Contribution of pollution gradient to the sediment microbiome and potential pathogens in urban streams draining into Lake Victoria (Kenya).

In sub-Saharan Africa (SSA), urban rivers/streams have long been subjected to anthropogenic pollution caused by urbanization, resulting in significantly altered chemical and biological properties of surface water and sediments. However, little is known about the diversity and structure of river microbial community composition and pathogens, as well as how they respond to anthropogenic inputs. High-throughput 16S rRNA amplicon sequencing and PICRUSt predictive function profiling were used in this study to conduct a comprehensive analysis of the spatial bacterial distribution and metabolic functions in sediment of two urban streams (Kisat and Auji) flowing through Kisumu City, Kenya. Results revealed that sediment samples from the highly urbanized mid and lower stream catchment zones of both streams had significantly higher levels of total organic carbon (TOC), total nitrogen (TN), total phosphorous (TP) than the less urbanized upper catchment zone, and were severely polluted with toxic heavy metals lead (Pb), cadmium (Cd), and copper (Cu). Differential distribution of Actinobacteria, Proteobacteria, Chloroflexi, and Verrucomicrobia in sediment bacterial composition was detected along stream catchment zones. The polluted mid and lower catchment zones were rich in Actinobacteria and Proteobacteria, as well as a variety of potential pathogenic taxa such as Corynebacterium, Staphylococcus, Cutibacterium, Turicella, Acinetobacter, and Micrococcus, as well as enteric bacteria such as Faecalibacterium, Shewanella, Escherichia, Klebsiella, Enterococcus, Prevotella, Legionella, Vibrio and Salmonella. Furthermore, PICRUSt metabolic inference analysis revealed an increasing enrichment in the sediments of genes associated with carbon and nitrogen metabolism, disease pathogenesis, and virulence. Environmental factors (TOC, Pb, Cd, TN, pH) and geographical distance as significant drivers of sediment bacterial community assembly, with the environmental selection to play a dominant role. In polluted river catchment zone sediment samples, Pb content was the most influential sediment property, followed by TOC and Cd content. Given the predicted increase in urbanization in SSA, further alteration of surface water and sediment microbiome due to urban river pollution is unavoidable, with potential long-term effects on ecosystem function and potential health hazards. As a result, this study provides valuable information for ecological risk assessment and management of urban rivers impacted by diffuse and point source anthropogenic inputs, which is critical for future proactive and sustainable urban waste management, monitoring, and water pollution control in low-income countries.

Cellular reactivity to the p. Falciparum protein trap in adult kenyans: novel epitopes, complex cytokine patterns, and the impact of natural antigenic variation.

Malaria vaccines based on thrombospondin-related adhesive protein of Plasmodium falciparum (Pf TRAP) are currently undergoing clinical trials in humans. This study was designed to investigate naturally acquired cellular immunity to Pf TRAP in adults from a target population for future trials of TRAP-based vaccines in Kilifi, Kenya. We first tested reactivity to a panel of 53 peptides spanning Pf TRAP and identified 26 novel T-cell epitopes. A panel of naturally occurring polymorphic variant epitope peptides were made to the most commonly recognized epitope regions and tested for ability to elicit IFN-gamma, IL-4, and IL-10 production. These data provide for the first time a complex cytokine matrix mapping naturally induced T-cell responses to TRAP and suggest that T-cell responses boosted by vaccination with Pf TRAP could stimulate the release of competing pro- and anti-inflammatory cytokines. They further define polymorphic variants able to boost specific Th1, Th2, and possibly Tr1 reactivity.

Ex vivo interferon-gamma immune response to thrombospondin-related adhesive protein in coastal Kenyans: longevity and risk of Plasmodium falciparum infection.

Thrombospondin-related adhesive protein (TRAP) of Plasmodium falciparum is currently being tested in human vaccine studies. However, its natural reactivity in the field remains poorly characterized. More than 40% of 217 Kenyan donors responded in an ex vivo interferon-gamma (IFN-gamma) enzyme-linked immunospot (ELISPOT) assay to at least one of 14 20mer peptides spanning 42% of the antigen. Reactivity was comparable from early childhood (>1 year of age) to old age, and the maximal precursor frequency of TRAP-specific cells to all 14 peptides was 1 in 4,000. Prospective follow-up for one year indicated that these low-level ex vivo responses to TRAP did not protect against the subsequent development of malaria. Retesting of selected donors after one year showed a complete change in the reactivity pattern, suggesting that malaria-specific ex vivo IFN-gamma ELISPOT assay responses are short lived in naturally exposed donors, even to conserved epitopes. This study provides important information regarding natural reactivity to a key malaria antigen.

Induction of T helper type 1 and 2 responses to 19-kilodalton merozoite surface protein 1 in vaccinated healthy volunteers and adults naturally exposed to malaria.

Plasmodium falciparum malaria is a major cause of death in the tropics. The 19-kDa subunit of P. falciparum merozoite surface protein 1 (MSP-1(19)), a major blood stage vaccine candidate, is the target of cellular and humoral immune responses in animals and humans. In this phase I trial of MSP-1(19), immunization of nonexposed human volunteers with either of the two allelic forms of recombinant MSP-1(19) induced high levels of antigen-specific Th1 (gamma interferon) and Th2 (interleukin 4 [IL-4] and IL-10) type lymphokines. The adjustment of the antigen dose and number of immunizations regulated the level of specificity of immune responses and Th1/Th2 bias of responses induced by vaccination. Novel conserved and allelic T-cell epitopes which induced cross-strain immune responses were identified. Importantly, responses to many of these novel epitopes were also present in adults exposed to malaria, both in east (Kenya) and west Africa (The Gambia). These data suggest that epitope-specific naturally acquired MSP-1(19) immune responses in endemic populations can be boosted by vaccination.