Peuplement phytoplanctonique et qualité des eaux en milieu lacustre anthropisé: Cas du lac municipal de Yaoundé (Cameroun)

An annual qualitative and quantitative evaluation of phytoplankton and chlorophylla, as well as of some physico-chemical parameters were recorded in the Yaounde Municipal Lake. Physico-chemical measurements were also regularly done in its main tributary (Mingoa stream). The study aimed at demonstrating the cultural eutrophication of this lake. The discharge of untreated urban effluents into the lake seriously threatens his health state. Indeed, the water transparency is globally low and exceptionally exceeds 1m. Water conductivity is higher near the lake bottom, reaching 408 μS cm-1. The strong deficiency in oxygen contents recorded from 2.5m depth leads to the production of high quantities of ammonium nitrogen. The total phosphorus concentrations vary from 80 to 1650 μgP l-1, and the total Kjeldhal nitrogen concentrations fluctuate between 3 and 15 mgNH4 + l-1.  Upstream, the Mingoa exhibits total phosphorus concentrations ranging from 600 to 3800 μgP l-1, and total Kjeldhal nitrogen concentrations ranging from 10 to 22 mgNH4 + l-1. Conditions prevailing in this biotope favour a massive growth of phytoplankton, dominated by Euglenophyta and Chlorophyta. Both spatio-temporal analysis of phosphorus, chlorophyll a, and the composition of the  phytoplanktonic community, stress the anthropogenic impact on the ecosystem. The progression of this hydrosystem towards a dystrophic state is going on, and implies an urgent need for its restoration, followed by a rehabilitation of the “Grand Messa” sewage treatment plant, and the elimination process of solid materials in the tributary, upstream. Key words: sewage, lake, phytoplankton, eutrophication, central Africa

Assessment of the effects of sulfate and nitrate on the temporal evolution of Klebsiella oxytoca and Staphylococcus aureus abundance under shaking conditions, in aquatic microcosm

