Urogenital chlamydia infection, caused by the bacterium Chlamydia trachomatis (CT), is the most common sexually transmitted bacterial infection in Sweden. In 2008 it was estimated by WHO that there were 105.7 million new cases of CT worldwide, an increase by 4.2 million cases (4.1%) compared to 2005. If untreated, CT infections can progress to serious reproductive health problems, especially in women. These complications include subfertility/infertility, ectopic pregnancy and chronic pain. The CT infection is often asymptomatic and reliable diagnostic methods and contact tracing are important tools for identifying infected individuals. CT infection is classified in the Swedish Communicable Diseases Act as a serious disease; consequently, written reporting and contact tracing are compulsory. Previous or ongoing CT infection is not uncommon in infertile couples, especially in women with tubal factor infertility (TFI). We have tested 244 infertile couples for CT antibodies, and CT IgG positive couples were tested for CT DNA in urine. The prevalence of CT antibodies was higher in infertile men and women, and ongoing CT infection was common. Our results support a role of CT in infertility and underscore the importance of prevention of CT infection. Contact tracing was studied during using questionnaires. A total of 544 questionnaires was sent to tracers in a Swedish county and 534 (98%) were completed. Centralized contact tracing performed by experienced tracers is effective; on average 65% of sexual contacts found by contact tracing are CT-infected. Our data show that it is worthwhile to extend the tracing period beyond 6 months as 30% of reported sexual contacts between months 7-12 were CT-infected. Contact tracing may be performed face-to-face at the clinic or by telephone. Because of the severe consequences of CT infection there is a need for useful methods for both primary and secondary prevention of CT and other sexually transmitted infections (STIs). An important sub-population for CT/STI-prevention is the “core group”, i.e. a subpopulation with high incidence of STIs combined with risky sexual behaviours. This subpopulation contributes particularly to the spread of STIs in the population. Therefore, we have developed and evaluated a brief standardised but flexible manual-based single-session intervention based on motivational interviewing (MI) for the reduction of high risk sexual behaviour. Women (n=105) and men (n=119) at high risk of contracting CT infection were randomly eighter offered brief MI counselling or standard care. Our findings support the effectiveness of brief MI-based counselling in reducing high-risk sexual behaviour and incident CT infection in women (p<0.01) but not in men. Our results suggest that gender aspects need to be considered and that men and women should be treated differently for achieving maximal risk-reduction. Whereas it might be sufficient to include information and motivation when performing risk-reducing counselling on women, counsellors may also add other components, such as behavioural skills and booster sessions, when counselling is performed on men. / Klamydiainfektion orsakas av Chlamydia trachomatis och är den vanligaste sexuellt överförda bakterieinfektionen. WHO har uppskattat att det år 2008 var 105,7 miljoner nya fall av klamydia i världen, en ökning med 4,2 miljoner fall (4,1 %) jämfört med år 2005. Klamydiainfektion är ett folkhälsoproblem och klassificeras i den svenska smittskyddslagen som en allmänfarlig sjukdom varför det är obligatoriskt att smittspåra och göra en skriftlig anmälan till