Comparative pharmacodynamic interaction analysis between ciprofloxacin, moxifloxacin and levofloxacin and antifungal agents against Candida albicans and Aspergillus fumigatus

Biofilm formation and increased mortality among cancer patients with candidemia in a Peruvian reference center

BACKGROUND

Candidemia is an invasive mycosis with an increasing global incidence and high mortality rates in cancer patients. The production of biofilms by some strains of Candida constitutes a mechanism that limits the action of antifungal agents; however, there is limited and conflicting evidence about its role in the risk of death. This study aimed to determine whether biofilm formation is associated with mortality in cancer patients with candidemia.

METHODS

This retrospective cohort study included patients treated at Peru's oncologic reference center between June 2015 and October 2017. Data were collected by monitoring patients for 30 days from the diagnosis of candidemia until the date of death or hospital discharge. Statistical analyses evaluated the association between biofilm production determined by XTT reduction and mortality, adjusting for demographic, clinical, and microbiological factors assessed by the hospital routinary activities. Survival analysis and bivariate and multivariate Cox regression were used, estimating the hazard ratio (HR) as a measure of association with a significance level of p < 0.05.

RESULTS

A total of 140 patients with candidemia were included in the study. The high mortality observed on the first day of post-diagnosis follow-up (81.0%) among 21 patients who were not treated with either antifungal or antimicrobial drugs led to stratification of the analyses according to whether they received treatment. In untreated patients, there was a mortality gradient in patients infected with non-biofilm-forming strains vs. low/medium and high-level biofilm-forming strains (25.0%, 66.7% and 82.3%, respectively, p = 0.049). In treated patients, a high level of biofilm formation was associated with increased mortality (HR, 3.92; 95% p = 0.022), and this association persisted after adjusting for age, comorbidities, and hospital emergency admission (HR, 6.59; CI: 1.87-23.24, p = 0.003).

CONCLUSIONS

The association between candidemia with in vitro biofilm formation and an increased risk of death consistently observed both in patients with and without treatment, provides another level of evidence for a possible causal association. The presence of comorbidities and the origin of the hospital emergency, which reflect the fragile clinical condition of the patients, and increasing age above 15 years were associated with a higher risk of death.

Strategies of Pharmacological Repositioning for the Treatment of Medically Relevant Mycoses

Fungal infections represent a worldwide concern for public health, due to their prevalence and significant increase in cases each year. Among the most frequent mycoses are those caused by members of the genera Candida, Cryptococcus, Aspergillus, Histoplasma, Pneumocystis, Mucor, and Sporothrix, which have been treated for years with conventional antifungal drugs, such as flucytosine, azoles, polyenes, and echinocandins. However, these microorganisms have acquired the ability to evade the mechanisms of action of these drugs, thus hindering their treatment. Among the most common evasion mechanisms are alterations in sterol biosynthesis, modifications of drug transport through the cell wall and membrane, alterations of drug targets, phenotypic plasticity, horizontal gene transfer, and chromosomal aneuploidies. Taking into account these problems, some research groups have sought new therapeutic alternatives based on drug repositioning. Through repositioning, it is possible to use existing pharmacological compounds for which their mechanism of action is already established for other diseases, and thus exploit their potential antifungal activity. The advantage offered by these drugs is that they may be less prone to resistance. In this article, a comprehensive review was carried out to highlight the most relevant repositioning drugs to treat fungal infections. These include antibiotics, antivirals, anthelmintics, statins, and anti-inflammatory drugs.

Inhibitory action of antibiotics on Kluyveromyces marxianus

A bioassay containing Kluyveromyces marxianus in microtiter plates was used to determine the inhibitory action of 28 antibiotics (aminoglycosides, beta-lactams, macrolides, quinolones, tetracyclines and sulfonamides) against this yeast in whey. For this purpose, the dose-response curve for each antibiotic was constructed using 16 replicates of 12 different concentrations of the antibiotic. The plates were incubated at 40°C until the negative samples exhibited their indicator (5-7h). Subsequently, the absorbances of the yeast cells in each plate were measured by the turbidimetric method (λ=600nm) and the logistic regression model was applied. The concentrations causing 10% (IC10) and 50% (IC50) of growth inhibition of the yeast were calculated. The results allowed to conclude that whey contaminated with cephalosporins, quinolones and tetracyclines at levels close to the Maximum Residue Limits inhibits the growth of K. marxianus. Therefore, previous inactivation treatments should be implemented in order to re-use this contaminated whey by fermentation with K. marxianus.

Terpene-Functionalized Fluoroquinolones as Potential Antimicrobials: Synthesis and Properties

This study was the first to synthesize terpene-containing conjugates of fluoroquinolones, ciprofloxacin and norfloxacin, and to evaluate their antibacterial activity against gram-positive methicillin sensitive (MSSA) and methicillin resistant (MRSA) S. aureus, gram-negative P. aeruginosa as well as antifungal activity against C. albicans. The ability of obtained fluoroquinolones to inhibit S. aureus growth was found to depend upon the presence of a linker separating the bulky terpene and fluoroquinolone fragments, and this activity diminished with increasing its length. The highest activity against MSSA was demonstrated by ciprofloxacin derivatives with campholenic (MIC 1 μg/mL) and 2-(isobornan-2-yl-sulfanyl)acetyl (MIC 0.5 μg/mL) substituents. The compound with the last fragment showed high activity against MRSA (MIC 8 μg/mL). The terpene-functionalized norfloxacin derivatives generally proved to be less active than those containing ciprofloxacin fragment. Camphor-10-sulfonylamide derivative with the ciprofloxacin fragment was the only one of all compounds that showed high antifungal activity against C. albicans (8 μg/mL). The study presents data on docking fluoroquinolones to S. aureus DNA gyrase to explain the reasons for manifestation or disappearance of antibacterial activity. The cytotoxicity of fluoroquinolones that showed any antimicrobial activity was investigated against bovine primary lung cells, and they were found to be not toxic in most cases.

