Evaluation of combination therapy for Burkholderia cenocepacia lung infection in different in vitro and in vivo models

Oxirapentyn A, Derived from Marine Amphichorda felina, Effectively Inhibits Quorum Sensing and Biofilm Formation Against Chromobacterium violaceum

The emergence of multidrug-resistant Chromobacterium violaceum, an opportunistic pathogen, poses a significant threat to human, animal, and environmental health, underscoring the urgent need for innovative strategies. Marine-derived natural compounds have gained attention as a promising source of quorum sensing inhibitors (QSIs) that can attenuate C. violaceum virulence without inducing resistance. This study reports, for the first time, the anti-quorum sensing (anti-QS) and anti-biofilm activities of oxirapentyn A, one marine natural compound, against C. violaceum. Results demonstrate oxirapentyn A (200 μg/mL) significantly inhibits biofilm formation, violacein production, and hemolysin synthesis by 48.8, 21.7, and 22.3%, respectively. Scanning electron microscopy (SEM) further corroborated the disruption of biofilm architecture. LC-MS analysis revealed a concentration-dependent reduction in the production of N-decanoyl-homoserine lactone (C10-HSL), a key QS signaling molecule. Furthermore, RT-qPCR analysis indicated oxirapentyn A downregulated critical QS-related genes (cviI, cviR, vioA, chiA, and pykF) by 20.7, 36.6, 31.1, 66.6, and 30.7%, respectively. Notably, in vivo experiments demonstrated that oxirapentyn A significantly improved the survival of Galleria mellonella larvae infected with C. violaceum. Collectively, these findings highlight oxirapentyn A as a novel QSI with dual anti-QS and biofilm-disrupting activities, offering a promising strategy to combat drug-resistant bacterial infections.

Recreating chronic respiratory infections in vitro using physiologically relevant models

Despite the need for effective treatments against chronic respiratory infections (often caused by pathogenic biofilms), only a few new antimicrobials have been introduced to the market in recent decades. Although different factors impede the successful advancement of antimicrobial candidates from the bench to the clinic, a major driver is the use of poorly predictive model systems in preclinical research. To bridge this translational gap, significant efforts have been made to develop physiologically relevant models capable of recapitulating the key aspects of the airway microenvironment that are known to influence infection dynamics and antimicrobial activity in vivo In this review, we provide an overview of state-of-the-art cell culture platforms and ex vivo models that have been used to model chronic (biofilm-associated) airway infections, including air-liquid interfaces, three-dimensional cultures obtained with rotating-wall vessel bioreactors, lung-on-a-chips and ex vivo pig lungs. Our focus is on highlighting the advantages of these infection models over standard (abiotic) biofilm methods by describing studies that have benefited from these platforms to investigate chronic bacterial infections and explore novel antibiofilm strategies. Furthermore, we discuss the challenges that still need to be overcome to ensure the widespread application of in vivo-like infection models in antimicrobial drug development, suggesting possible directions for future research. Bearing in mind that no single model is able to faithfully capture the full complexity of the (infected) airways, we emphasise the importance of informed model selection in order to generate clinically relevant experimental data.

Effect of malate on the activity of ciprofloxacin against Pseudomonas aeruginosa in different in vivo and in vivo-like infection models

