Characterisation of human pathogenic vibrios and methicillin-resistant staphylococcus aureus (MRSA) from wild and tank cultured dusky kob (agyrosomus japonicus) in the Eastern Cape Province, South Africa
- Authors: Justine, Fri
- Date: 2017
- Subjects: Marine microbiology Marine microbiology--South Africa--Eastern Cape Staphylococcus aureus infections--South Africa--Eastern Cape
- Language: English
- Type: Thesis , Doctoral , Microbiology
- Identifier: http://hdl.handle.net/10353/16047 , vital:40607
- Description: Introduction: Marine finfish including dusky kob (Agyrosomus japonicus), in addition to its high protein value, is bestowed with numerous health benefits including being heart friendly due to high proportion of omega 3 fatty acids. They are therefore used as powerful preventive measures against cardiovaslcular diseases. They are also important in neurological development during gestation and infancy, thus a regular recommendation by nutritionists. However, fish and its environment may be contaminated by bacteria pathogens. Human infections caused by members of the genus Vibrio, and Staphylococcus especially Methicillin-resistant S. aureus (MRSA) are of increased concern worldwide especially with increased Vibrio disease outbreaks and rapid spread of MRSA in the community. Methicillin-resistant Staphylococcus aureus is regarded as an emerging zoonotic agent, therefore marine fish may be considered as a reservoir for infection. The emergence of multi-drug resistant organisms in both farm animals and humans has also been a challenge that hurdles chemotherapy worldwide. Methods: We enumerated the bacteria flora of skin, gill and gut of marine dusky kob (Agyrosomus japonicus) raised in a recirculatory aquaculture system using metagenomic sequencing of the 16S rRNA. We further screened 120 dusky kob fishes (skin, gill and gut) and 80 water samples from two fish farms and Kariega estuary collected over a 10 month period for human pathogenic vibrios, and MRSA using standard procedures. Vibrio species were further subjected to species specific PCRs delineating them into V. cholerae, V. parahaemolyticus, V. vulnificus, and V. fluvialis. This was followed by elucidation of the genotypic virulence determinants. The Reverse Fragment Length Polymorphism (RFLP) of the cytotoxin hemolysin (vvhA) gene of V. vulnificus strains was carried out to determine the associated biotypes. A total of 277 Vibrio strains consisting of 126 V. fluvialis, 45 Vibrio vulnificus, 30 V. parahaemolyticus and 76 vibrios belonging to other species were subjected to susceptibility testing to 15 antibiotics by the disc diffusion method and resistant strains were further evaluated for their genotypic antimicrobial resistant determinants by polymerase chain reaction followed by plasmid profiling. For MRSA screening, we evaluated the reliability of cefoxitin disc diffusion, oxacillin screen agar and BrillianceTM MRSA 2 agar tests, in detecting methicillin resistance from fish (environmental) samples using PCR detection of the mecA as the gold standard. A total of 33 mecA positive S. aureus strains (MRSA) were subjected to PCR detection of enterotoxins (Staphylococcal enterotoxin A-E) and Panton Valentine Leucocidin (PVL) encoding genes. The SCCmec types were also investigated by multiplex PCR targeting genes encoding type I-V. The antibiogram profiles of MRSA strains to 12 antibiotics by the disc diffusion method and to vancomycin by broth micro dilution method were elucidated. Polymerase chain reaction was employed to evaluate the presence of antibiotic resistant genes. The nucleotide sequences of the rpoB gene were analysed to determine mutations that could lead to rifampicin resistance. Results: A broad diversity of pathogenic and non-pathogenic bacterial species of different taxonomic groups was observed with Proteobacteria revealed as the most common bacteria phyla. Fifty one families were identified with Enterobacteriaceae the most frequently detected in all the anatomical sites and the gut showing the highest species diversity. A total of 606 (60.23 percent ) presumptive Vibrio isolates were confirmed by PCR of which V. fluvialis