Formation of Mycobacterium abscessus colonies in cellular culture in an in vitro infection model.

Mycobacterium abscessus is one of the most important nontuberculous mycobacteria that cause lung diseases. In vitro infection models developed to analyze the immune response are frequently based on the addition of mycobacteria to mononuclear cells or neutrophils from peripheral blood. An important requirement of these assays is that most cells phagocytose mycobacteria, only accomplished by using large multiplicities of infection (1 or more bacteria per cell) which may not adequately reflect the inhalation of a few mycobacteria by the host. We propose modifications that try to mimic some of the conditions in which immune cells deal with mycobacteria. For the preparation of the inoculum mycobacteria are grown in solid media followed by preparation to a single cell suspension. Multiplicities of infection (number of bacteria per cell) are below 0.01. Serum-free cellular media is used to allow the growth of M. abscessus. After several days of incubation Bacterial Colonies in Cellular Culture (BCCC) develop, which are enumerated directly under an inverted microscope. These colonies may represent biofilm formation during chronic infections. •Low multiplicity of infection (below 0.01 bacteria per cell) reflects more realistically conditions encountered by immune cells in the lungs.•The surface of mycobacteria prepared for infection assays that are grown in solid media are less affected than that of mycobacteria grown in liquid media with detergents.•Colony formation in the infected cells may reflect the aggregation and biofilm formation in the lungs during chronic infection.

Nontuberculous Mycobacteria, Mucociliary Clearance, and Bronchiectasis.

Nontuberculous mycobacteria (NTM) are environmental and ubiquitous, but only a few species are associated with disease, often presented as nodular/bronchiectatic or cavitary pulmonary forms. Bronchiectasis, airways dilatations characterized by chronic productive cough, is the main presentation of NTM pulmonary disease. The current Cole's vicious circle model for bronchiectasis proposes that it progresses from a damaging insult, such as pneumonia, that affects the respiratory epithelium and compromises mucociliary clearance mechanisms, allowing microorganisms to colonize the airways. An important bronchiectasis risk factor is primary ciliary dyskinesia, but other ciliopathies, such as those associated with connective tissue diseases, also seem to facilitate bronchiectasis, as may occur in Lady Windermere syndrome, caused by M. avium infection. Inhaled NTM may become part of the lung microbiome. If the dose is too large, they may grow excessively as a biofilm and lead to disease. The incidence of NTM pulmonary disease has increased in the last two decades, which may have influenced the parallel increase in bronchiectasis incidence. We propose that ciliary dyskinesia is the main promoter of bronchiectasis, and that the bacteria most frequently involved are NTM. Restoration of ciliary function and impairment of mycobacterial biofilm formation may provide effective therapeutic alternatives to antibiotics.

Identificación rápida de micobacterias no tuberculosas mediante técnicas proteómicas (MALDI-TOF) / A rapid proteomic system (MALDI-TOF) for nontuberculous-mycobacteria identification

La identificación proteómica de micobacterias no tuberculosas (MNTs) mediante MALDI-TOF presenta una mayor complejidad debido a la especial composición de su pared celular, que complica la extracción de proteínas. Un total de 106 aislamientos pertenecientes a diferentes especies de MNTs procedentes de muestras clínicas del Complejo Asistencial Universitario de León recogidas durante los años 2019 y 2020 se han identificado por un método proteómico abreviado (MALDI-TOF Biotyper Bruker®) desarrollado en nuestro laboratorio. La identificación se ha comparado con la realizada en paralelo en el Centro de Referencia de Majadahonda. Se analizaron un total de 22 especies diferentes de MNTs obteniendo una concordancia del 91,5%. Las nueve discrepancias detectadas se dieron entre especies pertenecientes al mismo grupo taxonómico. En el 67,92% de las identificaciones el score fue superior a 1,8. En el tiempo de procesamiento se obtuvo un ahorro aproximado de 24 minutos con respecto al recomendado por el fabricante.(AU)

Proteomic techniques relaying upon mass spectrometry (MALDI_TOF) applied to nontuberculous mycobacteria (NTM) identification, constitute a difficult goal. Cell wall structure features complicates the protein extraction procedure. A total of 106 isolates belonging to a variety of MNTs species isolated from clinical samples taken at the Complejo Asistencial Universitario de León for a two years period (2019-20) were identified following a simplified method (MALDI-TOF Biotyper Bruker®) developped in our laboratory. The resultant identification was compared to a parallel one ruled on the Centro de Referencia de Majadahonda. A total of 22 different MNTs species were tested, obtaining an agreement of 91,5%. Only 9 minor discrepancies between species belonging to the same taxonomic group of MNTs were detected. The score obtained in the 67.92% of the cases was higher than 1.8. A time-saving of 24 minutes compared to the manufacturer‘s proceeding was achieved.(AU)

Mycobacterium abscessus Infected Neutrophils as an In Vitro Model for Bronchiectasis. Neutrophils Prevent Mycobacterial Aggregation

No disponible

A rapid proteomic system (MALDI-TOF) for nontuberculous-mycobacteria identification.