Most chemicals in natural aquatic media can be assimilated by bacteria. The impact of various environmental conditions on this microbial process is not always clear. This study aimed at investigating changes in the abundance of Klebsiella oxytoca and Staphylococcus aureus under different shaking conditions, in aquatic microcosms containing nitrate and sulfate. Sodium chloride solution (8.5 g NaCl•L-1), and nitrate and sulfate solutions (0.005, 0.05, 0.5 and 5 g•L-1) containing bacteria were supplemented with tryptic peptone at a final concentration of 10 g•L-1. The solutions were incubated under shaking conditions (300, 350 and 400 rev•min-1). Bacteriological analyses were performed hourly over a 6-h period. During the first 3 h of incubation, results showed that the highest values of the apparent cell growth rates (CAGRs) with K2SO4 in pure cultures, at a shaking speed 400 rev•min-1, were 0.656 h-1 for S. aureus, and 0.364 h-1 for K. oxytoca. In mixed culture, the CAGR was 0.235 h-1 for S. aureus, and 0.388 h-1 for K. oxytoca, both recorded at 300 rev•min-1. With KNO3 in pure culture solutions, the CAGR was 0.353 h-1 for S. aureus at 300 rev•min-1, and 0.367 h-1 for K. oxytoca at 350 rev•min-1. In mixed culture it was 0.454 h-1 for S. aureus and 0.393 h-1 for K. oxytoca, both recorded at 350 rev•min-1. The highest value of the apparent cell inhibition rate (CAIR) for S. aureus was 0.520 h-1 in K2SO4 (5 g•L-1, 400 rev•min-1), and 0.115 h-1 in KNO3 (5 g•L-1, 300 rev•min-1). For K. oxytoca, it was 0.07 h-1 in K2SO4 in pure culture (0.05 g•L-1, 300 rev•min-1), and 0.044 h-1 in mixed culture (0.05 g•L-1, 350 rev•min-1). In KNO3 it was 0.239 h-1 in mixed culture (5 g•L-1, 300 rev•min-1). The growth and inhibition potentials of different microbial species were impacted by the chemical concentrations and the movement speeds.L’impact de diverses conditions environnementales sur l’assimilation bactérienne dans l’eau, des composés chimiques est peu connu. La présente étude a visé l’évaluation de la dynamique d’abondance de Klebsiella oxytoca et Staphylococcus aureus sous diverses conditions, en milieu aquatique microcosme contenant du sulfate ou nitrate. Des solutions du NaCl (8,5 g•L-1), sulfate et nitrate (0,005, 0,05, 0,5 et 5 g•L-1) contenant des cellules ont été enrichies à la peptone trypsique (concentration finale 10 g•L-1), puis incubées sous conditions dynamiques (300, 350 et 400 tr•min-1). Les analyses bactériologiques ont été effectuées pendant 6 h. Il ressort qu’au cours des trois premières heures d'incubation, le taux de croissance cellulaire apparent (TCCA) le plus élevé en culture pure, contenant du K2SO4, est de 0,656 h-1 pour S. aureus, et 0,364 h-1 pour K. oxytoca, enregistrés à 400 tr•min-1. En culture mixte, il est de 0,235 h-1 pour S. aureus, et 0,388 h-1 pour K. oxytoca, enregistrés à 300 tr•min-1. Avec du KNO3, en culture pure, le TCCA est de 0,353 h-1 pour S. aureus à 300 tr•min-1, et 0,367 h-1 à 350 tr•min-1 pour K. oxytoka. En culture mixte, il est de 0,454 h-1 pour S. aureus et 0,393 h-1 pour K. oxytoca, enregistrés à 350 tr•min-1. Le taux d’inhibition cellulaire apparent (TICA) le plus élevé de S. aureus est de 0,520 h-1 en présence du K2SO4 (5 g•L-1, 400 tr•min-1), et 0,115 h-1 en présence de KNO3 (5 g•L-1, 300 tr•min-1). Pour K. oxytoca, il est de 0,07 h-1 avec du K2SO4 en culture pure (0,05 g•L-1, 300 tr•min-1), et 0,044 h-1 en culture mixte (0,05 g•L-1, 350 tr•min-1). Avec du KNO3, il est de 0,239 h-1 en culture mixte (5 g•L-1, 300 tr•min-1). La croissance et l’inhibition des microorganismes sont affectées par les concentrations en sels et la vitesse de mouvements du milieu

Intestinal parasite infections and associated risk factors in inhabitants of the city of Yaoundé, Cameroon

Intestinal parasite infections are still prevalent in developing countries and in Cameroon where over 90% of the population is at high risk. To assess the distribution of intestinal parasitic infections and risk factors of the city of Yaoundé, both household and parasitological surveys were conducted from October to December 2019 among inhabitants of lowlands aged from 15 years and over. Stools samples were collected and screened for intestinal parasites presence using Kato Katz and Formol-Ether methods. Sociodemographic status, prevention measures against intestinal parasitic diseases and practices with increase exposition to risky environments were then recorded.
 A total of 229 participants (142 females: 62.0%; 87 males: 38.0%) were enrolled for the study, and 24.02% (55/229) were found infected by helminthes (ten species) and/or protozoans (one species). Participant infection rates and risk varied by parasite species and socio-demographic factors. Global risk analysis showed that age (OR ranges: 3.78-15.96), anti-parasitic drug consumption (OR: 2.53), eating behavior,,hygiene (OR: 22.4), occupation (OR ranges: 1.92-3.53) and type of toilets (OR: 3.4) were strongly associated with risk of infection by intestinal parasites. The risk increased in 15-30 years age group for A. lumbricoïdes, T. trichiura and Schistosoma mansoni, unpredictably in those washing their hands before meals for A. lumbricoïdes and H. nana, in respondents using antiparasitic drugs as auto-medication for H. nana and in those using traditional toilets for A. lumbricoïdes. However, other variables with high OR values (> 5.0) might be potential risk factor for the occurrence of specific parasite infections. The study suggests the need for household sensitization and community actions including integrated environmental management as complement strategy to reduce intestinal parasite transmission in the city of Yaoundé