was the most predominant, 193 (31.85 percent ). This was followed by Vibrio vulnificus 74 (12.21 percent ), and V. parahaemolyticus 33 (5.45 percent ). No V. cholerae strain was detected. Only one of the V. parahaemolyticus strains possessed the trh virulent gene with no tdh detected. Virulence factors of V. fluvialis detected were stn (13.5 percent ), hupO (10.4 percent ), and vfpA (1.0 percent ). V. vulnificus biotype 3, formerly restricted to Isreal was identified. Generally, resistance among Vibrio isolates varied considerably with highest resistances recorded to amoxicillin (76.2 percent ), ampicillin (67.5 percent ), erythromycin (38.3 percent ), and doxycycline (35.0 percent ) while higher susceptibilities were revealed by gentamicin (100 percent ), norfloxacin (97.8 percent ), florfenicol (90.3 percent ), tetracycline (87.7 percent ), and chloramphenicol (87.4 percent ). Multiple antibiotic resistance (MAR) (resistance to ≥ 2 classes of antibiotics) was 58.5 percent . The MAR index did not vary significantly between sites (P>0.05) and values of >0.20 were recorded in 40 percent (108/277) of all the isolates. The resistant genes ampC, blaOXA, tetA, tetM, dfr1, sul1, sul2, ermB, nptII and strA were detected in two or more Vibrio isolates while the SXT intergrase was detected only in one isolate. Seven of the 18 extreme drug resistant isolates possessed 1–3 plasmids of 1.5–10 kb range. A total of 321 presumptive Staphylococcus aureus isolates were recovered by culture out of which 202 (62.9 percent ) were identified as S. aureus by PCR. Of these, 33 (16.3 percent ) strains were mecA positive while the rest, 169 (83.7 percent ) were mecA negative. The sensitivity and specificity of MRSA detection by use of cefoxitin disc (30 μg) test was 93.9 percent and 91.7 percent , that for oxacillin screen agar test (6 μg/mL) was 81.8 percent and 92.3 percent while that of BrillianceTM MRSATM 2 agar was 87.9 percent and 94.1 percent respectively. Staphylococcal enterotoxin SEE was detected in 12.1 percent (4/33) of total strains followed by SEA 3.0 percent (1/33), and SEC 3.0 percent (1/33). SEB and SED were absent. Six of the isolates had the PVL gene, giving a prevalence of 18.2 percent . The most frequently detected SCCmec type was SCCmec type III (17/33; 51.5 percent ), closely followed by SCCmec subtype IVc (10/33; 30.3 percent ) and the least were SCCmec types I and II with only 3.0 percent (1/33) each. The rest four (4/33; 12.1 percent ) did not belong to any of the above types and were therefore considered to belong to other subtypes of SCCmec type IV not tested in the study. For antibiogram patterns, 12 (36.4 percent ) strains were resistant to doxycyline, 10 (30.3 percent ) to trimethroprim-sulfamethoxazole, 9 (27.3 percent ) to tetracycline and only 1 (3.0 percent ) strain was resistant to ciprofloxacin. Nineteen (57.6 percent ) of the MRSA strains had vancomycin MIC of ≤ 2 μg/mL, 4 (12.1 percent ) with MIC range of 4-8 μg/mL, and 10 (30.3 percent ) with values ≥ 16 μg/mL. Overall, 27 (91.percent) isolates showed simultaneous resistance to 3 or more antibiotics. The resistant genes tetM, tetA, ermB, BlaZ femA were detected in two or more strains resistant to various antimicrobials. Resistance to rifampicin was not caused by mutations in the rpoB gene. Conclusions: To the best of our knowledge, this study is the first study reporting a broad, and diverse bacteria flora of skin, gill, and gut of the South African dusky kob as well as the first study on human pathogenic vibrios, and MRSA from marine finfish especially those from recirculatory aquaculture systems. Also, our study revealed that Vibrio species with pathogenic potential are present in marine dusky kob and its environs. Dusky kob is contaminated with CA- MRSA and HA- MRSA that may cause difficult to treat infections with regular antibiotics. Some of the MRSA strains contained toxins that can cause food-borne gastroeneteritis. The present study revealed that MRSA and Vibrio species are potential reservoirs for antibiotic resistant genes, which could be disseminated to other bacterial species probably through plasmids, a public health risk.
