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Recent Submissions
One-pot microwave-assisted synthesis of sizedependent L-glutathione-capped spherical silver nanoparticles suitable for materials with antibacterial properties
(British society for nanomedicine, 2019-06-20) Samuel N. Nyamu, Lucy Ombaka, Eric Masika & Margaret Ng’ang’a
In the last years, there has been an alarming increase in antibiotic resistance by pathogenic microbes, which has become a major public health concern. There is a great interest
in developing new antimicrobial for reducing the impact. Silver nanoparticles (AgNPs) as
antibacterial agents are currently being studied to be used to fight these pathogenic microbes. The aim of the present study was to synthesize AgNPs of different sizes through
the use of microwave and determine their antimicrobial activities. Synthesis of sizedependent L-glutathione-capped spherical nanoparticles through one-pot microwave synthesis was achieved, and their antimicrobial properties were determined. Different sizes
of AgNPs between 5–10, 15–35, and 50–80 nm were made by varying the concentration of
silver nitrate and using sodium borohydride (NaBH4) as a reducing agent. L-glutathione
was used to stabilize the AgNPs to prevent them from aggregation in the colloidal solution.
The synthesized AgNPs showed ultraviolet absorption at around 400 nm with high concentration of AgNO3 having sharp peaks. The formed particles were crystalline in nature with
uniform spherical shape. The formed AgNPs were of crystalline size of 9.94, 18.45, 34.96,
52.40, and 58.50 nm. Fourier transform infrared analysis confirmed conjugation of glutathione as a capping agent to AgNPs as the result of the formed spectra showing the absence
of ─SH stretch. The high temperature generated by microwave helped to synthesize nanoparticles within a short time and by varying the concentration of AgNO3 helped obtain the
desired particle size. Glutathione conjugated well with AgNPs as a result of interaction of
negative thiol resulting to colloidal stabilization and reduced aggregation. The antibacterial activity of AgNPs was found to be size dependent with the smaller size of 9.94 nm being more efficient than 18.45, 34.96, 52.40, and 58.50 nm against the tested strains
Bacillus subtilis (ATCC 6633), Escherichia coli (ATCC 25922), Salmonella spp. (ATCC
700623), and Staphylococcus aureus (ATCC 25923). Of the four stains, E. coli was found
to be the least affected by all three different particle sizes of the synthesized AgNPs
Antimicrobial Photodynamic Activity of Phthalocyanine Derivatives
(Hindawi Advances in Chemistry, 2018-03-19) Samuel N. Nyamu, Lucy Ombaka, Eric Masika, and Margaret Ng’ang’a
Microbial pathogens have increasingly shown multidrug resistance posing a serious threat to the public health. Advances in
technology are opening novel avenues for discovery of compounds that will mitigate the ever-increasing drug-resistant microbes.
Use of photodynamic photosensitizer is one of the promising alternative approaches since they ofer low risk of bacteria resistance
as they use generated reactive oxygen species to kill the microbes. Phthalocyanine (Pc) is one such photosensitizer which has
already shown promising antimicrobial photodynamic therapeutic properties. Previous studies have shown efectiveness of the Pc
against Gram-positive bacteria. However, its efectiveness toward Gram-negative bacteria is limited by the impermeability of the
bacteria’s outer membrane which is made up of lipopolysaccharides layer. Te efectiveness of this photosensitizer is determined by
its photophysical and photochemical properties such as singlet/triplet lifetimes, singlet oxygen quantum yields, and fuorescence
quantum yield. Terefore, this review focuses on the recent signifcance advances on designing Pc that have this improved property
by either conjugating with nanoparticles, quantum dots, functional groups in peripheral position, considering efect of cationic
charge, and its position on the macrocycle.
