Secondary Streptococcus pneumoniae infection increases morbidity and mortality during murine cryptococcosis

Microorganisms that cause pneumonia and translocate to the central nervous system (CNS) are responsible for high mortality worldwide. The fungus Cryptococcus gattii (Cg) and the bacteria Streptococcus pneumoniae (Sp) target the same infection organs. This study aimed to investigate the consequences of secondary Sp infection during murine cryptococcosis. Mice infected with Sp after Cg showed significantly increased lethality and a drop in scores of motor behaviour, neuropsychiatric status and autonomous function. Previous Cg infection favoured Sp multiplication in the lungs, causing intense inflammation and necrosis, with further increased bacterial translocation to the spleen, liver and brain. This phenotype was associated with increased platelet-activating factor receptor (Pafr) gene expression, reduced M1 macrophage recruitment, and high levels of proinflammatory mediators. Strategies to overcome early mortality (i.e., infection of Pafr-/- mice, treatment with IL-1 inhibitor or corticoid) were insufficient to revert this phenotype. These results suggest that Cg infection makes the lung microenvironment favourable for Sp colonization and dissemination. Altogether, it leads to an exacerbated and ineffective inflammatory response, decisive for the increased morbidity and mortality during coinfection. In conclusion, our results highlight the importance of more studies addressing coinfections and their consequences in the host, aiming to establish more effective therapeutical strategies.

Biocontrol potential of actinobacteria against Pantoea ananatis, the causal agent of maize white spot disease

Pantoea ananatis is the causal agent of maize white spot, a foliar disease responsible for significant maize yield reduction worldwide, especially in Brazil. In general, the maize foliar diseases control involves the adoption of resistant genotypes and pesticides application. However, the use of agrochemicals can significantly cause increase production costs, damage to human health and negative environmental impacts. In this sense, the use of biological control agents has been considered among the most promising eco-friendly technologies for sustainable agriculture. Actinobacteria, particularly of Streptomyces genus, has been widely recognized as agroindustrially important microorganism due to its potential in producing diverse range of secondary metabolites, including antibiotics and enzymes. Thus, the aim of this work is to characterize and to evaluate the potential of soil actinobacteria for P. ananatis control. We observed that 59 actinobacteria strains (85%) exhibited proteolytic or chitinolytic activity. Only the strains Streptomyces pseudovenezuelae ACSL 470, that also exhibited high proteolytic activity, S. novaecaesareae ACSL 432 and S. laculatispora ACP 35 demonstrated high or moderate antagonist activity in vitro against P. ananatis. Temporal analysis of metabolites produced by these strains growth in different liquid media indicated greater antibacterial activity at 72 h. In this condition, chromatographic and mass spectrometry analysis revealed that S. pseudovenezuelae ACSL 470 strain produced neomycin, an aminoglycoside antibiotic that displayed high bactericidal activity in vitro against P. ananatis. This is the first report of actinobacteria acting as potential microbial antagonists for P. ananatis control. Further studies are needed to determine the control efficacy of maize white spot disease by Streptomyces strains or their metabolites in greenhouse and field conditions.

Exposure to itraconazole influences the susceptibility to antifungals, physiology, and virulence of Trichophyton interdigitale

Dermatophytosis is the most common human skin infection worldwide caused by dermatophytes, such as Trichophyton interdigitale and Trichophyton rubrum. Itraconazole (ITZ) is one of the main antifungals used to treat these infections. However, especially for onychomycosis, the treatment requires long-term regimens, increasing the possibility of drug resistance. We evaluated the effects of ITZ in the physiology, virulence, and interaction of T. interdigitale with phagocytes and mice cutaneous infection. In a screening test, fungal growth in the presence of ITZ led to the spontaneous selection of less susceptible T. interdigitale and T. rubrum strains. Interestingly, this phenotype was permanent for some T. interdigitale strains. Then, we studied three T. interdigitale strains: one susceptible and two ITZ-adapted. The ITZ-adapted strains were also less susceptible to the cell wall and membrane stressors, suggesting a multidrug resistance (MDR) phenotype associated with the increased ERG11 and MDR3 expression. These strains also presented substantial alterations in ergosterol content, lipid peroxidation, biofilm, and extracellular matrix production. During interaction with macrophages, ITZ-adapted strains were less engulfed but increased the intracellular oxidative and nitrosative bursts. In addition, ITZ-adapted strains presented a reduced ability to grow in a murine model of dermatophytosis, although causing the same tissue damage as the parental strain. In conclusion, the T. interdigitale ITZ adaptation increases tolerance to antifungals and alters the interaction with macrophages and a mammalian host. We hypothesized that successive exposure to ITZ may influence the emergence of adapted strains and lead to the recalcitrance of dermatophytosis.