In vitro combination with doxycycline plus antifungals against clinical Mucorales pathogens

PURPOSE

Since systematic antifungals for mucormycosis showed variable MICs depending on strains, effective and safe antifungal therapy was still needed. This study is aimed to evaluate the in vitro activity of doxycycline combined with antifungal therapy against dominant Mucorales pathogens.

METHODS

Multidrug susceptibility testing was performed with doxycycline and antifungals, including itraconazole, posaconazole, and amphotericin, in 21 isolates of 8 dominant Mucorales pathogens.

RESULTS

The fractional inhibitory concentration index according to M38 showed one Rhizopus arrhizus isolate synergic (∑FICI = 0.375) and other isolates in addition (0.5 < ∑FICI < 4).

CONCLUSIONS

Doxycycline was found to have in vitro advantages in combined antifungal treatment over antifungals alone.

Study of the Effect of Antibiotics in Drinking Water on the Content of Antioxidant Compounds in Red Wines

The presence of antibiotic residues in drinking water may be a source of contamination, which could affect the diffusion of polyphenols into the wine must during the traditional fermentation process. Antibiotic residues such as ivermectin, hydroxychloroquine, ciprofloxacin, and azithromycin on the diffusion of polyphenols and anthocyanins during wine fermentation were studied. Different samples were taken at different periods (0, 48, 96, and 168 h) to analyse the total polyphenols, anthocyanin content, and antioxidant capacity, which were correlated with Peleg's equation to establish the diffusion kinetics of these compounds. The results indicated that the presence of antibiotics reduced between 40 and 50% the diffusion of the total polyphenols and monomeric anthocyanins in red wine. The use of ivermectin showed the highest kinetic parameter k₁ compared with the use of other antibiotics. This suggested that the chemical structure and molecular weight of the antibiotics could play an important role in inhibiting the metabolism of yeasts affecting the ethanol and CO₂ production. Consequently, cell membranes would be impermeable and would not allow the release of polyphenols and anthocyanins. Therefore, it is necessary to establish strategies that allow future water quality control in wine production companies.

The resistance mechanisms of bacteria against ciprofloxacin and new approaches for enhancing the efficacy of this antibiotic

For around three decades, the fluoroquinolone (FQ) antibiotic ciprofloxacin has been used to treat a range of diseases, including chronic otorrhea, endocarditis, lower respiratory tract, gastrointestinal, skin and soft tissue, and urinary tract infections. Ciprofloxacin's main mode of action is to stop DNA replication by blocking the A subunit of DNA gyrase and having an extra impact on the substances in cell walls. Available in intravenous and oral formulations, ciprofloxacin reaches therapeutic concentrations in the majority of tissues and bodily fluids with a low possibility for side effects. Despite the outstanding qualities of this antibiotic, Salmonella typhi, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa have all shown an increase in ciprofloxacin resistance over time. The rise of infections that are resistant to ciprofloxacin shows that new pharmacological synergisms and derivatives are required. To this end, ciprofloxacin may be more effective against the biofilm community of microorganisms and multi-drug resistant isolates when combined with a variety of antibacterial agents, such as antibiotics from various classes, nanoparticles, natural products, bacteriophages, and photodynamic therapy. This review focuses on the resistance mechanisms of bacteria against ciprofloxacin and new approaches for enhancing its efficacy.

Amphotericin B- and Levofloxacin-Loaded Chitosan Films for Potential Use in Antimicrobial Wound Dressings: Analytical Method Development and Its Application

Levofloxacin (LVX) and amphotericin B (AMB) have been widely used to treat bacterial and fungal infections in the clinic. Herein, we report, for the first time, chitosan films loaded with AMB and LVX as wound dressings to combat antimicrobial infections. Additionally, we developed and validated a high-performance liquid chromatography (HPLC) method coupled with a UV detector to simultaneously quantify both AMB and LVX. The method is easy, precise, accurate and linear for both drugs at a concentration range of 0.7-5 µg/mL. The validated method was used to analyse the drug release, ex vivo deposition and permeation from the chitosan films. LVX was released completely from the chitosan film after a week, while approximately 60% of the AMB was released. Ex vivo deposition study revealed that, after 24-hour application, 20.96 ± 13.54 µg of LVX and approximately 0.35 ± 0.04 µg of AMB was deposited in porcine skin. Approximately 0.58 ± 0.16 µg of LVX permeated through the skin. AMB was undetectable in the receptor compartment due to its poor solubility and permeability. Furthermore, chitosan films loaded with AMB and LVX were found to be able to inhibit the growth of both Candida albicans and Staphylococcus aureus, indicating their potential for antimicrobial applications.

Dual Drug Loaded Lipid Nanocarrier Formulations for Topical Ocular Applications

Introduction

Untreated ocular infections can damage the unique fine structures of the eye with possible visual impairments and blindness. Ciprofloxacin (CIP) ophthalmic solution is prescribed as first-line therapy in ocular bacterial infections. Natamycin (NT) ophthalmic suspension is one of the progenitors in ocular antifungal therapy. Nanostructured lipid carriers (NLCs) have been widely examined for ocular penetration enhancement and distribution to deeper ocular tissues. The objective of the current study was to prepare NLCs loaded with a combination of CIP and NT (CIP-NT-NLCs) and embed them in an in-situ gelling system (CIP-NT-NLCs-IG). This novel formulation will target the co-delivery of CIP and NT for the treatment of mixed ocular infections or as empirical treatment in case of limited access to healthcare diagnostic services.

Methods

CIP-NT-NLC and CIP-NT-NLC-IG formulations were evaluated based on physicochemical characteristics, in vitro release, and ex vivo transcorneal permeation studies and compared against commercial CIP and NT ophthalmic eye drops.