smittskyddsläkaren och Smittskyddsinstitutet. Klamydiainfektionen ger oftast inga symtom och tillförlitliga diagnostiska metoder och smittspårning är viktiga ”redskap” för att hitta smittade personer. Om klamydiainfektionen inte behandlas kan den leda till allvarliga hälsoproblem, speciellt hos kvinnor. Bland komplikationer efter klamydiainfektion ingår ofrivillig barnlöshet, utomkvedshavandeskap och kronisk buksmärta. Tecken på tidigare eller pågående klamydiainfektion är vanliga hos ofrivilligt barnlösa par, speciellt hos kvinnor med skadade äggledare som orsak till barnlösheten. Våra resultat ger stöd för betydelsen av klamydia vid ofrivillig barnlöshet och understryker vikten av förebyggande åtgärder mot klamydia samt klamydiaprovtagning av både män och kvinnor vid utredning av ofrivillig barnlöshet. Centraliserad klamydiasmittspårning utförd av erfarna smittspårare är effektiv och i genomsnitt är 65 % av spårade sexuella kontakter klamydiasmittade. Våra data visar att det lönar sig att förlänga smittspårningsperioden från 6 till 12 månader eftersom betydligt fler klamydiasmittade kontakter då hittas. Den så kallade ”Västerbottensmodellen” med en smittspårningsperiod på 12 månader rekommenderas nu av Socialstyrelsen. Kontaktspårning kan utföras antingen på mottagningen eller per telefon. På grund av risk för allvarliga konsekvenser av klamydia finns det behov av metoder för att förebygga klamydiasmitta. En viktig grupp för prevention är den så kallade ”kärngruppen", alltså de personer som har en hög förekomst av klamydia och andra sexuellt överförda infektioner i kombination med sexuellt riskbeteende. Denna grupp bidrar särskilt till spridningen av sexuellt överförda infektioner bland befolkningen. Därför har vi utvecklat och utvärderat en kort samtalsmetod som bygger på metoden motiverande samtal (MI, motivational interviewing) för att minska sexuellt risktagande. Våra fynd visar att kort MI-baserad rådgivning för att minska sexuellt riskbeteende och klamydiainfektion fungerar bra på kvinnor men inte lika bra på män. Resultaten tyder på att genusaspekter måste beaktas och att kvinnor och män ska behandlas på olika sätt för att uppnå maximal riskminskning. Det kan vara tillräckligt att fokusera på information och motivation vid rådgivning av kvinnor men för rådgivning av män kan man behöva komplettera med beteendemässiga färdigheter och/eller upprepad MI-baserad rådgivning för att nå god effekt.

Tissue culture studies were carried out on two ornamental plant species, Strongylodon macrobotrys A. Gray and Peperomia clusifolia Hook. Successful in vitro regeneration of plantlets was achieved in the latter species, using leaf and stem explants. The basal medium of Murashige and Skoog (1962), in combination with various levels of NAA and K, was utilised. Strongylodon proved refractory to both establishment of a thriving callus culture and in vitro formation of roots and shoots. Several media were utilised, Miller's (1963) medium proving the most successful for the production of callus. Different combinations of the growth regulators NAA, IBA, BA and K were used to determine optimum levels of these substances for callus production. Root/shoot induction studies were carried out using the basal medium of Miller (1963) plus various concentrations of IBA in combination with K or BA. Alternatively,the basal medium was used without added growth regulators. Internodes, nodal segments, leaves, pulvini, flower parts and seeds were used in the study. No plantlets were obtained from Strongylodon explants. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1982.