- Full Text:
- Date Issued: 2017
Gender equality in the provision and utilisation of women administrative personnel : a comparative study of the Camdeboo Local Municipality and Inxuba Yethemba Local Municipality
- Authors: Dywili, Mhlobo Douglas
- Date: 2016
- Subjects: Women -- Government policy -- South Africa -- Eastern Cape Sex discrimination against women -- South Africa -- Eastern Cape Women's rights -- South Africa -- Eastern Cape , Equality -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10353/2414 , vital:27817
- Description: In 2000, cabinet adopted the South African Policy framework for women’s empowerment and gender equality, 2000 (Policy framework) which provided for the establishment of the National Gender Machinery (NGM). The NGM is a network of coordinated structures within and outside government which operate cooperatively in facilitating political, social, economic and other forms of transformation to dismantle systemic gender inequality and promote equality between women and men. The implementation of gender equality policy as a function area has constitutionally been given to the national and provincial legislatures in South Africa. The constitution allocated this function to the local sphere of government. Camdeboo and Inxuba Yethemba local municipal authorities are the facilitators of sustainable gender equality policies to citizens on behalf of the national and provincial spheres of government. The study was thus conducted within the Camdeboo local municipality and Inxuba Yethemba local municipality. Camdeboo locoal municipality is one of nine local municipalities in Sarah Baartman district municipality. Inxuba Yethemba local municipality is in Chris Hani district municipality. The purpose of the study was to evaluate the implementation of gender equality in the Provision and Utilisation of Women administration Personnel a comparative study of the Camdeboo local municipality and the Inxuba Yethemba local municipality and to determine the impact of the existing policy on the gender equality policy on the needs of women of both municipalities. For this purpose the fundamental and overall study problem was found to be that the gender equality at the Camdeboo and Inxuba Yethemba is hampered by the implementation of an inadequate municipality gender equality policy and by incompetent municipal personnel in particular and in general by the municipality itself. These action do not satisfy the main purpose of the Employment Equity Act no 55 of 1998 to achieve in the workplace by promoting equal opportunity and fair treatment in all forms of employment through elimination of unfair discrimination as well as the implementation of affirmative action measures. The hypothesis was furthermore based on the fact that the existing gender policy of Camdeboo local municipality and Inxuba Yethemba local municipality gender equality policy are inadequate to satisfy women and impacts negatively if not harmfully on human being of women. The study revealed that besides the implementation of gender equality policy by these incompetent municipal personnel, there are economic, social, political and physical effects on women. In case of applications for senior management position, preference is always given to their male counterparts at the expense of equally qualified female applications. Secondly, Gender equality in human resource determination forms part of the processing phase in the system theory. These two municipalities should be made to commit themselves by appending their signatures to all control measures put in place to evaluate the level and the extent of gender equality across all the departments/ sections in the municipality. Any section/ department that implements gender equality more effectively should be identified applauded and given recognition. This would motivate and eliminate gender inequality. Personnel provision and utilization is of paramount importance to every organization. It then becomes extremely necessary to examine the gender equality on human resource determination.
- Full Text:
- Date Issued: 2016
An assessment of public accountability mechanisms towards eradicating corruption in the Eastern Cape
- Authors: Rulashe, Tando
- Date: 2015
- Subjects: Political corruption -- South Africa -- Eastern Cape Misconduct in office -- South Africa -- Eastern Cape Municipal government -- South Africa -- Eastern Cape , Local government -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10353/1960 , vital:27588
- Description: The study critically examined the implementation of Public Accountability strategies and mechanisms: A case of Buffalo City Municipality. The problem statement gave emphases on the multiple cases drawn from stats reflected in domestic surveys that shows how corruption and maladministration have impacted the province negatively as well as the extreme poverty lines that dominate the communities in the republic and also the province. The New Public Management Theory was used to interpret the manner in which the participants were expected to give their views on leadership and accountability among others key issues. The objectives of the study were to; To assess the mechanisms implemented by Buffalo City Municipality., To explore the challenges affecting public accountability enforcement mechanisms in Buffalo City Municipality towards eradicating corruption, Determine the manner through which the Buffalo City Municipality can adopt tried and tested mechanism from Regional, national & international case studies on how to effective enforce public accountability for the sustainable management and curbing of corruption for effective and efficient service delivery and to recommend new mechanisms which Buffalo City Municipality can utilise in enforcing public accountability towards eradicating corruption in its institutions in order to encourage sustainable community development through service delivery. The study adopted a case study approach based on a mixed method paradigm where data was collected through a questionnaire, interviews and document analysis. Case studies are normally associated with qualitative research, but can also be used as a method of inquiry employing a positivist epistemology and ontology. A total sample of 50 participants was chosen through a non-probability sampling technique. The major findings of the study reflected that there is a huge break in communication between government and the citizens in the locality while also establishing that the mechanisms currently being used were only as good as the factors influencing their implementation among other issues. Major recommendations included community engagement, capacity building and skills development, retention and expansion, lack of resources, promote individual independence of the community and the enhancement the Public Participation Unit.
