrophages, one of the first immune cell responses to clearing infections in mammals. Niosomes are artificial vesicles that can be loaded with drugs, offering an alternative strategy to treat intracellular pathogens as nanocarriers. Members of the mycobacteria genus are intracellular pathogens that have evolved to escape the immunological response, specifically in macrophages, the white cells responsible for the clearance of pathogens. This review analyzed the state-of-the-art niosome synthesis aimed at tackling the problem of intracellular pathogen therapy. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Ferritin from Mycobacterium abscessus is involved in resistance to antibiotics and oxidative stress

Mycobacterium abscessus subsp. massiliense (Mycma) is a rapidly growing Mycobacterium belonging to the M. abscessus complex that is often associated with lung and soft tissue infection outbreaks. Mycma is resistant to many antimicrobials, including those used for treating tuberculosis. Therefore, Mycma infections are difficult to treat and may lead to high infectious complication rates. Iron is essential for bacterial growth and establishment of infection. During infection, the host reduces iron concentrations as a defense mechanism. To counteract the host-induced iron deficiency, Mycma produces siderophores to capture iron. Mycma has two ferritins (encoded by mycma_0076 and mycma_0077) modulated by different iron concentrations, which allow the survival of this pathogen during iron scarcity. In this study, we constructed knockout (Mycma 0076KO) and complemented (Mycma 0076KOc) gene strains for mycma_0076 to understand the function of 0076 ferritin. Deletion of mycma_0076 in Mycma led to the transition in colony morphology from smooth to rough, alteration of the glycopeptidolipids spectra, increased permeability of the envelope, reduction in biofilm formation, increased susceptibility to antimicrobials and hydrogen peroxide-induced oxidative stress, and decreased internalization by macrophages. This study shows that Mycma_0076 ferritin in Mycma is involved in resistance to oxidative stress and antimicrobials, and alteration of cell envelope architecture. KEY POINTS: • Deletion of the mycma_0076 gene altered colony morphology to rough; • Mycma 0076KO changed GPL profile; • Absence of Mycma_0076 ferritin results in increased susceptibility to antimicrobials and oxidative stress in Mycma. Legend: a In wild-type M. abscessus subsp. massiliense strain, iron is captured from the environment by carboxymycobactins and mycobactins (1). Iron-dependent regulator (IdeR) proteins bind to ferrous iron (Fe⁺²) in the bacterial cytoplasm leading to the activation of the IdeR-Fe⁺² complex (2). The activated complex binds to the promoter regions of iron-dependent genes, called iron box, which in turn help in the recruitment of RNA polymerase to promote transcription of genes such as mycma_0076 and mycma_0077 ferritin genes (3). Mycma_0076 and Mycma_0077 ferritins bind to excess iron in the medium and promote Fe²⁺ oxidation into ferric iron (Fe³⁺) and store iron molecules to be released under iron scarcity conditions. (4) Genes related to biosynthesis and transport of glycopeptidolipids (GPL) are expressed normally and the cell envelope is composed of different GPL species (colored squares represented on the cell surface (GPLs). Consequently, WT Mycma present smooth colony phenotype (5). b In Mycma 0076KO strain, the lack of ferritin 0076 causes overexpression of mycma_0077 (6), but does not restore wild-type iron homeostasis and thus may result in free intracellular iron, even in the presence of miniferritins (MaDps). The excess iron potentiates oxidative stress (7) by generating hydroxyl radicals through Fenton Reaction. During this process, through an unknown mechanism, that could involve Lsr2 (8), the expression of GPL synthesis locus is regulated positively and/or negatively, resulting in alteration of GPL composition in the membrane (as represented by different colors of squares on the cell surface), resulting in a rough colony phenotype (9). The changes of GPL can increase cell wall permeability, contributing to antimicrobial susceptibility (10).