Results and Discussion

NLCs formulation (0.1% CIP and 0.3% NT) showed particle size, polydispersity index, and zeta potential of 196.2 ± 1.2 nm, 0.43 ± 0.06, and −28.1 ± 1.4 mV, respectively. Moreover, CIP-NT-NLCs showed entrapment efficiency of 80.9 ± 2.9 and 98.7 ± 1.9% for CIP and NT, respectively. CIP-NT-NLCs-IGformulation with 0.2% w/v gellan gum demonstrated the most favorable viscoelastic characteristics for ocular application. CIP-NT-NLCs and CIP-NT-NLCs-IG formulations exhibited a sustained release pattern for both drugs over 24 h. Moreover, CIP-NT-NLCs and CIP-NT-NLC-IG formulations showed 4.0- and 2.2-folds, and 5.0- and 2.5-folds enhancement in ex vivo transcorneal permeability of CIP and NT, respectively, compared to the control formulations.

Conclusion

The results suggest that this dual nanoparticulate-based in-situ gelling drug delivery system can serve as a promising topical delivery platform for the treatment of ocular infections.

Steroid-Functionalized Imidazolium Salts with an Extended Spectrum of Antifungal and Antibacterial Activity

It is established that high rates of morbidity and mortality caused by fungal infections are related to the current limited number of antifungal drugs and the toxicity of these agents. Imidazolium salts as azole derivatives can be successfully used in the treatment of fungal infections in humans. Steroid-functionalized imidazolium salts were synthesized using a new, more efficient method. As a result, 20 salts were obtained with high yields, 12 of which were synthesized and characterized for the first time. They were derivatives of lithocholic acid and 3-oxo-23,24-dinorchol-4-ene-22-al and were fully characterized by ¹H and ¹³C nuclear magnetic resonance (NMR), infrared spectroscopy (IR), and high resolution mass spectrometry (HRMS). Due to the excellent activity against bacteria and Candida albicans, new research was extended to include tests on five species of pathogenic fungi and molds: Aspergillus niger ATCC 16888, Aspergillus fumigatus ATCC 204305, Trichophyton mentagrophytes ATCC 9533, Cryptococcus neoformans ATCC 14116, and Microsporum canis ATCC 11621. The results showed that the new salts are almost universal antifungal agents and have a broad spectrum of activity against other human pathogens. To initially assess the safety of the synthesized salts, hemocompatibility with host cells and cytotoxicity were also examined. No toxicity was observed at the concentration at which the compounds were active against pathogens.

The Biochemical and Molecular Analysis of Changes in Melanogenesis Induced by UVA-Activated Fluoroquinolones-In Vitro Study on Human Normal Melanocytes

Fluoroquinolones cause phototoxic reactions, manifested as different types of skin lesions, including hyperpigmentation. The disturbances of melanogenesis indicate that fluoroquinolones may affect cellular processes in melanocytes. It has been reported that these antibiotics may bind with melanin and accumulate in pigmented cells. The study aimed to examine the changes in melanogenesis in human normal melanocytes exposed to UVA radiation and treated with lomefloxacin and moxifloxacin, the most and the least fluoroquinolone, respectively. The obtained results demonstrated that both tested fluoroquinolones inhibited melanogenesis through a decrease in tyrosinase activity and down-regulation of tyrosinase and microphthalmia-associated transcription factor production. Only lomefloxacin potentiated UVA-induced melanogenesis. Under UVA irradiation lomefloxacin significantly enhanced melanin content and tyrosinase activity in melanocytes, although the drug did not cause an increased expression of tyrosinase or microphthalmia-associated transcription factor. The current studies revealed that phototoxic activity of fluoroquinolones is associated with alterations in the melanogenesis process. The difference in phototoxic potential of fluoroquinolones derivatives may be connected with various effects on UVA-induced events at a cellular level.

Fluoroquinolone-Transition Metal Complexes: A Strategy to Overcome Bacterial Resistance

Fluoroquinolones (FQs) are antibiotics widely used in the clinical practice due to their large spectrum of action against Gram-negative and some Gram-positive bacteria. Nevertheless, the misuse and overuse of these antibiotics has triggered the development of bacterial resistance mechanisms. One of the strategies to circumvent this problem is the complexation of FQs with transition metal ions, known as metalloantibiotics, which can promote different activity and enhanced pharmacological behaviour. Here, we discuss the stability of FQ metalloantibiotics and their possible translocation pathways. The main goal of the present review is to frame the present knowledge on the conjunction of biophysical and biological tools that can help to unravel the antibacterial action of FQ metalloantibiotics. An additional goal is to shed light on the studies that must be accomplished to ensure stability and viability of such metalloantibiotics. Potentiometric, spectroscopic, microscopic, microbiological, and computational techniques are surveyed. Stability and partition constants, interaction with membrane porins and elucidation of their role in the influx, determination of the antimicrobial activity against multidrug-resistant (MDR) clinical isolates, elucidation of the mechanism of action, and toxicity assays are described for FQ metalloantibiotics.

Drug repurposing strategies in the development of potential antifungal agents

Abstract

The morbidity and mortality caused by invasive fungal infections are increasing across the globe due to developments in transplant surgery, the use of immunosuppressive agents, and the emergence of drug-resistant fungal strains, which has led to a challenge in terms of treatment due to the limitations of three classes of drugs. Hence, it is imperative to establish effective strategies to identify and design new antifungal drugs. Drug repurposing is a potential way of expanding the application of existing drugs. Recently, various existing drugs have been shown to be useful in the prevention and treatment of invasive fungi. In this review, we summarize the currently used antifungal agents. In addition, the most up-to-date information on the effectiveness of existing drugs with antifungal activity is discussed. Moreover, the antifungal mechanisms of existing drugs are highlighted. These data will provide valuable knowledge to stimulate further investigation and clinical application in this field.