Skin cancer is the most widely diagnosed form of cancer and it is split in to non-melanoma skin cancer (NMSC) and cutaneous malignant melanoma (CMM). Cutaneous melanoma has a high propensity for malignancy and it has the highest mortality rate of all skin cancers (de Gruijl, 1999:2004). The first line of treatment for most skin cancers is surgical excision but instances do arise in which surgery is not feasible due to the health of the patient or the location of the lesion. Therefore, viable alternatives are necessary in cases where surgery is not possible (Telfer et al., 2008:36). The skin is readily available for delivery of cytotoxic drugs to treat carcinomas and melanomas so the topical delivery of 5-fluorouracil was investigated in this study. 5-Fluorouracil is a pyrimidine anti-metabolite which interferes with deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) synthesis by inhibiting the nucleotide synthetic enzyme thymidylate synthase (TS) and by becoming misincorporated into RNA and DNA. Thymidylate is essential for replication as well as repair of DNA, in the event of TS inhibition thymidylate is not formed and “thymineless deaths” of cells occur (Chu & Sartorelli, 2009:935; Longley et al., 2003:330). This active pharmaceutical ingredient (API) causes death of atypical and rapidly dividing cells (Tsuji & Karasek, 1986:474). The intravenous and topical routes are approved for 5-fluorouracil and in the case of skin cancer the obvious choice would be topical application (Chu & Sartorelli, 2009:935). Topical application of 5-fluorouracil results in the occurrence of terrible side effects such as severe inflammation, stomatitis, photosensitivity and dermatitis. A reduction in side effects would reduce the stigma associated with topical 5-fluorouracil and in turn increase patient compliance. Topical drug delivery entails the delivery of an API onto or into the various layers of the skin (Flynn & Weiner, 1993:33) in order to treat conditions on or within the skin. Topical application of APIs is non-invasive, painless and simple plus the target site is readily accessible for topical therapy, thus the API is delivered directly to the site of action (Naik et al., 2000:318). In the case of skin cancer, 5-fluorouracil should be able to reach the epidermis because NMSC originates from the keratinocytes (Marks & Hanson, 2010:305) and CMM from melanocytes (de Gruijl, 1999:2004) which are both found in the epidermis. The barrier function of the skin limits the penetration of molecules into the skin and the rate-limiting step is usually penetration into the stratum corneum (Foldvari, 2000:418). The aim of this study was to investigate the diffusion of 5-fluorouracil from formulations into and through the skin. Two physico-chemical properties of 5-fluorouracil that influence skin permeation were determined (aqueous solubility and n-octanol-buffer partition coefficient (log D)). The Pheroid™ drug delivery system was used to enhance the delivery of 5-fluorouracil (Grobler et al., 2008:284). Pheroid™ is a novel technology that is used in the delivery of APIs in pharmaceutical products. It enhances the efficacy of delivered compounds while allowing for the reduction of unwanted adverse effects (Grobler et al., 2008:284). Franz cell skin diffusion studies and tape-stripping were conducted with Pheroid™ and non-Pheroid™ formulations to allow for comparison and determination of the effect of Pheroid™. The in vitro efficacy of 5-fluorouracil in inducing apoptosis of human melanoma cells was investigated using a flow cytometric apoptosis assay. Different concentrations of 5-fluorouracil in formulation were utilised in the experiments so as to observe the cytotoxic effect of 5-fluorouracil. The effect of the drug delivery vehicle on the efficacy of 5-fluorouracil was investigated by utilising API solutions in addition to Pheroid™ and non-Pheroid™ formulations in the experiments. Relatively high concentrations of 5-fluorouracil diffused into and through the skin with Pheroid™ formulations resulting in a greatly enhanced in vitro skin permeation of 5-fluorouracil. The tape-stripping revealed that the Pheroid™ lotions resulted in higher concentrations of 5-fluorouracil in the epidermis and dermis after 12 h as compared to the lotions. There was no deducible trend with respect to the distribution of 5-fluorouracil between the epidermis and dermis. Subsequent to the apoptosis assay it was found that 5-fluorouracil was able to induce apoptosis in A375 cells after a 24 h incubation period. The Pheroid™ treatment of cells resulted in a greater response (mean fluorescence intensity) as compared to treatments with the other drug delivery vehicles at three of the four concentrations. This showed that the drug delivery vehicle played a role in the in vitro efficacy of 5-fluorouracil. Further research must be done in order to combine these results. Optimum and highly effective topical formulations with low doses of 5-fluorouracil must be formulated for the purpose of treating cutaneous cancers with a reduced incidence of side effects. / Thesis (MSc (Pharmaceutics))--North-West University, Potchefstroom Campus, 2013.

