Project name: Antibody neutralization profiles in human and wildlife sera against arboviruses
Institution: Universidad de Costa Rica
Mentor: Eugenia Corrales
Costa Rica has several risk factors for viral emergence and spread, including climatic conditions, exorbitant species richness and an intense flux of humans due to tourism. Some of the most important emerging infectious diseases are grouped under arthropod-borne viruses (arboviruses) because of their transmission cycle involving arthropods as vectors. The recent introduction of Zika and Chikungunya virus into the Americas, now affecting millions of people on the continent, illustrate the importance of emerging arboviruses. Several of the most relevant arboviruses belong to viral genera Flavivirus and Alphavirus. Flaviviruses such as Dengue and Zika cause from asymptomatic disease to febrile illness, hemorrhagic complications, congenital complications or death. Alphaviruses include a variety of important human and animal pathogens and can cause a wide range of clinical diseases from asymptomatic or flu-like to fatal encephalitic disease. No published data are available for human alphavirus infections in Costa Rica so far. However, according to anecdotal evidence from public health institutes, several human cases of VEEV and EEEV have been suspected. Although the presence of these emerging viruses is documented in Costa Rica, misdiagnosis as Dengue and Zika disease is frequent since clinical diagnostics fail due to overlap in symptoms. Our group has conducted intense sampling fieldtrips in rural areas for collection of samples belonging to humans and animals (birds, bats, domestic animals, horses). Sera collected will be tested in several serological tests, but mainly by neutralization assays (PRNT). The selected student will aid in the neutralization assays against several arboviruses including Dengue, Zika, WNV, YFV and alphaviruses in these panels of different sera. The main goal is to determine antibody neutralization profiles against arboviruses.
Experimental Methods: cell culture, arboviruses (Dengue, Zika, WNV, SLE, YFV, Alphaviruses) stock production and titration, neutralization by plaque reduction assays, data analysis and determination of antibody profiles. Field work for sampling may be necessary.
This project requires in person participation.
Project name: Role of receptor specificity in the biological activity of Toxin B variants produced by Clostridium difficile.
Institution: Universidad de Costa Rica
Mentor: Esteban Chavez Olarte
Clostridium difficile NAP1/027 hypervirulent strain possesses an epidemic character and is responsible of severe outbreaks worldwide. The reason for this behavior has been attributed to several characteristics, among those to the hyper production of toxin A and toxin B, increased sporulation and resistance to fluoroquinolones. We and others have determined that this strain produces a toxin B (TcdBNAP1) that departs at the sequence level and biological activity, from toxin B derived from classic reference strains. In a zebra fish model, TcdBNAP1 is clearly more toxic than the classic toxin B. In addition, when TcdBNAP1 is injected in the ligated ileal loop model, it induces more damage and pro inflammatory reaction than classic toxin B. This increased biological activity was originally attributed to a more efficient autoprocessing activity resulting in a more rapid release of the enzymatically active N-terminal domain into the cytosol. We, however, were not able to detect such an increased autoprocessing activity, an instead detected a difference in the ability TcdBNAP1 to interact with the surface of cells in culture when compared with classic toxin B. This latter toxin, derived from reference strain C. difficile VPI 10463 has been shown to use frizzled proteins and CSPG4 as cell surface receptors. Our early results on the differential binding of TcdBNAP1 as compared to classic toxin B lead us to postulate that TcdBNAP1 should use different receptor(s). This concept was addressed also by other groups with results supporting our initial postulate that indicate that TcdBNAP1 does not bind frizzled proteins. Considering all the above, the general hypothesis of this project is that the increased biological behavior of TcdBNAP1 is explained by the use of receptor(s), other than the one(s) used by classic toxin B and that TcdBNAP1 receptor(s) allow an increased binding, internalization and thus biological effects of this toxin.
We intend to address this hypothesis using the following general strategy: We will express and purify the recombinant receptor binding domains (RBDs) of TcdBNAP1 and TcdBVPI in Escherichia coli. These RBDs will be used in competition experiments to neutralize and decrease the binding of the corresponding native toxins, TcdBNAP1 and TcdBVPI. We expect each RBD to neutralize and outcompete only its corresponding toxin. The RBDs will be fluorescently labelled and used to monitor the binding to the surface of different cell lines and correlate the intensity of the binding with the susceptibility of the cells to the toxins. Furthermore, we will test the binding of the fluorescent RBDs to human intestine organoids. We expect that RBDNAP1 will bind more to the surface cultured cells and intestine organoids that RBDVPI. We will analyze the cristal structure of the recombinant RBDs to understand the differential binding to cell-surfaces and we will scan CRISPR CAS eucaryotic cell mutants libraries to find candidates for the TcdBNAP1 receptor(s).
Project name: Cellular and Molecular determinants of the intracellular lifestyle of bacteria from the genus Brucella
Institution: Universidad de Costa Rica
Mentor: Esteban Chavez Olarte
Brucellosis is a zoonotic disease that affects domestic and wild animals inducing abortions and infections in the genito urinary tract. Humans are infected by contact with animal fluids or ingestion of unpasteurized milk derived products. The pathogenesis of brucellosis relies on the ability of bacteria of the genus Brucella to invade and survive within eukaryotic cell lines. Brucella binds to cell surface receptors induces its own internalization and evades the lysosomal route and instead re directs its trafficking to the endoplasmic reticulum where it multiplies. Several virulence related molecular systems have been described to be involved in this interaction. Among them, the two-component system BvrR/BvrS has been shown to work as a sensor that indicates to the bacteria the transition from the extracellular milieu to the intracellular environment, triggering the transcriptional response required to adapt to the new niche. Among the genes expressed upon BvrR/BvrS activation, stands up the virB operon that encodes for a type IV secretion system (T4SS VirB). This secretion machinery is assembled during the early stages of the intracellular cycle of Brucella and secretes protein effectors that modulate the intracellular trafficking of the bacterium. Our group has contributed to understand the process described above and is currently interested in understanding the proteomic modifications induced by Brucella in the transit compartment that transports the bacterium to the endoplasmic reticulum. In addition, we are exploring how extended is this strategy among the different species of the genus.
Main goal: To characterize at the proteomic and immunochemical level the compartments transporting intracellularly bacteria of the genus Brucella.
Experimental Methods: cell culture, bacterial infections, cell fractionation, ultracentrifugation, automated immuno fluorescence, bio informatics, western blotting.
This project requires in person participation.