Proteomic techniques relaying upon mass spectrometry (MALDI_TOF) applied to nontuberculous mycobacteria (NTM) identification, constitute a difficult goal. Cell wall structure features complicates the protein extraction procedure. A total of 106 isolates belonging to a variety of MNTs species isolated from clinical samples taken at the Complejo Asistencial Universitario de León for a two years period (2019-20) were identified following a simplified method (MALDI-TOF Biotyper Bruker®) developped in our laboratory. The resultant identification was compared to a parallel one ruled on the Centro de Referencia de Majadahonda. A total of 22different MNTs species were tested, obtaining an agreement of 92,45%. Only 8 minor discrepancies between species belonging to same taxonomic group of MNTs were detected. The score obtained in the 67.92% of the cases was higher than 1.8. A time-saving of 24min compared to the manufacturer's proceeding was achieved.

Mycobacterium avium complex infected cells promote growth of the pathogen Pseudomonas aeruginosa.

Bronchiectasis is considered a consequence of the neutrophilic inflammatory response to infection. Mycobacterial infections, mainly from the Mycobacterium avium complex and M. abscessus, have been inextricably linked to bronchiectasis development. The most important pathogen that infect patients with bronchiectasis is Pseudomonas aeruginosa, associated with an increased risk of death. Patients with bronchiectasis are often co-infected with P. aeruginosa and M. avium complex, and it was studied whether they interacted in immune cell cultures. Peripheral blood mononuclear cells from healthy volunteers were infected overnight with clinical isolates of mycobacteria, 18 h later co-infected with P. aeruginosa and Pseudomonas multiplication was quantified. Inoculated P. aeruginosa multiply faster when cells were previously infected in vitro with M. avium complex or M. tuberculosis, but not with M. kansasii or M. gordonae, mycobacteria not regularly isolated from patients with bronchiectasis. The interaction between mycobacteria and P. aeruginosa also takes place in the absence of cells, but to a lower degree. Growth of Staphylococcus aureus, less frequently co-isolated with mycobacteria, was not affected by previous infection with mycobacteria. Surprisingly, multiplication of P. aeruginosa in neutrophil cultures did not vary in the presence of mycobacteria. Nevertheless, co-infection of mycobacteria and P. aeruginosa induced the production of IL-1ß, a mediator of neutrophilic inflammation. P. aeruginosa stimulation by mycobacteria provides evidence for explaining their common clinical association. Strategies to control mycobacteria may be useful to impair P. aeruginosa colonization.

A rapid proteomic system (MALDI-TOF) for nontuberculous-mycobacteria identification. / Identificación rápida de micobacterias no tuberculosas mediante técnicas proteómicas (MALDI-TOF).

Proteomic techniques relaying upon mass spectrometry (MALDI_TOF) applied to nontuberculous mycobacteria (NTM) identification, constitute a difficult goal. Cell wall structure features complicates the protein extraction procedure. A total of 106 isolates belonging to a variety of MNTs species isolated from clinical samples taken at the Complejo Asistencial Universitario de León for a two years period (2019-20) were identified following a simplified method (MALDI-TOF Biotyper Bruker®) developped in our laboratory. The resultant identification was compared to a parallel one ruled on the Centro de Referencia de Majadahonda. A total of 22 different MNTs species were tested, obtaining an agreement of 91,5%. Only 9 minor discrepancies between species belonging to the same taxonomic group of MNTs were detected. The score obtained in the 67.92% of the cases was higher than 1.8. A time-saving of 24 minutes compared to the manufacturer's proceeding was achieved.

A strategy based on Amplified Fragment Length Polymorphism (AFLP) for routine genotyping of nontuberculous mycobacteria at the clinical laboratory.

