Bicarbonate Inhibits Bacterial Growth and Biofilm Formation of Prevalent Cystic Fibrosis Pathogens

Putting bicarbonate on the spot: pharmacological insights for CFTR correction in the airway epithelium

Introduction: Cystic fibrosis (CF) is caused by defective Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) proteins. CFTR controls chloride (Cl-) and bicarbonate (HCO3 -) transport into the Airway Surface Liquid (ASL). We investigated the impact of F508del-CFTR correction on HCO3 - secretion by studying transepithelial HCO3 - fluxes. Methods: HCO3 - secretion was measured by pH-stat technique in primary human respiratory epithelial cells from healthy subjects (WT) and people with CF (pwCF) carrying at least one F508del variant. Its changes after CFTR modulation by the triple combination VX445/661/770 and in the context of TNF-α+IL-17 induced inflammation were correlated to ASL pH and transcriptional levels of CFTR and other HCO3 - transporters of airway epithelia such as SLC26A4 (Pendrin), SLC26A9 and NBCe1. Results: CFTR-mediated HCO3 - secretion was not detected in F508del primary human respiratory epithelial cells. It was rescued up to ∼ 80% of the WT level by VX-445/661/770. In contrast, TNF-α+IL-17 normalized transepithelial HCO3 - transport and increased ASL pH. This was related to an increase in SLC26A4 and CFTR transcript levels. VX-445/661/770 induced an increase in pH only in the context of inflammation. Effects on HCO3 - transport were not different between F508del homozygous and F508del compound heterozygous CF airway epithelia. Conclusion: Our studies show that correction of F508del-CFTR HCO3 - is not sufficient to buffer acidic ASL and inflammation is a key regulator of HCO3 - secretion in CF airways. Prediction of the response to CFTR modulators by theratyping should take into account airway inflammation.

Biotin-dependent cell envelope remodelling is required for Mycobacterium abscessus survival in lung infection

Mycobacterium abscessus is an emerging pathogen causing lung infection predominantly in patients with underlying structural abnormalities or lung disease and is resistant to most frontline antibiotics. As the pathogenic mechanisms of M. abscessus in the context of the lung are not well-understood, we developed an infection model using air-liquid interface culture and performed a transposon mutagenesis and sequencing screen to identify genes differentially required for bacterial survival in the lung. Biotin cofactor synthesis was required for M. abscessus growth due to increased intracellular biotin demand, while pharmacological inhibition of biotin synthesis prevented bacterial proliferation. Biotin was required for fatty acid remodelling, which increased cell envelope fluidity and promoted M. abscessus survival in the alkaline lung environment. Together, these results indicate that biotin-dependent fatty acid remodelling plays a critical role in pathogenic adaptation to the lung niche, suggesting that biotin synthesis and fatty acid metabolism might provide therapeutic targets for treatment of M. abscessus infection.

Attenuating the virulence of the resistant superbug Staphylococcus aureus bacteria isolated from neonatal sepsis by ascorbic acid, dexamethasone, and sodium bicarbonate

Background

Infections affecting neonates caused by Staphylococcus aureus are widespread in healthcare facilities; hence, novel strategies are needed to fight this pathogen. In this study, we aimed to investigate the effectiveness of the FDA-approved medications ascorbic acid, dexamethasone, and sodium bicarbonate to reduce the virulence of the resistant Staphylococcus aureus bacteria that causes neonatal sepsis and seek out suitable alternatives to the problem of multi-drug resistance.

Methods

Tested drugs were assessed phenotypically and genotypically for their effects on virulence factors and virulence-encoding genes in Staphylococcus aureus. Furthermore, drugs were tested in vivo for their ability to reduce Staphylococcus aureus pathogenesis.

Results

Sub-inhibitory concentrations (1/8 MIC) of ascorbic acid, dexamethasone, and sodium bicarbonate reduced the production of Staphylococcus aureus virulence factors, including biofilm formation, staphyloxanthin, proteases, and hemolysin production, as well as resistance to oxidative stress. At the molecular level, qRT-PCR was used to assess the relative expression levels of crtM, sigB, sarA, agrA, hla, fnbA, and icaA genes regulating virulence factors production and showed a significant reduction in the relative expression levels of all the tested genes.

Conclusions

The current findings reveal that ascorbic acid, dexamethasone, and sodium bicarbonate have strong anti-virulence effects against Staphylococcus aureus. Thus, suggesting that they might be used as adjuvants to treat infections caused by Staphylococcus aureus in combination with conventional antimicrobials or as alternative therapies.