Skin cancer is the most widely diagnosed form of cancer and it is split in to non-melanoma skin cancer (NMSC) and cutaneous malignant melanoma (CMM). Cutaneous melanoma has a high propensity for malignancy and it has the highest mortality rate of all skin cancers (de Gruijl, 1999:2004). The first line of treatment for most skin cancers is surgical excision but instances do arise in which surgery is not feasible due to the health of the patient or the location of the lesion. Therefore, viable alternatives are necessary in cases where surgery is not possible (Telfer et al., 2008:36). The skin is readily available for delivery of cytotoxic drugs to treat carcinomas and melanomas so the topical delivery of 5-fluorouracil was investigated in this study. 5-Fluorouracil is a pyrimidine anti-metabolite which interferes with deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) synthesis by inhibiting the nucleotide synthetic enzyme thymidylate synthase (TS) and by becoming misincorporated into RNA and DNA. Thymidylate is essential for replication as well as repair of DNA, in the event of TS inhibition thymidylate is not formed and “thymineless deaths” of cells occur (Chu & Sartorelli, 2009:935; Longley et al., 2003:330). This active pharmaceutical ingredient (API) causes death of atypical and rapidly dividing cells (Tsuji & Karasek, 1986:474). The intravenous and topical routes are approved for 5-fluorouracil and in the case of skin cancer the obvious choice would be topical application (Chu & Sartorelli, 2009:935). Topical application of 5-fluorouracil results in the occurrence of terrible side effects such as severe inflammation, stomatitis, photosensitivity and dermatitis. A reduction in side effects would reduce the stigma associated with topical 5-fluorouracil and in turn increase patient compliance. Topical drug delivery entails the delivery of an API onto or into the various layers of the skin (Flynn & Weiner, 1993:33) in order to treat conditions on or within the skin. Topical application of APIs is non-invasive, painless and simple plus the target site is readily accessible for topical therapy, thus the API is delivered directly to the site of action (Naik et al., 2000:318). In the case of skin cancer, 5-fluorouracil should be able to reach the epidermis because NMSC originates from the keratinocytes (Marks & Hanson, 2010:305) and CMM from melanocytes (de Gruijl, 1999:2004) which are both found in the epidermis. The barrier function of the skin limits the penetration of molecules into the skin and the rate-limiting step is usually penetration into the stratum corneum (Foldvari, 2000:418). The aim of this study was to investigate the diffusion of 5-fluorouracil from formulations into and through the skin. Two physico-chemical properties of 5-fluorouracil that influence skin permeation were determined (aqueous solubility and n-octanol-buffer partition coefficient (log D)). The Pheroid™ drug delivery system was used to enhance the delivery of 5-fluorouracil (Grobler et al., 2008:284). Pheroid™ is a novel technology that is used in the delivery of APIs in pharmaceutical products. It enhances the efficacy of delivered compounds while allowing for the reduction of unwanted adverse effects (Grobler et al., 2008:284). Franz cell skin diffusion studies and tape-stripping were conducted with Pheroid™ and non-Pheroid™ formulations to allow for comparison and determination of the effect of Pheroid™. The in vitro efficacy of 5-fluorouracil in inducing apoptosis of human melanoma cells was investigated using a flow cytometric apoptosis assay. Different concentrations of 5-fluorouracil in formulation were utilised in the experiments so as to observe the cytotoxic effect of 5-fluorouracil. The effect of the drug delivery vehicle on the efficacy of 5-fluorouracil was investigated by utilising API solutions in addition to Pheroid™ and non-Pheroid™ formulations in the experiments. Relatively high concentrations of 5-fluorouracil diffused into and through the skin with Pheroid™ formulations resulting in a greatly enhanced in vitro skin permeation of 5-fluorouracil. The tape-stripping revealed that the Pheroid™ lotions resulted in higher concentrations of 5-fluorouracil in the epidermis and dermis after 12 h as compared to the lotions. There was no deducible trend with respect to the distribution of 5-fluorouracil between the epidermis and dermis. Subsequent to the apoptosis assay it was found that 5-fluorouracil was able to induce apoptosis in A375 cells after a 24 h incubation period. The Pheroid™ treatment of cells resulted in a greater response (mean fluorescence intensity) as compared to treatments with the other drug delivery vehicles at three of the four concentrations. This showed that the drug delivery vehicle played a role in the in vitro efficacy of 5-fluorouracil. Further research must be done in order to combine these results. Optimum and highly effective topical formulations with low doses of 5-fluorouracil must be formulated for the purpose of treating cutaneous cancers with a reduced incidence of side effects. / Thesis (MSc (Pharmaceutics))--North-West University, Potchefstroom Campus, 2013.

