Our studies have demonstrated that ROS play a central role in mediating host-pathogen interactions in our model. Using our novel pathogenesis assay with S. cerevisiae as a model pathogen and C. elegans as the model host, we found that yeast can infect worms, resulting in intestinal distension, a deformity in the postanal region (DAR phenotype), and death of the host nematode. In this study we show that ROS play an important role in fungalpathogenesis and host defense. The C. elegans bli-3 gene encodes a dual oxidase known to have mammalian homologs capable of producing ROS. Our results show that two bli-3 mutants with point mutations in the peroxidase do- main (44) do not produce hydrogen peroxide in the Amplex Red assay. This may seem surprising, because classically, su- peroxide produced by NADPH oxidase is converted to hydro- gen peroxide by dismutation and then to antimicrobial oxi- dants by peroxidase. According to this model, a mutation in the peroxidase domain would not be expected to alter production of the hydrogen peroxide. However, it has been suggested that the peroxidase domain of the dual oxidases catalyzes dismuta- tion as well as production of antimicrobial oxidants (30). In that case, a mutation in the peroxidase domain might well cause a decrease in hydrogen peroxide production. Alterna- tively, a mutation in the peroxidase domain may alter the topology of the oxidase domain and decrease its activity. Fur- ther studies of the dual oxidases will be required to understand the details of their catalytic mechanisms.
with hypoxia responses have been investigated for their roles in fungalpathogenesis. In C. albicans, these include EFG1, EFH1, ACE2, and TYE7 (2, 30, 79, 105). EFG1 null mutants are hyper- filamentous under low-oxygen conditions, possibly due to down- regulation of the filamentous repressor NRG1 under these condi- tions, and thus, EFG1 negatively regulates hypoxia-induced filamentation in C. albicans (105). Consequently, in an in vivo infection model, an efg1 null mutant grew more than a wild-type strain (66). Thus, this in vivo result partially supports a role for hypoxia in C. albicans pathogenesis, as the yeast-to-hypha switch is generally thought to be a major virulence attribute of this or- ganism. In general, the in vivo phenotype of the EFG1 null mutant is surprising given the importance of this transcription factor in regulating gene expression in C. albicans. Furthermore, a recent study observed that under hypoxic conditions EFG1 induces all major classes of genes known to be associated with biofilm forma- tion, a major cause of persistence and antifungal resistance in C. albicans infections, and that EFG1 is required for biofilm forma- tion (112). As biofilms contain significant layers of hypoxia, it is tempting to speculate that regulators of biofilm formation may also have roles in fungal hypoxia adaptation that have been largely unexamined (39, 81, 97). Another important role for the Efg1/ Efh1 gene expression network, and thus hypoxia, is in Candida commensalism. EFH1/EFH1 null mutants of C. albicans are able to persist in the gastrointestinal (GI) tract at higher levels than wild-type strains, while cells that overexpress EFH1 are signifi- cantly reduced in GI tract colonization (126). Thus, given the hypoxic environment in the GI tract and the propensity of Can- dida to colonize this location, it is tempting to speculate that Can- dida responses to hypoxia are critical for evasion of the host im- mune system under these conditions to allow commensalism. FIG 2 Confirmed and potential effects of hypoxia on fungalpathogenesis. Molecular oxygen is critical for numerous cellular processes, including ATP production and the biosynthesis of key molecules such as sterols, fatty acids, and NAD. Thus, loss of oxygen at sites of fungal infections influences the physiology of both the fungal pathogen and immune cells of the host that affect the final outcome of the fungus-host interaction. Images, from left to right: A. fumigatus colony on nutrient agar; C. neoformans yeast; and monocytes, neutrophils, and macrophages from lung bronchoalveolar lavage fluid. PAMP, pathogen- associated molecular pattern, PRR, pattern recognition receptor. Suggested impacts on the host side are based on data largely from bacterial pathosystems and have not been confirmed to be active in fungus-host interactions to date.
All three chitin deacetylases share similar protein sequence motifs for a cleavable N-terminal signal sequence and for C-terminal addition of a glycosylphosphatidylinosi- tol (GPI) anchor. C. neoformans Cda2 (initially named MP98) was shown to be a potent stimulator of CD4 T cells (33). Recently, recombinant proteins of C. neoformans Cda1, Cda2, and Cda3 expressed in Escherichia coli were shown to induce protective immunity in mice against a C. neoformans infection when used as vaccines and delivered by glucan particles (34). These data indicate that C. neoformans Cda proteins have an inherent ability to modulate host immune responses. Therefore, we wanted to rule out the possibility that the absence of Cda1 protein in cda1 ⌬ cells is responsible for its attenuated virulence. We also sought to distinguish whether the role of Cda1 in fungalpathogenesis depends on the presence of the protein as a component of the cell wall, its enzyme activity, or both of these features. To address this, we introduced loss-of- function point mutations in the catalytic residues of Cda1. Our ﬁndings revealed that Cda1 with its intact chitin deacetylase enzyme activity rather than its mere presence in the cell wall is necessary for virulence, implicating its role in chitin deacetylation as a critical factor for mediating fungalpathogenesis.