The Medium Composition Impacts Staphylococcus aureus Biofilm Formation and Susceptibility to Antibiotics Applied in the Treatment of Bone Infections

The biofilm-associated infections of bones are life-threatening diseases, requiring application of dedicated antibiotics in order to counteract the tissue damage and spread of microorganisms. The in vitro analyses on biofilm formation and susceptibility to antibiotics are frequently carried out using methods that do not reflect conditions at the site of infection. To evaluate the influence of nutrient accessibility on Staphylococcus aureus biofilm development in vitro, a cohesive set of analyses in three different compositional media was performed. Next, the efficacy of four antibiotics used in bone infection treatment, including gentamycin, ciprofloxacin, levofloxacin, and vancomycin, against staphylococcal biofilm, was also assessed. The results show a significant reduction in the ability of biofilm to grow in a medium containing elements occurring in the serum, which also translated into the diversified changes in the efficacy of used antibiotics, compared to the setting in which conventional media were applied. The differences indicate the need for implementation of adequate in vitro models that closely mimic the infection site. The results of the present research may be considered an essential step toward the development of in vitro analyses aiming to accurately indicate the most suitable antibiotic to be applied against biofilm-related infections of bones.

Development of saline loaded mask materials, evaluation of the antimicrobial efficacy and survivability of selected bacteria on these mask materials

Objective

Surgical face masks have been recommended by World Health Organization (WHO) during the COVID-19 pandemic. Nowadays wearing masks have become a norm and lifestyle around the globe. The present investigation was carried out to evaluate the feasibility of developing masks loaded with analytical grade sodium chloride (NaCl), Iodized salts (IS) and Omani sea salt (OSS) with or without sodium bicarbonate (NaHCO₃).

Methods

The saline loaded masks were prepared by soaking the middle layer of the mask in 30% (w/v) saline solutions (NaCl, IS, OSS) with or without 10% NaHCO₃ for 24 h followed by drying at room temperature. The prepared saline solutions and its combinations were evaluated for antimicrobial efficacy against the bacteria like Escherichia coli, Pseudomonas aeruginosa, Proteus vulgaris, Salmonella typhi, and Staphylococcus aureus, and antifungal activity against the Penicillium spp. and Rhizopus spp. by agar diffusion. Optical microscopy was employed to observe the formation of salt crystal in the mask material. Survivability of S. aureus and P. aeruginosa was tested on the mask material loaded with 30% OSS + 10% NaHCO₃ at particular time intervals.

Results

The results showed that a combination of 30% OSS + 10% NaHCO₃ exhibited promising antimicrobial activity against all the bacteria as well as Rhizopus spp. compared to the 30% IS + 10% NaHCO₃. Moreover, the middle layer of the mask loaded with saline solutions of 30% OSS + 10% NaHCO₃ or 30% IS + 10% NaHCO₃ have antibacterial activity, particularly for oral microbiome. On dehydration, the masks materials showed the presence of a significant amount of salt crystals. Survivability tests showed that both S. aureus and P. aeruginosa were killed within 3 h of contact with the salt crystals on the mask materials.

Conclusions

A combination of 30% OSS + 10% NaHCO₃ possessed significant antimicrobial activities on the tested microorganisms. Presence of a significant amount of salt crystals on dehydration of the saline loaded masks can be used as an effective protective barrier to infectious respiratory agents.

Safety of chronic hypertonic bicarbonate inhalation in a cigarette smoke-induced airway irritation guinea pig model

BACKGROUND

Cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) are often associated with airway fluid acidification. Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene leads to impaired bicarbonate secretion contributing to CF airway pathology. Chronic cigarette smoke (CS) -the major cause of COPD- is reported to induce acquired CFTR dysfunction underlying airway acidification and inflammation. We hypothesize that bicarbonate-containing aerosols could be beneficial for patients with CFTR dysfunctions. Thus, we investigated the safety of hypertonic sodium bicarbonate (NaHCO3) inhalation in CS-exposed guinea pigs.

METHODS

Animals were divided into groups inhaling hypertonic NaCl (8.4%) or hypertonic NaHCO3 (8.4%) aerosol for 8 weeks. Subgroups from each treatment groups were further exposed to CS. Respiratory functions were measured at 0 and after 2, 4, 6 and 8 weeks. After 8 weeks blood tests and pulmonary histopathological assessment were performed.

RESULTS

Neither smoking nor NaHCO3-inhalation affected body weight, arterial and urine pH, or histopathology significantly. NaHCO3-inhalation did not worsen respiratory parameters. Moreover, it normalized the CS-induced transient alterations in frequency, peak inspiratory flow, inspiratory and expiratory times.

CONCLUSION

Long-term NaHCO3-inhalation is safe in chronic CS-exposed guinea pigs. Our data suggest that bicarbonate-containing aerosols might be carefully applied to CF patients.