FREQUENCY OF SULFADOXINE PYRIMETHAMINE RESISTANCE ASSOCIATED GENE MUTATIONS IN PLASMODIUM FALCIPARUM CLINICAL ISOLATES FROM KWALE COUNTY, KENYA
(2020-01) WINFRED KENDI MUTWIRI
Malaria persists to be one of the world’s complex and dynamic disease. The disease is more
devastating in sub-Saharan Africa as it constitutes high cases of childhood mortality and
morbidity. Management of the disease remains a problem as a result of the spread of parasites
that are resistant to the available drugs. Due to the broadened spread of resistance to
Sulfadoxine Pyrimethamine (SP), the artemether-lumefantrine which is a more effective and
well-tolerated anti-malarial drug replaced the SP as the first-line regimen in treatment of
uncomplicated malaria in Kenya. However, SP remains the suggested drug to treat and prevent
malaria in expectant women and children under the age of five. This study sought to assess the
presence of mutation in dihydrofolate reductase and dihydropteroate synthase genes associated
with SP resistance a decade after Sulfadoxine-Pyrimethamine was withdrawn as the first-line
anti-malarial drug of choice in Kenya. Smear-positive samples (N = 134) collected from a 2013
cross-sectional study in infants managed at Msambweni District Hospital were evaluated for
mutations in dhfr and dhps (SP).The findings obtained were matched up with molecular data
from infants in Western Kenya in a study carried out in 2003/05. In all the 134 samples,
mutations at codons N51I, C59R, S108N had a high predominance at 80.6%, 72.4% and 93.3%
respectively. The double mutant of Pfdhps A437G/ K540E had an occurrence rate of 82.1%
and 78.4% respectively. Compared to the molecular data of 2003/05 study, the Pfdhfr triple
mutant (S108N/N51I/C59R) genotype decreased to 63.4% in 2013 up from 68%. However,
this reduction was not significant (p=0.387). There was no significant change in the prevalence
of Pfdhps double mutant (A437G/K540E) genotype (p=0.485). The percentage of isolates
which had the Pfdhps A437G/K540E/ Pfdhfr N51I/C59R/S108N quintuple mutant linked with
SP-resistance did not change significantly over the two study periods under consideration
(53.5% in 2003/05 versus 53.7% in 2013, p = 0.967).The high prevalence of SP resistance
marker in the coastal Kenya could be attributed to circulation and SP drugs being sold over the
counter which has maintained a selection pressure for the mutations and fixation in the key
mutations in the inhabitants. Also the mutation could have a little effect on the fitness of fit of
the parasite such that withdrawal of drug pressure did not offer any survival disadvantage hence
the continued spread of resistant parasites. Further investigations should be done to determine
the linkage between SP drug resistance associated mutations and efficacy of IPTi-SP since the
mutation levels are still high. It is also recommended that doctors using SP for IPTi and IPTp
should be more cautious and their use monitored to ensure cases of poor response are managed
with a different drug.
SEROPROFILE, GENETIC DIVERSITY AND DRUG RESISTANCE OF HEPATITIS B VIRUS AMONG INFECTED INDIVIDUAL ATTAENDING MAMA LUCY KIBAKI
(2016) SEPHA NYATICHI MABEYA
Human immune deficiency virus (HIV) and Hepatitis B virus(HBV) coinfection is
highly prevalent among high risk populations including pregnant women and infants.
This poses a global public health challenge in laboratory diagnosis and is a major
consideration for anti-HIV treatment. These viruses share common modes of
transmission that is; through blood and body fluids. Further, there is little
information on sero-profiles and circulating HBV genotypes in Kenya. This study
aimed at determining seroprofiles, genetic diversity and drug resistance of HBV
among HIV infected individuals attending comprehensive care clinic of Mama Lucy
Kibaki Hospital Nairobi, Kenya. Ethical approval was sought from Kenyatta
university ethics review committee and a cross-sectional study was conducted
whereby the participants/guardians who gave consent/assent were included into the
study. Their demographic data was collected using a questionnaire and 5ml of blood
was collected from each participant using systematic sampling technique. The HBV
seroprofiles were determined using the HBV-5 panel rapid diagnostic cassette
according to the manufacturer’s instructions (Healthaw Medical limited, Hangzhou,
China) . Viral DNA was extracted using Qiagen® Miniviral DNA isolation kit and
the HBV-pol gene amplified by nested PCR. The amplified products were sequenced
using the Big Dye® sequence terminator kit (Applied Biosystem®) on an automated
ABI 310 sequencer (Applied Biosystem, Foster City CA). The generated sequences
of HBV were analysed for drug resistance and genetic diversity determined using
Molecular Evolutionary Genetics Analysis (MEGA5). Four hundred participants
were recruited and 293 were females, 107 were males with their age ranging between
4 months and 73 years. Of the 400 sera; (111) 27.8% were HBV immunized, 19
(4.8%) were recovery cases, 12 (3%) had acute disease, 10 (2.5%) were chronic, 9
(2.3%) had occult HBV and 7 (1.8%) asymptomatic. The prevalence of HBV/HIV
was found to be 7.25% based on the presence of surface antigen. After the
confirmation of HBV DNA by gel electrophoresis, 13 samples were successfully
amplified, purified and sequenced.