Fungi are important pathogens of plants and cause more significant yield losses than bacteria or viruses. However, bac- teria and viruses are more important than fungi as pathogens of animals; indeed, whether or not a fungus even becomes pathogenic on an animal often depends on the immune status of the host. Until the rapid rise of opportunistic fungal infec- tions in humans, pathogenicity mechanisms in plant pathogens were better understood than those in animal pathogens. In- creased research activity in medical mycology has coincided with the development of molecular genetic and genomic re- sources, which are being exploited to develop a detailed un- derstanding of fungalpathogenesis in both animals and plants. Several constraints and peculiarities govern the types of infor- mation that can be derived from such studies. For instance, analyses of human-pathogenic fungi generally rely on cell lines and experimental animal models, in contrast to plant patho- gens, which can be studied directly on their hosts. Many more fungal species infect plants than animals, and thus, more plant- fungus systems than animal-fungus systems are studied. This is mainly because there are far more plant hosts than animal hosts that are of economic importance, with the obvious ex- ception of human disease, and because plants can be manipu- lated without the ethical issues associated with animal experi- mentation.
Here we demonstrated that both the Rad53-dependent and Chk1-dependent path- ways contribute to the pathogenicity of C. neoformans. Although the role of DNA damage response pathways in fungal pathogenicity has been also reported in other fungal pathogens, their modes of action appear to be different. In C. albicans, a dimorphic transition between yeast and hyphal forms in response to external signals is one of critical virulence factors (60). Interestingly, genotoxic stress induces a morpho- genetic change from the yeast form to the ﬁlamentous form (45). Deletion of RFX2 causes hyperﬁlamentous growth and thereby attenuates virulence in C. albicans (57). Similarly to C. albicans, morphogenetic changes such as production of infectious dikaryotic hypha are regulated by the cell cycle in U. maydis (61). The impaired cell cycle arrest caused by deletion of CHK1 or ATR1 leads to inappropriate formation of infective ﬁlament, which results in attenuated virulence (46, 48). Upon infection through the respiratory tract, C. neoformans encounters alveolar macrophages and is internalized through opsonic and nonopsonic phagocytosis. After internalization of cells, the phagosome, which is a single-membraned vesicle that contains C. neoformans, under- goes maturation. During this process, C. neoformans is exposed to a harsh antimicrobial environment including such elements as the respiratory burst (oxidative burst) and addition of antimicrobial degrading enzymes (62). Consequently, inherent resistance against phagocytosis and phagosome maturation is an indispensable virulence attri- bute for C. neoformans. Interestingly, our data suggest that Chk1 is in part required for the survival of Cryptococcus inside macrophages, since mutation in CHK1 enhanced phagosome maturation. Similarly, we demonstrated that the rad53Δ chk1Δ mutants showed a lower survival rate than the WT strain within the macrophage. In addition, we found that antioxidant effects such as melanin production mediated
While recent studies have highlighted the importance of mitochondrial function for tolerance of antifungal drugs and for virulence, our understanding of the roles of this organelle in human fungal pathogens is still limited. Functions in lipid homeostasis are likely to be at the heart of the involvement of mitochondria in tolerance of antifungal drugs, but the exact molecular mechanisms are not fully understood. Biochemical experiments in mitochondrial mutants addressing lipid compo- sition, activities of plasma membrane enzymes, and the struc- ture of the cell wall should answer some of the outstanding questions. Also important is to test the virulence of many more mutants affected in diverse mitochondrial functions. This could produce a list of potentially attractive targets for future anti- fungal drug development. It is of interest that a large number of mitochondrial proteins are likely to be essential for viability in petite-negative pathogens, such as C. albicans and C. neo- formans. An important point is that several of these mitochon- drial factors do not have close orthologs in humans; for exam- ple, see reference 65. Collectively, these observations indicate that studies into how mitochondria contribute to the fitness, pathogenicity, and drug tolerance of human fungal pathogens are worthwhile.