Study of Antibacterial Chemical Substances and Molecular Investigation among Sulfamethoxazole-trimethoprim (SXT)-Resistant Escherichia coli Isolates

Background

Escherichia coli (E. coli) remains one of the leading agents of urinary tract infection (UTIs), it has become resistant to many drugs. Current work aimed to evaluate some chemical substances as antibacterial agents and molecular study of virulence factors associated with UTIs.

Methods

This work involved 133 urine specimens obtained from females' patients suffering from UTIs, Methods of well diffusion and disk diffusion were achieved to assay the effect of some chemical substances and antibiogram profiles toward Sulfamethoxazole-trimethoprim (SXT)-resistant E. coli respectively. Virulence genes were done based on the technique of Polymerase Chain Reaction (PCR).

Results

The results recorded 49/133 (36.84%) E. coli among women suffering UTIs, 28/49 (57.14%) were resistant to SXT drug. imipenem, meropenem, and nitrofurantoin were recorded more effectively. Chemicals substances at the concentration 0.3 (g/ml) recorded percentages of inhibition, reaching 9.143±1.442, 15.36±0.5914, and 21.82±0.8699 for NaHCO3, Ch4c, and Viroxide Super™ respectively. PCR demonstrated that 28/28 (100%) of SXT-resistant E. coli isolates were harbored Sul-2, FeoB and PapC genes, while 14/28 (50%), 15/28 (53.57%), 19/28 (67.85%) and 26/28 (92.85%) in U250 (pet), FumC, Sul-1 and IutA genes, respectively. Sul-3 gene was not observed.

Conclusion

Observed a high percentage of E. coli that were resistant to SXT drug, and having several virulence genes, poses a real threat, it requires a real pause to create substitutions to limit the spreading of this threat.

Bicarbonate modulates delafloxacin activity against MDR Staphylococcus aureus and Pseudomonas aeruginosa

OBJECTIVES

To investigate the utility of recently approved delafloxacin and other fluoroquinolones against leading MDR bacterial pathogens under physiologically relevant conditions.

METHODS

MIC and MBC assays were conducted for MDR strains of Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter baumannii and Klebsiella pneumoniae in the standard antibiotic susceptibility testing medium CAMHB, amended Roswell-Park Memorial Institute tissue culture medium (RPMI+) or 20% fresh human whole blood. In vivo correlation of in vitro findings was performed in a murine P. aeruginosa pneumonia model. Mechanistic bases for the findings were explored by altering media conditions and with established fluoroquinolone accumulation assays.

RESULTS

Fluoroquinolone MICs were increased in RPMI+ compared with CAMHB for all four MDR pathogens. Specifically, delafloxacin MICs were increased 32-fold versus MDR S. aureus and 8-fold versus MDR P. aeruginosa. MBC assays in 20% human whole blood and a murine MDR P. aeruginosa pneumonia model both confirmed that delafloxacin activity was reduced under physiological conditions. Bicarbonate (HCO3-), a key component of host physiology found in RPMI+ but absent from CAMHB, dictated delafloxacin susceptibility in CAMHB and RPMI+ by impairing its intracellular accumulation.

CONCLUSIONS

Standard in vitro antibiotic susceptibility testing conditions overpredicted the effectiveness of delafloxacin against MDR pathogens by failing to capture the role of the biological buffer HCO3- to impair delafloxacin accumulation. This work showcases limitations of our current antibiotic susceptibility testing paradigm and highlights the importance of understanding host microenvironmental conditions that impact true clinical efficacy.

Acidic Microenvironment Determines Antibiotic Susceptibility and Biofilm Formation of Pseudomonas aeruginosa

Pseudomonas aeruginosa is the most prevalent bacterial species that contribute to cystic fibrosis (CF) respiratory failure. The impaired function of CF transmembrane conductance regulator leads to abnormal epithelial Cl^-/HCO₃ ^- transport and acidification of airway surface liquid. However, it remains unclear why the CF lung is most commonly infected by Pseudomonas aeruginosa versus other pathogens. We carried out studies to investigate if lower pH helps Pseudomonas aeruginosa adapt and thrive in the CF-like acidic lung environment. Our results revealed that Pseudomonas aeruginosa generally forms more biofilm, induces antibiotic resistance faster in acidic conditions, and can be reversed by returning the acidic environment to physiologically neutral conditions. Pseudomonas aeruginosa appears to be highly adaptive to the CF-like acidic pH environment. By studying the effects of an acidic environment on bacterial response, we may provide a new therapeutic option in preventing chronic Pseudomonas aeruginosa infection and colonization.