- Full Text:
- Date Issued: 2015
Towards the modeling of indigenous poultry production in the Eastern Cape Province, South Africa: characterization and extension evaluation for poverty reduction
- Authors: Yusuf, Shehu Folaranmi Gbolahan Shehu
- Date: 2014
- Subjects: Poultry -- Breeding -- South Africa -- Eastern Cape , Chickens -- Breeding -- South Africa -- Eastern Cape , Economic development -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD (Agricultural Economics)
- Identifier: vital:11223 , http://hdl.handle.net/10353/d1019833 , Poultry -- Breeding -- South Africa -- Eastern Cape , Chickens -- Breeding -- South Africa -- Eastern Cape , Economic development -- South Africa -- Eastern Cape
- Description: Poverty remains a critical issue mostly in the rural South Africa. Various initiatives, policies and programs have been enacted by the government with attempting to reduce poverty at the national and provincial levels; poverty is yet to be abated. The target of the Millennium Development Goal 1 (MDG1) of halving poverty by the year 2015 notwithstanding, poverty remains a threat to quality livelihoods. Agriculture has continued to be one of the pillars of government efforts to address poverty. However, in livestock production interventions, efforts of government had largely been on cattle, sheep, goats, pigs and exotic poultry with little attention being given to indigenous poultry production (IPP). This study explores the option of using IPP to address rural poverty by capitalizing on its minimal inputs while recognizing its prevalence in a variety of households. The study addresses the characterization of the IPP from the perspectives of housing, feeding, healthcare management, breeding and marketing options.Skill competencies of the indigenous poultry farmers (IPFs) and the Agricultural Development Technicians (ADTs) were examined. This study reviewed poultry models in different parts of the world with special attention to Africa. The human resource development program of the department of rural development and agrarian reform was discussed. The study employed the use of multi-methods approach, the quantitative and qualitative research methodologies. Descriptive statistical analysis, frequent count, percentage, means, standard deviation, chisquare, and principal component analysis was used in the quantitative data analysis while the “open social system” was used for the qualitative methodology. Findings revealed that IPFs face some challenges among which are, the poor housing that exposed the birds to inclement weather, predator attacks and stock theft, high mortality of chicks after hatching and expensive feed for the flock. The IPFs showed competencies in nine skill items that included ability to identify chicken predators (x=3.92) and high yielding chickens (x=3.79); control of predators(x=3.77); methods of using ethno veterinary drugs to treat chicken diseases and pests (x=3.72), and identify signs of diseases (x=3.69), among others. However, the ADTs did not show any competency in any of the 32 skills items. The principal component analysis with Varimax rotation was performed to ascertain the dimensionality of the measures. Six factors with eigen value of >1, which accounted for 77.317% were extracted, with each factor loading ranging from 0.523 to 0.93. Factor loading after rotation that emerged on the same component was described; as brooding, shelter and care of the chicks; predators and healthcare; hygiene and litter management; feeds and feeding stuff; and record keeping and marketing. The findings on the human resource development revealed that staff meetings were the most common method of capacity development. This was followed by in-service-training, formal study, workshop, and on the job training. The farmers’ field school and study tours were sparingly used. However, respondents were in favor of on-site training, staff meetings, formal study and in-service training. The findings on the appropriate model suggest a theoretical indigenous poultry production model (IPPM) for the Eastern Cape Province (ECP). The “open social system” was used to develop a framework for an indigenous poultry cooperative society (to be known as Abafuyi Benkukhu Zemveli [ABZ]). This was meant to create a binding force for capacity development, a strong economic foundation through equity contributions, creation of marketing channels, and the development of a concept of ‘‘our own'' product in the market. Lastly, the study offers options for a training program that would accommodate the new initiatives, with a strong capacity development training approach. In this context, the study advocates for institutional support for the IPFs and the incorporation of indigenous poultry in the curriculum of the agricultural training programs at higher education institutions in South Africa.
