Biosurfactant complexed with arginine has antibiofilm activity against methicillin-resistant Staphylococcus aureus.

Aim: The present study investigated the antimicrobial effectiveness of a rhamnolipid complexed with arginine (RLMIX_Arg) against planktonic cells and biofilms of methicillin-resistant Staphylococcus aureus (MRSA). Methodology: Susceptibility testing was performed using the Clinical & Laboratory Standards Institute protocol: M07-A10, checkerboard test, biofilm in plates and catheters and flow cytometry were used. Result: RLMIX_Arg has bactericidal and synergistic activity with oxacillin. RLMIX_Arg inhibits the formation of MRSA biofilms on plates at sub-inhibitory concentrations and has antibiofilm action against MRSA in peripheral venous catheters. Catheters impregnated with RLMIX_Arg reduce the formation of MRSA biofilms. Conclusion: RLMIX_Arg exhibits potential for application in preventing infections related to methicillin-resistant S. aureus biofilms.

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Analysis of possible pathways on the mechanism of action of minocycline and doxycycline against strains of Candida spp. resistant to fluconazole.

Species of the genus Candida, characterized as commensals of the human microbiota, are opportunistic pathogens capable of generating various types of infections with high associated costs. Considering the limited pharmacological arsenal and the emergence of antifungal-resistant strains, the repositioning of drugs is a strategy used to search for new therapeutic alternatives, in which minocycline and doxycycline have been evaluated as potential candidates. Thus, the objective was to evaluate the in vitro antifungal activity of two tetracyclines, minocycline and doxycycline, and their possible mechanism of action against fluconazole-resistant strains of Candida spp. The sensitivity test for antimicrobials was performed using the broth microdilution technique, and the pharmacological interaction with fluconazole was also analysed using the checkerboard method. To analyse the possible mechanisms of action, flow cytometry assays were performed. The minimum inhibitory concentration obtained was 4-427 µg ml-1 for minocycline and 128-512 µg ml-1 for doxycycline, and mostly indifferent and additive interactions with fluconazole were observed. These tetracyclines were found to promote cellular alterations that generated death by apoptosis, with concentration-dependent reactive oxygen species production and reduced cell viability. Therefore, minocycline and doxycycline present themselves as promising study molecules against Candida spp.

Effects of ketamine in methicillin-resistant Staphylococcus aureus and in silico interaction with sortase A.

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the main human pathogens and is responsible for many diseases, ranging from skin infections to more invasive infections. These infections are dangerous and expensive to treat because these strains are resistant to a large number of conventional antibiotics. Thus, the antibacterial effect of ketamine against MRSA strains, its mechanism of action, and in silico interaction with sortase A were evaluated. The antibacterial effect of ketamine was assessed using the broth microdilution method. Subsequently, the mechanism of action was assessed using flow cytometry and molecular docking assays with sortase A. Our results showed that ketamine has a significant antibacterial activity against MRSA strains in the range of 2.49-3.73 mM. Their mechanism of action involves alterations in membrane integrity and DNA damage, reducing cell viability, and inducing apoptosis. In addition, ketamine had an affinity for S. aureus sortase A. These results indicate that this compound can be used as an alternative to develop new strategies to combat infections caused by MRSA.

Synergistic effects of ketamine and azole derivatives on Candida spp. resistance to fluconazole.

The emergence of Candida spp. with resistance to antifungal molecules, mainly the azole class, is an increasing complication in hospitals around the globe. Aim: In the present research, we evaluated the synergistic effects of ketamine with two azole derivatives, itraconazole and fluconazole, on strains of Candida spp. to fluconazole. Materials & methods: The drug synergy was evaluated by quantifying the fractional inhibitory concentration index and by fluorescence microscopy and flow cytometry techniques. Results: Our achievements showed a synergistic effect between ketamine in addition to the two antifungal agents (fluconazole and itraconazole) against planktonic cells and biofilms of Candida spp. Conclusion: This combination promoted alteration of membrane integrity, generation of reactive oxygen species, damage to and DNA and externalization of phosphatidylserine.

Action mechanism of naphthofuranquinones against fluconazole-resistant Candida tropicalis strains evidenced by proteomic analysis: The role of increased endogenous ROS.

