University of the Algarve

About: University of the Algarve is a education organization based out in Faro, Portugal. It is known for research contribution in the topics: Population & Tourism. The organization has 3649 authors who have published 10303 publications receiving 233536 citations.

Antimicrobial activity of essential oils isolated from Portuguese endemic species of Thymus.

Abstract: Aims:Thymus species are wild species mostly found in the arid lands of Portugal. Possible antimicrobial properties of Thymus essential oils have been investigated. The chemical composition of the essential oils and the antimicrobial activity of Thymus mastichina (L) L. subsp. mastichina, T. camphoratus and T. lotocephalus from different regions of Portugal were analysed. Methods and Results: Hydrodistillation was used to isolate the essential oils and the chemical analyses were performed by gas chromatography (GC) and GC coupled to mass spectrometry. The antimicrobial activity was tested by the disc agar diffusion technique against Candida albicans, Escherichia coli, Listeria monocytogenes, Proteus mirabilis, Salmonella spp. and Staphylococcus aureus. Pure linalool, 1,8-cineole and a mixture (1 : 1) of these compounds were included. Linalool, 1,8-cineole or linalool/1,8-cineole and linalool/1,8-cineole/linalyl acetate were the major components of the essential oils, depending on the species or sampling place. The essential oils isolated from the Thymus species studied demonstrated antimicrobial activity but the micro-organisms tested had significantly different sensitivities. Conclusions: The antimicrobial activity of essential oils may be related to more than one component. Significance and Impact of the Study: Portuguese endemic species of Thymus can be used for essential oil production for food spoilage control, cosmetics and pharmaceutical use. Further studies will be required to elucidate the cell targets of the essential oil components.

In vivo selection of Plasmodium falciparum parasites carrying the chloroquine-susceptible pfcrt K76 allele after treatment with artemether-lumefantrine in Africa

Abstract: The development and spread of Plasmodium falciparum antimalarial drug resistance has spurred a global change in policy from the use of the former first-line antimalarials chloroquine (CQ) and sulfadoxine-pyrimethamine (SP) to the use of artemisinin-based combination therapies (ACTs). In 2006, Tanzania changed its drug policy to the use of artemether-lumefantrine (AL; Coartem [Novartis]), which is currently the most favored ACT used in Africa. AL is highly effective on the African continent [1–3]. Nevertheless, AL has been associated with a relatively high frequency of reinfection events during the post-treatment period, when lumefantrine, the longer-lasting partner drug (with a plasma half-life of 4–5 days vs. 3–11 h for artemether), remains in the blood in subtherapeutic concentrations. During this period, selection of less-susceptible parasites (which have the ability to cause infection in the presence of plasma drug concentrations higher than those associated with susceptible parasites causing infection) may occur. One gene that has been found to influence susceptibility to lumefantrine is the P. falciparum multidrug resistance gene 1 (pfmdr1), which encodes a transporter located on the digestive vacuole (DV) membrane of the erythrocytic stages. Allelic exchange experiments with culture-adapted lines, as well as field studies of clinical isolates, have shown that pfmdr1 single-nucleotide polymorphisms (SNPs) influence the in vitro response to various antimalarial drugs, such as the artemisinin derivatives and the arylaminoalcohols lumefantrine, mefloquine (MQ), and halofantrine (HF) [4–7]. An increased pfmdr1 copy number has also been associated with treatment failure after short 4-dose AL therapy [8], as well as after MQ or artesunate-MQ therapy [9]. So far, these associations have been observed only in Southeast Asia. However, an increased number of pfmdr1 copies has been found in a few patient samples in Gabon, subsequent to a trial with low-dose MQ treatment, thereby suggesting the potential of selection of multicopy pfmdr1 in this region [10]. Hence, the pfmdr1 copy number may also become important on the African continent after wide-scale deployment of AL. Our previous studies in Zanzibar showed that treatment with AL selected for reinfecting parasites harboring pfmdr1 alleles encoding the N86, 184F, and D1246 residues [11, 12]. These findings are consistent with reports from other East African field sites [13, 14] and suggest the selection of lumefantrine-tolerant parasites, which may constitute a first step toward full resistance and associated clinical failure [15]. Nonetheless, it remains unclear whether this selection is the result of specific influences on the drug target or is caused by nonspecific selection of parasites that are generally more fit and able to thrive in the presence of environmental stressors. This is an important distinction, considering that mutations at codons 1034, 1042, and 1246 in pfmdr1 have been reported to incur fitness costs in vitro [16]. Another question arising from our previous studies is the role of the chloroquine resistance transporter gene (pfcrt), which encodes a transmembrane protein that localizes to the membrane of the DV and is a key determinant of the chloroquine response of P. falciparum [17]. The pfcrt K76T mutation has been consistently associated with CQ resistance in vitro and in vivo [18 –20]. This putative transporter also appears to influence the parasite response to arylaminoalcohols. Accordingly, mutations at the pfcrt amino acid 76 position have been suggested to play a role in MQ susceptibility [19 –21]. In addition, in vitro selection of HF resistance has been associated with a novel pfcrt S163R mutation, which also has been shown to affect the in vitro response to MQ [22]. In light of these data, we hypothesized that pfcrt SNPs might also influence susceptibility to lumefantrine. To evaluate the influence of pfmdr1 and pfcrt mutations on the mechanism of resistance to lumefantrine, we searched for selection of these mutations in samples collected during a clinical trial in Fukayosi, Tanzania, in which children with uncomplicated P. falciparum malaria were treated with AL or SP [2]. SP inhibits the synthesis of folate by targeting the dihydropteroate synthetase and dihydrofolate reductase enzymes, respectively. This treatment arm therefore enabled us to test whether any evidence of selection for pfcrt or pfmdr1 mutations in the AL arm was drug dependent and was not a result of general fitness issues associated with the parasite response to any antimalarial drug treatment. Furthermore, the availability of isogenic parasites resulting from allelic exchange experiments at pfcrt amino acid position 76 [19, 20] allowed us to evaluate the specific influence of mutant pfcrt alleles (in particular, the K76T mutation) on the response of P. falciparum to lumefantrine.

Social modulation of androgen levels in male teleost fish.

Abstract: Androgens are classically thought of as the sex steroids controlling male reproduction. However, in recent years evidence has accumulated showing that androgens can also be affected by the interactions between conspecifics, suggesting reciprocal interactions between androgens and behaviour. These results have been interpreted as an adaptation for individuals to adjust their agonistic motivation and to cope with changes in their social environment. Thus, male-male interactions would stimulate the production of androgens, and the levels of androgens would be a function of the stability of its social environment ['challenge hypothesis', Gen. Comp. Endocrinol. 56 (1984) 417]. Here the available data on social modulation of androgen levels in male teleosts are reviewed and some predictions of the challenge hypothesis are addressed using teleosts as a study model. We investigate the causal link between social status, territoriality and elevated androgen levels and the available evidence suggests that the social environment indeed modulates the endocrine axis of teleosts. The association between higher androgen levels and social rank emerges mainly in periods of social instability. As reported in the avian literature, in teleosts the trade-off between androgens and parental care is indicated by the fact that during the parental phase breeding males decreased their androgen levels. A comparison of androgen responsiveness between teleost species with different mating and parenting systems also reveals that parenting explains the variation observed in androgen responsiveness to a higher degree than the mating strategy. Finally, the adaptive value of social modulation of androgens and some of its evolutionary consequences are discussed.