Key points

• Conventional antifungal agents have limitations due to the occurrence of drug-resistant strains.

• Non-antifungal drugs act as antifungal agents in various ways toward different targets.

• Non-antifungal drugs with antifungal activity are demonstrated as effective antifungal strategies.

Topoisomerase II as a target for repurposed antibiotics in Candida albicans: an in silico study

Fluoroquinolines, the widely used antibacterial antibiotics, have been shown to interact with human DNA topoisomerases supporting their use as repurposed cancer drugs in humans. In this communication molecular docking of eleven Fluoroquinolines against predicted structure of Candida albicans DNA Topoisomerase II is reported for the first time. C. albicans topoisomerase II structure prediction was done by using homology modeling tool. Ligand preparation and molecular docking with C. albicans topoisomerase II were done by using Autodock tool. These antibiotics formed hydrogen bond with good binding affinity at ARG 841, GLN803, ALA840 amino acid residues in the active site of C. albicans Topoisomerase II. We hypothesize that DNA toposiomerases may be the targets of Fluroquinoline group of antibiotics in C. albicans causing inhibition of growth.

Pathogenesis and Clinical Relevance of Candida Biofilms in Vulvovaginal Candidiasis

The ability of Candida spp. to form biofilms is crucial for its pathogenicity, and thus, it should be considered an important virulence factor in vulvovaginal candidiasis (VVC) and recurrent VVC (RVVC). Its ability to generate biofilms is multifactorial and is generally believed to depend on the site of infection, species and strain involved, and the microenvironment in which the infection develops. Therefore, both cell surface proteins, such as Hwp1, Als1, and Als2, and the cell wall-related protein, Sun41, play a critical role in the adhesion and virulence of the biofilm. Immunological and pharmacological approaches have identified the NLRP3 inflammasome as a crucial molecular factor contributing to host immunopathology. In this context, we have earlier shown that Candida albicans associated with hyphae-secreted aspartyl proteinases (specifically SAP4-6) contribute to the immunopathology of the disease. Transcriptome profiling has revealed that non-coding transcripts regulate protein synthesis post-transcriptionally, which is important for the growth of Candida spp. Other studies have employed RNA sequencing to identify differences in the 1,245 Candida genes involved in surface and invasive cellular metabolism regulation. In vitro systems allow the simultaneous processing of a large number of samples, making them an ideal screening technique for estimating various physicochemical parameters, testing the activity of antimicrobial agents, and analyzing genes involved in biofilm formation and regulation (in situ) in specific strains. Murine VVC models are used to study C. albicans infection, especially in trials of novel treatments and to understand the cause(s) for resistance to conventional therapeutics. This review on the clinical relevance of Candida biofilms in VVC focuses on important advances in its genomics, transcriptomics, and proteomics. Moreover, recent experiments on the influence of biofilm formation on VVC or RVVC pathogenesis in laboratory animals have been discussed. A clear elucidation of one of the pathogenesis mechanisms employed by Candida biofilms in vulvovaginal candidiasis and its applications in clinical practice represents the most significant contribution of this manuscript.

Alternative treatment of fungal infections: Synergy with non-antifungal agents

Fungal infections are responsible for high mortality rates in immunocompromised and high-risk surgical patients. Therapy failures during the last decades due to increasing multidrug resistance demand innovative strategies for novel and effective antifungal drugs. Synergistic combinations of antifungals with non-antifungal agents highlight a pragmatic strategy to reduce the development of drug resistance and potentially repurpose known compounds with other functions to bypass costly and time-consuming novel drug development.

Pitfalls Associated with Discriminating Mixed-Species Biofilms by Flow Cytometry

Since biofilms are ubiquitous in different settings and act as sources of disease for humans, reliable methods to characterize and quantify these microbial communities are required. Numerous techniques have been employed, but most of them are unidirectional, labor intensive and time consuming. Although flow cytometry (FCM) can be a reliable choice to quickly provide a multiparametric analysis, there are still few applications on biofilms, and even less on the study of inter-kingdom communities. This work aimed to give insights into the application of FCM in order to more comprehensively analyze mixed-species biofilms, formed by different Pseudomonas aeruginosa and Candida albicans strains, before and after exposure to antimicrobials. For comparison purposes, biofilm culturability was also assessed determining colony-forming units. The results showed that some aspects, namely the microbial strain used, the morphological state of the cells and the biofilm matrix, make the accurate analysis of FCM data difficult. These aspects were even more challenging when double-species biofilms were being inspected, as they could engender data misinterpretations. The outcomes draw our attention towards the need to always take into consideration the characteristics of the biofilm samples to be analyzed through FCM, and undoubtedly link to the need for optimization of the processes tailored for each particular case study.

Candida albicans Antifungal Resistance and Tolerance in Bloodstream Infections: The Triad Yeast-Host-Antifungal

Candida albicans represents the most frequent isolated yeast from bloodstream infections. Despite the remarkable progress in diagnostic and therapeutic approaches, these infections continue to be a critical challenge in intensive care units worldwide. The economic cost of bloodstream fungal infections and its associated mortality, especially in debilitated patients, remains unacceptably high. Candida albicans is a highly adaptable microorganism, being able to develop resistance following prolonged exposure to antifungals. Formation of biofilms, which diminish the accessibility of the antifungal, selection of spontaneous mutations that increase expression or decreased susceptibility of the target, altered chromosome abnormalities, overexpression of multidrug efflux pumps and the ability to escape host immune defenses are some of the factors that can contribute to antifungal tolerance and resistance. The knowledge of the antifungal resistance mechanisms can allow the design of alternative therapeutically options in order to modulate or revert the resistance. We have focused this review on the main factors that are involved in antifungal resistance and tolerance in patients with C. albicans bloodstream infections.

