The Mla system and its role in maintaining outer membrane barrier function in Stenotrophomonas maltophilia

Stenotrophomonas maltophilia are ubiquitous Gram-negative bacteria found in both natural and clinical environments. It is a remarkably adaptable species capable of thriving in various environments, thanks to the plasticity of its genome and a diverse array of genes that encode a wide range of functions. Among these functions, one notable trait is its remarkable ability to resist various antimicrobial agents, primarily through mechanisms that regulate the diffusion across cell membranes. We have investigated the Mla ABC transport system of S. maltophilia, which in other Gram-negative bacteria is known to transport phospholipids across the periplasm and is involved in maintaining outer membrane homeostasis. First, we structurally and functionally characterized the periplasmic substrate-binding protein MlaC, which determines the specificity of this system. The predicted structure of the S. maltophilia MlaC protein revealed a hydrophobic cavity of sufficient size to accommodate the phospholipids commonly found in this species. Moreover, recombinant MlaC produced heterologously demonstrated the ability to bind phospholipids. Gene knockout experiments in S. maltophilia K279a revealed that the Mla system is involved in baseline resistance to antimicrobial and antibiofilm agents, especially those with divalent-cation chelating activity. Co-culture experiments with Pseudomonas aeruginosa also showed a significant contribution of this system to the cooperation between both species in the formation of polymicrobial biofilms. As suggested for other Gram-negative pathogenic microorganisms, this system emerges as an appealing target for potential combined antimicrobial therapies.

Synthesis and evaluation of aromatic BDSF bioisosteres on biofilm formation and colistin sensitivity in pathogenic bacteria

The diffusible signal factor family (DSF) of molecules play an important role in regulating intercellular communication, or quorum sensing, in several disease-causing bacteria. These messenger molecules, which are comprised of cis-unsaturated fatty acids, are involved in the regulation of biofilm formation, antibiotic tolerance, virulence and the control of bacterial resistance. We have previously demonstrated how olefinic N-acyl sulfonamide bioisosteric analogues of diffusible signal factor can reduce biofilm formation or enhance antibiotic sensitivity in a number of bacterial strains. This work describes the design and synthesis of a second generation of aromatic N-acyl sulfonamide bioisosteres. The impact of these compounds on biofilm production in Acinetobacter baumannii, Escherichia coli, Burkholderia multivorans, Burkholderia cepacia, Burkholderia cenocepacia, Pseudomonas aeruginosa and Stenotrophomonas maltophilia is evaluated, in addition to their effects on antibiotic tolerance. The ability of these molecules to increase survival rates on co-administration with colistin is also investigated using the Galleria infection model.

A Stenotrophomonas maltophilia TetR-Like Transcriptional Regulator Involved in Fatty Acid Metabolism Is Controlled by Quorum Sensing Signals

Stenotrophomonas maltophilia is an environmental bacterium as well as an emerging opportunistic multidrug-resistant pathogen. They use the endogenous diffusible signal factor (DSF) quorum sensing (QS) system to coordinate population behavior and regulate virulence processes but can also respond to exogenous N-acyl-homoserine lactone (AHL) signals produced by neighboring bacteria. The effect of these QS signals on the global gene expression of this species remains, however, unknown. Whole-transcriptome sequencing analyses were performed for exponential cultures of S. maltophilia K279a treated with exogenous DSF or AHLs. Addition of DSF and AHLs signals resulted in changes in expression of at least 2-fold for 28 and 82 genes, respectively. Interestingly, 22 of these genes were found upregulated by both QS signals, 14 of which were shown to also be induced during the stationary phase. Gene functions regulated by all conditions included lipid and amino acid metabolism, stress response and signal transduction, nitrogen and iron metabolism, and adaptation to microoxic conditions. Among the common top upregulated QS core genes, a putative TetR-like regulator (locus tag SMLT2053) was selected for functional characterization. This regulator controls its own β-oxidation operon (Smlt2053-Smlt2051), and it is found to sense long-chain fatty acids (FAs), including the QS signal DSF. Gene knockout experiments reveal that operon Smlt2053-Smlt2051 is involved in biofilm formation. Overall, our findings provide clues on the effect that QS signals have in S. maltophilia QS-related phenotypes and the transition from the exponential to the stationary phase and bacterial fitness under high-density growth. IMPORTANCE The quorum sensing system in Stenotrophomonas maltophilia, in addition to coordinating the bacterial population, controls virulence-associated phenotypes, such as biofilm formation, motility, protease production, and antibiotic resistance mechanisms. Biofilm formation is frequently associated with the persistence and chronic nature of nosocomial infections. In addition, biofilms exhibit high resistance to antibiotics, making treatment of these infections extremely difficult. The importance of studying the metabolic and regulatory systems controlled by quorum sensing autoinducers will make it possible to discover new targets to control pathogenicity mechanisms in S. maltophilia.