- Full Text:
- Date Issued: 2014
Afro-communitarianism and the nature of reconciliation
- Authors: Oelofsen, Rianna
- Date: 2013
- Subjects: Ubuntu (Philosophy) Reconciliation -- South Africa Communitarianism -- Africa Philosophy, African
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:2736 , http://hdl.handle.net/10962/d1006809
- Description: In this dissertation I sketch a conception of personhood as understood from within an Afrocommunitarian worldview, and argue that this understanding of personhood has implications for understanding the concept of reconciliation. Understanding ‘being human’ as a collective, communal enterprise has implications for how responsibility, justice, forgiveness and humanization (all cognate concepts of reconciliation) are conceptualized. In line with this understanding of reconciliation and its cognate concepts, I argue that the humanization of self and other (according to the Afrocommunitarian understanding of personhood) is required for addressing the ‘inferiority’ and concurrent ‘superiority’ racial complexes as diagnosed by Franz Fanon and Steve Biko. These complexes reach deeply within individual and collective psyches and political identities, and I argue that political solutions to protracted conflict (in South Africa and other racially charged contexts) which do not address these deeply entrenched pathologies will be inadequate according to an Afrocommunitarian framework.
- Full Text:
- Date Issued: 2013
The druggable antimalarial target 1-deoxy-D-xylulose-5-phosphate reductoisomerase: purfication, kinetic characterization and inhibition studies
- Authors: Goble, Jessica Leigh
- Date: 2011
- Subjects: Antimalarials -- Development Plasmodium falciparum Drug development Plasmodium falciparum -- Purification Plasmodium falciparum -- Inhibitors Enzyme kinetics Malaria -- Chemotherapy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3949 , http://hdl.handle.net/10962/d1004008
- Description: Plasmodium falciparum 1–deoxy–D–xylulose–5 phosphatereductoisomerase (PfDXR) plays a role in isoprenoid biosynthesis in the malaria parasite and is absent in the human host, making this parasite enzyme an attractive target for antimalarial drug design. To characterize PfDXR, it is necessary to produce large quantities of the enzyme in a soluble and functional form. However, the over–production of malarial proteins in prokaryotic host systems often results in the formation of truncated proteins or insoluble protein aggregates. A heterologous expression system was developed for the production of active PfDXR using codon harmonization and tight control of expression in the presence of lac repressor. Yields of up to 2 mg/l of enzyme were reported using the optimised expression system, which is 8 to 10– fold greater than previously reported yields. The kinetic parameters Km, Vmax and kcat were determined for PfDXR; values reported in this study were consistent with those reported in the literature for other DXR enzymes. A three–dimensional model of the malarial drug target protein PfDXR was generated, and validated using structure–checking programs and protein docking studies. Structural and functional features unique to PfDXR were identified using the model and comparative sequence analyses with apicomplexan and non–apicomplexan DXR proteins. Residues Val44 and Asn45, essential for NADPH binding; and catalytic hatch residues Lys224 and Lys226, which are unique to the species of Plasmodium, were mutated to resemble those of E. coli DXR. Interestingly,these mutations resulted in significant reductions in substrate affinity, when compared to the unmutated PfDXR. Mutant enzymes PfDXR(VN43,44AG) and PfDXR(KK224,226NS) also demonstrated a decreased ability to turnover substrate by 4–fold and 2–fold respectively. This study indicates a difference in the role of the catalytic hatch of PfDXR with regards to the way in which it captures substrates. The study also highlights subtle differences in cofactor binding to PfDXR, compared with the well characterized EcDXR enzyme. The validated PfDXR model was also used to develop a novel efficient in silico screening method for potential tool compounds for use in the rational design of novel DXR inhibitors. Following in silico screening of 46 potential DXR inhibitors, a two–tiered in vitro screening approach was undertaken. DXR inhibition was assessed for the 46 novel compounds using an NADPH– ependant DXP enzyme inhibition assay and antimalarial potential was assessed using P.falciparum–infected erythrocyte growth assays. Select compounds were tested in human cells in order to determine whether they were toxic to the host. From the parallel in silico and in vitro drug screening, it was evident that only a single compound demonstrated reasonable potential binding to DXR (determined using in silico docking), inhibited DXR in vitro and inhibited P. falciparum growth, without being toxic to human cells. Its potential as a lead compound in antimalarial drug development is therefore feasible. Two outcomes were evident from this work. Firstly, analogues of known antimalarial natural products can be screened against malaria, which may then lead towards the rational design of novel compounds that are effective against a specific antimalarial drug target enzyme, such as PfDXR. Secondly, the rational design of novel compounds against a specific antimalarial drug target enzyme can be untaken by adopting a coupled in silico and in vitro approach to drug discovery.