Calcium Chloride Treated Highly Elastane Cotton Fabrics as Antibacterial, Comfortable and Environmentally Friendly Materials

In the paper, the results of experiments on high elastane cotton crochet warp knitting fabrics treated with different calcium chloride solutions by the pad-dry-cure method have been reported. The tests for evaluating the antibacterial activity, thermophysiological comfort properties, physical performance of the samples were performed. In addition, the characterization analyses, including SEM, EDX, FTIR-attenuated total reflectance (ATR), and XRD, afforded indications of the good crosslinking of the CaCl2 onto the cotton/elastane samples. At a higher degree of activity, the calcium-chloride-treated fabrics were rated as having good antibacterial activity, being exceptionally breathable, and being comfortable with good physical properties such as stiffness, handle, and whiteness properties.

The High Impact of Staphylococcus aureus Biofilm Culture Medium on In Vitro Outcomes of Antimicrobial Activity of Wound Antiseptics and Antibiotic

The staphylococcal biofilm-based infections of wounds still pose a significant therapeutical challenge. Treated improperly, they increase the risk of limb amputation or even death of the patient. The present algorithms of infected wound treatment include, among others, the application of antiseptic substances. In vitro wound biofilm models are applied in order to scrutinize their activity. In the present work, using a spectrum of techniques, we showed how the change of a single variable (medium composition) in the standard in vitro model translates not only to shift in staphylococcal biofilm features but also to the change of efficacy of clinically applied wound antimicrobials such as octenidine, polyhexamethylene biguanide, chlorhexidine, hypochlorite solutions, and locally applied gentamycin. The data presented in this study may be of a pivotal nature, taking into consideration the fact that results of in vitro analyses are frequently used to propagate application of specific antimicrobials in hospitals and ambulatory care units.

CFTR Protein: Not Just a Chloride Channel?

Cystic fibrosis (CF) is a recessive genetic disease caused by mutations in a gene encoding a protein called Cystic Fibrosis Transmembrane Conductance Regulator (CFTR). The CFTR protein is known to acts as a chloride (Cl-) channel expressed in the exocrine glands of several body systems where it also regulates other ion channels, including the epithelial sodium (Na+) channel (ENaC) that plays a key role in salt absorption. This function is crucial to the osmotic balance of the mucus and its viscosity. However, the pathophysiology of CF is more challenging than a mere dysregulation of epithelial ion transport, mainly resulting in impaired mucociliary clearance (MCC) with consecutive bronchiectasis and in exocrine pancreatic insufficiency. This review shows that the CFTR protein is not just a chloride channel. For a long time, research in CF has focused on abnormal Cl- and Na+ transport. Yet, the CFTR protein also regulates numerous other pathways, such as the transport of HCO3-, glutathione and thiocyanate, immune cells, and the metabolism of lipids. It influences the pH homeostasis of airway surface liquid and thus the MCC as well as innate immunity leading to chronic infection and inflammation, all of which are considered as key pathophysiological characteristics of CF.

Non-Photosynthetic CO2 Utilization to Increase Fatty Acid Production in Yarrowia lipolytica

Metabolic engineering of non-photosynthetic microorganisms to increase the utilization of CO₂ has been focused on as a green strategy to convert CO₂ into valuable products such as fatty acids. In this study, a CO₂ utilization pathway involving carbonic anhydrase and biotin carboxylase was formed to recycle CO₂ in the oleaginous yeast Yarrowia lipolytica, thereby increasing the production of fatty acids. In the recombinant strain in which the CO₂ utilization pathway was introduced, the production of fatty acids was 10.7 g/L, which was 1.5-fold higher than that of the wild-type strain. The resulting strain had a 1.4-fold increase in dry cell mass compared to the wild-type strain. In addition, linoleic acid was 47.7% in the fatty acid composition of the final strain, which was increased by 11.6% compared to the wild-type strain. These results can be applied as an essential technology for developing efficient and eco-friendly processes by directly utilizing CO₂.

Cautionary Notes on the Use of Arabinose- and Rhamnose-Inducible Expression Vectors in Pseudomonas aeruginosa

