No description available.

Plasmodium falciparum is a protozoan parasite that causes malaria, a disease that is widely spread in the tropical world. Chloroquine has been very effective against malaria since it was introduced into the field until the emergence of chloroquine resistant malaria. Chloroquine resistant malaria has become widely spread in the endemic area. In addition, cross resistance to other antimalarial drugs that are different in structure and function has been reported, even though some of these drugs had not been previously used in that particular region. The objective of this study was to determine the molecular mechanism of this resistance. Actinomycin D resistant Plasmodium falciparum was selected in vitro from the drug sensitive parental clone, 3D7. Interestingly, we found that the selected strain is resistant to chloroquine, mefloquine, antimalarial drugs, and Rhodamine 123. Comparison between 3D7 parental and 3D7R/act-D2 resistant P. falciparum did not show a difference in the level of expression of pfmdr1 previously implicated in the drug resistance. In addition we found that the level of accumulation of two drugs actinomycin D is reduced in the resistant parasite as compared with the sensitive one. Further studies indicated that the reduction in the drug accumulation was due to the increase in drug efflux. Furthermore, to identify if other P-glycoprotein homologues are involved in the resistance, oligonucleotide primers to conserved sequences in ABC domains have been used. An ABC protein homologous to subunit 4 of the 26S proteasome complex has been cloned. In vitro transcription, translation and immunoprecipitation analysis were done using reticulocytes lysate and polyclonal antibodies generated against peptide sequence in the P. falciparum S4 subunit. Surprisingly a decrease in the expression of this gene was found in the resistant clone, 3D7R/act-D2, compared to its parental cell line as determined by Northern blot analysis. Studies are in progress to determine

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This project was designed to assess the ability of natural sediment microbial communities and single species microbial populations to preferentially utilize inorganic forms of nitrogen (ammonium, NH4-N, and nitrate, NO3-N, specifically). The first chapter addressed two primary questions: 1) Do sediment microbial communities preferentially assimilate NH4-N or NO3-N?; and, 2) Does preferential uptake of nitrogen change with increased NH4-N or NO3-N availability? The second chapter furthered these analyses by assessing shifts in microbial nitrogen assimilation in response to sustained nitrogen enrichments. Primary questions addressed were: 1) Are microbial communities able to adapt to nitrogen enrichment and preferentially utilize a more available source?; and, 2) Are initial microbial responses to nitrogen enrichment different from sustained responses? Questions were addressed with in vitro laboratory experiments quantifying microbial activity. Overall, microbial community activity changed in response to the form of nitrogen available, enrichment type, and duration of exposure. Data demonstrate sediment microbial communities in the Midwestern US may prefer NO3-N over other forms of nitrogen. However, microbial communities became saturated with NO3-N with increases in concentrations >0.75 mg NO3-N/L. Microbial communities were able to adapt to higher nitrogen concentration and increase rates of assimilation for both NH4-N and NO3-N. Thus, microbial communities are robust in response to nitrogen increases in and ecosystem, even in high nitrogen environments like the Midwestern US. / Preferential uptake of available nitrogen forms -- Adaptive uptake in microbial communities. / Department of Biology

Bacteriological survey of the fish pathogens in Greek mariculture between 1994- 1997 was followed by analysis of prevalence in sea bass, sea bream, sharpsnout bream and common Dentex and discussion of the impact of various fish pathogens. In addition antibiotic resistance profiles and frequencies were studied using quantitative antibiogram and MIC analysis for the two most commonly used antibiotics Oxolinic acid and Oxytetracycline and clinically relevant MIC breakpoints were extrapolated for different fish species and main fish pathogens. The kinetics of the above antimicrobials were analysed in eight experiments where two fish species namely sea bass and sea bream as well as two water temperatures were employed. Muscle, liver, serum, skin samples were analysed by two HPLC methods and two bioassay methods were developed. The relative importance and significance of these findings was evaluated in the general context of pharmacokinetic studies in fish. Kinetic data were compared to clinical data and practical implications were evaluated. Issues like antibiotic resistance and its implications, the implications of residues and resistance in human health and the environment were analysed in order to put this study in context. Conclusions tackled important aspects of antimicrobial chemotherapy and future work was suggested.

Plasmodium falciparum is a protozoan parasite and the causative agent of the most lethal form of malaria, a major disease in the tropical world. Chloroquine has been very effective in treatment of this disease, however the emergence of chloroquine-resistant strains in most geographical regions where malaria is endemic has made difficult the control of malaria. In addition, resistance to other antimalarials has been observed in these regions. The objective of this study was to determine the molecular mechanisms of multidrug resistance in P. falciparum. We have selected in vitro a P. falciparum strain resistant to actinomycin D from a parental drug sensitive clone, 3D7. Interestingly, we found that the actinomycin D resistant clone is less sensitive to chloroquine and mefloquine (antimalarial drugs) and rhodamine123. Comparison between parental 3D7 and resistant P. falciparum did not show differences in the copy number or level of expression of pfmdr1 previously implicated in chloroquine or mefloquine resistance. Furthermore, to identify if other P-glycoprotein homologues are involved in resistance, we used oligonucleotide primers to conserved sequences in ABC domains. An ABC protein, a homologue to the subunit 4, of the 26S proteasome complex has been cloned. To determine if this gene was involved in resistance to actinomycin D, a Northern blot was done. Surprisingly it was found a decreased in the expression of this gene in the resistant cell line, 3D7R/actD2, in comparison with its parental cell line, 3D7. Studies are in progress to determine the role of the PFS4 subunit in the resistance phenotype of 3D7R/actD2.