Transferable Mechanisms of Quinolone Resistance from 1998 Onward

While the description of resistance to quinolones is almost as old as these antimicrobial agents themselves, transferable mechanisms of quinolone resistance (TMQR) remained absent from the scenario for more than 36 years, appearing first as sporadic events and afterward as epidemics. In 1998, the first TMQR was soundly described, that is, QnrA. The presence of QnrA was almost anecdotal for years, but in the middle of the first decade of the 21st century, there was an explosion of TMQR descriptions, which definitively changed the epidemiology of quinolone resistance. Currently, 3 different clinically relevant mechanisms of quinolone resistance are encoded within mobile elements: (i) target protection, which is mediated by 7 different families of Qnr (QnrA, QnrB, QnrC, QnrD, QnrE, QnrS, and QnrVC), which overall account for more than 100 recognized alleles; (ii) antibiotic efflux, which is mediated by 2 main transferable efflux pumps (QepA and OqxAB), which together account for more than 30 alleles, and a series of other efflux pumps (e.g., QacBIII), which at present have been sporadically described; and (iii) antibiotic modification, which is mediated by the enzymes AAC(6')Ib-cr, from which different alleles have been claimed, as well as CrpP, a newly described phosphorylase.

A complex suite of loci and elements in eukaryotic type II topoisomerases determine selective sensitivity to distinct poisoning agents

Type II topoisomerases catalyze essential DNA transactions and are proven drug targets. Drug discrimination by prokaryotic and eukaryotic topoisomerases is vital to therapeutic utility, but is poorly understood. We developed a next-generation sequencing (NGS) approach to identify drug-resistance mutations in eukaryotic topoisomerases. We show that alterations conferring resistance to poisons of human and yeast topoisomerase II derive from a rich mutational 'landscape' of amino acid substitutions broadly distributed throughout the entire enzyme. Both general and discriminatory drug-resistant behaviors are found to arise from different point mutations found at the same amino acid position and to occur far outside known drug-binding sites. Studies of selected resistant enzymes confirm the NGS data and further show that the anti-cancer quinolone vosaroxin acts solely as an intercalating poison, and that the antibacterial ciprofloxacin can poison yeast topoisomerase II. The innate drug-sensitivity of the DNA binding and cleavage region of human and yeast topoisomerases (particularly hTOP2β) is additionally revealed to be significantly regulated by the enzymes' adenosine triphosphatase regions. Collectively, these studies highlight the utility of using NGS-based methods to rapidly map drug resistance landscapes and reveal that the nucleotide turnover elements of type II topoisomerases impact drug specificity.

Anti-Candida activity of existing antibiotics and their derivatives when used alone or in combination with antifungals

Fungal infections are a growing challenge in immunocompromised patients, especially candidiasis. The prolonged use of traditional antifungals to treat Candida infection has caused the emergence of drug resistance, especially fluconazole. Therefore, new therapeutic strategies for Candida infection are warranted. Recently, attention has been paid to the anti-Candida activity of antibiotics and their derivatives. Studies revealed that a series of antibiotics/derivatives displayed potential anti-Candida activity and some of them could significantly increase the susceptibility of antifungals. Interestingly, the derivatives of aminoglycosides were even more active than fluconazole/itraconazole/posaconazole. This article reviews the anti-Candida activities and mechanisms of antibiotics/derivatives used alone or in combination with antifungals. This review will helpfully provide novel insights for overcoming Candida resistance and discovering new antifungals.

Cure Rate of Fungal Keratitis With Antibacterial Therapy

PURPOSE

To study the cure rate of fungal keratitis with moxifloxacin 0.3% monotherapy.

METHODS

A retrospective review of patients with culture-proven fungal keratitis who initially received moxifloxacin 0.3% monotherapy was performed.

RESULTS

Eleven patients with culture-proven fungal keratitis were initially treated with moxifloxacin. One case each of Curvularia and Alternaria keratitis resolved with moxifloxacin monotherapy (18%).

CONCLUSIONS

Moxifloxacin may have a significant clinical therapeutic effect in a subset of patients with fungal keratitis. Review of the literature in combination with the current study suggests that in patients with clinical features suggestive of fungal keratitis, if rapid diagnostic tests are negative or not available, pending culture results, initial therapy should include a fluoroquinolone (moxifloxacin or gatifloxacin) and/or an aminoglycoside (tobramycin or gentamicin).

The antibacterial agent, moxifloxacin inhibits virulence factors of Candida albicans through multitargeting

Fluoroquinolines are broad spectrum fourth generation antibiotics. Some of the Fluoroquinolines exhibit antifungal activity. We are reporting the potential mechanism of action of a fluoroquinoline antibiotic, moxifloxacin on the growth, morphogenesis and biofilm formation of the human pathogen Candida albicans. Moxifloxacin was found to be Candidacidal in nature. Moxifloxacin seems to inhibit the yeast to Hyphal morphogenesis by affecting signaling pathways. It arrested the cell cycle of C. albicans at S phase. Docking of moxifloxacin with predicted structure of C. albicans DNA Topoisomerase II suggests that moxifloxacin may bind and inhibit the activity of DNA Topoisomerase II in C. albicans. Moxifloxacin could be used as a dual purpose antibiotic for treating mixed infections caused by bacteria as well as C. albicans. In addition chances of developing moxifloxacin resistance in C. albicans are less considering the fact that moxifloxacin may target multiple steps in yeast to hyphal transition in C. albicans.

