Antimicrobial potential of a biosurfactant gel for the prevention of mixed biofilms formed by fluconazole-resistant C. albicans and methicillin-resistant S. aureus in catheters

Dual-species biofilms formed by Candida albicans and Staphylococcus aureus have high virulence and drug resistance. In this context, biosurfactants produced by Pseudomonas aeruginosa have been widely studied, of which a new derivative (RLmix_Arg) stands out for possible application in formulations. The objective of this study was to evaluate the antibiofilm activity of RLmix_Arg, both alone and incorporated in a gel prepared with Pluronic F-127, against dual-species biofilms of fluconazole-resistant C. albicans (FRCA) and methicillin-resistant S. aureus (MRSA) in impregnated catheters. Broth microdilution tests, MTT reduction assays of mature biofilms, impregnation of RLmix_Arg and its gel in peripheral venous catheters, durability tests and scanning electron microscopy (SEM) were performed. RLmix_Arg showed antimicrobial activity against Candida spp. and S. aureus, by reducing the cell viability of mixed biofilms of FRCA and MRSA, and preventing their formation in a peripheral venous catheter. The incorporation of this biosurfactant in the Pluronic F-127 gel considerably enhanced its antibiofilm activity. Thus, RLmix_Arg has potential application in gels for impregnation in peripheral venous catheters, helping to prevent development of dual-species biofilms of FRCA and MRSA.

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 S. 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. Having said that, Antibacterial effect of ketamine against MRSA strains, its mechanism of action and in silico interaction with sortase A was evaluated. The antibacterial effect of ketamine was assessed by 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 to 3.73 mM. Their mechanism of action involves alterations in the membrane integrity and DNA damage, reducing cell viability that provoke death by apoptosis. In addition, Ketamine compound had affinity for S. aureus sortase A. These results indicate that this compound can be an alternative to develop new strategies to combat of infections caused by MRSA.

Anti-MRSA activity of curcumin in planktonic cells and biofilms and determination of possible action mechanisms

Staphylococcus aureus is a commensal bacterium and opportunistic human pathogen that can cause a wide variety of clinical infections. It is recognized for its ability to acquire antimicrobial resistance, so methicillin-resistant Staphylococcus aureus (MRSA) infections are a global healthcare challenge. Therefore, the development of new therapeutic options and alternative therapies for treatment is necessary. Curcumin, a polyphenolic substance found in the rhizome of turmeric longa L, has been shown to have several therapeutic properties, including antimicrobial activity. The objective of the study was to evaluate the in vitro antibacterial activity of curcumin alone and associated with oxacillin against MRSA strains, to analyze the mechanism of cell death involved in the isolated action of curcumin by means of flow cytometry and molecular docking, and to verify its superbiofilm action. Curcumin showed antibacterial activity in the range of 125-500 μg/mL against the tested strains, since it caused an increase in membrane permeability and DNA fragmentation, as revealed by flow cytometry analysis. Moreover, it was possible to observe interactions of curcumin with wild-type S. aureus DHFR, S. aureus gyrase and S. aureus gyrase complex with DNA, DNA (5'-D(*CP*GP*AP*TP*GP*CP*G)-3') and Acyl-PBP2a from MRSA by molecular docking. Curcumin also had a synergistic and additive effect when associated with oxacillin, and significantly reduced the cell viability of the analyzed biofilms. Thus, curcumin is a possible candidate for pharmaceutical formulation development for the treatment of MRSA infections.

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.

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.