The clinical significance of Pseudomonas aeruginosa infections and the tolerance of this opportunistic pathogen to antibiotic therapy makes the development of novel antimicrobial strategies an urgent need. We previously found that D,L-malic acid potentiates the activity of ciprofloxacin against P. aeruginosa biofilms grown in a synthetic cystic fibrosis sputum medium by increasing metabolic activity and tricarboxylic acid cycle activity. This suggested a potential new strategy to improve antibiotic therapy in P. aeruginosa infections. Considering the importance of the microenvironment on microbial antibiotic susceptibility, the present study aims to further investigate the effect of D,L-malate on ciprofloxacin activity against P. aeruginosa in physiologically relevant infection models, aiming to mimic the infection environment more closely. We used Caenorhabditis elegans nematodes, Galleria mellonella larvae, and a 3-D lung epithelial cell model to assess the effect of D,L-malate on ciprofloxacin activity against P. aeruginosa. D,L-malate was able to significantly enhance ciprofloxacin activity against P. aeruginosa in both G. mellonella larvae and the 3-D lung epithelial cell model. In addition, ciprofloxacin combined with D,L-malate significantly improved the survival of infected 3-D cells compared to ciprofloxacin alone. No significant effect of D,L-malate on ciprofloxacin activity against P. aeruginosa in C. elegans nematodes was observed. Overall, these data indicate that the outcome of the experiment is influenced by the model system used which emphasizes the importance of using models that reflect the in vivo environment as closely as possible. Nevertheless, this study confirms the potential of D,L-malate to enhance ciprofloxacin activity against P. aeruginosa-associated infections.

The development and characterization of in vivo-like three-dimensional models of bronchial epithelial cell lines

In vitro models of differentiated respiratory epithelium that allow high-throughput screening are an important tool to explore new therapeutics for chronic respiratory diseases. In the present study, we developed in vivo-like three-dimensional (3-D) models of bronchial epithelial cell lines that are commonly used to study chronic lung disease (16HBE14o-, CFBE41o- and CFBE41o- 6.2 WT-CFTR). To this end, cells were cultured on porous microcarrier beads in the rotating wall vessel (RWV) bioreactor, an optimized suspension culture method that allows higher throughput experimentation than other physiologically relevant models. Cell differentiation was compared to conventional two-dimensional (2-D) monolayer cultures and to the current gold standard in the respiratory field, i.e. air-liquid interface (ALI) cultures. Cellular differentiation was assessed in the three model systems by evaluating the expression and localization of markers that reflect the formation of tight junctions (zonula occludens 1), cell polarity (intercellular adhesion molecule 1 at the apical side and collagen IV expression at the basal cell side), multicellular complexity (acetylated α-tubulin for ciliated cells, CC10 for club cells, keratin-5 for basal cells) and mucus production (MUC5AC) through immunostaining and confocal laser scanning microscopy. Results were validated using Western Blot analysis. We found that tight junctions were expressed in 2-D monolayers, ALI cultures and 3-D models for all three cell lines. All tested bronchial epithelial cell lines showed polarization in ALI and 3-D cultures, but not in 2-D monolayers. Mucus secreting goblet-like cells were present in ALI and 3-D cultures of CFBE41o- and CFBE41o- 6.2 WT-CFTR cells, but not in 16HBE14o- cells. For all cell lines, there were no ciliated cells, basal cells, or club cells found in any of the model systems. In conclusion, we developed RWV-derived 3-D models of commonly used bronchial epithelial cell lines and showed that these models are a valuable alternative to ALI cultures, as they recapitulate similar key aspects of the in vivo parental tissue.

A Three-Dimensional Lung Cell Model to Leptospira Virulence Investigations

Leptospirosis is a worldwide zoonosis and a serious public health threat in tropical and subtropical areas. The etiologic agents of leptospirosis are pathogenic spirochetes from the genus Leptospira. In severe cases, patients develop a pulmonary hemorrhage that is associated with high fatality rates. Several animal models were established for leptospirosis studies, such as rodents, dogs, and monkeys. Although useful to study the relationship among Leptospira and its hosts, the animal models still exhibit economic and ethical limitation reasons and do not fully represent the human infection. As an attempt to bridge the gap between animal studies and clinical information from patients, we established a three-dimensional (3-D) human lung cell culture for Leptospira infection. We show that Leptospira is able to efficiently infect the cell lung spheroids and also to infiltrate in deeper areas of the cell aggregates. The ability to infect the 3-D lung cell aggregates was time-dependent. The 3-D spheroids infection occurred up to 120 h in studies with two serovars, Canicola and Copenhageni. We standardized the number of bacteria in the initial inoculum for infection of the spheroids and we also propose two alternative culture media conditions. This new approach was validated by assessing the expression of three genes of Leptospira related to virulence and motility. The transcripts of these genes increased in both culture conditions, however, in higher rates and earlier times in the 3-D culture. We also assessed the production of chemokines by the 3-D spheroids before and after Leptospira infection, confirming induction of two of them, mainly in the 3-D spheroids. Chemokine CCL2 was expressed only in the 3-D cell culture. Increasing of this chemokine was observed previously in infected animal models. This new approach provides an opportunity to study the interaction of Leptospira with the human lung epithelium in vitro.