Updated Review on the Mechanisms of Pathogenicity in Mycobacterium abscessus, a Rapidly Growing Emerging Pathogen

In recent years, Mycobacterium abscessus has appeared as an emerging pathogen, with an increasing number of disease cases reported worldwide that mainly occur among patients with chronic lung diseases or impaired immune systems. The treatment of this pathogen represents a challenge due to the multi-drug-resistant nature of this species and its ability to evade most therapeutic approaches. However, although predisposing host factors for disease are well known, intrinsic pathogenicity mechanisms of this mycobacterium are still not elucidated. Like other mycobacteria, intracellular invasiveness and survival inside different cell lines are pathogenic factors related to the ability of M. abscessus to establish infection. Some of the molecular factors involved in this process are well-known and are present in the mycobacterial cell wall, such as trehalose-dimycolate and glycopeptidolipids. The ability to form biofilms is another pathogenic factor that is essential for the development of chronic disease and for promoting mycobacterial survival against the host immune system or different antibacterial treatments. This capability also seems to be related to glycopeptidolipids and other lipid molecules, and some studies have shown an intrinsic relationship between both pathogenic mechanisms. Antimicrobial resistance is also considered a mechanism of pathogenicity because it allows the mycobacterium to resist antimicrobial therapies and represents an advantage in polymicrobial biofilms. The recent description of hyperpathogenic strains with the potential interhuman transmission makes it necessary to increase our knowledge of pathogenic mechanisms of this species to design better therapeutic approaches to the management of these infections.

In Vitro Antimycobacterial Activity of Human Lactoferrin-Derived Peptide, D-hLF 1-11, against Susceptible and Drug-Resistant Mycobacterium tuberculosis and Its Synergistic Effect with Rifampicin

Tuberculosis is a highly contagious disease caused by the Mycobacterium tuberculosis complex (MTBC). Although TB is treatable, multidrug-resistant, extensively drug-resistant, and totally drug-resistant forms of M. tuberculosis have become a new life-threatening concern. New anti-TB drugs that are capable of curing these drug-resistant strains are urgently needed. The purpose of this study is to determine the antimycobacterial activity of D-enantiomer human lactoferricin 1-11 (D-hLF 1-11) against mycobacteria in vitro using a 3-(4,5-dimethylthiazol-2-yl)-2,5-dephenyltetrazolium bromide colorimetric assay, resazurin microplate assay, and microscopic observation drug susceptibility assay. Three previously described antimicrobial peptides, protegrin-1, AK 15-6, and melittin, with potent anti-TB activity, were included in this study. The findings suggest that D-hLF 1-11 can inhibit the growth of M. tuberculosis with a minimum inhibitory concentration of 100−200 µg/mL in susceptible, isoniazid (INH)-monoresistant, rifampicin (RF)-monoresistant, and MDR strains. The peptide can also inhibit some nontuberculous mycobacteria and other MTBC in similar concentrations. The antibiofilm activity of D-hLF 1-11 against the biofilm-forming M. abscessus was determined by crystal violet staining, and no significant difference is observed between the treated and untreated biofilm control. The checkerboard assay was subsequently carried out with M. tuberculosis H37Rv and the results indicate that D-hLF 1-11 displays an additive effect when combined with INH and a synergistic effect when combined with RF, with fractional inhibitory concentration indices of 0.730 and 0.312, respectively. The red blood cell hemolytic assay was initially applied for the toxicity determination of D-hLF 1-11, and negligible hemolysis (<1%) was observed, despite a concentration of up to 4 mg/mL being evaluated. Overall, D-hLF 1-11 has potential as a novel antimycobacterial agent for the future treatment of drug-sensitive and drug-resistant M. tuberculosis infections.