All the 13 sequences were confirmed as HBV genotype A. Nucleotide drug
resistance mutations were found in six (6) participants’ samples. These were
rtV173L, rtL180M, rtM204V which are major mutations associated with lamivudine,
telbivudine and emtricitabine resistance. This study indicates that the utility of HBV
seromarkers and infection staging are important in disease diagnosis. The findings
confirm that, HBV genotype A remains the most predominant genotype circulating
in Nairobi.This study proposes a need for a continuous surveillance of HBV
genotype trends and evolution of drug resistance because the current findings have
major implications on treatment of HBV in Kenya
SYNTHESIS AND SPECTROPHOTOMETRIC ACTIVITY OF PHTHALOCYANINE CONJUGATED TO METAL NANOPARTICLES AND EVALUATION OF THEIR ANTIBACTERIAL PROPERTIES
(2021-11) NYAMU N, SAMUEL (MSc. Chemistry)
ABSTRACT
{In recent times, microbial pathogens have increasingly shown multi-drug resistance leading to a growing concern. Analysis of 624 isolates from Kenya revealed 88% of isolates tested Were multi-drug resistant. It is estimated that about 4,150,000 deaths will be attributed to antimicrobial resistance (AMR) in Africa by 2050. Therefore, current research is increasingly focusing on antimicrobial photodynamic therapy that utilizes non-toxic photo. sensitizer exhibiting visible light activity towards the generation of free radicals and singlet oxygen which kill pathogens. The photo-sensitizer may be conjugated to visible-light responsive nanoparticles to further increase their photochemical activities, Phthalocyanine (Pc) is one of the promising dyes that have shown notable photochemical stability, a high degree of aromaticity and ease of structural modification resulting in increased activities. Despite these attractive properties, its antibacterial properties remain under researched,
therefore, this study aimed to tuning the photodynamic antibacterial activity of Pc by using electron withdrawing and electron donating group, conjugating the obtained compounds to silver nanoparticles (AgNps) and 2ine oxide nanoparticles (Zn0-Nps) and evaluating the activity of the resulting composites against drug resistant strains Escherichia coli, Staphylococeus aureus, Bacillus subtilis and Salmonella typhi. 2,9,1623-tetraciodo. 3.10,17,24-tetra-(3 methoxyprop-I-nyl) Pc (6) and. 2,9,16,23-tetra-iodo-3,10,17.24-tetra
cthylsulfonyl Pc (10) were synthesized respectively. The Pc derivatives were synthesized upon exposure to microwave radiation under solvent-free conditions. Both Pc 6 and 10 Were B-form in nature with monoclinic structure confirmed by powder XRD. Pc (6) had two absorption bands between 345-364 nm for B-band and 660-680 nm for Q-band while Pc (10) indicated two major absorption bands between 354-360 nm for B-band and 685,689 nm bands for Q-band of UV-Vis absorption in different solvents, FTIR confirmed the Presence of attached substituent groups to the Pes. Pc 6 and 10 showed singlet oxygen quantum yield (A) values of 0.53 and 0.63 and fluorescence quantum yield (DE) value of 0.14 and 0.13 respectively. The Pc 10 exhibited zone of inhibition >230.12 ug/ml for all the strains, making it more effective as compared to Pc 6. In addition, all strains of tested bacteria were susceptible to Pc 10 at a concentration > 31.25 jig/ml. ‘This implies that Substituting Pc with electron withdrawing allows it to release more singlet oxygen in Presence of light and which results to oxidation of the bacterial wall. AgNp and Zn0-Np
were synthesized by microwave assisted extraction, The UV-Vis was used to confirm the formation of nanoparticles and also characterization done using FTIR, TEM and SEM, AgNps were of diameters < 58.5 nm that easily conjugated to Pc while Zn0-Nps were of large grain size > 95, the particles aggregated making it difficult to conjugate with Pes, Conjugation of Pc 10 with AgNp < 10 nm resulted to a more superior antibacterial as compared to unconjugated Pe 10. There was no significant different for zone' of inhibition for Pc 10 conjugated to AgNp when compared to positive control ciprofloxacin at $00
ua/ml for all the strains except for B. subtilis. It had minimum inhibitory concentration (MIC) values of 3.91, 1.96, 1.96 and 15.63 ug/ml, for E. coli, S aureus, B. subtilis and S phi respectively. Both Pc showed no toxicity on Vero cells at concentration of 600 jig/ml In overall, this work reports the successful tuning of the photo-chemical and antibacterial Photodynamic properties of Pc using electron withdrawing and donating substituent, The Pc 10 with electron withdrawing group exhibit superior antibacterial activity which is further enhanced by conjugation with AgNp of < 10 nm.