This project developed methodology for in vitro toxicity assessment of contaminated sites using the Promega?? MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxy-methoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] assay performed on human cells (HepG2 and Skin fibroblasts). The project included the development of a method for extracting contaminants from soil based on leaching and centrifugation. A number of solvents and surfactants were assessed for their suitability as extracting agents. The Zwitterionic surfactant CHAPS ({3[(3-Cholamidopropyl) dimethylammonio] propanesulphonic acid}), which is an irritant in vivo, was found suitable for in vitro toxicity assessment applications. CHAPS was found to be the least toxic surfactant in vitro when tested on skin fibroblasts (NOEC: 1800??577 ppm, IC50: 4000??577 ppm) and HepG2 cells (NOEC: 833??289 ppm, IC50: 5300??287 ppm). The chosen surfactant was used in three different methods for extraction of Toluene and Xylene spiked in 2 g and 10g soil. The combination comprising of 0.1% (s/w) CHAPS and cosolvent 1% (w/w) Isopropanol, at their respective NOEC (No Observed Effective Concentration) toxicity values, showed good recovery of the nonpolar organic compounds in comparison to the recovery by 0.1% CHAPS and 0.5% CHAPS. The study found additive interactions to be the most common form of toxicity for 16 concentration combinations of Formaldehyde (polar), Toluene and Xylene (nonpolar) when compared to predicted toxicity (R2=0.943, P&lt0.0001). When assessing the in vitro toxicity of unknown (blind) contaminated soil samples, the Hazard Index (HI) predicted from the chemical analyses results showed a relatively good correlation (R2&gt0.7062, n=26) when compared to the experimental toxicity results on HepG2 cells. Furthermore, the comparison of Australian Health Investigation Levels (HIL) with in vitro toxicity testing gave similar correlation (R2&gt0.6882, n=26) on HepG2 cells. The overall project suggests the potential application of the zwitterionic surfactant (CHAPS) in sampling contaminants from soils in an in vitro toxicity assessment. This study demonstrates the application of in vitro toxicity assessment using human cells for the prediction of toxic risk as a sentinel to human toxicity from a contaminated site.

A common problem observed in large-scale cell cultivation is reduced culture performance compared with small-scale processes due to the existence of concentration gradients caused by poor mixing. Small-scale simulations using microbial cell suspensions have shown that circulation of cells through concentration gradients of oxygen, pH and glucose can result in reduction of cell growth and product formation similar to the effects observed in large-scale bioreactors. This study was aimed at using scale-down studies to investigate poor mixing in large-scale bioreactors used for suspended plant and animal cell culture. Two plant cell suspensions and a hybridoma cell line were used in this work. The range of oxygen transfer coefficients achieved in the hybridoma and plant suspensions were about 50???20 h-1 and 12???6 h-1, respectively. One-vessel simulation was developed to induce fluctuations of dissolved oxygen tension in a 2-L bioreactor using intermittent sparging of air and nitrogen. The effect of dissolved oxygen fluctuations on the cells was examined by comparing the performance of the cultures with those operated at constant dissolved oxygen tension. In the hybridoma suspension culture, only slight effects on cell growth were observed at circulation times above 300 s. No effect on the specific glucose uptake rate or antibody production was observed at the circulation times tested. Analysis of gene expression for selected hypoxia-related genes also suggested that the overall effect was limited. In plant cell suspensions, the specific growth rates and biomass yields on total sugar in the cultures under fluctuating dissolved oxygen tension were essentially the same as those at constant dissolved oxygen tension for both transgenic Nicotiana tabacum and Thalictrum minus. Under fluctuating dissolved oxygen tension, no effect on antibody accumulation was observed in transgenic N. tabacum suspensions, but a decrease in berberine accumulation was observed in T. minus. From the results, it can be concluded that only minimal effects due to the development of concentration gradients would be expected in large-scale bioreactors used for the cultivation of the hybridoma and plant cell suspensions tested in this work.