Here we utilized a C. elegans experimental host system to identify novel measures of host ﬁtness associated with fungal infection. By tracking the number of progeny produced per day, we can quickly and quantitatively assess three aspects of host ﬁtness: early mortality, total viable offspring produced, and reproductive timing. We show that exposure to Candida albicans in healthy Caenorhabditis elegans hosts not only reduces survival (Fig. 1) but modestly reduces total progeny produced and dramatically delays reproductive timing (Fig. 2). This reproductive delay has long-term consequences for lineage expansion, since single founder nematodes exposed to C. albicans reduce its population growth by ⬃ 30% (Fig. 2D). Furthermore, reductions in host population growth are dependent on C. albicans virulence rather than a general host response to foreign fungal cells since host population growth was minimally affected in C. albicans virulence deletion strains (Fig. 3). We found similar delays in reproductive timing in immunocompromised hosts exposed to C. albicans, although immunocompromised hosts are more susceptible to infection and have higher inci- dence of early mortality and smaller brood sizes compared to healthy hosts (Fig. 4). Importantly, the delayed reproduction phenotype in infected C. elegans is easily ascertained, highly quantitative, and reproducible and can be used as a screening method to detect relatively small differences in virulence across Candida strains or other fungal species. Furthermore, by utilizing different host contexts, this assay revealed the pathogenic potential of other important, yet understudied, Candida species (Fig. 5), including C. parapsilosis, which has dramatically higher levels of virulence in immunocompromised hosts compared to healthy hosts.
Although the MEKK-MEK-MAPK cascades are conserved, the upstream signal inputs and downstream transcription fac- tors in pathogens are different from those of S. cerevisiae. Fungal pathogens may have novel receptors for sensing host and environmental signals to regulate penetration and infec- tious growth. Although Ras proteins have been shown to ac- tivate downstream MAPKs in several fungi, sequenced fungal genomes lack significant homologs of receptor kinase genes that function upstream from Ras in mammalian cells. Related to this subject, pathway specificity in fungal pathogens is not well studied. To date, no Ste5 homolog or Ste5-like scaffold protein in pathogenic fungi has been identified. With genomic resources becoming available for more and more fungi, com- parative and functional genomic analyses will be useful to identify the missing regulatory and structural components of these MAPK pathways and their downstream targets or net- work of transcription factors.
At this point it is unclear why some filamentous fungi lack orthologues, or proteins with any similarity whatsoever, to ZtGT2. For example, the model basidiomycete plant pathogens Puccinia graminis and Ustilago maydis have no similar proteins to ZtGT2, but they do grow hyphae over plant surfaces (including wheat leaves for the former). As presence / absence of proteins with similarity to ZtGT2 appears discontinuous, even within the ascomycete king- dom, it is possible that some fungal species use a different protein, or mechanism, to provide the equivalent functionality. This might again be reflected in the chemical composition of the outer cell wall surfaces in these fungi. However, for ZtGT2 and its close orthologues, some conclusions can be made. Firstly, the gene is present in almost all analysed ascomycete plant pathogens and in several opportunistic animal pathogens (for example Aspergillus fumigatus). However, it is also frequently observed to be present in many saprophytic fungi including those which perform the primary events in leaf litter decay. Thus, we speculate that the impor- tance of this gene for the evolution of fungalpathogenesis likely derived “inadvertently” from an ancient requirement for fungi to evolve the hyphal growth form, to extend filaments over solid surfaces for purposes such as nutrient acquisition. By acquiring this basic functionality, fungi also acquired a key competency which subsequently enabled them to develop parasitic (as well as potentially mutualistic) interactions with many plants and animals. Based upon all the available data it is likely that ZtGT2 synthesises or modifies a potentially widespread and essential extracellular matrix or outer cell wall polysaccharide component, which may be only a minor constituent (Fig 7). This may function to alleviate surface friction and shear stresses normally imposed on rapid hyphal tip growth over solid matrices [13, 14]. This currently structurally undefined, polysaccharide may be functionally important for many plant (and perhaps animal) pathogens and may therefore represent a viable target for future widespread control of fungal diseases. This study also emphasises the tractability of Z. tritici as a model organism for isolating genes which may be essential for contact-dependent filamentous fungal growth.
4.2.1. Mouse (Mus musculus). The majority of Cryptococcus- related work utilising mammalian systems has been carried out using mice. Due to the fact that murine models are well established as valuable study systems in many research areas including fungalpathogenesis, an in-depth discussion of mice in Cryptococcus research is not within the scope of the present review. Briefly, however, mouse models are a popular choice because they are well established and characterised in medical research, and a variety of genetic backgrounds are available. Infection with Cryptococcus can be achieved by a variety of methods, including intranasally, intraperitoneally, intracerebrally, intravenously, intratracheally, and via inhala- tion [88, 89], which opens up a range of experimental opportunities. In addition, the vast array of information available on the mouse immune system means that parallels and pitfalls can be readily identified, allowing for the design of highly refined experiments.
