N-Chlorotaurine Exhibits Fungicidal Activity against Therapy-Refractory Scedosporium Species and Lomentospora prolificans

N-chlorotaurine is highly active against respiratory viruses including SARS-CoV-2 (COVID-19) in vitro

N-chlorotaurine (NCT) a long-lived oxidant generated by leukocytes, can be synthesized chemically and applied topically as an anti-infective to different body sites, including the lung via inhalation. Here, we demonstrate the activity of NCT against viruses causing acute respiratory tract infections, namely severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), influenza viruses, and respiratory syncytial virus (RSV). Virucidal activity of NCT was tested in plaque assays, confirmed by RT-qPCR assays. Attack on virus proteins was investigated by mass spectrometry. NCT revealed broad virucidal activity against all viruses tested at 37°C and pH 7. A significant reduction in infectious particles of SARS-CoV-2 isolates from early 2020 by 1 log₁₀ was detected after 15 min of incubation in 1% NCT. Proteinaceous material simulating body fluids enhanced this activity by transchlorination mechanisms (1 −2 log₁₀ reduction within 1–10 min). Tested SARS-CoV-2 variants B.1.1.7 (Alpha) und B.1.351 (Beta) showed a similar susceptibility. Influenza virus infectious particles were reduced by 3 log₁₀ (H3N2) to 5 log₁₀ (H1N1pdm), RSV by 4 log₁₀ within a few min. Mass spectrometry of NCT-treated SARS-CoV-2 spike protein and 3C-like protease, influenza virus haemagglutinin and neuraminidase, and RSV fusion glycoprotein disclosed multiple sites of chlorination and oxidation as the molecular mechanism of action. Application of 1.0% NCT as a prophylactic and therapeutic strategy against acute viral respiratory tract infections deserves comprehensive clinical investigation.

Comparative Fungicidal Activities of N-Chlorotaurine and Conventional Antiseptics against Candida spp. Isolated from Vulvovaginal Candidiasis

N-chlorotaurine (NCT), the N-chloro derivative of the amino acid taurine, is a long-lived oxidant produced by stimulated human leucocytes. NCT has antimicrobial activities which are generally enhanced in the presence of organic material. The aim of this study was to investigate fungicidal effects of NCT and conventional antiseptics against Candida isolated from vulvovaginal candidiasis (VVC). Chlorhexidine (CHX, 1.6%), octenidine dihydrochloride (OCT, 0.08%), povidone iodine (PVP-I, 8%), boric acid (8%), and NCT (0.1% (5.5 mM)) were evaluated against forty-four Candida isolates, according to European Standard methods, at 30, 60, 90, and 120 min and 24 h in the presence of skim milk as an organic material. CHX, OCT, and PVP-I showed rapid fungicidal activity against all Candida isolates with 5–6 log10 reduction of viable counts after 30 min, whereas boric acid and NCT needed 1 h against Candida albicans and 2 h against non-albicans Candida for a significant 3 log10 reduction. NCT showed fungicidal activity (defined as ≥4 log10 reduction) against C. albicans within 90 min and C. non–albicans within 24 h. Based upon all presently available data, including our results, NCT could be used as a new agent for treatment of local fungal infections such as VVC.

Efficacy of Inhaled N-Chlorotaurine in a Mouse Model of Lichtheimia corymbifera and Aspergillus fumigatus Pneumonia