The Pseudomonas aeruginosa virulence factor regulator (Vfr) is a cyclic AMP (cAMP)-responsive transcription factor homologous to the Escherichia coli cAMP receptor protein (CRP). Unlike CRP, which plays a central role in E. coli energy metabolism and catabolite repression, Vfr is primarily involved in the control of P. aeruginosa virulence factor expression. Expression of the Vfr regulon is controlled at the level of vfr transcription, Vfr translation, cAMP synthesis, and cAMP degradation. While investigating mechanisms that regulate Vfr translation, we placed vfr transcription under the control of the rhaBp rhamnose-inducible promoter system (designated P_Rha) and found that P_Rha promoter activity was highly dependent upon vfr. Vfr dependence was also observed for the araBp arabinose-inducible promoter (designated P_BAD). The observation of Vfr dependence was not entirely unexpected. Both promoters are derived from E. coli, where maximal promoter activity is dependent upon CRP. Like CRP, we found that Vfr directly binds to promoter probes derived from the P_Rha and P_BAD promoters in vitro. Because Vfr-cAMP activity is highly integrated into numerous global regulatory systems, including c-di-GMP signaling, the Gac/Rsm system, MucA/AlgU/AlgZR signaling, and Hfq/sRNAs, the potential exists for significant variability in P_Rha and P_BAD promoter activity in a variety of genetic backgrounds, and use of these promoter systems in P. aeruginosa should be employed with caution. IMPORTANCE Heterologous gene expression and complementation constitute a valuable and widely utilized tool in bacterial genetics. The arabinose-inducible P_araBAD (P_BAD) and rhamnose-inducible P_rhaBAD (P_Rha) promoter systems are commonly used in P. aeruginosa genetics and prized for the tight control and dynamic expression ranges that can be achieved. In this study, we demonstrate that the activity of both promoters is dependent upon the cAMP-dependent transcription factor Vfr. While this poses an obvious problem for use in a vfr mutant background, the issue is more pervasive, considering that vfr transcription/synthesis and cAMP homeostasis are highly integrated into the cellular physiology of the organism and influenced by numerous global regulatory systems. Fortunately, the synthetic P_Tac promoter is not subject to Vfr regulatory control.

Rheological effects of hypertonic saline and sodium bicarbonate solutions on cystic fibrosis sputum in vitro

BACKGROUND

Cystic fibrosis (CF) is a life-threatening multiorgan genetic disease, particularly affecting the lungs, where recurrent infections are the main cause of reduced life expectancy. In CF, mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein impair transepithelial electrolyte and water transport, resulting in airway dehydration, and a thickening of the mucus associated with abnormal viscoelastic properties. Our aim was to develop a rheological method to assess the effects of hypertonic saline (NaCl) and NaHCO₃ on CF sputum viscoelasticity in vitro, and to identify the critical steps in sample preparation and in the rheological measurements.

METHODS

Sputum samples were mixed with hypertonic salt solutions in vitro in a ratio of either 10:4 or 10:1. Distilled water was applied as a reference treatment. The rheological properties of sputum from CF patients, and the effects of these in vitro treatments, were studied with a rheometer at constant frequency and strain, followed by frequency sweep tests, where storage modulus (G'), loss modulus (G″) and loss factor were determined.

RESULTS

We identified three distinct categories of sputum: (i) highly elastic (G' > 100,000 Pa), (ii) elastic (100,000 Pa > G' > 1000 Pa), and (iii) viscoelastic (G' < 1000). At the higher additive ratio (10:4), all of the added solutions were found to significantly reduce the gel strength of the sputum, but the most pronounced changes were observed with NaHCO₃ (p < 0.001). Samples with high elasticity exhibited the greatest changes while, for less elastic samples, a weakening of the gel structure was observed when they were treated with water or NaHCO₃, but not with NaCl. For the viscoelastic samples, the additives did not cause significant changes in the parameters. When the lower additive ratio (10:1) was used, the mean values of the rheological parameters usually decreased, but the changes were not statistically significant.

CONCLUSION

Based on the rheological properties of the initial sputum samples, we can predict with some confidence the treatment efficacy of each of the alternative additives. The marked differences between the three categories suggest that it is advisable to evaluate each sample individually using a rheological approach such as that described here.

Bicarbonate Evokes Reciprocal Changes in Intracellular Cyclic di-GMP and Cyclic AMP Levels in Pseudomonas aeruginosa

The formation of Pseudomonas aeruginosa biofilms in cystic fibrosis (CF) is one of the most common causes of morbidity and mortality in CF patients. Cyclic di-GMP and cyclic AMP are second messengers regulating the bacterial lifestyle transition in response to environmental signals. We aimed to investigate the effects of extracellular pH and bicarbonate on intracellular c-di-GMP and cAMP levels, and on biofilm formation. P. aeruginosa was inoculated in a brain−heart infusion medium supplemented with 25 and 50 mM NaCl in ambient air (pH adjusted to 7.4 and 7.7 respectively), or with 25 and 50 mM NaHCO3 in 5% CO2 (pH 7.4 and 7.7). After 16 h incubation, c-di-GMP and cAMP were extracted and their concentrations determined. Biofilm formation was investigated using an xCelligence real-time cell analyzer and by crystal violet assay. Our results show that HCO3− exposure decreased c-di-GMP and increased cAMP levels in a dose-dependent manner. Biofilm formation was also reduced after 48 h exposure to HCO3−. The reciprocal changes in second messenger concentrations were not influenced by changes in medium pH or osmolality. These findings indicate that HCO3− per se modulates the levels of c-di-GMP and cAMP, thereby inhibiting biofilm formation and promoting the planktonic lifestyle of the bacteria.