A common problem observed in large-scale cell cultivation is reduced culture performance compared with small-scale processes due to the existence of concentration gradients caused by poor mixing. Small-scale simulations using microbial cell suspensions have shown that circulation of cells through concentration gradients of oxygen, pH and glucose can result in reduction of cell growth and product formation similar to the effects observed in large-scale bioreactors. This study was aimed at using scale-down studies to investigate poor mixing in large-scale bioreactors used for suspended plant and animal cell culture. Two plant cell suspensions and a hybridoma cell line were used in this work. The range of oxygen transfer coefficients achieved in the hybridoma and plant suspensions were about 50???20 h-1 and 12???6 h-1, respectively. One-vessel simulation was developed to induce fluctuations of dissolved oxygen tension in a 2-L bioreactor using intermittent sparging of air and nitrogen. The effect of dissolved oxygen fluctuations on the cells was examined by comparing the performance of the cultures with those operated at constant dissolved oxygen tension. In the hybridoma suspension culture, only slight effects on cell growth were observed at circulation times above 300 s. No effect on the specific glucose uptake rate or antibody production was observed at the circulation times tested. Analysis of gene expression for selected hypoxia-related genes also suggested that the overall effect was limited. In plant cell suspensions, the specific growth rates and biomass yields on total sugar in the cultures under fluctuating dissolved oxygen tension were essentially the same as those at constant dissolved oxygen tension for both transgenic Nicotiana tabacum and Thalictrum minus. Under fluctuating dissolved oxygen tension, no effect on antibody accumulation was observed in transgenic N. tabacum suspensions, but a decrease in berberine accumulation was observed in T. minus. From the results, it can be concluded that only minimal effects due to the development of concentration gradients would be expected in large-scale bioreactors used for the cultivation of the hybridoma and plant cell suspensions tested in this work.

A common problem observed in large-scale cell cultivation is reduced culture performance compared with small-scale processes due to the existence of concentration gradients caused by poor mixing. Small-scale simulations using microbial cell suspensions have shown that circulation of cells through concentration gradients of oxygen, pH and glucose can result in reduction of cell growth and product formation similar to the effects observed in large-scale bioreactors. This study was aimed at using scale-down studies to investigate poor mixing in large-scale bioreactors used for suspended plant and animal cell culture. Two plant cell suspensions and a hybridoma cell line were used in this work. The range of oxygen transfer coefficients achieved in the hybridoma and plant suspensions were about 50???20 h-1 and 12???6 h-1, respectively. One-vessel simulation was developed to induce fluctuations of dissolved oxygen tension in a 2-L bioreactor using intermittent sparging of air and nitrogen. The effect of dissolved oxygen fluctuations on the cells was examined by comparing the performance of the cultures with those operated at constant dissolved oxygen tension. In the hybridoma suspension culture, only slight effects on cell growth were observed at circulation times above 300 s. No effect on the specific glucose uptake rate or antibody production was observed at the circulation times tested. Analysis of gene expression for selected hypoxia-related genes also suggested that the overall effect was limited. In plant cell suspensions, the specific growth rates and biomass yields on total sugar in the cultures under fluctuating dissolved oxygen tension were essentially the same as those at constant dissolved oxygen tension for both transgenic Nicotiana tabacum and Thalictrum minus. Under fluctuating dissolved oxygen tension, no effect on antibody accumulation was observed in transgenic N. tabacum suspensions, but a decrease in berberine accumulation was observed in T. minus. From the results, it can be concluded that only minimal effects due to the development of concentration gradients would be expected in large-scale bioreactors used for the cultivation of the hybridoma and plant cell suspensions tested in this work.