Comparative analysis of different methods used for molecular characterization of Burkholderia cepacia complex isolated from noncystic fibrosis conditions

PURPOSE

Burkholderia is a Gram-negative opportunistic bacterium capable of causing severe nosocomial infections. The aim of this study was to characterize Burkholderia cepacia complex and to compare different molecular methods used in its characterization.

METHODS

In this study, 45 isolates of Burkholderia cepacia complex (Bcc) isolated from clinical cases were subjected to RAPD (Random amplified polymorphic DNA), recA-RFLP (Restriction fragment length polymorphism), 16SrDNA-RFLP, whole-cell protein analysis, recA DNA sequencing and biofilm assay.

RESULTS

Of the 45 isolates tested, 97.7% were sensitive to ceftazidime, 82.2% were sensitive to Cotrimoxazole, 73.3% were sensitive to meropenem, 55.5% were sensitive to minocycline and 42.2% were sensitive to levofloxacin. Majority of the isolates harbored all the tested virulence genes except bpeA and cblA. The RAPD generated 11 groups (R1-R11), recA-RFLP 10 groups (A1-A10), 16SrRNA-RFLP 5 groups (S1-S5) and SDS-PAGE (Sodium Dodecyl Sulphate-Polyacrylamide gel electrophoresis) whole cell protein analysis revealed 12 groups (C1-C12). recA sequencing revealed that most of the isolates belonging to the genomovar III Burkholderia cenocepacia. Though all the methods are found to be efficient in differentiating Burkholderia spp., recA-RFLP was highly discriminatory at 96% similarity value. The study also identified a new strain Burkholderia pseudomultivorans for the first time in the country. Further, recA sequencing could identify the strains to species level. Majority of the multidrug-resistant strains also showed moderate to strong biofilm-forming ability, which further contributes to the virulence characteristics of the pathogens.

CONCLUSIONS

The study highlights the importance of combination of molecular methods to characterize Burkholderia cepacia complex. Molecular typing of these human pathogens yields important information for the clinicians in order to initiate the most appropriate therapy in the case of severe infections and to implement preventive measures for the effective control of transmission of Burkholderia spp.

Role of RND Efflux Pumps in Drug Resistance of Cystic Fibrosis Pathogens

Drug resistance represents a great concern among people with cystic fibrosis (CF), due to the recurrent and prolonged antibiotic therapy they should often undergo. Among Multi Drug Resistance (MDR) determinants, Resistance-Nodulation-cell Division (RND) efflux pumps have been reported as the main contributors, due to their ability to extrude a wide variety of molecules out of the bacterial cell. In this review, we summarize the principal RND efflux pump families described in CF pathogens, focusing on the main Gram-negative bacterial species (Pseudomonas aeruginosa, Burkholderia cenocepacia, Achromobacter xylosoxidans, Stenotrophomonas maltophilia) for which a predominant role of RND pumps has been associated to MDR phenotypes.