N-chlorotaurine (NCT) can be used topically as a well-tolerated anti-infective at different body sites. The aim of this study was to investigate the efficacy of inhaled NCT in a mouse model of fungal pneumonia. Specific pathogen-free female C57BL/6JRj seven-week-old mice were immune-suppressed with cyclophosphamide. After 4 days, the mice were inoculated intranasally with 1.5 × 10E7 spores of Lichtheimia corymbifera or 1.0 × 10E7 spores of Aspergillus fumigatus. They were randomized and treated three times daily for 10 min with aerosolized 1% NCT or 0.9% sodium chloride starting 1 h after the inoculation. The mice were observed for survival for two weeks, and fungal load, blood inflammation parameters, bronchoalveolar lavage, and histology of organs were evaluated upon their death or at the end of this period. Inhalations were well-tolerated. After challenge with L. corymbifera, seven out of the nine mice (77.8%) survived for 15 days in the test group, which was in strong contrast to one out of the nine mice (11.1%) in the control group (p = 0.0049). The count of colony-forming units in the homogenized lung tissues came to 1.60 (1.30; 1.99; median, quartiles) log₁₀ in the test group and to 4.26 (2.17; 4.53) log₁₀ in the control group (p = 0.0032). Body weight and temperature, white blood count, and haptoglobin significantly improved with NCT treatment. With A. fumigatus, all the mice except for one in the test group died within 4 days without a significant difference from the control group. Inhaled NCT applied early demonstrated a highly significant curative effect in L. corymbifera pneumonia, while this could not be shown in A. fumigatus pneumonia, probably due to a too high inoculum. Nevertheless, this study for the first time disclosed efficacy of NCT in pneumonia in vivo.

Activity of N-Chlorotaurine against Long-Term Biofilms of Bacteria and Yeasts

Background: N-chlorotaurine (NCT), an antiseptic that originates from the human defense system, has broad-spectrum microbicidal activity and is well tolerated by human tissue and applicable to sensitive body regions. Bacteria in short-term biofilms, too, have been shown to be killed by NCT. It was the aim of the present study to demonstrate the activity of NCT against bacteria and yeasts in longer-lasting biofilms, including their co-culture. Materials and methods: Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella variicola biofilms were grown for 14 weeks in MBECTM inoculator with 96 well base. Some pegs were pinched off weekly and incubated in 1% NCT in PBS (PBS only for controls) at pH 7.1 and 37 °C, for 30 and 60 min. Subsequently, bacteria were resuspended by ultrasonication and subjected to quantitative cultures. Similar tests were conducted with C. albicans biofilms grown on metal (A2-steel) discs for 4 weeks. Mixed co-cultures of C. albicans plus each of the three bacterial strains on metal discs were grown for 5-7 weeks and weekly evaluated, as mentioned above. Results: Single biofilms of S. aureus, P. aeruginosa, and K. variicola grew to approximately 1 × 106 colony forming units (CFU)/mL and C. albicans to 1 × 105 CFU/mL. In combined biofilms, the CFU count was about 1 log10 lower. Viable counts of biofilms of single bacteria were reduced by 2.8 to 5.6 log10 in 1% NCT after 60 min (0.9 to 4.7 log10 after 30 min) with Gram-negative bacteria being more susceptible than S. aureus. Significant reduction of C. albicans by 2.0 to 2.9 log10 occurred after 4 h incubation. In combined biofilms, viable counts of C. albicans were reduced by 1.1 to 2.4 log10 after 4 h, while they reached the detection limit after 1 to 2 h with bacteria (2.0 to > 3.5 log10 reduction). Remarkably, older biofilms demonstrated no increase in resistance but constant susceptibility to NCT. This was valid for all tested pathogens. In electron microscopy, morphological differences between NCT-treated and non-treated biofilms could be found. Conclusions: NCT is active against long-term biofilms of up to several months irrespective of their age. Combined biofilm cultures of yeasts and bacteria show a similar susceptibility pattern to NCT as single ones. These results contribute to the explanation of the clinical efficacy of NCT, for instance, in infected chronic wounds and purulently coated crural ulcerations.

N-chlorotaurine, a potent weapon against multiresistant bacteria

Aims

N‐chlorotaurine (NCT) is a body‐own mild oxidizing antiseptic that can be applied topically as a well‐tolerated anti‐infective at many body sites. The objective of this study was to demonstrate its activity against representative nosocomial multidrug‐resistant bacteria.

Methods and Results

The bactericidal activity of NCT was tested in quantitative killing assays against a panel of multiresistant Gram‐positive and Gram‐negative clinical isolates. N‐chlorotaurine (1%, 55 mmol l⁻¹) reduced the number of CFU of strains of methicillin‐resistant Staphylococcus aureus, linezolid‐resistant Staphylococcus epidermidis, vancomycin‐resistant, and linezolid‐ and vancomycin‐resistant Enterococcus faecium, 3MRGN and 4MRGN Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii and Klebsiella pneumoniae by at least 2 log₁₀ steps after 15 min and completely or nearly to the detection limit after 30 min at pH 7·1 and 37°C.