Improved mini-Tn7 Delivery Plasmids for Fluorescent Labeling of Stenotrophomonas maltophilia

Fluorescently labeled bacterial cells have become indispensable for many aspects of microbiological research, including studies on biofilm formation as an important virulence factor of various opportunistic bacteria of environmental origin such as Stenotrophomonas maltophilia. Using a Tn7-based genomic integration system, we report the construction of improved mini-Tn7 delivery plasmids for labeling of S. maltophilia with sfGFP, mCherry, tdTomato and mKate2 by expressing their codon-optimized genes from a strong, constitutive promoter and an optimized ribosomal binding site. Transposition of the mini-Tn7 transposons into single neutral sites located on average 25 nucleotides downstream of the 3'-end of the conserved glmS gene of different S. maltophilia wild-type strains did not have any adverse effects on the fitness of their fluorescently labeled derivatives. This was demonstrated by comparative analyses of growth, resistance profiles against 18 antibiotics of different classes, the ability to form biofilms on abiotic and biotic surfaces, also independent of the fluorescent protein expressed, and virulence in Galleria mellonella. It is also shown that the mini-Tn7 elements remained stably integrated in the genome of S. maltophilia over a prolonged period of time in the absence of antibiotic selection pressure. Overall, we provide evidence that the new improved mini-Tn7 delivery plasmids are valuable tools for generating fluorescently labeled S. maltophilia strains that are indistinguishable in their properties from their parental wild-type strains. IMPORTANCE The bacterium S. maltophilia is an important opportunistic nosocomial pathogen that can cause bacteremia and pneumonia in immunocompromised patients with a high rate of mortality. It is now considered as a clinically relevant and notorious pathogen in cystic fibrosis patients but has also been isolated from lung specimen of healthy donors. The high intrinsic resistance to a wide range of antibiotics complicates treatment and most likely contributes to the increasing incidence of S. maltophilia infections worldwide. One important virulence-related trait of S. maltophilia is the ability to form biofilms on any surface, which may result in the development of increased transient phenotypic resistance to antimicrobials. The significance of our work is to provide a mini-Tn7-based labeling system for S. maltophilia to study the mechanisms of biofilm formation or host-pathogen interactions with live bacteria under non-destructive conditions.

Synthesis and evaluation of novel furanones as biofilm inhibitors in opportunistic human pathogens

Diseases caused by biofilm-forming pathogens are becoming increasingly prevalent and represent a major threat to human health. This trend has prompted a search for novel inhibitors of microbial biofilms which could, for example, be used to potentiate existing antibiotics. Naturally-occurring, halogenated furanones isolated from marine algae have proven to be effective biofilm inhibitors in several bacterial species. In this work, we report the synthesis of a library of novel furanones and their subsequent evaluation as biofilm inhibitors in several opportunistic human pathogens including S. enterica, S. aureus, E. coli, S. maltophilia, P. aeruginosa and C. albicans. A number of the most potent compounds were subjected to further analysis by confocal laser-scanning microscopy for their effects on P. aeruginosa and C. albicans biofilms individually, in addition to mixed polymicrobial biofilms. Lastly, we investigated the impact of a promising candidate on survival rates in vivo using a Galleria mellonella model.

Effects of cigarette smoke on the administration of isoniazid and rifampicin to macrophages infected with Mycobacterium tuberculosis

BACKGROUND

Smoking is a cause behind many diseases, including tuberculosis, and it is a risk factor for tuberculosis infection and mortality. Moreover, smoking is associated with a poor tuberculosis treatment outcome.

OBJECTIVES

In this study, we focus on the effects of cigarette smoke on an infected cell culture treated with anti-tuberculosis drugs.

MATERIALS AND METHODS

Cytotoxicity on THP-1, J774A.1 and MH-S cell lines and growth of Mycobacterium tuberculosis exposed to a reference or a commercial cigarette was evaluated. THP-1 cell line was exposed to cigarette smoke, infected with Mycobacterium tuberculosis and treated with anti-tuberculosis drugs. Apoptosis and death cell were also tested on M. bovis BCG infected cells. Minimal inhibitory concentrations of anti-tuberculosis drugs were analyzed.

RESULTS

All cells lines showed viability values higher than 80% when exposed to cigarette smoke extract. However, THP-1 cell line infected with M. bovis BCG and exposed to Marlboro cigarette smoke showed up to a 54% reduction of apoptotic cells than cells unexposed to smoke. M. tuberculosis exposed to Marlboro cigarette smoke for 11 days had an optical density 16% lower than unexposed bacteria. When cells were infected with M. tuberculosis, the intracellular recovery of CFUs showed up to a 0.66 log reduction in cells exposed to cigarette smoke extract because of a potential impairment in the phagocytosis. Macrophages treated with drugs showed up to a 2.55 log reduction in the intracellular load burden compared with non-treated ones. Despite poor treatment outcome on TB smoker patients, minimal inhibitory concentration of rifampicin increased only 2-fold in M. tuberculosis exposed to cigarette smoke.

CONCLUSION

Smoking interferes with tuberculosis treatment impairing the immunity of the host.