Interaction between Lactobacillus reuteri and periodontopathogenic bacteria using in vitro and in vivo (G. mellonella) approaches

Periodontitis is a multifactorial inflammatory disease, and the major cause of tooth loss in adults. New therapies have been proposed for its treatment, including the use of probiotics such as Lactobacillus reuteri. The objective of this study was to evaluate the antimicrobial effects of L. reuteri: live, heat-killed and culture filtrate (cell-free supernatant), on periodontopathogenic bacteria (Fusobacterium nucleatum and Aggregatibacter actinomycetemcomitans) in vitro, as well as the in vivo survival curve, hemocyte density and microbial recovery using Galleria mellonella. For in vitro assays, all preparations reduced colony forming units of F. nucleatum, while only live L. reuteri reduced the growth of A. actinomycetemcomitans. All treatments reduced periodontopathogenic bacteria growth in vivo. The treatment with the supernatant increased the survival of larvae infected with F. nucleatum more than the treatment with live L. reuteri, and none of the treatments altered the survival of A. actinomycetemcomitans-infected larvae. In addition, the treatment with L. reuteri preparations did not alter the hemocyte count of F. nucleatum- and A. actinomycetemcomitans-infected larvae. This study demonstrated that L. reuteri preparations exerted antimicrobial effects and increased the survival of G. mellonella infected by F. nucleatum, although only live L. reuteri was able to reduce the growth of A. actinomycetemcomitans in vitro.

Galleria mellonella as a consolidated in vivo model hosts: New developments in antibacterial strategies and novel drug testing

A greater ethical conscience, new global rules and a modified perception of ethical consciousness entail a more rigorous control on utilizations of vertebrates for in vivo studies. To cope with this new scenario, numerous alternatives to rodents have been proposed. Among these, the greater wax moth Galleria mellonella had a preponderant role, especially in the microbiological field, as demonstrated by the growing number of recent scientific publications. The reasons for its success must be sought in its peculiar characteristics such as the innate immune response mechanisms and the ability to grow at a temperature of 37°C. This review aims to describe the most relevant features of G. mellonella in microbiology, highlighting the most recent and relevant research on antibacterial strategies, novel drug tests and toxicological studies. Although solutions for some limitations are required, G. mellonella has all the necessary host features to be a consolidated in vivo model host.

Optimization and Characterization of a Galleria mellonella Larval Infection Model for Virulence Studies and the Evaluation of Therapeutics Against Streptococcus pneumoniae

Streptococcus pneumoniae is the leading cause of bacterial pneumonia. Infection is linked to high morbidity and mortality rates and antibiotic resistance within this pathogen is on the rise. Therefore, there is a need for novel antimicrobial therapies. To lower the time and costs of the drug discovery process, alternative in vivo models should be considered. As such, Galleria mellonella larvae can be of great value. The larval immunity consisting of several types of haemocytes is remarkably similar to the human innate immune system. Furthermore, these larvae don’t require specific housing, are cheap and are easy to handle. In this study, the use of a G. mellonella infection model to study early pneumococcal infections and treatment is proposed. Firstly, the fitness of this model to study pneumococcal virulence factors is confirmed using streptococcal strains TIGR4, ATCC^®49619, D39 and its capsule-deficient counterpart R6 at different inoculum sizes. The streptococcal polysaccharide capsule is considered the most important virulence factor without which streptococci are unable to sustain an in vivo infection. Kaplan–Meier survival curves showed indeed a higher larval survival after infection with streptococcal strain R6 compared to strain D39. Then, the infection was characterized by determining the number of haemocytes, production of oxygen free radicals and bacterial burden at several time points during the course of infection. Lastly, treatment of infected larvae with the standard antibiotics amoxicillin and moxifloxacin was evaluated. Treatment has proven to have a positive outcome on the course of infection, depending on the administered dosage. These data imply that G. mellonella larvae can be used to evaluate antimicrobial therapies against S. pneumoniae, apart from using the larval model to study streptococcal properties. The in-depth knowledge acquired regarding this model, makes it more suitable for use in future research.

