Genetic markers of resistance to pyrimethamine and sulfonamides in Plasmodium falciparum parasites compared with the resistance patterns in isolates of Escherichia coli from the same children in Guinea-Bissau.

The antifolate drugs sulphadoxine and pyrimethamine are used for treatment of chloroquine-resistant Plasmodium falciparum in Africa. Resistance to pyrimethamine has been associated with point mutations in the dhfr-gene and resistance to sulphadoxine with mutations in the dhps-gene. There is concern that the use of the antifolates trimethoprim and sulphamethoxazole for treatment of other infectious diseases will result in the selection of malaria parasites with mutations in these genes. In Guinea-Bissau, where sulfonamide and trimethoprim-containing drugs have been used extensively, we decided to assess the prevalence of mutations in the dhfr-and dhps-gene in P. falciparum isolated from children suffering from acute malaria and to assess the resistance patterns to trimethoprim/sulphamethoxazole in Escherichia coli isolated from the same patients. A thick film and a blood sample for polymerase chain reaction (PCR) were obtained from 100 children attending the Bandim Health Centre in Bissau with symptoms compatible with malaria. Furthermore, a stool sample was collected from the same children and cultured for E. coli. Of the cultured E. coli, 67% were resistant both to sulfonamides and trimethoprim, 4% to sulfonamides alone, 3% to trimethoprim alone while 26% were fully sensitive to both drugs. PCR was successfully performed in 97 blood samples. Of these, 41% had triple mutations at the dhfr-gene (at codons 51, 59 and 108), and 15% had triple mutations plus mutation at codon 437 in the dhps-gene. Only 45% harboured the wild-type dhfr-gene. Thus both bacterial resistance and mutations in the parasitic genes were common, but not linked in the individual child. As sulphadoxine-pyrimethamine has only been used as a second line treatment for chloroquine resistant malaria in Guinea-Bissau for a few years, it is worrying to find a high prevalence of mutations in the parasitic genes coding for resistance to these drugs. Therefore, restricting the use of sulphadoxine-pyrimethamine for the treatment of chloroquine resistant malaria might not be sufficient to prevent the development of resistance in the parasites as long as antifolate drugs are used extensively

The effects of manipulation of sedimentary iron and organic matter on sediment biogeochemistry and seagrasses in a subtropical carbonate environment

The microbial metabolism of organic matter (OM) in seagrass beds can create sulfidic conditions detrimental to seagrass growth; iron (Fe) potentially has ameliorating effects through titration of the sulfides and the precipitation of iron-sulfide minerals into the sediment. In this study, the biogeochemical effects of Fe availability and its interplay with sulfur and OM on sulfide toxicity, phosphorous (P) availability, seagrass growth and community structure were tested. The availability of Fe and OM was manipulated in a 2 × 2 factorial experiment arranged in a Latin square, with four replicates per treatment. The treatments included the addition of Fe, the addition of OM, the addition of both Fe and OM as well as no addition. The experiment was conducted in an oligotrophic, iron-deficient seagrass bed. Fe had an 84.5% retention efficiency in the sediments with the concentration of Fe increasing in the seagrass leaves over the course of the experiment. Porewater chemistry was significantly altered with a dramatic decrease in sulfide levels in Fe addition plots while sulfide levels increased in the OM addition treatments. Phosphorus increased in seagrass leaves collected in the Fe addition plots. Decreased sulfide stress was evidenced by heavier δ34S in leaves and rhizomes from plots to which Fe was added. The OM addition negatively affected seagrass growth but increased P availability; the reduced sulfide stress in Fe added plots resulted in elevated productivity. Fe availability may be an important determinant of the impact that OM has on seagrass vitality in carbonate sediments vegetated with seagrasses