Polymicrobial Ventilator-Associated Pneumonia: Fighting In Vitro Candida albicans-Pseudomonas aeruginosa Biofilms with Antifungal-Antibacterial Combination Therapy

The polymicrobial nature of ventilator-associated pneumonia (VAP) is now evident, with mixed bacterial-fungal biofilms colonizing the VAP endotracheal tube (ETT) surface. The microbial interplay within this infection may contribute for enhanced pathogenesis and exert impact towards antimicrobial therapy. Consequently, the high mortality/morbidity rates associated to VAP and the worldwide increase in antibiotic resistance has promoted the search for novel therapeutic strategies to fight VAP polymicrobial infections. Under this scope, this work aimed to assess the activity of mono- vs combinational antimicrobial therapy using one antibiotic (Polymyxin B; PolyB) and one antifungal (Amphotericin B; AmB) agent against polymicrobial biofilms of Pseudomonas aeruginosa and Candida albicans. The action of isolated antimicrobials was firstly evaluated in single- and polymicrobial cultures, with AmB being more effective against C. albicans and PolyB against P. aeruginosa. Mixed planktonic cultures required equal or higher antimicrobial concentrations. In biofilms, only PolyB at relatively high concentrations could reduce P. aeruginosa in both monospecies and polymicrobial populations, with C. albicans displaying only punctual disturbances. PolyB and AmB exhibited a synergistic effect against P. aeruginosa and C. albicans mixed planktonic cultures, but only high doses (256 mg L^-1) of PolyB were able to eradicate polymicrobial biofilms, with P. aeruginosa showing loss of cultivability (but not viability) at 2 h post-treatment, whilst C. albicans only started to be inhibited after 14 h. In conclusion, combination therapy involving an antibiotic and an antifungal agent holds an attractive therapeutic option to treat severe bacterial-fungal polymicrobial infections. Nevertheless, optimization of antimicrobial doses and further clinical pharmacokinetics/pharmacodynamics and toxicodynamics studies underpinning the optimal use of these drugs are urgently required to improve therapy effectiveness and avoid reinfection.

Unveiling the Synergistic Interaction Between Liposomal Amphotericin B and Colistin

Patients with multiple comorbidities are often administered simultaneously or sequentially antifungals and antibacterial agents, without full knowledge of the consequences of drug interactions. Considering the clinical relevance of liposomal amphotericin B (L-AMB), the association between L-AMB and six antibacterial agents was evaluated against four clinical isolates and one type strain of Candida spp. and two clinical isolates and one type strain of Aspergillus fumigatus. In order to evaluate such combined effects, the minimal inhibitory concentration (MIC) of L-AMB was determined in the presence of 0.5-, 1-, 2-, and 4-fold peak plasma concentrations of each of the antibacterial drugs. Since the L-AMB/colistin (CST) association was the most synergic, viability assays were performed and the physiological status induced by this association was characterized. In addition, computational molecular dynamics studies were also performed in order to clarify the molecular interaction. The maximum synergistic effect with all antibacterial agents, except CST, was reached at fourfold the usual peak plasma concentrations, resulting in 2-to 8-fold L-AMB MIC reduction for Candida and 2-to 16-fold for Aspergillus. For CST, the greatest synergism was registered at peak plasma concentration (3 mg/L), with 4-to 8-fold L-AMB MIC reduction for Candida and 16-to 32-fold for Aspergillus. L-AMB at subinhibitory concentration (0.125 mg/L) combined with CST 3 mg/L resulted in: a decrease of fungal cell viability; an increase of cell membrane permeability; an increase of cellular metabolic activity soon after 1 h of exposure, which decreased until 24 h; and an increase of ROS production up to 24 h. From the molecular dynamics studies, AMB and CST molecules shown a propensity to form a stable molecular complex in solution, conferring a recognition and binding added value for membrane intercalation. Our results demonstrate that CST interacts synergistically with L-AMB, forming a stable complex, which promotes the fungicidal activity of L-AMB at low concentration.

The effect of antibacterial and non-antibacterial compounds alone or associated with antifugals upon fungi

During the last 30 years the incidence of fungal infections has increased dramatically. While the antifungal therapeutic options available are somewhat reduced, most pathogenic microorganisms have an incredible capacity to mutate and acquire resistance. In addition, multiple drugs are often required concomitantly to manage clinically complex disorders. The combination of antibiotics or other compounds with antifungal drugs, simultaneously or sequentially, is commonly adopted in clinical practice, although without a full knowledge of the consequences. Thus, the role of combined therapy and the effect of antibiotics upon fungal growth promotion need to be critically evaluated and understood in order to avoid undesirable drug interactions. With this review we intend discuss the studies that report about antibiotics inhibiting fungal growth, as well as studies describing the synergistic effect of the combined therapy, i.e., associations between antibiotics or other compounds with antifungal drugs. Alternative therapeutic protocols for fungal disease could be designed, taking advantage of such drug combinations. Critical revision of previously published data is crucial in order to define future research strategies.

Antiviral, antifungal, and antiparasitic activities of fluoroquinolones optimized for treatment of bacterial infections: a puzzling paradox or a logical consequence of their mode of action?

This review summarizes evidence that commercially available fluoroquinolones used for the treatment of bacterial infections are active against other non-bacterial infectious agents as well. Any of these fluoroquinolones exerts, in parallel to its antibacterial action, antiviral, antifungal, and antiparasitic actions at clinically achievable concentrations. This broad range of anti-infective activities is due to one common mode of action, i.e., the inhibition of type II topoisomerases or inhibition of viral helicases, thus maintaining the selective toxicity of fluoroquinolones inhibiting microbial topoisomerases at low concentrations but mammalian topoisomerases at much higher concentrations. Evidence suggests that standard doses of the fluoroquinolones studied are clinically effective against viral and parasitic infections, whereas higher doses administered topically were active against Candida spp. causing ophthalmological infections. Well-designed clinical studies should be performed to substantiate these findings.