The increasing worldwide incidence of mycobacteriosis and the need to achieve improved clinical management makes nontuberculous mycobacteria (NTM) genotyping a useful tool. However, because of technical difficulties, medium size microbiology laboratories do not attempt to compare the genetic patterns that each of their isolates present. We have aimed to optimize a genotyping method with a reduced hands-on experimental time and that requires few technical resources. A strategy based on the Amplified Fragment Length Polymorphism (AFLP) methodology was developed using two rare-cutters enzymes (SacI and BglII). One out of seven primers was sequentially used in each amplification reaction that was analyzed by agarose gel electrophoresis. This approach makes it possible the timely genotyping of a moderate number of strains and its characterization without the need of image analysis software. We have genotyped 28 Mycobacterium intracellulare and 4 M. abscessus. Clinical researchers are encouraged to routinely genotype their NTM isolates.

The unexplained increase of nontuberculous mycobacteriosis.

Epidemiological data show a worldwide increase in nontuberculous mycobacteriosis. Although it has been partially attributed to the improvement of microbiological methodologies that has allowed a better recovery and identification of nontuberculous mycobacteria (NTM), it is generally accepted that there is a genuine incidence augmentation. The reasons of the increase are likely multifactorial, depending on the nature of the pathogen, the host, and their interaction. Mycobacteria from the Mycobacterium tuberculosis complex has been regarded as pathogenic and NTM as opportunistic and nontransmissible. Nevertheless, few differences have been found in either their phenotypic or genotypic characteristics. The phenomenon of M. tuberculosis adaptation to the human host may be taking place again in NTM as a consequence of human environmental alterations that facilitate the interaction with the pathogen. The current worsening of the immunological status of increasing numbers of individuals, a result of factors such as malnutrition (obesity and diabetes), population aging or the widespread use of immunosuppressive medication, may be allowing the rapid evolution and person-to-person transmission of NTM. It is likely that mycobacteriosis incidence will keep escalating. New measures should be taken to deal with these diseases, including their reportability and the implementation of strain genotyping that would shed light on the NTM dissemination routes from the environment or human hosts.

In vitro infection with Mycobacterium tuberculosis induces a distinct immunological pattern in blood from healthy relatives of tuberculosis patients.

Part of the susceptibility to tuberculosis has a genetic basis, which is clear in primary immunodeficiencies, but is less evident in apparently immunocompetent subjects. Immune responses were analysed in blood samples from tuberculosis patients and their healthy first-degree relatives who were infected in vitro with mycobacteria (either Mycobacterium tuberculosis or M. bovis BCG). The antimicrobial activity against M. tuberculosis in blood from relatives was significantly lower than that observed in healthy controls. Tuberculosis patients exhibited a higher number of neutrophils, and monocyte phagocytosis was inhibited in both relatives and tuberculosis patients. A remarkable finding was that the production of reactive oxygen species by infected neutrophils was higher in relatives than in healthy controls. A higher production of TNFα in infected blood from relatives was also observed. These results may indicate that relatives display a stronger inflammatory response and that their immune response to M. tuberculosis is different from those of unrelated controls. First-degree relatives may represent a highly informative group for the analysis of tuberculosis susceptibility.

Blood antimicrobial activity varies against different Mycobacterium spp.

In vitro analysis of mycobacterial pathogenicity or host susceptibility has traditionally relied on the infection of macrophages, the target cell of mycobacteria, despite difficulties reproducing their antimycobacterial activity. We have employed alternative models, namely whole blood and leukocytes in plasma, from QuantiFERON negative individuals, and performed infections with the pathogenic M. tuberculosis, the less pathogenic M. avium, M. kansasii and M. chelonae and the occasionally pathogenic M. gordonae and M. bovis. The anticoagulant used in blood extraction, heparin or EDTA, had a major influence in the outcome of the infection. Thus, while in the heparinized models a similar number of bacteria were enumerated in the inoculum and after seven days, in the presence of EDTA a killing effect was observed, despite the inhibitory effect of EDTA on cellular functions like the production of cytokines or reactive oxygen species (ROS). A special case was the rapidly growing mycobacteria M. chelonae, that multiplied in heparinized models but was eliminated in models with EDTA. We verified that EDTA is not responsible for the bactericidal effect, but acts as a bacteriostatic agent. Further work will determine whether blood derived models are a better alternative to the classical macrophage.

Immunological response to Mycobacterium tuberculosis infection in blood from type 2 diabetes patients.

