College of Biological and Physical Sciences (CBPS)

Salmonella Typhi Haplotype 58 biofilm formation and genetic variation in isolates from typhoid fever patients with gallstones in an endemic setting in Kenya

Wed, 13 Nov 2024 00:00:00 GMT

Salmonella Typhi Haplotype 58 biofilm formation and genetic variation in isolates from typhoid fever patients with gallstones in an endemic setting in Kenya Wachira, Peter; Muturi, Peter; Wagacha, Maina; Maina, Cecilia; Kavai, Susan M.; Mugo, Michael M.; Mohamed, Musa; Gonza´ lez, Juan F; Kariuki, Samuel; Gunn, John S. Although typhoid fever has largely been eliminated in high-income countries, it remains a major global public health concern especially among low- and middle-income countries. The causative agent, Salmonella enterica serovar Typhi (S. Typhi), is a human restricted pathogen with a limited capacity to replicate outside the human host. Human carriers, 90% of whom have gallstones in their gallbladder, continue to shed the pathogen for an ill-defined period of time after treatment. The genetic mechanisms involved in establishing the carrier state are poorly understood, but S. Typhi is thought to undergo specific genetic changes within the gallbladder as an adaptive mechanism. In the current study, we aimed to identify the genetic differences in longitudinal clinical S. Typhi isolates from asymptomatic carriers with gallstones in a typhoid endemic setting in Nairobi, Kenya. Whole-genome sequences were analyzed from 22 S. Typhi isolates, 20 from stool samples, and 2 from blood samples, all genotype 4.3.1 (H58). Out of this, 19 strains were from four patients also diagnosed with gallstones, of whom three had typhoid symptoms and continued to shed S. Typhi after treatment. All isolates had point mutations in the quinolone resistance-determining region (QRDR), and only sub-lineage 4.3.1.2.EA3 encoded multidrug resistance genes. There was no variation in antimicrobial resistance patterns among strains from the same patient/household. Non-multidrug resistant (MDR) isolates formed significantly stronger biofilms in vitro than the MDR isolates, p<0.001. A point mutation within the treB gene (treB A383T) was observed in strains isolated after clinical resolution from patients living in 75% of the households. For missense mutations in Vi capsular polysaccharide genes, tviE P263S was also observed in 18% of the isolates. This study provides insights into the role of typhoid carriage, biofilm formation, AMR genes, and genetic variations in S. Typhi during asymptomatic carriage.

DFT study of cubic, tetragonal and trigonal structures of KGeCl3 perovskites for photovoltaic applications

Sun, 01 Jan 2023 00:00:00 GMT

DFT study of cubic, tetragonal and trigonal structures of KGeCl3 perovskites for photovoltaic applications Aduda, Bernard O.; Namisi, Mauwa .M; Musembi, Robinson J; Mulwa, Winfred M. The study of suitable compounds for photovoltaic applications is one of the most fascinating research areas in the world. One of the less studied materials is KGeCl3 and its potential is yet to be fully determined. Investigations of the structural, electronic, optical and mechanical properties of cubic, tetragonal and trigonal structures of pure inorganic KGeCl3 perovskite have been done. All calculations have been performed using first-principle calculations based on density functional theory (DFT) in generalized gradient approximation with Perdew-Burke-Ernzerhof, PBE-GGA as the exchange correlation functional, as implemented in the Quantum ESPRESSO code. Further calculations using GW approximation have been performed on electronic band structures of the three phases of KGeCl3 in order to validate the accuracy of GGA-PBE functional. The structural properties of the materials have been found to be consistent with previous observations in literature. All compounds have been found to display direct band gaps, with the top of the valence band (VB) dominated by Cl 2p orbitals and the conduction band (CB) dominated by the Ge 2p orbitals. The trigonal perovskite has been observed to have the largest band gap of 2.7 eV, with the cubic and tetragonal counterparts having 0.8 eV and 1.2 eV respectively. Calculated elastic constants, bulk and shear moduli have shown that the trigonal structure is mechanically unstable and brittle at ground state. Generally, the three phases of KGeCl3 have been observed to possess a broad absorption spectrum covering the UV–Vis region and therefore making them suitable candidates for photovoltaic applications.

Bühlmann Credibility Approach to Systematic Mortality Risk Modeling for Sub-saharan Africa Populations (Kenya)

Sat, 01 Jan 2022 00:00:00 GMT

Bühlmann Credibility Approach to Systematic Mortality Risk Modeling for Sub-saharan Africa Populations (Kenya) Odhiambo, Joab; Weke, Patrick; Ngare, Philip The classical mortality models such as the Cairns-Blake-Dowd (CBD), Lee-Carter (LC), Linear Regression (LR) models are used to model Systematic Mortality Risk (SMR) for many developed countries populations for actuarial product valuations. This research study aims at incorporating the Bühlmann credibility approach (BCA) to improve the SMR models to fit sub-Saharan African populations like Kenya. Since the Kenyan population does not exhibit the Gaussian properties used in modeling the classical error terms, we proposed using Normal Inverse Gaussian distribution to model these error terms instead of a Gaussian distribution. We model the error terms of the classical models (LC, CBD, and LR) as a Normal Inverse Gaussian (NIG) distribution through the Bühlmann credibility approach. This novel approach demonstrates an improved precision of the predicted SMR as shown by the values of MAPE and RMSE measures compared to those under classical mortality risk models. Ultimately, we have done actuarial valuations of annuities and assurances using our determined SMR, thus concluding that this BCA approach improves the accuracy of actuarial products sold in the Kenyan market.

Effect Of Deposition Temperature On The optical Properties Of Iron-Doped Cadmium Stannate Thin Films Deposited By Spray Pyrolysis

Tue, 01 Jan 2019 00:00:00 GMT

Effect Of Deposition Temperature On The optical Properties Of Iron-Doped Cadmium Stannate Thin Films Deposited By Spray Pyrolysis Ongwen, Nicholas O.; Oduor, Andrew O; Ayieta, Elijah O Spray Pyrolysis Technique (SPT) was used to deposit thin films (TFs) of cadmium stannate, doped with iron (Fe) for the first time. The precursor solutions that were used wereprepared at a concentration of 0.1M, doped with Feand then sprayed onto the pre-heated glass slides immediately at deposition temperatures of 350 ± 7°C, 400 ± 7°C and 450 ± 7°C. The optical properties of the deposited Fe-doped TFs were studied in the wavelength range of 300-1100nm. The X-Ray diffraction (XRD) studies showed that the TFs were orthorhombic with growth orientation along the (2 0 0) direction. Film thickness of 85 ± 10 nm was obtained. It was found out that anincrease in the deposition temperature increased transmittance and band gap, but decreased absorption coefficient, extinction coefficient and refractive index, which was attributed to the improvement in crystallinity of the deposited TFs. Doping reduced transmittance and band gap, but increased refractive index, absorption coefficient and extinction coefficient, which was attributed to the increase in free carriers