Conclusion

The activity of NCT against these clinical isolates is similar to that against non‐resistant ATCC strains and therefore not influenced by antibiotic resistance. This can be explained by the oxidizing and chlorinating mechanism of action of NCT, which leads to an attack of multiple targets in the microorganisms.

Significance and Impact of the Study

The bactericidal spectrum of NCT is not restricted by resistance against antibiotics. Therefore, it can be used against resistant strains, too.

Exposure to N-chlorotaurine induces oxidative stress responses in Aspergillus fumigatus

PURPOSE

The neutrophil-derived oxidant N-chlorotaurine (NCT) displays remarkable in vivo tolerability and efficacy against a range of pathogens. The aim of this study was to characterize the response of the pulmonary pathogen Aspergillus fumigatus to NCT.

METHODOLOGY

The effect of NCT on the growth and viability of A. fumigatus was characterized. NCT-induced alteration of amino acids and gliotoxin from A. fumigatus mycelium was assessed. Label-free shotgun quantitative proteomic analysis was performed on A. fumigatus exposed to NCT for 24 h.

RESULTS

Incubation of A. fumigatus with NCT at concentrations ranging from 6.8 to 55 mM decreased conidial growth and viability, and mycelium biomass relative to the controls. Exposure to NCT (13.77 mM) resulted in increased amino acids and gliotoxin levels from A. fumigatus mycelium. Exposure of A. fumigatus mycelium to NCT (6.8 mM) revealed an enrichment in proteins associated with the ribosome, transcription and translation and non-ribosomal peptide biosynthesis (e.g. Pes1, Pes3), which play an essential role in oxidative stress resistance in A. fumigatus. A decrease in the abundance of proteins associated with fumagillin and pseurotin biosynthesis highlighted the anti-virulence activity of NCT.

CONCLUSION

These results indicate that NCT induces an oxidative stress response in A. fumigatus as evidenced by alterations in the proteome and inhibits conidial and mycelial growth. Clinical investigations of topical application of NCT to treat Aspergillus infections are encouraged.

Scedosporium and Lomentospora: an updated overview of underrated opportunists

Species of Scedosporium and Lomentospora are considered as emerging opportunists, affecting immunosuppressed and otherwise debilitated patients, although classically they are known from causing trauma-associated infections in healthy individuals. Clinical manifestations range from local infection to pulmonary colonization and severe invasive disease, in which mortality rates may be over 80%. These unacceptably high rates are due to the clinical status of patients, diagnostic difficulties, and to intrinsic antifungal resistance of these fungi. In consequence, several consortia have been founded to increase research efforts on these orphan fungi. The current review presents recent findings and summarizes the most relevant points, including the Scedosporium/Lomentospora taxonomy, environmental distribution, epidemiology, pathology, virulence factors, immunology, diagnostic methods, and therapeutic strategies.

Taurine chloramine potentiates phagocytic activity of peritoneal macrophages through up-regulation of dectin-1 mediated by heme oxygenase-1-derived carbon monoxide