E-cigarettes: Effects in phagocytosis and cytokines response against Mycobacterium tuberculosis

Cigarette smoking and tuberculosis are a significant cause of death worldwide. Several epidemiological studies have demonstrated cigarette smoking is a risk factor for tuberculosis. Electronic cigarettes have recently appeared as a healthier alternative to conventional smoking, although their impact in tuberculosis is not well understood. The aim of this study was to explore the effect of electronic cigarettes in phagocytosis of Mycobacterium tuberculosis and cytokines production. In vitro infection was carried out by exposing THP-1 macrophages to four electronic vapor extracts and the intracellular burden of M. tuberculosis was determined. The percentage of infection was evaluated by confocal microscopy and the cytokine production by Luminex. A reduction of intracellular M. tuberculosis burden in THP-1 macrophages was found after its exposure to electronic vapor extract; the same trend was observed by confocal microscopy when Mycobacterium bovis BCG-GFP strain was used. Electronic cigarettes stimulate a pro-inflammatory cytokine response. We conclude that electronic cigarettes impair the phagocytic function and the cytokine response to M. tuberculosis.

Assessment of the influence of direct tobacco smoke on infection and active TB management

BACKGROUND

Smoking is a risk factor for tuberculosis (TB) infection and disease progression. Tobacco smoking increases susceptibility to TB in a variety of ways, one of which is due to a reduction of the IFN-γ response. Consequently, an impaired immune response could affect performance of IFN-γ Release Assays (IGRAs).

OBJECTIVE

In the present study, we assess the impact of direct tobacco smoking on radiological manifestations, sputum conversion and immune response to Mycobacterium tuberculosis, analyzing IFN-γ secretion by IGRAs.

METHODS

A total of 525 participants were studied: (i) 175 active pulmonary TB patients and (ii) 350 individuals coming from contact tracing studies, 41 of whom were secondary TB cases. Clinical, radiological and microbiological data were collected. T-SPOT.TB and QFN-G-IT were processed according manufacturer's instructions.

RESULTS

In smoking patients with active TB, QFN-G-IT (34.4%) and T-SPOT.TB (19.5%) had high frequencies of negative results. In addition, by means of an unconditional logistic regression, smoking was a main factor associated with IGRAs' false-negative results (aOR: 3.35; 95%CI:1.47-7.61; p<0.05). Smoking patients with active TB presented a high probability of having cavitary lesions (aOR: 1.88; 95%CI:1.02-3.46;p<0.05). Mean culture negativization (months) ± standard deviation (SD) was higher in smokers than in non-smokers (2.47±1.3 versus 1.69±1.4). Latent TB infection (LTBI) was favored in smoking contacts, being a risk factor associated with infection (aOR: 11.57; 95%CI:5.97-22.41; p<0.00005). The IFN-γ response was significantly higher in non-smokers than in smokers. Smoking quantity and IFN-γ response analyzed by IGRAs were dose-dependent related.

CONCLUSIONS

Smoking had a negative effect on radiological manifestations, delaying time of sputum conversion. Our data establish a link between tobacco smoking and TB due to a weakened IFN-γ response caused by direct tobacco smoke.

[Pigment dispersion syndrome in a patient with megalocornea]

CASE REPORT

A case of a patient of 12 years old with megalocornea and bilateral pigment dispersion syndrome is reported. An ultrasound biomicroscopic study was performed with the UBM 840 (Zeiss-Humphrey, 50 MHz) and an iris concavity with an iridolenticular and iridozonular contact was observed. A new exam after pilocarpine instillation drops showed the resolution of the iris concavity, zonular and lenticular contact.

DISCUSSION

The anterior chamber configuration of this patient analyzed with ultrasound biomicroscopy allowed us to understand the mechanism of the pigment dispersion syndrome.

Bioavailability of two oral formulations of cyclosporin A in uremic children before renal transplantation

The bioavailability of two oral formulations of cyclosporin A (Sandimmun and Neoral) was assessed in 10 children with end-stage renal disease (ESRD), while at a steady state on a dialytic procedure. The study was performed according to a randomized, double blind, cross-over design, allowing a 1-month washout period between studies. Each patient received 2.5 mg/microg of oral cyclosporin A every 12 h, either Sandimmun (SAN) or Neoral (NEO). Serum concentrations of cyclosporin A were determined serially during a 24 h period, after the 5th dose of cylosporin. Serum concentrations against time curves were constructed and bioavailability of both medications, expressed as AUC and Cmax, were compared. A statistically significant increase was observed in the AUC and Cmax of NEO, which were 90% and 130% higher, respectively, than those of SAN. Considering that the internationally accepted criteria for bioequivalence allows a 20% variation in AUC and Cmax, it appears that Neoral and Sandimmun do not bear bioequivalence in children with ESRD. Notwithstanding, there were no significant differences in trough levels between both formulations. We conclude that, if trough levels are the only source of information for dosing design, Neoral could be substituted for Sandimmun on a 1:1 basis. However, a 1:1 drug substitution is not suitable when AUC is used in children with ESRD.