The physiology of oxygen metabolism in Group B N. meningitidis was investigated. The respiratory components of the electron transport chain included dehydrogenases, ubiquinone, multiple b- and c-type cytochromes, and cytochromes o and a as terminal oxidases. Independent variations in the respiratory components were determined for cells grown under different conditions of iron concentrations and aeration (including anaerobiosis). Studies on oxidase activities in envelope preparations suggested branching of the respiratory chain at the levels of dehydrogenases, cytochrome b and terminal oxidases. Work on L-cysteine oxidase activity associated with the envelope preparations indicated the presence of an additional "alternate" oxidase insensitive to terminal oxidase inhibitors. A soluble CO- and NO-binding c-type cytochrome was shown to be present in the supernatant fluids and might be involved in an ascorbate-TMPD oxidase activity. A model of a branched electron transport system is proposed. The levels of catalase, peroxidase and superoxide dismutase in the organism were shown to vary with the growth conditions.

The organisms in this study were chosen due to their associations with foods and their potential as food borne pathogens. Food borne diseases are an import public health problem in most countries. Bacteria of the genera Campylobacter, Salmonella and Listeria can be transported by poultry and poultry products to humans. Gastroenteritis, typhoid fever, diarrhea, dysentery may originate from the infection. This study was undertaken to determine the incidence of pathogens in a poultry processing plant using polymerase chain reaction and conventional tests and to determine the formation and survival of biofilm cells of food pathogens in trisodium phosphate.

<p>The microbial life of sub-Antarctic islands plays a key role in the islands ecosystem, with microbial activities providing the majority of nutrients available for primary production. Knowledge of microbial diversity is still in its infancy and this is particularly true regarding the diversity of micro-organisms in the Antarctic and sub-Antarctic regions. One particularly important functional group of micro-organisms is the diazotrophs, or nitrogen-fixing bacteria and archaea. This group have not been well studied in the sub-Antarctic region, but play an important role in the nutrient cycling of the island. This thesis explored the diversity of nitrogen-fixing organisms in the soil of different ecological habitats on the sub-Antarctic Marion Island.</p>

The entrainment of microbes from agricultural land into overland flow during rainfall events is recognised as an important source of pathogenic microbes to surface water bodies and yet this transport process is poorly understood. In this study, a method has been developed to separate bacteria into the forms in which they have been postulated to exist in overland flow. Then Escherichia coli was used as a model organism to investigate the transported state of bacteria eroded from cowpats and their subsequent transport in overland flow. Simulated rainfall experiments were used to generate runoff direct from cowpats. Concentrations of E. coli in the runoff direct from cowpats were found to be directly proportional to the concentration in the cowpat, regardless of the age of the cowpat. It was also observed that E. coli were predominantly eroded from cowpats as individual cells. The interactions between E. coli and soil particles in overland flow were then examined in a small laboratory scale model system and showed that E. coli attached to large (>45 [mu]m) soil particles were transported significantly less than unattached cells. However, in the runoff from the model system, E. coli were found to be attached mainly to clay particles that were similar in size to the bacterial cells. Furthermore, the transport of E. coli through the model system appeared to follow the transport of a conservative chemical tracer implying that (a) the cells were being transported as a solute with the bulk of the water flow, and (b) that E. coli attached to small clay particles were as mobile in the overland flow as unattached cells. These observations imply that E. coli predominantly interact with small clay particles that are also being carried along in the overland flow. The transport of E. coli at a larger scale was then investigated using 5-metre long, 1-metre wide buffer strips operated under saturation excess conditions. In buffer strips using intact soils and existing pasture cover, E. coli removal was very poor (26 % removal) at the low flow rate of 2 L min⁻� with no removal observed at the higher flow rates of 6 and 20 L min⁻�. E. coli removal rates were increased to 41 % removal at 2 L min⁻� by cultivating the soils, with the removal rate again decreasing with increasing flow rate. E. coli in the overland flow from the buffer strips did not form into large flocs or attach to large soil particles, but were transported in small neutrally buoyant particles that remain entrained in the overland flow. Under saturation excess runoff conditions, E. coli in overland flow were not effectively removed by buffer strips as the small particles are transported either over the soil surface or, through large pores in the soil. This Thesis has shown that E. coli is transported in overland flow in small particle sizes that are difficult to trap or remove from overland flow thereby explaining the high fluxes of faecal bacteria observed in overland flow from agricultural land.