Resolution of inflammation that occurs after microbial infection or tissue damage is an important physiologic process in maintaining or restoring host homeostasis. Taurine chloramine (TauCl) is formed by a reaction between taurine and hypochlorite in leukocytes, and it is especially abundant in activated neutrophils that encounter an oxidative burst. As neutrophils undergo apoptosis, TauCl is released to the extracellular matrix at the inflamed sites, thereby affecting coexisting macrophages in the inflammatory microenvironment. In this study, we investigated the role of TauCl in phagocytosis by macrophages during resolution of fungal infection-induced inflammation. We found that exogenous TauCl substantially increased the phagocytic efficiency of macrophages through up-regulation of dectin-1, a receptor for fungal β-1,3-glucans, which is present on the membrane of macrophages. Our previous studies demonstrated the induction of heme oxygenase-1 (HO-1) expression in murine peritoneal macrophages treated with TauCl. In the present study, knocking out HO-1 or pharmacologic inhibition of HO-1 with zinc protoporphyrin IX attenuated the TauCl-induced expression of dectin-1 and subsequent phagocytosis. Furthermore, carbon monoxide (CO), a by-product of the HO-1-catalyzed reaction, induced expression of dectin-1 and potentiated phagocytic capability of the macrophages, which appeared to be mediated through up-regulation of peroxisome proliferator-activated receptor γ. Taken together, induction of HO-1 expression and subsequent CO production by TauCl are essential for phagocytosis of fungi by macrophages. Our results suggest that TauCl has important roles in host defense against fungal infection and has therapeutic potential in the management of inflammatory diseases.-Kim, S. H., Zhong, X., Kim, W., Kim, K., Suh, Y.-G., Kim, C., Joe, Y., Chung, H. T., Cha, Y.-N., Surh, Y.-J. Taurine chloramine potentiates phagocytic activity of peritoneal macrophages through up-regulation of dectin-1 mediated by heme oxygenase-1-derived carbon monoxide.

Microbicidal activity of N-chlorotaurine in combination with hydrogen peroxide

N-chlorotaurine (NCT) and hydrogen peroxide are powerful endogenous antiseptics. In vivo, the reaction between hydrogen peroxide and metal ions leads to the formation of free hydroxyl radicals, which have an increased bactericidal activity. This study examined whether there is an additive antimicrobial effect of NCT combined with hydrogen peroxide. Additionally, it was tested if the additive effect is based on the formation of free radicals. We found by luminometry that, in the presence of H₂O₂, NCT caused a slow and long-lasting production of singlet oxygen in contrast to HOCl, where this burst occurred instantaneously. Both NCT and hydrogen peroxide (1.0 and 0.1%) demonstrated bactericidal and fungicidal activity. At pH 7.1 and 37 °C, hydrogen peroxide (1%, 294 mM) showed a stronger bactericidal and particularly fungicidal activity than NCT (1%, 55 mM), whereas at pH 4.0 and also in the presence of 5.0% peptone NCT revealed a stronger bactericidal activity. A combination of NCT and hydrogen peroxide led to an increased bactericidal but no increased fungicidal activity compared to both substances alone. The additive effect against bacteria was not removed in the presence of the radical scavengers NaN₃, DMSO, or peptone. As a conclusion, NCT and hydrogen peroxide used concurrently interact additive against a range of microorganisms. However, the results of this study suggest that the additive effect of NCT combined with hydrogen peroxide is rather not based on the formation of free radicals.

N-Chlorotaurine, a Promising Future Candidate for Topical Therapy of Fungal Infections

N-Chlorotaurine (NCT) is a mild long-lived oxidant that can be applied to sensitive body regions as an endogenous antiseptic. Enhancement of its microbicidal activity in the presence of proteinaceous material because of transchlorination, a postantibiotic/postantifungal effect and antitoxic activity renders it interesting for treatment of fungal infections, too. This is confirmed by first case applications in skin and mucous membranes of different body sites. Recent findings of good tolerability of inhaled NCT suggest further investigations of this substance for treatment of bronchopulmonary diseases, where microorganisms play a role, particularly multi-resistant ones. The availability of a well-tolerated and effective inhaled antiseptic with anti-inflammatory properties could be a significant progress, in particular for chronic pulmonary diseases, such as chronic obstructive pulmonary disease or cystic fibrosis.

Changes in the epidemiological landscape of invasive mould infections and disease