The Application of Bicarbonate Recovers the Chemical-Physical Properties of Airway Surface Liquid in Cystic Fibrosis Epithelia Models

Cystic fibrosis (CF) is a genetic disease associated with the defective function of the cystic fibrosis transmembrane conductance regulator (CFTR) protein that causes obstructive disease and chronic bacterial infections in airway epithelia. Deletion of phenylalanine at position 508, p.F508del, the most frequent mutation among CF patients, causes a folding and traffic defect, resulting in a dramatic reduction in the CFTR expression. To investigate whether the direct application of bicarbonate could modify the properties of the airway surface liquid (ASL), we measured the micro-viscosity, fluid transport and pH of human bronchial epithelial cells monolayers. We have demonstrated that the treatment of a CF-epithelia with an iso-osmotic solution containing bicarbonate is capable of reducing both, the ASL viscosity and the apical fluid re-absorption. We suggest the possibility of design a supportive treatment based on topical application of bicarbonate, or any other alkaline buffer.

Airway Surface Liquid pH Regulation in Airway Epithelium Current Understandings and Gaps in Knowledge

Knowledge on the mechanisms of acid and base secretion in airways has progressed recently. The aim of this review is to summarize the known mechanisms of airway surface liquid (ASL) pH regulation and their implication in lung diseases. Normal ASL is slightly acidic relative to the interstitium, and defects in ASL pH regulation are associated with various respiratory diseases, such as cystic fibrosis. Basolateral bicarbonate (HCO3-) entry occurs via the electrogenic, coupled transport of sodium (Na+) and HCO3-, and, together with carbonic anhydrase enzymatic activity, provides HCO3- for apical secretion. The latter mainly involves CFTR, the apical chloride/bicarbonate exchanger pendrin and paracellular transport. Proton (H+) secretion into ASL is crucial to maintain its relative acidity compared to the blood. This is enabled by H+ apical secretion, mainly involving H+/K+ ATPase and vacuolar H+-ATPase that carry H+ against the electrochemical potential gradient. Paracellular HCO3- transport, the direction of which depends on the ASL pH value, acts as an ASL protective buffering mechanism. How the transepithelial transport of H+ and HCO3- is coordinated to tightly regulate ASL pH remains poorly understood, and should be the focus of new studies.

The Balance between Two Branches of RAS Can Protect from Severe COVID-19 Course

The COVID-19 pandemic has swept the world and required the mobilization of scientists and clinicians around the world to combat this serious disease. Along with SARS-CoV-2 virology research, understanding of the fundamental physiological processes, molecular and cellular mechanisms and intracellular signaling pathways underlying the clinical manifestations of COVID-19 is important for effective therapy of this disease. The review describes in detail the interaction of the components of the renin-angiotensin system (RAS) and receptors of end-glycosylated products (RAGE), which plays a special role in normal lung physiology and in pathological conditions in COVID-19, including the development of acute respiratory distress syndrome and "cytokine storm". A separate section is devoted to the latest developments aimed at correcting the dysfunction of the RAS caused by the binding of the virus to angiotensin converting enzyme 2 (ACE2)- the central element of this system. Analysis of published theoretical, clinical, and experimental data indicates the need for a complex treatment to prevent a severe course of COVID-19 using MasR agonists, blockers of the AT1R and NF-κB signaling pathway, as well as compounds with neuroprotective and neuroregenerative effects.

Current and novel therapeutic strategies for the management of cystic fibrosis

Introduction: Cystic fibrosis (CF), is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene and affects thousands of people throughout the world. Lung disease is the leading cause of death in CF patients. Despite the advances in treatments, the management of CF mainly targets symptoms. Recent CFTR modulators however target common mutations in patients, alleviating symptoms of CF. Unfortunately, there is still no approved treatments for patients with rare mutations to date.Areas covered: This paper reviews current treatments of CF that mitigate symptoms and target genetic defects. The use of gene and drug delivery systems such as viral or non-viral vectors and nano-compounds to enhance CFTR expression and the activity of antimicrobials against chronic pulmonary infections respectively, will also be discussed.Expert opinion: Nano-compounds tackle biological barriers to drug delivery and revitalize antimicrobials, anti-inflammatory drugs and even genes delivery to CF patients. Gene therapy and gene editing are of particular interest because they have the potential to directly target genetic defects. Nanoparticles should be formulated to more specifically target epithelial cells, and biofilms. Finally, the development of more potent gene vectors to increase the duration of gene expression and reduce inflammation is a promising strategy to eventually cure CF.