Interaction between caspofungin or voriconazole and cefoperazone-sulbactam or piperacillin-tazobactam by in vitro and in vivo methods

Immunosuppressive patients are at risk of fungal and bacterial infections. Therefore, these patients receive prophylactic, preemptive, empirical or target antifungal and concomitant antibiotic therapy. To this end, caspofungin (CAS) or voriconazole (VRC) antifungals and cefoperazone-sulbactam (CPZ/SAM) or piperacillin-tazobactam (PIP/TAZ) antibiotics may be used. Here, we aimed to investigate the interaction between these antifungals and antibiotics by in vitro and in vivo methods. The interaction was tested by chequerboard analysis and fractional inhibitory concentration index (FICI). It was also tested in a neutropenic mice-invasive candidiasis model and evaluated by fungal burden in kidney tissue of infected animals from the first day to the fifth day of treatment with 24 h intervals. A synergism was detected between CAS and CPZ/SAM (FICI = 0.1) and PIP/TAZ (FICI = 0.3). Fungal burden in tissues of drug-treated mice was reduced compared with controls in a time-dependent manner. In comparison with CAS-alone treated group, there were 1.32 log10 reductions of fungal burden in CAS + CPZ/SAM (p = 0.002) and in CAS + PIP/TAZ group (p = 0.14). The same interactions were not found with VRC and antibiotics. CPZ/SAM had stronger synergistic interaction with CAS than PIP/TAZ. The mechanism of synergism is not well understood. This is most likely due to an increase in the anticandidal effect of CAS plus antibiotics.

Ciprofloxacin shows synergism with classical antifungals against Histoplasma capsulatum var. capsulatum and Coccidioides posadasii

This study evaluated the in vitro interaction between ciprofloxacin (CIP) and classical antifungals against Histoplasma capsulatum var. capsulatum in mycelial (n = 16) and yeast-like forms (n = 9) and Coccidioides posadasii in mycelial form (n = 16). This research was conducted through broth microdilution and macrodilution, according to Clinical Laboratory Standards Institute. Inocula were prepared to obtain from 0.5 × 10(3) to 2.5 × 10(4)  cfu ml(-1) for H. capsulatum and from 10(3) to 5 × 10(3)  cfu ml(-1) for C. posadasii. Initially, minimum inhibitory concentration (MIC) for each drug alone was determined. Then, these MICs were used as the highest concentration for each drug during combination assays. The procedures were performed in duplicate. For all combination assays, MICs were defined as the lowest concentration capable of inhibiting 80% of visible fungal growth, when compared to the drug-free control. Drug interaction was evaluated by paired sample t-Student test. The obtained data showed a significant MIC reduction for most tested combinations of CIP with antifungals, except for that of CIP and voriconazole against yeast-like H. capsulatum. This study brings potential alternatives for the treatment of histoplasmosis and coccidioidomycosis, raising the possibility of using CIP as an adjuvant antifungal therapy, providing perspectives to delineate in vivo studies.

Antifungal Activity against Candida Biofilms

Candida species have two distinct lifestyles: planktonic, and surface-attached communities called biofilms. Mature C. albicans biofilms show a complex three-dimensional architecture with extensive spatial heterogeneity, and consist of a dense network of yeast, hyphae, and pseudohyphae encased within a matrix of exopolymeric material. Several key processes are likely to play vital roles at the different stages of biofilm development, such as cell-substrate and cell-cell adherence, hyphal development, and quorum sensing. Biofilm formation is a survival strategy, since biofilm yeasts are more resistant to antifungals and environmental stress. Antifungal resistance is a multifactorial process that includes multidrug efflux pumps, target proteins of the ergosterol biosynthetic pathway. Most studies agree in presenting azoles as agents with poor activity against Candida spp. biofilms. However, recent studies have demonstrated that echinocandins and amphotericin B exhibit remarkable activity against C. albicans and Candida non-albicans biofilms. The association of Candida species with biofilm formation increases the therapeutic complexity of foreign body-related yeast infections. The traditional approach to the management of these infections has been to explant the affected device. There is a strong medical but also economical motivation for the development of novel anti-fungal biofilm strategies due to the constantly increasing resistance of Candida biofilms to conventional antifungals, and the high mortality caused by related infections. A better description of the extent and role of yeast in biofilms may be critical for developing novel therapeutic strategies in the clinical setting.

Ultrashort peptide bioconjugates are exclusively antifungal agents and synergize with cyclodextrin and amphotericin B

Many natural broad-spectrum cationic antimicrobial peptides (AMPs) possess a general mode of action that is dependent on lipophilicity and charge. Modulating the lipophilicity of AMPs by the addition of a fatty acid has been an effective strategy to increase the lytic activity and can further broaden the spectrum of AMPs. However, lipophilic modifications that narrow the spectrum of activity and exclusively direct peptides to fungi are less common. Here, we show that short peptide sequences can be targeted to fungi with structured lipophilic biomolecules, such as vitamin E and cholesterol. The conjugates were active against Aspergillus fumigatus, Cryptococcus neoformans, and Candida albicans but not against bacteria and were observed to cause membrane perturbation by transmission electron microscopy and in membrane permeability studies. However, for C. albicans, selected compounds were effective without the perturbation of the cell membrane, and synergism was seen with a vitamin E conjugate and amphotericin B. Moreover, in combination with β-cyclodextrin, antibacterial activity emerged in selected compounds. Biocompatibility for selected active compounds was tested in vitro and in vivo using toxicity assays on erythrocytes, macrophages, and mice. In vitro cytotoxicity experiments led to selective toxicity ratios (50% lethal concentration/MIC) of up to 64 for highly active antifungal compounds, and no in vivo murine toxicity was seen. Taken together, these results highlight the importance of the conjugated lipophilic structure and suggest that the modulation of other biologically relevant peptides with hydrophobic moieties, such as cholesterol and vitamin E, generate compounds with unique bioactivity.