2,4-Disubstituted pyridine derivatives are effective against intracellular and biofilm-forming tubercle bacilli

It was recently reported that 4-substituted picolinohydrazonamides carrying hydrophilic cyclic amines, such as morpholine and pyrrolidine, at the end of their thiosemicarbazide chain have potent antimycobacterial activity in vitro at concentrations below 1 μg/ml. Here, two selected compounds, 2,4-disubstituted pyridine derivatives 11 and 15, revealed significant bactericidal activity against Mycobacterium tuberculosis localized intracellularly within human macrophages, as well as against biofilm-forming tubercle bacilli. Mutants were selected that were resistant to the investigated compounds at an efficiency similar to that identified in the presence of the first line antituberculosis drug rifampicin. The resistant mutants were viable in the presence of the tested compounds exclusively on solid media. Genome-wide sequencing of the mutants selected in the presence of compound 11 revealed the accumulation of nonsynonymous mutations in the mmpR5 gene encoding a transcriptional repressor of the MmpS5-MmpL5 efflux pump, whose upregulation has been associated with bedaquiline resistance. The depletion of MmpR5 in wild-type M. tuberculosis using CRISPR–Cas9 technology increased the resistance of this strain to compound 11. Mass spectrometry-based proteomics (LC–MS/MS) of wild-type tubercle bacilli growing in subinhibitory concentrations of compounds 11 or 15 revealed 15 overproduced proteins not detectable in the control cells, including virulence-related proteins.

Mycobacterium abscessus: It's Complex

Mycobacterium abscessus (M. abscessus) is an opportunistic pathogen usually colonizing abnormal lung airways and is often seen in patients with cystic fibrosis. Currently, there is no vaccine available for M. abscessus in clinical development. The treatment of M. abscessus-related pulmonary diseases is peculiar due to intrinsic resistance to several commonly used antibiotics. The development of either prophylactic or therapeutic interventions for M. abscessus pulmonary infections is hindered by the absence of an adequate experimental animal model. In this review, we outline the critical elements related to M. abscessus virulence mechanisms, host-pathogen interactions, and treatment challenges associated with M. abscessus pulmonary infections. The challenges of effectively combating this pathogen include developing appropriate preclinical animal models of infection, developing proper diagnostics, and designing novel strategies for treating drug-resistant M. abscessus.

Glby, Encoded by MAB_3167c, Is Required for In Vivo Growth of Mycobacteroides abscessus and Exhibits Mild β-Lactamase Activity

Mycobacteroides abscessus (Mab; also known as Mycobacterium abscessus) is an emerging opportunistic pathogen. Patients with structural lung conditions such as bronchiectasis, cystic fibrosis, and chronic obstructive pulmonary disease are at high risk of developing pulmonary Mab disease. This disease is often chronic as the current treatment regimens are sub-efficacious. Here, we characterize the phenotype of a Mab strain lacking the MAB_3167c locus, which encodes a protein hereafter referred to as Glby. We demonstrate that the loss of Glby impairs normal planktonic growth in liquid broth, results in longer average cell length, and a melding of surfaces between cells. Glby also exhibits a mild β-lactamase activity. We also present evidence that amino acid substitutions that potentially alter Glby function are not favored. Lastly, we demonstrate that, in a mouse model of pulmonary Mab infection, the mutant lacking Glby was unable to proliferate, gradually cleared, and was undetectable after 3 weeks. These data suggest that an agent that inhibits Glby in vivo may be an efficacious treatment against Mab disease. IMPORTANCE Mycobacteroides abscessus can cause chronic pulmonary infections requiring administration of multiple antibiotics, still resulting in a low cure rate. The incidence of M. abscessus disease is increasing in the United States and the developed regions of the world. We show for the first time that a protein, Glby, affects growth of this bacterium. Using a mouse model of lung M. abscessus disease, we demonstrate that Glby is required for this bacterium to cause disease.

An Artefactual Cluster of Mycobacterium abscessus Pneumonia among Cancer Patients Arising from Contamination

The Mycobacteriumabscessus complex (MABC) is a group of rapidly growing, nontuberculous mycobacteria that are ubiquitous in soil, urban water pipes, swimming pools, and drinking water. Members of the MABC are considered opportunistic pathogens. The aim of this study was to investigate the origins of MABC detected in broncho-lavage (BL) samples from asymptomatic cancer patients. We turned our attention to washing and disinfection procedures for bronchoscopes; we also assessed water and disinfectant samples. Of 10 BL and 34 environmental samples tested, four BL samples (40%) and seven environmental samples (20.6%) tested positive for MABC. We hypothesized that contamination could arise from the prewashing machine and/or the water used because no patient had clinical or radiological signs consistent with MABC respiratory tract infection. Our study highlights the importance of evaluating cleaning and disinfection procedures for endoscope channels to reduce the potential spread of microorganisms and artefactual results arising from contamination.