Antibacterial Effects of Bicarbonate in Media Modified to Mimic Cystic Fibrosis Sputum

Cystic fibrosis (CF) is a hereditary disease caused by mutations in the gene encoding an epithelial anion channel. In CF, Cl⁻ and HCO₃⁻ hyposecretion, together with mucin hypersecretion, leads to airway dehydration and production of viscous mucus. This habitat is ideal for colonization by pathogenic bacteria. We have recently demonstrated that HCO₃⁻ inhibits the growth and biofilm formation of Pseudomonas aeruginosa and Staphylococcus aureus when tested in laboratory culture media. Using the same bacteria our aim was to investigate the effects of HCO₃⁻ in artificial sputum medium (ASM), whose composition resembles CF mucus. Control ASM containing no NaHCO₃ was incubated in ambient air (pH 7.4 or 8.0). ASM containing NaHCO₃ (25 and 100 mM) was incubated in 5% CO₂ (pH 7.4 and 8.0, respectively). Viable P. aeruginosa and S. aureus cells were counted by colony-forming unit assay and flow cytometry after 6 h and 17 h of incubation. Biofilm formation was assessed after 48 h. The data show that HCO₃⁻ significantly decreased viable cell counts and biofilm formation in a concentration-dependent manner. These effects were due neither to extracellular alkalinization nor to altered osmolarity. These results show that HCO₃⁻ exerts direct antibacterial and antibiofilm effects on prevalent CF bacteria.

Antimicrobial Susceptibility Testing of Antimicrobial Peptides to Better Predict Efficacy

During the development of antimicrobial peptides (AMP) as potential therapeutics, antimicrobial susceptibility testing (AST) stands as an essential part of the process in identification and optimisation of candidate AMP. Standard methods for AST, developed almost 60 years ago for testing conventional antibiotics, are not necessarily fit for purpose when it comes to determining the susceptibility of microorganisms to AMP. Without careful consideration of the parameters comprising AST there is a risk of failing to identify novel antimicrobials at a time when antimicrobial resistance (AMR) is leading the planet toward a post-antibiotic era. More physiologically/clinically relevant AST will allow better determination of the preclinical activity of drug candidates and allow the identification of lead compounds. An important consideration is the efficacy of AMP in biological matrices replicating sites of infection, e.g., blood/plasma/serum, lung bronchiolar lavage fluid/sputum, urine, biofilms, etc., as this will likely be more predictive of clinical efficacy. Additionally, specific AST for different target microorganisms may help to better predict efficacy of AMP in specific infections. In this manuscript, we describe what we believe are the key considerations for AST of AMP and hope that this information can better guide the preclinical development of AMP toward becoming a new generation of urgently needed antimicrobials.

Nutrient-dependent morphological variability of Bacteroides thetaiotaomicron

Unique morphologies can enable bacteria to survive in their native environment. Furthermore, many bacteria change their cell shape to adapt to different environmental conditions. For instance, some bacteria increase their surface area under carbon or nitrogen starvation. Bacteriodes thetaiotaomicron is an abundant human gut species; it efficiently degrades a number of carbohydrates and also supports the growth of other bacteria by breaking down complex polysaccharides. The gut provides a variable environment as nutrient availability is subject to the diet and health of the host, yet how gut bacteria adapt and change their morphologies under different nutrient conditions has not been studied. Here, for the first time, we report an elongated B. thetaiotaomicron morphology under sugar-limited conditions using live-cell imaging; this elongated morphology is enhanced in the presence of sodium bicarbonate. Similarly, we also observed that sodium bicarbonate produces an elongated-length phenotype in another Gram-negative gut bacterium, Escherichia coli . The increase in cell length might provide an adaptive advantage for cells to survive under nutrient-limited conditions.

Sterol-Response Pathways Mediate Alkaline Survival in Diverse Fungi

The ability for cells to maintain homeostasis in the presence of extracellular stress is essential for their survival. Stress adaptations are especially important for microbial pathogens to respond to rapidly changing conditions, such as those encountered during the transition from the environment to the infected host. Many fungal pathogens have acquired the ability to quickly adapt to changes in extracellular pH to promote their survival in the various microenvironments encountered during a host infection. For example, the fungus-specific Rim/Pal alkaline response pathway has been well characterized in many fungal pathogens, including Cryptococcus neoformans However, alternative mechanisms for sensing and responding to host pH have yet to be extensively studied. Recent observations from a genetic screen suggest that the C. neoformans sterol homeostasis pathway is required for growth at elevated pH. This work explores interactions among mechanisms of membrane homeostasis, alkaline pH tolerance, and Rim pathway activation. We find that the sterol homeostasis pathway is necessary for growth in an alkaline environment and that an elevated pH is sufficient to induce Sre1 activation. This pH-mediated activation of the Sre1 transcription factor is linked to the biosynthesis of ergosterol but is not dependent on Rim pathway signaling, suggesting that these two pathways are responding to alkaline pH independently. Furthermore, we discover that C. neoformans is more susceptible to membrane-targeting antifungals under alkaline conditions, highlighting the impact of microenvironmental pH on the treatment of invasive fungal infections. Together, these findings further connect membrane integrity and composition with the fungal pH response and pathogenesis.IMPORTANCE The work described here further elucidates how microorganisms sense and adapt to changes in their environment to establish infections in the human host. Specifically, we uncover a novel mechanism by which an opportunistic human fungal pathogen, Cryptococcus neoformans, responds to increases in extracellular pH in order to survive and thrive within the relatively alkaline environment of the human lung. This mechanism, which is intimately linked with fungal membrane sterol homeostasis, is independent of the previously well-studied alkaline response Rim pathway. Furthermore, this ergosterol-dependent alkaline pH response is present in Candida albicans, indicating that this mechanism spans diverse fungal species. These results are also relevant for novel antimicrobial drug development as we show that currently used ergosterol-targeting antifungals are more active in alkaline environments.

