The antivirulence compound myricetin possesses remarkable synergistic effect with antibacterials upon multidrug resistant Staphylococcus aureus.

Staphylococcus aureus is an opportunistic pathogen involved in several human diseases and presents ability to produce many virulence factors and resistance to antibacterial agents. One of the current strategies to combat such multidrug resistant bacteria is the antibacterial combination therapy. Myricetin is a flavonoid capable of inhibiting several S. aureus virulence factors without influencing on bacterial growth. Therefore, the combination of antibacterials with the antivirulence compound myricetin may provide a positive interaction to control multidrug resistant-bacteria. This work aims to evaluate the effect of the combination of myricetin with oxacillin and vancomycin against methicillin resistant S. aureus (MRSA) and vancomycin intermediate resistant S. aureus (VISA) strains. Concentrations used in combination assays were determined according to the minimum inhibitory concentration (MIC) for antibacterials and to the biofilm minimum inhibitory concentration (BMIC) for myricetin. Checkerboard evaluations showed reduction in MIC for antibacterials in presence of myricetin and time-kill assays confirmed the synergism for these combinations, except for VISA strain when the flavonoid was combined with vancomycin. Importantly, when myricetin was combined with oxacillin, MRSA strain became susceptible to the antibacterial. Myricetin did not reduce staphyloxanthin production, indicating that the oxacillin susceptibility seems not to be related to this step of functional membrane microdomains. In vivo evaluations using Galleria mellonella confirmed the efficacy of oxacillin plus myricetin in treatment of MRSA infected-larvae when compared to the control groups, increasing in 20% host survival. The present work points out the potential of antibacterial and antivirulence compounds combinations as new alternative to control infections by multidrug resistant-bacteria.

Participation of Zip3, a ZIP domain-containing protein, in stress response and virulence in Cryptococcus gattii.

Cryptococcus gattii is an etiologic agent of cryptococcosis, a potentially fatal disease that affects humans and animals. The successful infection of mammalian hosts by cryptococcal cells relies on their ability to infect and survive in macrophages. Such phagocytic cells present a hostile environment to intracellular pathogens via the production of reactive nitrogen and oxygen species, as well as low pH and reduced nutrient bioavailability. To overcome the low-metal environment found during infection, fungal pathogens express high-affinity transporters, including members of the ZIP family. Previously, we determined that functional zinc uptake driven by Zip1 and Zip2 is necessary for full C.gattiivirulence. Here, we characterized the ZIP3 gene of C. gattii, an ortholog of the Saccharomyces cerevisiae ATX2, which codes a manganese transporter localized to the membrane of the Golgi apparatus. Cryptococcal cells lacking Zip3 were tolerant to toxic concentrations of manganese and had imbalanced expression of intracellular metal transporters, such as the vacuolar Pmc1 and Vcx1, as well as the Golgi Pmr1. Moreover, null mutants of the ZIP3 gene displayed higher sensitivity to reactive oxygen species (ROS) and substantial alteration in the expression of ROS-detoxifying enzyme-coding genes. In line with these phenotypes, cryptococcal cells displayed decreased virulence in a non-vertebrate model of cryptococcosis. Furthermore, we found that the ZIP3 null mutant strain displayed decreased melanization and secretion of the major capsular component glucuronoxylomannan, as well as an altered extracellular vesicle dimensions profile. Collectively, our data suggest that Zip3 activity impacts the physiology, and consequently, several virulence traits of C. gattii.