- Full Text:
- Date Issued: 2011
Application of dermal microdialysis and tape stripping methods to determine the bioavailability and/or bioequivalence of topical ketoprofen formulations
- Authors: Tettey-Amlalo, Ralph Nii Okai
- Date: 2008
- Subjects: Drugs -- Therapeutic equivalency Transdermal medication High performance liquid chromatography Nonsteroidal anti-inflammatory agents -- Bioavailability Nonsteroidal anti-inflammatory agents -- Effectiveness Nonsteroidal anti-inflammatory agents -- Testing Nonsteroidal anti-inflammatory agents -- Side effects
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3796 , http://hdl.handle.net/10962/d1003274
- Description: The widespread acceptance of topical formulations intended for local and/or regional activity has prompted renewed interest in developing a model to determine the bioavailability of drugs in order to establish bioequivalence as a means of evaluating formulation performance of multisource products and also for use during formulation development. Current in vivo techniques such as blister suction and skin biopsy amongst others used to determine the bioavailability and/or bioequivalence of topical formulations are either too invasive to generate appropriate concentration-time profiles or require large numbers of study subjects thereby making the study expensive and time-consuming. Moreover, there are currently no sampling techniques that can demonstrate dermal bioavailability and/or bioequivalence of topical formulations intended for local and/or regional activity. Dermal microdialysis is a relatively new application of microdialysis that permits continuous monitoring of endogenous and/or exogenous solutes in the interstitial fluid. The technique is involves the implantation of semi-permeable membranes which are perfused with an isotonic medium at extremely slow flow rates and collection of microlitre sample volumes containing diffused drugs. Tape stripping, a relatively older technique, has been extensively used in comparative bioavailability studies of various topical formulations. However, due to shortcomings arising from reproducibility and inter-subject variation amongst others, the published FDA guidance outlining the initial protocol was subsequently withdrawn. The incorporation of transepidermal water loss with tape stripping has garnered renewed interest and has been used for the determination of drug bioavailability from a number of topical formulations. Hence the primary objective of this research is to develop and evaluate microdialysis sampling and tape stripping techniques, including the incorporation of the determination of transepidermal water loss, to assess the dermal bioavailability of ketoprofen from topical gel formulations and to develop models for bioequivalence assessment. A rapid UPLC-MS/MS method with requisite sensitivity for the analysis of samples generated from dermal microdialysis was developed and validated which accommodated the microlitre sample volumes collected. An HPLC-UV method was developed and validated for the analysis of samples generated from the in vitro microdialysis and in vivo tape stripping studies. The work presented herein contributes to a growing body of scientific knowledge seeking to develop a model for the determination of bioequivalence of pharmaceutically equivalent topical formulations intended for local and/or regional activity in human subjects.