Evolution of Antibacterial Drug Screening Methods: Current Prospects for Mycobacteria

The increasing resistance of infectious agents to available drugs urges the continuous and rapid development of new and more efficient treatment options. This process, in turn, requires accurate and high-throughput techniques for antimicrobials’ testing. Conventional methods of drug susceptibility testing (DST) are reliable and standardized by competent entities and have been thoroughly applied to a wide range of microorganisms. However, they require much manual work and time, especially in the case of slow-growing organisms, such as mycobacteria. Aiming at a better prediction of the clinical efficacy of new drugs, in vitro infection models have evolved to closely mimic the environment that microorganisms experience inside the host. Automated methods allow in vitro DST on a big scale, and they can integrate models that recreate the interactions that the bacteria establish with host cells in vivo. Nonetheless, they are expensive and require a high level of expertise, which makes them still not applicable to routine laboratory work. In this review, we discuss conventional DST methods and how they should be used as a first screen to select active compounds. We also highlight their limitations and how they can be overcome by more complex and sophisticated in vitro models that reflect the dynamics present in the host during infection. Special attention is given to mycobacteria, which are simultaneously difficult to treat and especially challenging to study in the context of DST.

Unique Features of Mycobacterium abscessus Biofilms Formed in Synthetic Cystic Fibrosis Medium

Characterizing Mycobacterium abscessus complex (MABSC) biofilms under host-relevant conditions is essential to the design of informed therapeutic strategies targeted to this persistent, drug-tolerant, population of extracellular bacilli. Using synthetic cystic fibrosis medium (SCFM) which we previously reported to closely mimic the conditions encountered by MABSC in actual cystic fibrosis (CF) sputum and a new model of biofilm formation, we show that MABSC biofilms formed under these conditions are substantially different from previously reported biofilms grown in standard laboratory media in terms of their composition, gene expression profile and stress response. Extracellular DNA (eDNA), mannose-and glucose-containing glycans and phospholipids, rather than proteins and mycolic acids, were revealed as key extracellular matrix (ECM) constituents holding clusters of bacilli together. None of the environmental cues previously reported to impact biofilm development had any significant effect on SCFM-grown biofilms, most likely reflecting the fact that SCFM is a nutrient-rich environment in which MABSC finds a variety of ways of coping with stresses. Finally, molecular determinants were identified that may represent attractive new targets for the development of adjunct therapeutics targeting MABSC biofilms in persons with CF.

Stringent Response in Mycobacteria: From Biology to Therapeutic Potential

Mycobacterium tuberculosis is a human pathogen that can thrive inside the host immune cells for several years and cause tuberculosis. This is due to the propensity of M. tuberculosis to synthesize a sturdy cell wall, shift metabolism and growth, secrete virulence factors to manipulate host immunity, and exhibit stringent response. These attributes help M. tuberculosis to manage the host response, and successfully establish and maintain an infection even under nutrient-deprived stress conditions for years. In this review, we will discuss the importance of mycobacterial stringent response under different stress conditions. The stringent response is mediated through small signaling molecules called alarmones “(pp)pGpp”. The synthesis and degradation of these alarmones in mycobacteria are mediated by Rel protein, which is both (p)ppGpp synthetase and hydrolase. Rel is important for all central dogma processes—DNA replication, transcription, and translation—in addition to regulating virulence, drug resistance, and biofilm formation. Rel also plays an important role in the latent infection of M. tuberculosis. Here, we have discussed the literature on alarmones and Rel proteins in mycobacteria and highlight that (p)ppGpp-analogs and Rel inhibitors could be designed and used as antimycobacterial compounds against M. tuberculosis and non-tuberculous mycobacterial infections.