STAPHYLOCOCCUS EPIDERMIDIS AND MYCOBACTERIUM ULCERANS IMPACT ATTRACTION OF AEDES AEGYPTI (L.) (DIPTERA: CULICIDAE) TO A BLOOD-FEEDING SOURCE

Aedes aegypti, is a vector of pathogens transmitting many infectious diseases, such as Zika, Dengue, and Yellow Fever. Skin-inhabiting bacteria, such as Staphylococcus epidermidis, produce specific volatile organic compounds (VOCs) which participate in attracting mosquitoes to human hosts. However, little is known about the ecology of the bacteria and its role in mosquito behavior; specifically whether bacterial communication through quorum sensing (QS) modulates mosquito behavior. This study determined if the QS system could be manipulated chemically (e.g., quorum sensing inhibitor (QSI), C-30, furanone) to suppress mosquito responses. The results showed disrupting QS by S. epidermidis with an inhibitor (QSI) reduced the VOC composition by 35.0% and suppressed mosquito attraction by 55.1%. To explore further questions, mycolactone as a potential QS compound produced by the environmental pathogen, Mycobacterium ulcerans, regulating mosquito behavior was determined. A blood-feeder treated with M. ulcerans wildtype elicited a 126.0% and 171.0% greater attraction than M. ulcerans mutant or control, respectively. In terms of polymicrobial interactions, the addition of M. ulcerans to S. epidermidis resulted in 23.7% and 72.1% greater mosquito attraction than S. epidermidis and M. ulcerans alone. Most interestingly, S. epidermidis concentrations are typically low on the extremities. In this study, an interdisciplinary approach was used to elucidate the ecological ramifications associated with interkingdom cross-talk between bacteria and eukaryotic. This knowledge can lead to the development of a new class of odor-masking or inhibitory compounds as it is thought to be the less selective pressure than pre-existing pesticide or repellent use, which can be exploited in the protection from mosquito bites, aiming at compounds that reduce the production of attractive volatiles on the human skin. It has a broad range of potential applications in agriculture, medicine, pest-management, and etc

Threshold dynamics of stochastic cholera epidemic model with direct transmission

This paper extends the cholera human-to-human direct transmission model from a deterministic to a stochastic framework. This is expressed as mixed system of stochastic and deterministic differential equations. A Lyapunov function is created to investigate the global stability of the stochastic cholera epidemic, which shows the existence of global positivity of the solution using the theory of stopping time. We then find the threshold quantity of the extended stochastic cholera epidemic model. We derive a parametric condition $\widetilde{R}_0$, and for additive white noise, we establish sufficient conditions for the extinction and the persistence of the cholera infection. Finally, for a suitable choice of the parameter of the system for $\widetilde{R}_0$, we perform numerical simulations for both scenarios of extinction and persistence of the dynamic of the cholera infection

Deciphering electron transfer and cytochrome P450 activity in Mycobacterium marinum

Cytochrome P450s are haem-monooxygenase enzymes, responsible for the catalytic hydroxylation of a large variety of organic molecules. The bacterium Mycobacterium marinum, has a larger genome than its close relatives, the causative agents of human tuberculosis (Mycobacterium tuberculosis) and Buruli ulcer (Mycobacterium ulcerans), which have undergone substantial reductive evolution. The genome of M. marinum contains an unusually large number of P450 genes (47). Twelve ferredoxin genes are associated with the CYPome and eleven of these are uncharacterised ferredoxins of the 3/4Fe-4S type. In their iron-sulfur cluster binding motif (CXX?XXC(X)nCP), these ferredoxins (Fdx1 – Fdx11) have non-standard residues at the ? position of the sequence. Instead of the cysteine residue expected of a [4Fe-4S] ferredoxin, or the alanine/glycine residue expected in a [3Fe-4S] ferredoxin, they contain histidine, asparagine, tyrosine, serine, threonine and phenylalanine residues. In the course of this work, they have been purified aerobically and anaerobically. When isolated anaerobically, three of these ferredoxins were determined, by non-denaturing ESI-MS and EPR to contain 3Fe-4S clusters. The reduction potentials for the three varied from +150 mV to -360 mV, which are highly anomalous for [3Fe-4S] ferredoxins. Similar ferredoxins were found to accompany P450s in the biosynthetic gene clusters of other bacteria, especially in Actinomycete species. These ferredoxins were demonstrated to support the activity of a number of the M. marinum P450s, some of which were from previously uncharacterised families. CYP147G1, in combination with the electron transfer partners Fdx3 and FdR1 was demonstrated to act as a ω-1 fatty acid hydroxylase. CYP147G1 selectivity favoured the ω carbon when branched methyl substrates were used. The same ferredoxin reductase, FdR1, was also shown to support the activity of CYP278A1 (with Fdx2), and CYP150A5 (with Fdx8), both of which were shown to regioselectively hydroxylate β-ionone. CYP150A5 binds terpenes and polycyclic substrates. An additional CYP150 enzyme, CYP150A6, was crystallised and structurally resolved to 1.6 Å in the substrate-free form. CYP268A2, when reconstituted with a non-native electron transfer chain, hydroxylated the branched fatty acetate derivatives, pseudoionone and geranyl acetate, at the terminal position. The structure of CYP268A2 with trans-pseudoionone bound in the active site was solved by X-ray crystallography to a resolution of 2.0 Å and from this the selectivity of the enzyme was rationalised. Several M. marinum P450s that have close counterparts in M. tuberculosis were selected for comparison, in order to investigate whether the substrate and inhibitor binding affinities were preserved between species. The P450s investigated were analogues of the steroid metabolising P450s in M. tuberculosis. CYP125A6 and CYP125A7 have a single counterpart in M. tuberculosis (CYP125A1). The sequence identity and cholesterol binding affinity of CYP125A7 indicates it more closely resembles CYP125A1. However, CYP125A7 interacts differently to CYP125A1 with a range of inhibitors. CYP142A3 bound sterols with similar affinities as the M. tuberculosis CYP142A1. CYP124A1 from M. marinum was structurally characterised by X-ray crystallography, and showed a very closely preserved active site when compared to the M. tuberculosis analogue. These results suggest that individual P450 enzymes have maintained similar substrate specificities and roles between Mycobacterium species. However, for effective inhibitor design cross-species differences should be noted.Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 201

2016 GREAT Day Program

SUNY Geneseo’s Tenth Annual GREAT Day.https://knightscholar.geneseo.edu/program-2007/1010/thumbnail.jp

Mathematical models for the coinfection dynamics of cholera and typhoid

Abstract: Due to deteriorating infrastructure and declining infrastructure funding in African countries, There is a resurgence of cholera and typhoid fever. Poor waste disposal systems, poor hygiene and seasonal rains have been the main drivers of these two infections. Recently in Zimbabwe, an outbreak of the two infections was observed. Given that both infections are water-borne, a logical question is: was the outbreak of these two diseases a coincidence, or is there more structural mechanism to explain the observed coinfection? In this work, we attempt to answer such a question. We develop a system of ordinary differential equations to model the transmission dynamics of both diseases. We further add time dependant infection rates to model the dynamics of diseases in fluctuating environments. The model steady states are determined and analysed, and the role of fear is incorporated into the models. Impact analysis - how the diseases impact each other - is carried out. Numerical simulations and sensitivity analysis are used to verify the analytic results. We discover that for the greatest impact of disease control, the management of the diseases should be carried out in tandem. The public health implications of these results are articulated. Keywords: Fear, Seasonality, Stability analysis, Basic reproduction number, Cholera, Typhoid, Coinfection, Impact analysis.Ph.D. (Mathematics and Applied Mathematics