The Effect of Sodium Bicarbonate, a Beneficial Adjuvant Molecule in Cystic Fibrosis, on Bronchial Epithelial Cells Expressing a Wild-Type or Mutant CFTR Channel

Clinical and experimental results with inhaled sodium bicarbonate as an adjuvant therapy in cystic fibrosis (CF) are promising due to its mucolytic and bacteriostatic properties, but its direct effect has not been studied on respiratory epithelial cells. Our aim was to establish and characterize co-culture models of human CF bronchial epithelial (CFBE) cell lines expressing a wild-type (WT) or mutant (deltaF508) CF transmembrane conductance regulator (CFTR) channel with human vascular endothelial cells and investigate the effects of bicarbonate. Vascular endothelial cells induced better barrier properties in CFBE cells as reflected by the higher resistance and lower permeability values. Activation of CFTR by cAMP decreased the electrical resistance in WT but not in mutant CFBE cell layers confirming the presence and absence of functional channels, respectively. Sodium bicarbonate (100 mM) was well-tolerated by CFBE cells: it slightly reduced the impedance of WT but not that of the mutant CFBE cells. Sodium bicarbonate significantly decreased the more-alkaline intracellular pH of the mutant CFBE cells, while the barrier properties of the models were only minimally changed. These observations indicate that sodium bicarbonate is beneficial to deltaF508-CFTR expressing CFBE cells. Thus, sodium bicarbonate may have a direct therapeutic effect on the bronchial epithelium.

A Mathematical Model for the Hydrogenotrophic Metabolism of Sulphate-Reducing Bacteria

Sulphate-reducing bacteria (SRB) are studied across a range of scientific fields due to their characteristic ability to metabolise sulphate and produce hydrogen sulphide, which can lead to significant consequences for human activities. Importantly, they are members of the human gastrointestinal microbial population, contributing to the metabolism of dietary and host secreted molecules found in this environment. The role of the microbiota in host digestion is well studied, but the full role of SRB in this process has not been established. Moreover, from a human health perspective, SRB have been implicated in a number of functional gastrointestinal disorders such as Irritable Bowel Syndrome and the development of colorectal cancer. To assist with the study of SRB, we present a mathematical model for the growth and metabolism of the well-studied SRB, Desulfovibrio vulgaris in a closed system. Previous attempts to model SRB have resulted in complex or highly specific models that are not easily adapted to the study of SRB in different environments, such as the gastrointestinal tract. We propose a simpler, Monod-based model that allows for easy alteration of both key parameter values and the governing equations to enable model adaptation. To prevent any incorrect assumptions about the nature of SRB metabolic pathways, we structure the model to consider only the concentrations of initial and final metabolites in a pathway, which circumvents the current uncertainty around hydrogen cycling by SRB. We parameterise our model using experiments with varied initial substrate conditions, obtaining parameter values that compare well with experimental estimates in the literature. We then validate our model against four independent experiments involving D. vulgaris with further variations to substrate availability. Further use of the model will be possible in a number of settings, notably as part of larger models studying the metabolic interactions between SRB and other hydrogenotrophic microbes in the human gastrointestinal tract and how this relates to functional disorders.

High levels of cAMP inhibit Pseudomonas aeruginosa biofilm formation through reduction of the c-di-GMP content

The human pathogen Pseudomonas aeruginosa can cause both acute infections and chronic biofilm-based infections. Expression of acute virulence factors is positively regulated by cAMP, whereas biofilm formation is positively regulated by c-di-GMP. We provide evidence that increased levels of cAMP, caused by either a lack of degradation or increased production, inhibit P. aeruginosa biofilm formation. cAMP-mediated inhibition of P. aeruginosa biofilm formation required Vfr, and involved a reduction of the level of c-di-GMP, as well as reduced production of biofilm matrix components. A mutant screen and characterization of defined knockout mutants suggested that a subset of c-di-GMP-degrading phosphodiesterases is involved in cAMP-Vfr-mediated biofilm inhibition in P. aeruginosa.