Synergistic interaction of the triple combination of amphotericin B, ciprofloxacin, and polymorphonuclear neutrophils against Aspergillus fumigatus

Aspergillus is damaged by polymorphonuclear neutrophils (PMNs) by means of nonoxidative and oxidative mechanisms, which may be affected by antifungal and antibacterial agents that patients with invasive pulmonary aspergillosis often receive. The pharmacodynamic interactions among deoxycholate amphotericin B (AMB), ciprofloxacin (CIP), and human PMNs against Aspergillus fumigatus growth are unknown. We therefore studied the interactions between 0.032 to 2.0 μg/ml of AMB, 0.1 to 50 μg/ml of CIP at a fixed AMB/CIP ratio of 1:3.125, and PMNs from six donors at an effector-to-target (E:T) ratio of 400:1 against a clinical A. fumigatus isolate using an XTT metabolic assay and the Bliss independence pharmacodynamic-interaction model. CIP exhibited no antifungal activity alone or in combination with PMNs. Synergy was found between AMB and PMNs, with interaction indices (II) of 0.06 to 0.21; the highest interaction of 21% ± 3.6% was observed at 0.22 ± 0.09 μg/ml of AMB. The AMB and CIP (AMB+CIP) combination was synergistic (II = 0.39) at low AMB concentrations and antagonistic (II = 1.39) at high AMB concentrations, with a maximal synergistic interaction of 16% ± 3.7% observed at 0.16 ± 0.08 μg/ml of AMB. The triple combination AMB+CIP+PMNs was synergistic, with interaction indices of 0.05 to 0.20, and a maximal synergistic interaction of 24% ± 4% was observed at 0.20 ± 0.07 μg/ml of AMB. The increased percentage of Bliss synergy of the triple combination AMB+CIP+PMNs (24% ± 4%) was the product of those of the constituent double combinations AMB+PMNs (21% ± 3.6%) and AMB+CIP (16% ± 3.7%). Thus, the antifungal activity of AMB, at clinically relevant concentrations, was enhanced in combination with PMNs and CIP against A. fumigatus growth in a concentration-dependent manner.

Rapid detection of ciprofloxacin effects on Fusarium graminearum and F. avenaceum cells in modulating environmental pH using a reactive, non-toxic food-dye indicator

The objective of the study was to assess the effect of ciprofloxacin antibiotic on the physiological or phenotypic characteristics of food-borne toxigenic Fusarium graminearum and F. avenaceum molds under in vitro conditions. In the presence of ciprofloxacin, Fusarium mycelia growth and morphology were altered based on the antibiotic concentration range used. Results showed that ciprofloxacin in concentrations ≥40μg/mL induced chlamydospore formation in Fusaria and as such, this antibiotic should be considered as an important abiotic stress factor and growth inhibitor. A novel method was investigated to correlate chlamydospore formation with the colour changes observed in FD&C Green Number 3, a common water soluble food dye. The antibiotic-treated F. graminearum and F. avenaceum isolates produced chamydospores, which in turn altered environmental pH with concomitant changes in the colour and intensity of the dye. The colour changes observed as a function of environmental pH were supported by instrumental methods (pH meter and spectroscopy), and a commercial pH indicator (thymol blue) results. In conclusion, we propose that FD&C Green Number 3 can be used as an accurate indicator for the rapid assessment of Fusarium molds when grown on ciprofloxacin antibiotic-containing substrate. Special emphasis should be given to an indirect risk assessment of antibiotic effects on toxic molds.

Direct effects of non-antifungal agents used in cancer chemotherapy and organ transplantation on the development and virulence of Candida and Aspergillus species

Conventional antineoplastic, novel immunosuppressive agents and antibiotics used in cancer treatment can directly affect the growth, development and virulence of Candida and Aspergillus species. Cytotoxic and cisplatin compounds have anti-Candida activity and may be synergistic with antifungal drugs; they also inhibit Candida and Aspergillus filamentation/conidation and effect increased virulence in vitro. Glucocorticoids enhance Candida adherence to epithelial cells, germination in serum and in vitro secretion of phospholipases and proteases, as well as growth of A. fumigatus. Calcineurin and target of rapamycin inhibitors perturb Candida and Aspergillus morphogenesis, stress responses and survival in serum, reduce azole tolerance in Candida, but yield conflicting in vivo data. Inhibition of candidal heat shock protein 90 and candidal-specific histone deacetylase represent feasible therapeutic approaches for candidiasis. Tyrosine kinase inhibitors inhibit fungal cell entry into epithelial cells and phagocytosis. Quinolone and other antibiotics may augment activity of azole and polyene agents. The correlation of in vitro effects with clinically meaningful in vivo systems is warranted. 

In vitro antifungal activities of amphotericin B in combination with acteoside, a phenylethanoid glycoside from Colebrookea oppositifolia

This study was undertaken to investigate the synergistic interaction between amphotericin B (AmB) and acteoside, isolated from the aerial parts of the shrub Colebrookea oppositifolia (Lamiaceae). Acteoside alone exhibited no intrinsic antifungal activity but showed a potent synergism in combination with AmB against selected pathogenic species, with fractional inhibitory concentration indices in the range of 0.0312-0.1562. The combination of acteoside at 3.12 and 12.5 µg ml(-1) with subinhibitory concentrations of AmB resulted in a potent fungicidal effect and also exhibited a significantly extended post-antifungal effect. Furthermore, the combination also reduced the minimum biofilm reduction concentration values of AmB (2-16-fold) in preformed biofilms of Candida albicans, Cryptococcus neoformans and Aspergillus fumigatus. There was decreased viability of the cells, increased uptake of propidium iodide and enhanced leakage of 260 nm-absorbing material by Candida albicans cells when exposed to AmB in the presence of acteoside. The reason for potentiation is likely to be that the subinhibitory concentrations of AmB facilitated the uptake of acteoside, which resulted in increased killing of the fungal cells. Administration of acteoside in mice at up to 2000 mg (kg body weight)(-1) by the intraperitoneal or oral route produced no overt toxicity. The data presented here support synergism between acteoside and AmB, and it is therefore proposed that a prospective new management strategy for therapeutic application of this combination should be explored.