Anopheles gambiae distribution and insecticide resistance in the cities of Douala and Yaoundé (Cameroon): influence of urban agriculture and pollution

Background: Urban malaria is becoming a major health priority across Africa. A study was undertaken to assess the importance of urban pollution and agriculture practice on the distribution and susceptibility to insecticide of malaria vectors in the two main cities in Cameroon. Methods: Anopheline larval breeding sites were surveyed and water samples analysed monthly from October 2009 to December 2010. Parameters analysed included turbidity, pH, temperature, conductivity, sulfates, phosphates,nitrates, nitrites, ammonia, aluminium, alkalinity, iron, potassium, manganese, magnesium, magnesium hardness and total hardness. Characteristics of water bodies in urban areas were compared to rural areas and between urban sites. The level of susceptibility of Anopheles gambiae to 4% DDT, 0.75% permethrin, 0.05% deltamethrin, 0.1% bendiocarb and 5% malathion were compared between mosquitoes collected from polluted, non polluted and cultivated areas. Results: A total of 1,546 breeding sites, 690 in Yaoundé and 856 in Douala, were sampled in the course of the study. Almost all measured parameters had a concentration of 2- to 100-fold higher in urban compare to rural breeding sites. No resistance to malathion was detected, but bendiocarb resistance was present in Yaounde. Very low mortality rates were observed following DDT or permethrin exposure, associated with high kdr frequencies. Mosquitoes collected in cultivated areas, exhibited the highest resistant levels. There was little difference in insecticide resistance or kdr allele frequency in mosquitoes collected from polluted versus non-polluted sites. Conclusion: The data confirm high selection pressure on mosquitoes originating from urban areas and suggest urban agriculture rather than pollution as the major factor driving resistance to insecticide

Impact of altitude on spring macroinvertebrates and water quality in South West region of Cameroon

We evaluated the impact of altitude on the biodiversity and water quality of 13 springs located from 82 to 1,189 m a.s.l. on Mount Cameroon. The springs were of good chemical and ecological quality whatever the altitude. The analysis of the physicochemical variables showed low temperature levels (19.50 ± 2.09 °C), high turbidity (13.0 ± 7.17 FTU), and an acceptable mineralization level (324.95 ± 260.0 μS/cm), with high amounts of phosphate nutrients (0.83 ± 0.47 mg/L). We observed a strong seasonal effect, with a decrease in temperature and nutrient content during the dry season whereas pH and dissolved oxygen increased. A total of 10,265 organisms, distributed into 56 families, were collected. They mostly included insects (47.8%), closely followed by Arachnida (34.8%). Only two stygobite taxa were recorded, namely Darwinulidae and Stenasellidae. Total diversity slightly decreased with altitude, especially during the dry season. Despite lower temperature and more oxygen at higher altitudes, diversity, including EPT did not increase. Therefore, African fauna are less sensitive to rising temperature than the faunas of other areas of the world. This result may be explained either by the fact that African species are better adapted to warm, low-oxygen waters than species from other parts of the world, or by the absence of refuges in Mount Cameroon that are home to temperature-sensitive species. Consequently, the impact of climate change on aquatic macroinvertebrates in tropical Africa could be reduced.We evaluated the impact of altitude on the biodiversity and water quality of 13 springs located from 82 to 1,189m a.s.l. on Mount Cameroon. Despite lower temperature and more oxygen at higher altitudes, diversity, including EPT did not increase. Therefore, African fauna reacts similarly to the faunas of other areas of the world. African species appear to be well adapted to warm and poorly oxygenated water compared to species from other parts of the world