Although a wide variety of pathogens are associated with invasive mould diseases, Aspergillus spp. have historically been one of the most common causative organisms. Most invasive mould infections are caused by members of the Aspergillus fumigatus species complex and an emerging issue is the occurrence of azole resistance in A. fumigatus, with resistance to amphotericin B documented in other Aspergillus spp. The epidemiology of invasive fungal disease has shifted in recent years as non-A. fumigatus Aspergillus spp. and other moulds have become progressively more important, although there are no consolidated data on the prevalence of less common species of moulds. The incidence of mucormycosis may have been underestimated, which is a potential concern since species belonging to the order Mucorales are more resistant to antifungal agents than Aspergillus spp. All species of Mucorales are unaffected by voriconazole and most show moderate resistance in vitro to echinocandins. Fusarium spp. may be the second most common nosocomial fungal pathogen after Aspergillus in some tertiary hospitals, and show a susceptibility profile marked by a higher level of resistance than that of Aspergillus spp. Recently, Scedosporium aurantiacum has been reported as an emerging opportunistic pathogen, against which voriconazole is the most active antifungal agent. Other mould species can infect humans, although invasive fungal disease occurs less frequently. Since uncommon mould species exhibit individual susceptibility profiles and require tailored clinical management, accurate classification at species level of the aetiological agent in any invasive fungal disease should be regarded as the standard of care.

Pathobiology of Lomentospora prolificans: could this species serve as a model of primary antifungal resistance?

The number of fungal isolates resistant to antifungal drugs has increased dramatically over the last few years and has become an important concern for clinicians. Among these isolates, fungi showing multidrug resistance are particularly worrying because of the difficulties associated with their treatment. These factors hamper the successful recovery of patients and drastically raise mortality rates. Antifungal resistance is multifactorial and several mechanisms in different fungi have been described. There is a need to study these mechanisms in depth; however, the study of antifungal drug resistance separately for each individual species makes progress in the field very slow and tedious. The selection of a multiresistant microorganism as a model for understanding resistance mechanisms and extrapolating the results to other species could help in the search for a solution. In this mini-review, we describe the pathobiology of Lomentospora (Scedosporium) prolificans, paying special attention to its intrinsic resistance to all currently available antifungal agents. The characteristics of L. prolificans offer several advantages: the possibility of using a single microorganism for the study of resistance to different drugs, even cases of double and triple resistance; it is biologically safe for society in general as no new genetically-modified strains are needed for the experiments; it is homologous with other fungal species, and there is repetitiveness between different strains. In conclusion, we propose L. prolificans as a candidate for consideration as a fungal model for the study of resistance mechanisms against antifungal agents.

Bactericidal and Fungicidal Activity of N-Chlorotaurine Is Enhanced in Cystic Fibrosis Sputum Medium

Lung infections with multiresistant pathogens are a major problem among patients suffering from cystic fibrosis (CF). N-Chlorotaurine (NCT), a microbicidal active chlorine compound with no development of resistance, is well tolerated upon inhalation. The aim of this study was to investigate the in vitro bactericidal and fungicidal activity of NCT in artificial sputum medium (ASM), which mimics the composition of CF mucus. The medium was inoculated with bacteria (Staphylococcus aureus, including some methicillin-resistant S. aureus [MRSA] strains, Pseudomonas aeruginosa, and Escherichia coli) or spores of fungi (Aspergillus fumigatus, Aspergillus terreus, Candida albicans, Scedosporium apiospermum, Scedosporium boydii, Lomentospora prolificans, Scedosporium aurantiacum, Scedosporium minutisporum, Exophiala dermatitidis, and Geotrichum sp.), to final concentrations of 10⁷ to 10⁸ CFU/ml. NCT was added at 37°C, and time-kill assays were performed. At a concentration of 1% (10 mg/ml, 55 mM) NCT, bacteria and spores were killed within 10 min and 15 min, respectively, to the detection limit of 10² CFU/ml (reduction of 5 to 6 log₁₀ units). Reductions of 2 log₁₀ units were still achieved with 0.1% (bacteria) and 0.3% (fungi) NCT, largely within 10 to 30 min. Measurements by means of iodometric titration showed oxidizing activity for 1, 30, 60, and >60 min at concentrations of 0.1%, 0.3%, 0.5%, and 1.0% NCT, respectively, which matches the killing test results. NCT demonstrated broad-spectrum microbicidal activity in the milieu of CF mucus at concentrations ideal for clinical use. The microbicidal activity of NCT in ASM was even stronger than that in buffer solution; this was particularly pronounced for fungi. This finding can be explained largely by the formation, through transhalogenation, of monochloramine, which rapidly penetrates pathogens.