Reactive oxygen and nitrogen species are crucial for the antifungal activity of amorolfine and ciclopirox olamine against the dermatophyte Trichophyton interdigitale

Onychomycosis is a nail infection caused by Trichophyton interdigitale and other fungi, which can be treated with topical amorolfine (AMR) and ciclopirox olamine (CPX). Although these drugs are widely used, little is known about the role of reactive oxygen (ROS) and nitrogen (RNS) in their mechanism of action. Aiming to better understand the effects of AMR and CPX in dermatophytes, we evaluated whether they act through the production of ROS and peroxynitrite (PRN). We tested a set of strains, all susceptible to AMR and CPX, and these antifungals significantly reduced T. interdigitale viability within 24 hours. This effect occurred concomitantly with reduced ergosterol, increased production of ROS and PRN, and consequently increased lipid peroxidation. Together, these mechanisms lead to cell damage and fungal death. These fungicidal effects were abolished when PRN and superoxide scavengers were used in the assays, demonstrating the role of these species in the mechanism of action. We also studied the antioxidant system when T. interdigitale was exposed to AMR and CPX. Interestingly, superoxide dismutase and catalase inhibition lead to altered ROS and PRN production, lipid peroxidation, and ergosterol levels. In fact, the combination of AMR or CPX with a superoxide dismutase inhibitor was antagonistic. Together, these data demonstrate the importance of ROS and PRN in the antifungal action of AMR and CPX against the evaluated T. interdigitale strains.

Pseudomonas aeruginosa Infection Modulates the Immune Response and Increases Mice Resistance to Cryptococcus gattii

Cryptococcosis is an invasive mycosis caused by Cryptococcus spp. that affects the lungs and the central nervous system (CNS). Due to the severity of the disease, it may occur concomitantly with other pathogens, as a coinfection. Pseudomonas aeruginosa (Pa), an opportunistic pathogen, can also cause pneumonia. In this work, we studied the interaction of C. gattii (Cg) and Pa, both in vitro and in vivo. Pa reduced growth of Cg by the secretion of inhibitory molecules in vitro. Macrophages previously stimulated with Pa presented increased fungicidal activity. In vivo, previous Pa infection reduced morbidity and delayed the lethality due to cryptococcosis. This phenotype was correlated with the decreased fungal burden in the lungs and brain, showing a delay of Cg translocation to the CNS. Also, there was increased production of IL-1β, CXCL-1, and IL-10, together with the influx of iNOS-positive macrophages and neutrophils to the lungs. Altogether, Pa turned the lung into a hostile environment to the growth of a secondary pathogen, making it difficult for the fungus to translocate to the CNS. Further, iNOS inhibition reverted the Pa protective phenotype, suggesting its important role in the coinfection. Altogether, the primary Pa infection leads to balanced pro-inflammatory and anti-inflammatory responses during Cg infection. This response provided better control of cryptococcosis and was decisive for the mild evolution of the disease and prolonged survival of coinfected mice in a mechanism dependent on iNOS.

Nicotiana benthamiana as a model for studying Cryptococcus-plant interaction

Cryptococcus gattii, an environmental yeast isolated from plants, is one of the agents of cryptococcosis. Here, we aimed to develop a plant model to study C. gattii-plant interaction, since it is unclear how it affects the plant and the yeast. We tested three inoculation methods (scarification, infiltration, and abrasion) in three plant species: Arabidopsis thaliana, Nicotiana tabacum, and N. benthamiana. Cryptococcus gattii was able to grow in all three models, with a peak of yeast cell burden after 7 days, without any pathological effects. Furthermore, the fungal burden was reduced later, confirming that C. gattii is not a phytopathogen. Cryptococcus gattii proliferation was higher in N. benthamiana, which presented an increase in the hydrogen peroxide content, antioxidant system activity, and indoleacetic acid (IAA) production. Cryptococcus gattii colonies recovered from N. benthamiana presented lower ergosterol content, reduced capsule, and increased growth rate in vitro and inside macrophages. In vitro, IAA altered C. gattii morphology and susceptibility to antifungal drugs. We hypothesize that C. gattii can temporarily colonize plant living tissues, which can be a potential reservoir of yeast virulence, with further dissemination to the environment, birds, and mammals. In conclusion, N. benthamiana is suitable for studying C. gattii-plant interaction.

Essential oils of Taxandria fragrans and Melaleuca alternifolia have effective antidermatophytic activities in vitro and in vivo that are antagonised by ketoconazole and potentiated in gold nanospheres

The investigation of the effects of three essential oils (EOs) from Taxandria fragrans (FRA), Melaleuca alternifolia (TTO) and Boswellia serrata (IF), alone and combined with ketoconazole (KTZ), and their functionalised gold nanoparticles (AuNP) against Trichophyton interdigitale both in vitro and in vivo indicated that EOs presented activity against T. interdigitale. The combination of EOs and KTZ was antagonistic. FRA, TTO, gold nanoparticles capped with T. fragrans (AuNPFRA) and gold nanoparticles capped with M. alternifolia (AuNPTTO) presented antidermatophytic activity in vivo, with the capacity to reduce fungal burden and to preserve tissue architecture; however, combination treatment with KTZ increased fungal burden and caused tissue damage. The combination of EO with KTZ exhibited antagonistic activity and was histologically harmful. In contrast, FRA, TTO, AuNPFRA and AuNPTTO are promising treatments for dermatophytosis.