The convergence of tuberculosis and diabetes represents a co-epidemic that threatens progress against tuberculosis. We have investigated type 2 diabetes as a risk factor for tuberculosis susceptibility, and have used as experimental model whole blood infected in vitro with Mycobacterium tuberculosis. Blood samples from diabetic patients were found to have a higher absolute neutrophil count that non-diabetic controls, but their immune functionality seemed impaired because they displayed a lower capacity to phagocytose M. tuberculosis, a finding that had been previously reported only for monocytes. In contrast, an increased production of TNFα was detected in infected blood from diabetic patients. Despite the altered phagocytic capacity showed by cells from these patients, the antimicrobial activity measured in both whole blood and monocyte derived macrophages was similar to that of controls. This unexpected result prompts further improvements in the whole blood model to analyze the immune response of diabetes patients to tuberculosis.

Plasma contributes to the antimicrobial activity of whole blood against Mycobacterium tuberculosis.

The whole blood model for infection has proven useful to analyze the immunological response to Mycobacterium tuberculosis, because it exerts a significant antimicrobial activity. Although this activity has been generally assumed to be cellular, we have found that the leukocyte fraction of blood from healthy volunteers did not kill the bacilli. We have discovered that plasma was responsible for a large proportion, but not all, of the antimicrobial activity. Furthermore, infected monocytes controlled the mycobacterial multiplication when cultivated in the presence of plasma. Intriguingly, serum from the same donors did not share this activity, although it was able to eliminate the non-pathogenic Mycobacterium gordonae To identify the remaining components that participate in the antimycobacterial activity we fractionated blood in leukocytes, plasma, erythrocytes and platelets, and analyzed the bactericidal power of each fraction and their combinations using a factorial design. We found that erythrocytes, but not platelets, participated and showed by flow cytometry that mycobacteria physically associated with erythrocytes. We propose that in exposed healthy individuals that show 'early clearance' of the mycobacteria, the innate response is predominantly humoral, probably through the effect of antimicrobial peptides and proteins.

Preparation of inocula for experimental infection of blood with Streptococcus pneumoniae.

Experimental infections of either cells or animals require the preparation of good quality inocula. Unfortunately, the important pulmonary pathogen Streptococcus pneumoniae is a fastidious microorganism that suffers an autolysis process when cultured in vitro. Supplementation of Todd-Hewitt broth with a biological buffer (20 mM Tris-HCl, pH = 7.8) promotes a six hours delay in the beginning of the autolysis process. Additional improvements include washing bacteria before freezing, avoiding manipulations after thawing, and the use of glycerol (<18%) as a cryoprotectant, instead of reagents like skimmed milk that may affect cell cultures. With the proposed protocol >70% of the frozen bacteria was viable after 28 weeks at -80 °C, and aliquots were highly homogeneous. We have tested their utility in a whole blood infection model and have found that human plasma exhibits a higher microbicidal activity than whole blood, a result that we have not found previously reported. Additionally, we have also observed significant variations in the antimicrobial activity against different strains, which might be related to their virulence.•Media culture buffering extends S. pneumoniae viability for 6 h.•Washing before freezing of single use aliquots minimizes manipulation after thawing.•Experimental infection with the frozen inocula has shown that plasma has higher bactericidal activity than blood.

Non-chemotactic influence of CXCL7 on human phagocytes. Modulation of antimicrobial activity against L. pneumophila.

We have investigated the role of CXCL7 in the immune response of human phagocytes against the intracellular bacteria Mycobacterium tuberculosis and Legionella pneumophila. We have observed that polymorphonuclear neutrophil (PMN) chemotaxis induced by the supernatants of infected monocyte derived macrophages (MDM) may be attributed to CXCL8 rather than CXCL7, although both chemokines are present in large quantities. We have also found that CXCL7 is present not only in the supernatants of MDM, but also in the supernatants of PMN of some, but not all, individuals. Western blot analysis revealed that, in both MDM and PMN supernatants appeared two bands with molecular weights consistent with the platelet basic protein (PBP) and the neutrophil activating protein-2 (NAP-2) sizes. Regarding the influence on infected cells, recombinant NAP-2 enhanced the antimicrobial activity of IFNγ activated MDM against L. pneumophila, but not against M. tuberculosis. In addition, U937 cells transfected with a NAP-2 construct inhibited the intracellular multiplication of L. pneumophila, supporting its role in the modulation of the antimicrobial activity. Finally, U937 cells transfected with the NAP-2 construct showed an adherence that was dramatically enhanced when the substrate was fibronectin. We conclude that human phagocytes produce CXCL7 variants that may have a significant influence on the immune response against bacterial pathogens.