The increased incidence of candidemia in terciary hospitals worldwide and the cross-resistance frequency require the new therapeutic strategies development. Recently, our research group demonstrated three semi-synthetic naphthofuranquinones (NFQs) with a significant antifungal activity in a fluconazole-resistant (FLC) C. tropicalis strain. The current study aimed to investigate the action's preliminary mechanisms of NFQs by several standardized methods such as proteomic and flow cytometry analyzes, comet assay, immunohistochemistry and confocal microscopy evaluation. Our data showed C. tropicalis 24 h treated with all NFQs induced an expression's increase of proteins involved in the metabolic response to stress, energy metabolism, glycolysis, nucleosome assembly and translation process. Some aspects of proteomic analysis are in consonance with our flow cytometry analysis which indicated an augmentation of intracellular ROS, mitochondrial dysfunction and DNA strand breaks (neutral comet assay and γ-H2AX detection). In conclusion, our data highlights the great contribution of ROS as a key event, probably not the one, associated to anti-candida properties of studied NFQs.

In vitro anti-Candida activity of selective serotonin reuptake inhibitors against fluconazole-resistant strains and their activity against biofilm-forming isolates.

Recent research has shown broad antifungal activity of the classic antidepressants selective serotonin reuptake inhibitors (SSRIs). This fact, combined with the increased cross-resistance frequency of the genre Candida regarding the main treatment today, fluconazole, requires the development of novel therapeutic strategies. In that context, this study aimed to assess the antifungal potential of fluoxetine, sertraline, and paroxetine against fluconazole-resistant Candida spp. planktonic cells, as well as to assess the mechanism of action and the viability of biofilms treated with fluoxetine. After 24 h, the fluconazole-resistant Candida spp. strains showed minimum inhibitory concentration (MIC) in the ranges of 20-160 µg/mL for fluoxetine, 10-20 µg/mL for sertraline, and 10-100.8 µg/mL for paroxetine by the broth microdilution method (M27-A3). According to our data by flow cytometry, each of the SSRIs cause fungal death after damaging the plasma and mitochondrial membrane, which activates apoptotic signaling pathways and leads to dose-dependant cell viability loss. Regarding biofilm-forming isolates, the fluoxetine reduce mature biofilm of all the species tested. Therefore, it is concluded that SSRIs are capable of inhibit the growth in vitro of Candida spp., both in planktonic form, as biofilm, inducing cellular death by apoptosis.

Berberine Antifungal Activity in Fluconazole-Resistant Pathogenic Yeasts: Action Mechanism Evaluated by Flow Cytometry and Biofilm Growth Inhibition in Candida spp.

The incidence of fungal infections and, in particular, the incidence of fungal antibiotic resistance, which is associated with biofilm formation, have significantly increased, contributing to morbidity and mortality. Thus, new therapeutic strategies need to be developed. In this context, natural products have emerged as a major source of possible antifungal agents. Berberine is a protoberberine-type isoquinoline alkaloid isolated from the roots, rhizomes, and stem bark of natural herbs, such as Berberis aquifolium, Berberis vulgaris, Berberis aristata, and Hydrastis canadensis, and of Phellodendron amurense Berberine has been proven to have broad antibacterial and antifungal activity. In the present study, the potential antifungal effect of berberine against fluconazole-resistant Candida and Cryptococcus neoformans strains, as well as against the biofilm form of Candida spp., was assessed. The antifungal effect of berberine was determined by a broth microdilution method (the M27-A3 method of the Clinical and Laboratory Standards Institute) and flow cytometry techniques, in which the probable mechanism of action of the compound was also assessed. For biofilm assessment, a colorimetric 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay was used to determine the susceptibility of sessile cells. The isolates used in the study belonged to the Laboratory of Bioprospection and Experiments in Yeast (LABEL) of the Federal University of Ceará. After 24 and 72 h, fluconazole-resistant Candida and Cryptococcus neoformans strains showed berberine MICs equal to 8 µg/ml and 16 µg/ml, respectively. Cytometric analysis showed that treatment with berberine caused alterations to the integrity of the plasma and mitochondrial membranes and DNA damage, which led to cell death, probably by apoptosis. Assessment of biofilm-forming isolates after treatment showed statistically significant reductions in biofilm cell activity (P < 0.001).