Growth medium-dependent antimicrobial activity of early stage MEP pathway inhibitors

The in vivo microenvironment of bacterial pathogens is often characterized by nutrient limitation. Consequently, conventional rich in vitro culture conditions used widely to evaluate antibacterial agents are often poorly predictive of in vivo activity, especially for agents targeting metabolic pathways. In one such pathway, the methylerythritol phosphate (MEP) pathway, which is essential for production of isoprenoids in bacterial pathogens, relatively little is known about the influence of growth environment on antibacterial properties of inhibitors targeting enzymes in this pathway. The early steps of the MEP pathway are catalyzed by 1-deoxy-d-xylulose 5-phosphate (DXP) synthase and reductoisomerase (IspC). The in vitro antibacterial efficacy of the DXP synthase inhibitor butylacetylphosphonate (BAP) was recently reported to be strongly dependent upon growth medium, with high potency observed under nutrient limitation and exceedingly weak activity in nutrient-rich conditions. In contrast, the well-known IspC inhibitor fosmidomycin has potent antibacterial activity in nutrient-rich conditions, but to date, its efficacy had not been explored under more relevant nutrient-limited conditions. The goal of this work was to thoroughly characterize the effects of BAP and fosmidomycin on bacterial cells under varied growth conditions. In this work, we show that activities of both inhibitors, alone and in combination, are strongly dependent upon growth medium, with differences in cellular uptake contributing to variance in potency of both agents. Fosmidomycin is dissimilar to BAP in that it displays relatively weaker activity in nutrient-limited compared to nutrient-rich conditions. Interestingly, while it has been generally accepted that fosmidomycin activity depends upon expression of the GlpT transporter, our results indicate for the first time that fosmidomycin can enter cells by an alternative mechanism under nutrient limitation. Finally, we show that the potency and relationship of the BAP-fosmidomycin combination also depends upon the growth medium, revealing a striking loss of BAP-fosmidomycin synergy under nutrient limitation. This change in BAP-fosmidomycin relationship suggests a shift in the metabolic and/or regulatory networks surrounding DXP accompanying the change in growth medium, the understanding of which could significantly impact targeting strategies against this pathway. More generally, our findings emphasize the importance of considering physiologically relevant growth conditions for predicting the antibacterial potential MEP pathway inhibitors and for studies of their intracellular targets.

Human Organotypic Models for Anti-infective Research

The use of human organotypic models for biomedical research is experiencing a significant increase due to their biological relevance, the possibility to perform high-throughput analyses, and their cost efficiency. In the field of anti-infective research, comprising the search for novel antipathogenic treatments including vaccines, efforts have been made to reduce the use of animal models. That is due to two main reasons: unreliability of data obtained with animal models and the increasing willingness to reduce the use of animals in research for ethical reasons. Human three-dimensional (3-D) models may substitute and/or complement in vivo studies, to increase the translational value of preclinical data. Here, we provide an overview of recent studies utilizing human organotypic models, resembling features of the cervix, intestine, lungs, brain, and skin in the context of anti-infective research. Furthermore, we focus on the future applications of human skin models and present methodological protocols to culture human skin equivalents and human skin explants.

Effective inhibition of Cbf-14 against Cryptococcus neoformans infection in mice and its related anti-inflammatory activity

Cbf-14 (RLLRKFFRKLKKSV), a designed peptide derived from cathelicidin family AMP, has proven to be potent against drug-resistant bacteria. In the present study, we investigated the anti-cryptococcal activity of Cbf-14 in vitro and in a pulmonary infection mouse model. Sensitivity test indicated that Cbf-14 possessed effective antifungal activity against Cryptococcus neoformans with an MIC of 4-16 µg/ml, and killing experiments showed that fungicidal activity was achieved after only 4 h treatment with Cbf-14 at 4× MIC concentrations in vitro. Meanwhile, Cbf-14 was effective at prolonging the survival of infected mice when compared with controls, and significantly inhibited the secretion of pro-inflammatory cytokines TNF-α, IL-1β and IL-6, suggesting its anti-inflammatory activity against fungal infections. As a positively charged peptide, Cbf-14 was proven to neutralize the negative zeta potential of the fungal cell surface, disrupt the capsule polysaccharide of fungi, and further damage cell membrane integrity. These results were confirmed by flow cytometry analysis of the fluorescence intensity after PI staining, while cell membrane damage could be clearly observed by transmission electron microscopy after Cbf-14 (4× MIC) treatment for 1 h. In addition, Cbf-14 increased the IL-10 levels in cultured RAW 264.7 cells, which were stimulated by C. neoformans infection. The obtained data demonstrated that Cbf-14 could rapidly kill C. neoformans cells in vitro, effectively inhibit C. neoformans induced-infection in mice, and inhibit inflammation in vitro / vivo. Therefore, Cbf-14 could potentially be used for the treatment of fungal infections clinically.