- Full Text:
- Date Issued: 2008
Effects of substituents on the photosensitizing and electrocatalytic properties of phthalocyanines
- Authors: Maree, Suzanne Elizabeth
- Date: 2002
- Subjects: Phthalocyanines
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4554 , http://hdl.handle.net/10962/d1018247
- Description: In this work a selection of octasubstituted phthalocyaninato Zinc, Ge(IV) and Sn(IV) complexes were synthesized for possible use in photodynamic therapy and their photochemistry, photophysics and electrochemistry studied. Third-generation complexes containing steroids, e.g. cholesterol and estrone, were synthesized to improve tumour selectivity. The zinc phthalocyanine complexes (ZnPc) showed that complexes containing electron-donating groups have higher photostability. Germanium phthalocyanine complexes (GePc) undergo phototransformation rather than direct photobleaching and the tin phthalocyanine complexes (SnPc) undergo photobleaching mediated by photoreduction of the phthalocyanine ring. Singlet oxygen production showed increased in the following order: GePc>SnPc>ZnPc. Triplet lifetimes of the GePc (168-340μs) are very similar to that of the ZnPc (197 - 366μs), but the triplet lifetimes of the SnPc are ten fold shorter (10 - 32μs ). Triplet quantum yields are higher for the GePc (0.20 - 0.50) and SnPc (0.08 - 0.45) than for the ZnPc (0.02 - 0.25). Fluorescence lifetimes of GePc ( 4.0 - 5.1 ns) are significantly longer than that of ZnPc (1.9 - 3.0 ns) and SnPc (0.2 - 0.4 ns). Fluorescence quantum yields decrease in the following order: GePc(0.21-0.31)>ZnPc(0.02-0.21)>SnPc(0.02- 0.06). Ring-substituted cobalt phthalocyanine complexes of the form CoPc(R)4 (R= NH2, N02, C(CH3)3, S03H and COOH) are compared for their catalytic activities towards the oxidation of cysteine. The potential for the electrocatalytic oxidation of cysteine is closely related to the Com/Co11 couple of the CoPc(R)4 complexes in acidic media and to the Con/Co1 couple in basic media. The catalytic current and the oxidation potential for cysteine are dependent on the pH of the solution, the potential becoming less positive and the currents increasing with increase in pH.
- Full Text:
- Date Issued: 2002
The evolution of heteronomous host relationships in Aphelinidaa (Hymenoptera Chalcidoidea) with special reference to the biology of Coccophagus Bartletti Annecke and Insley
- Authors: Walter, Grenville Hugh
- Date: 1984
- Subjects: Hymenoptera
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5620 , http://hdl.handle.net/10962/d1003746
- Description: Résumé: Heteronomous host relationships are unique to parasitoids in about 8 aphelinid genera. Males have host relationships quite distinct from those of their females. Females of ALL species are primary endoparasitoids of homopterous hosts. Males, on the other hand, may be either primary ectoparasitoids of the same host species as their conspecific females, or they may be hyperparasitic upon parasitoids within Homoptera, and some are primary endoparasitoids of moth eggs. Species in these groups are termed DIPHAGOUS PARASITOIDS, HETERONOMOUS HYPERPARASITOIDS and HETEROTROPHIC PARASITOIDS, respectively. The selective advantages proposed to explain the evolution of these unusual host relationships are examined in this thesis. The biology of a diphagous parasitoid was examined in detail because diphagous parasitism is considered the most primitive of heteronomous host relationships. Diphagous parasitism is thought to have evolved during a period when ovipositing females continuously encountered large proportions of parasitised hosts. Larval competition may have generated the selection pressures that favoured male ectoparasitism. Ectoparasitoids are known to be superior in competition against other larvae, even older ones. A series of observations was carried out on the diphagous parasitoid, Coccophagus bartletti. Information was gathered on oviposition and host-feeding behaviour, daily activity patterns, and sex ratios in the laboratory and field. This enabled the design and interpretation of a series of observations on the responses of mated C. bartletti females to already-parasitised hosts. The results indicate that competition from other parasitoids probably played no role in the evolution of diphagous host relationships. Heteronomous hyperparasitoids, thought to have evolved from diphagous parasitoids, appear to be strong competitors because their males kill other parasitoids. However, an alternative hypothesis to the competition one, and based on the present study, is presented. Implications for the generally-held view, that competition is important in moulding species' characters, are discussed.
- Full Text:
- Date Issued: 1984