A common problem observed in large-scale cell cultivation is reduced culture performance compared with small-scale processes due to the existence of concentration gradients caused by poor mixing. Small-scale simulations using microbial cell suspensions have shown that circulation of cells through concentration gradients of oxygen, pH and glucose can result in reduction of cell growth and product formation similar to the effects observed in large-scale bioreactors. This study was aimed at using scale-down studies to investigate poor mixing in large-scale bioreactors used for suspended plant and animal cell culture. Two plant cell suspensions and a hybridoma cell line were used in this work. The range of oxygen transfer coefficients achieved in the hybridoma and plant suspensions were about 50???20 h-1 and 12???6 h-1, respectively. One-vessel simulation was developed to induce fluctuations of dissolved oxygen tension in a 2-L bioreactor using intermittent sparging of air and nitrogen. The effect of dissolved oxygen fluctuations on the cells was examined by comparing the performance of the cultures with those operated at constant dissolved oxygen tension. In the hybridoma suspension culture, only slight effects on cell growth were observed at circulation times above 300 s. No effect on the specific glucose uptake rate or antibody production was observed at the circulation times tested. Analysis of gene expression for selected hypoxia-related genes also suggested that the overall effect was limited. In plant cell suspensions, the specific growth rates and biomass yields on total sugar in the cultures under fluctuating dissolved oxygen tension were essentially the same as those at constant dissolved oxygen tension for both transgenic Nicotiana tabacum and Thalictrum minus. Under fluctuating dissolved oxygen tension, no effect on antibody accumulation was observed in transgenic N. tabacum suspensions, but a decrease in berberine accumulation was observed in T. minus. From the results, it can be concluded that only minimal effects due to the development of concentration gradients would be expected in large-scale bioreactors used for the cultivation of the hybridoma and plant cell suspensions tested in this work.

A common problem observed in large-scale cell cultivation is reduced culture performance compared with small-scale processes due to the existence of concentration gradients caused by poor mixing. Small-scale simulations using microbial cell suspensions have shown that circulation of cells through concentration gradients of oxygen, pH and glucose can result in reduction of cell growth and product formation similar to the effects observed in large-scale bioreactors. This study was aimed at using scale-down studies to investigate poor mixing in large-scale bioreactors used for suspended plant and animal cell culture. Two plant cell suspensions and a hybridoma cell line were used in this work. The range of oxygen transfer coefficients achieved in the hybridoma and plant suspensions were about 50???20 h-1 and 12???6 h-1, respectively. One-vessel simulation was developed to induce fluctuations of dissolved oxygen tension in a 2-L bioreactor using intermittent sparging of air and nitrogen. The effect of dissolved oxygen fluctuations on the cells was examined by comparing the performance of the cultures with those operated at constant dissolved oxygen tension. In the hybridoma suspension culture, only slight effects on cell growth were observed at circulation times above 300 s. No effect on the specific glucose uptake rate or antibody production was observed at the circulation times tested. Analysis of gene expression for selected hypoxia-related genes also suggested that the overall effect was limited. In plant cell suspensions, the specific growth rates and biomass yields on total sugar in the cultures under fluctuating dissolved oxygen tension were essentially the same as those at constant dissolved oxygen tension for both transgenic Nicotiana tabacum and Thalictrum minus. Under fluctuating dissolved oxygen tension, no effect on antibody accumulation was observed in transgenic N. tabacum suspensions, but a decrease in berberine accumulation was observed in T. minus. From the results, it can be concluded that only minimal effects due to the development of concentration gradients would be expected in large-scale bioreactors used for the cultivation of the hybridoma and plant cell suspensions tested in this work.