Novel antibiotic combinations proposed for treatment of Burkholderia cepacia complex infections

Effective strategies to manage Burkholderia cepacia complex (Bcc) infections in cystic fibrosis (CF) patients are lacking. We tested combinations of clinically available antibiotics and show that moxifloxacin-ceftazidime could inhibit 16 Bcc clinical isolates at physiologically achievable concentrations. Adding low dose of colistin improved the efficacy of the combo, especially at conditions mimicking CF respiratory secretions.

Environmental Burkholderia cenocepacia Strain Enhances Fitness by Serial Passages during Long-Term Chronic Airways Infection in Mice

Burkholderia cenocepacia is an important opportunistic pathogen in cystic fibrosis (CF) patients, and has also been isolated from natural environments. In previous work, we explored the virulence and pathogenic potential of environmental B. cenocepacia strains and demonstrated that they do not differ from clinical strains in some pathogenic traits. Here, we investigated the ability of the environmental B. cenocepacia Mex1 strain, isolated from the maize rhizosphere, to persist and increase its virulence after serial passages in a mouse model of chronic infection. B. cenocepacia Mex1 strain, belonging to the recA lineage IIIA, was embedded in agar beads and challenged into the lung of C57Bl/6 mice. The mice were sacrificed after 28 days from infection and their lungs were tested for bacterial loads. Agar beads containing the pool of B. cenocepacia colonies from the four sequential passages were used to infect the mice. The environmental B. cenocepacia strain showed a low incidence of chronic infection after the first passage; after the second, third and fourth passages in mice, its ability to establish chronic infection increased significantly and progressively up to 100%. Colonial morphology analysis and genetic profiling of the Mex1-derived clones recovered after the fourth passage from infected mice revealed that they were indistinguishable from the challenged strain both at phenotypic and genetic level. By testing the virulence of single clones in the Galleria mellonella infection model, we found that two Mex1-derived clones significantly increased their pathogenicity compared to the parental Mex1 strain and behaved similarly to the clinical and epidemic B. cenocepacia LMG16656^T. Our findings suggest that serial passages of the environmental B. cenocepacia Mex1 strain in mice resulted in an increased ability to determine chronic lung infection and the appearance of clonal variants with increased virulence in non-vertebrate hosts.

Burkholderia cenocepacia Infections in Cystic Fibrosis Patients: Drug Resistance and Therapeutic Approaches

Burkholderia cenocepacia is an opportunistic pathogen particularly dangerous for cystic fibrosis (CF) patients. It can cause a severe decline in CF lung function possibly developing into a life-threatening systemic infection known as cepacia syndrome. Antibiotic resistance and presence of numerous virulence determinants in the genome make B. cenocepacia extremely difficult to treat. Better understanding of its resistance profiles and mechanisms is crucial to improve management of these infections. Here, we present the clinical distribution of B. cenocepacia described in the last 6 years and methods for identification and classification of epidemic strains. We also detail new antibiotics, clinical trials, and alternative approaches reported in the literature in the last 5 years to tackle B. cenocepacia resistance issue. All together these findings point out the urgent need of new and alternative therapies to improve CF patients’ life expectancy.