Antimicrobial peptides (AMPs) are natural antibiotics produced by various organisms such as mammals, arthropods, plants and bacteria. In addition to antimicrobial activity, AMPs can induce chemokine production, accelerate angiogenesis and wound healing and modulate apoptosis in multicellular organisms. Originally, their antimicrobial mechanism of action was thought to consist solely of an increase in pathogen cell membrane permeability, but it has already been shown that several AMPs do not modulate membrane permeability in the minimal lethal concentration. Instead, they exert their effects by inhibiting processes such as protein and cell wall synthesis, as well as enzyme activity, among others. Although resistance to these molecules is uncommon several pathogens developed different strategies to overcome AMPs killing such as surface modification, expression of efflux pumps and secretion of proteases among others. This review describes the various mechanisms of action of AMPs and how pathogens evolve resistance to them.

Quorum sensing (QS) is a mechanism of microbial communication dependent on cell density that can regulate several behaviors in bacteria such as secret

The fungal genus Sporothrix includes at least four human pathogenic species. One of these species, S. brasiliensis, is the causal agent of a major ongoing zoonotic outbreak of sporotrichosis in Brazil. Elsewhere, sapronoses are caused by S. schenckii and S. globosa. The major aims on this comparative genomic study are: 1) to explore the presence of virulence factors in S. schenckii and S. brasiliensis; 2) to compare S. brasiliensis, which is cat-transmitted and infects both humans and cats with S. schenckii, mainly a human pathogen; 3) to compare these two species to other human pathogens (Onygenales) with similar thermo-dimorphic behavior and to other plant-associated Sordariomycetes. The genomes of S. schenckii and S. brasiliensis were pyrosequenced to 17x and 20x coverage comprising a total of 32.3 Mb and 33.2 Mb, respectively. Pair-wise genome alignments revealed that the two species are highly syntenic showing 97.5% average sequence identity. Phylogenomic analysis reveals that both species diverged about 3.8-4.9 MYA suggesting a recent event of speciation. Transposable elements comprise respectively 0.34% and 0.62% of the S. schenckii and S. brasiliensis genomes and expansions of Gypsy-like elements was observed reflecting the accumulation of repetitive elements in the S. brasiliensis genome. Mitochondrial genomic comparisons showed the presence of group-I intron encoding homing endonucleases (HE’s) exclusively in S. brasiliensis. Analysis of protein family expansions and contractions in the Sporothrix lineage revealed expansion of LysM domain-containing proteins, small GTPases, PKS type1 and leucin-rich proteins. In contrast, a lack of polysaccharide lyase genes that are associated with decay of plants was observed when compared to other Sordariomycetes and dimorphic fungal pathogens, suggesting evolutionary adaptations from a plant pathogenic or saprobic to an animal pathogenic life style. Comparative genomic data suggest a unique ecological shift in the Sporothrix lineage from plant-association to mammalian parasitism, which contributes to the understanding of how environmental interactions may shape fungal virulence. . Moreover, the striking differences found in comparison with other dimorphic fungi revealed that dimorphism in these close relatives of plant-associated Sordariomycetes is a case of convergent evolution, stressing the importance of this morphogenetic change in fungal pathogenesis.

Paracoccidioides brasiliensis is the causative agent of paracoccidioidomycosis, a disease that affects 10 million individuals in Latin America. This report depicts the results of the analysis of 6,022 assembled groups from mycelium and yeast phase expressed sequence tags, covering about 80% of the estimated genome of this dimorphic, thermo-regulated fungus. The data provide a comprehensive view of the fungal metabolism, including overexpressed transcripts, stage-specific genes, and also those that are up- or down-regulated as assessed by in silico electronic subtraction and cDNA microarrays. Also, a significant differential expression pattern in mycelium and yeast cells was detected, which was confirmed by Northern blot analysis, providing insights into differential metabolic adaptations. The overall transcriptome analysis provided information about sequences related to the cell cycle, stress response, drug resistance, and signal transduction pathways of the pathogen. Novel P. brasiliensis genes have been identified, probably corresponding to proteins that should be addressed as virulence factor candidates and potential new drug targets.

A unique aspect of the interaction of the fungusCryptococcus neoformanswith macrophages is the phenomenon of nonlytic exocytosis, also referred to as “vomocytosis” or phagosome extrusion/expulsion, which involves the escape of fungal cells from the phagocyte with the survival of both cell types. This phenomenon has been observed onlyin vitrousing subjective and time-consuming microscopic techniques. In spite of recent advances in our knowledge about its mechanisms, a major question still remaining is whether this phenomenon also occursin vivo. In this study, we describe a novel flow cytometric method that resulted in a substantial gain in throughput for studying phagocytosis and nonlytic exocytosisin vitroand used it to explore the occurrence of this phenomenon in a mouse model of infection. Furthermore, we tested the hypothesis that host cell phagosomal pH affected nonlytic exocytosis. The addition of the weak bases ammonium chloride and chloroquine resulted in a significant increase of nonlytic exocytosis events, whereas the vacuolar ATPase inhibitor bafilomycin A1 had the opposite effect. Although all three agents are known to neutralize phagosomal acidity, their disparate effects suggest that phagosomal pH is an important and complex variable in this process. Our experiments established that nonlytic exocytosis occurredin vivowith a frequency that is possibly much higher than that observedin vitro. These results in turn suggest that nonlytic exocytosis has a potential role in the pathogenesis of cryptococcosis.IMPORTANCECryptococcus neoformanscauses disease in people with immune deficiencies such as AIDS. Upon infection,C. neoformanscells are ingested by macrophage immune cells, which provide a niche for survival and replication. After ingestion, macrophages can expel the fungi without causing harm to either cell type, a process named nonlytic exocytosis. To dissect this phenomenon, we evaluated its dependence on the pH inside the macrophage and addressed its occurrence during infection of mice. We developed new techniques using flow cytometry to measureC. neoformansinternalization by and nonlytic exocytosis from macrophages. Neutralizing the phagosome acidity changed the rate of nonlytic exocytosis: activity increased with the weak bases chloroquine and ammonium chloride, whereas the vacuolar ATPase inhibitor bafilomycin A1 caused it to decrease. Experiments in mice suggested that nonlytic exocytosis occurred during infection withC. neoformans. These results shed new light on the interaction betweenC. neoformansand host macrophages.