Prevalence of the disease is related to environment as well as individual host conditions. People of low socioeconomic group living in overcrowded and damp environment, suffer the most. It involves both sexes and all age groups but is seen more commonly in males among the ages of 22-50 years. Aggressive nasal polyposis and multi-sinus involvement is a hallmark of fungal sinusitis. Aspergillus species found in 90 (40.70%) cases reflected a higher incidence of fungal sinusitis in our community. CT findings of intra-sinus calcification proved helpful in differentiating fungal from non-fungal entities and it is also a better way to assess the extent of the disease. MRI is helpful if there is a suspicion of intracranial extension of the disease.
Furthermore, severe burn trauma causes devascularization of the wound environ- ment, which prevents neutrophils and other innate effector cells from migrating into the wound and clearing the bacterial infection. The avascular state of the burn wound results in a decreased supply of oxygen and other essential nutrients to the damaged tissue, which can lead to ischemia (19). Despite these limitations, P. aeruginosa can ﬂourish within the burn wound and aggressively disseminate through the surrounding tissue and into the bloodstream. Reports have indicated that the availability of key amino acids, especially arginine, can inﬂuence the lifestyle and activity of P. aeruginosa within the cystic ﬁbrosis (CF) lung environment by acting as an environmental cue (20, 21). In this study, we investigated the impact of arginine availability in a thermally injured mouse model of infection to assess whether limited access to this substrate inﬂuences the behavior of P. aeruginosa pathogenesis in burn wound infections.
detoxification of host-derived NO. Our investigations indicate that, together with Hmp, cytochrome bd is an important compo- nent of the adaptive antinitrosative arsenal of Salmonella in vivo. Our biochemical and microbiological approaches suggest that Hmp is more important than cytochrome bd in protecting the respiratory and replicative capacity of Salmonella exposed to chemically generated NO. The competitive assays recorded in mice indicate, however, that both Hmp and cytochrome bd con- tribute to similar extents to Salmonella pathogenesis. Several rea- sons may explain the ranking of importance for Hmp and cyto- chrome bd as antinitrosative defenses of Salmonella depending on the experimental conditions tested. First, limited O 2 concentra-
Indole acetic acid (IAA) production is major properties of certain funguses that stimulates and facilitate plant growth. The present work deals with isolation, characterization and identification of indole acetic acid producing bacteria from the Aspergillus sp. Partial purification of IAA was done and purity was confirmed with Thin layer chromatography. Qualitative analysis by HPLC carried out for identification of Indole acetic acid. In conclusion, fungal can further be initiated towards purifying and standardizing for cell suspension cultures for enhanced production of secondary metabolites.
Fungal infections in both their invasive and non-invasive forms can prove difcult to diagnose. The often characteristic appearances on imaging are of great assistance. CT is the primary imaging modality and is probably more accurate than MRI in diagnostic specicity and determining the extent of bone erosion. However this may require a modied scanning technique to adequately demonstrate the typical soft tissue density variations of fungi. MRI should be used to supplement CT when intra-cranial or intra-orbital extension is suspected.
ABSTRACT: Tuberculosis is a bacterial infection which is caused by the bacteria Mycobacterium tuberculosis. It is next to AIDS and causes morbidity and mortality. These bacteria can stay in the host’s body for decades. In this article we have mentioned about the pathogenesis of pulmonary tuberculosis followed by the pathogenesis of tuberculous meningitis wherein the bacteria first enter to the lungs which then form into macrophages, these macrophages form into granulomas which get ruptured and enter the brain and then enter the subarachnoid space causing tuberculous meningitis. The current treatment methods available, their dosage forms and penetrance into the CSF is also mentioned. Usually, the first line drugs are used in combination to treat the disease but in the case of resistance second-line drugs are used. The duration of the treatment depends on the severity of the disease. Even though, there are many drugs available to treat the disease the amount of drug entering the brain is minimal due to the presence of the blood-brain barrier (BBB). So, due to this reason many new technologies like niosomes, liposomes, nanoemulsions, microspheres, etc. are being used. Hence, in this paper, we are explaining about tuberculosis as well as tuberculous meningitis and its possible strategies for overcoming the problems associated with the failure of the treatment.
Mature, healthy plant materials were collected and identified by expertise from Department of Botany, Moolji Jaitha College Jalgaon, India. Collected plant samples were immediately brought to laboratory and were used within 8 hours for isolation of fungal endophytes. Healthy plants were selected growing in different regions of Jalgaon geographically located at 21.01 0 N75.56 0 E and average elevation about 209 meters (Figure 1.) Endophytic flora were isolated from roots of Aloe vera (L.), Ocimum sanctum (L.) and rhizomes of Curcuma longa (L.) .
In children, the main causes of eosino- philia include allergies and parasitic infestations. In rare cases it may be associated with some fungal or viral infections, malignant tumors, gastro- enteritis, or autoimmune diseases. We present here a case of prolonged ex- treme eosinophilia in a preterm infant complicated by thrombocytopenia. There was no obvious underlying etiol- ogy or speciﬁc treatment required.