François-Xavier Etoa

Antimicrobial activity of the crude extracts and five flavonoids from the twigs of Dorstenia barteri (Moraceae).

The aim of this study was to evaluate the antimicrobial activity of the crude extract of the twigs of Dorstenia barteri (DBT) as well as that of four of the five flavonoids isolated from this extract. Gram-positive bacteria (six species), Gram-negative bacteria (12 species) and fungi (four species) were used. The agar disc diffusion test was used to determine the sensitivity of the tested samples while the well micro-dilution was used to determine the minimal inhibition concentrations (MIC) and the minimal microbicidal concentration (MMC) of the active samples. The results of the disc diffusion assay showed that DBT, isobavachalcone (1), and kanzonol C (4) prevented the growth of all the 22 tested microbial species. Other compounds showed selective activity. The inhibitory activity of the most active compounds namely compounds 1 and 4 was noted on 86.4% of the tested microorganisms and that of 4-hydroxylonchocarpin (3) was observed on 72.7%. This lowest MIC value of 19.06microg/ml was observed with the crude extract on seven microorganisms namely Citrobacter freundii, Enterobacter aerogens, Proteus mirabilis, Proteus vulgaris, Bacillus megaterium, Bacillus stearothermophilus and Candida albicans. For the tested compounds, the lowest MIC value of 0.3microg/ml (on six of the 22 organisms tested) was obtained only with compound 1, which appeared as the most active compound. This lowest MIC value (0.3microg/ml) is about 4-fold lower than that of the RA, indicating the powerful and very interesting antimicrobial potential of isobavachalcone (1). The antimicrobial activities of DBT, as well as that of compounds 1, 3, 4, amentoflavone (5) are being reported for the first time. The overall results provide promising baseline information for the potential use of the crude extracts from DBT as well as some of the isolated compounds in the treatment of bacterial and fungal infections.

Anthropogenic habitat disturbance and ecological divergence between incipient species of the malaria mosquito Anopheles gambiae.

Background Anthropogenic habitat disturbance is a prime cause in the current trend of the Earth’s reduction in biodiversity. Here we show that the human footprint on the Central African rainforest, which is resulting in deforestation and growth of densely populated urban agglomerates, is associated to ecological divergence and cryptic speciation leading to adaptive radiation within the major malaria mosquito Anopheles gambiae. Methodology/Principal Findings In southern Cameroon, the frequency of two molecular forms–M and S–among which reproductive isolation is strong but still incomplete, was correlated to an index of urbanisation extracted from remotely sensed data, expressed as the proportion of built-up surface in each sampling unit. The two forms markedly segregated along an urbanisation gradient forming a bimodal cline of ∼6-km width: the S form was exclusive to the rural habitat, whereas only the M form was present in the core of densely urbanised settings, co-occurring at times in the same polluted larval habitats of the southern house mosquito Culex quinquefasciatus–a species association that was not historically recorded before. Conclusions/Significance Our results indicate that when humans create novel habitats and ecological heterogeneities, they can provide evolutionary opportunities for rapid adaptive niche shifts associated with lineage divergence, whose consequences upon malaria transmission might be significant.

Synthesis of cyclopropane fatty acids in Lactobacillus helveticus and Lactobacillus sanfranciscensis and their cellular fatty acids changes following short term acid and cold stresses

An implemented GC method to separate and quantify the cell cyclopropane fatty acids lactobacillic (C19cyc11) and dehydrosterculic (C19cyc9) was used to study the adaptive response to sublethal acid and cold stresses in Lactobacillus helveticus and Lactobacillus sanfranciscensis. The comparison of the composition of cellular fatty acids of the two strains and their changes after 2 h of stress exposure under micro-aerobic and anaerobic conditions indicated that the aerobic biosynthetic pathway for unsaturated fatty acids is prevalent in L. sanfranciscensis, while the anaerobic pathway is prevalent in L. helveticus. Indeed in the latter strain, in the presence of a source of oleic acid and under micro-aerobic conditions, C18:1n11 and its post-synthetic derivative C19cyc11 accounted for overall proportion ranging from 52 to 28% of the total FAs. On the other hand L. sanfranciscensis synthesizes by aerobic pathway C18:1n9 and transforms it to C19cyc9. However in this species the cumulative level of these two FAs did not exceed 30%. The relevant proportion of dodecanoic acid in the latter species suggests that carbon chain shortening is the principal strategy of L. sanfranciscensis to modulate fluidity or chemico-physical properties of the membranes.

Antibacterial activity of selected Cameroonian dietary spices ethno-medically used against strains of Mycobacterium tuberculosis

ETHNOPHARMACOLOGICAL RELEVANCE Tuberculosis (TB) is considered as a re-emerging disease and one of the most important public health problems worldwide. The use or (in most cases) misuse of existint anti-tuberculosis drugs over the years has led to an increasing prevalence of resistant strains, establishing an urgent need to search for new effective agents. Spices are largely used ethno-medically across Africa. AIM OF THE STUDY The present study aimed to evaluate the in vitro antimycobacterial activities of a total of 20 methanol crude extracts prepared from 20 Cameroonian dietary spices for their ability to inhibit the growth of or kill Mycobacterium tuberculosis strains H(37)Rv (ATCC 27294) and H(37)Ra (ATCC 25177). MATERIALS AND METHODS The antituberculosis screening was performed using the Microplate Alamar Blue Assay (MABA) method to determine the minimum inhibitory concentration (MIC) and the minimum mycobactericidal concentration (MBC). RESULTS Fifteen (15) plant extracts out of 20 showed varied levels of antimycobacterial activity against the strains M. tuberculosis H(37)Rv and H(37)Ra, with MICs in the range of 2.048-0.016 mg/ml. The extract of Echinops giganteus exhibited the most significant activity with a MIC value of 32 μg/ml and 16 μg/ml, respectively against H(37)Ra and H(37)Rv. To the best of our knowledge, the antimycobacterial activity of the tested spices has not been reported before and therefore our results can be evaluated as the first report about the antimycobacterial properties. CONCLUSIONS The results of this study suggest that Echinops giganteus and Piper guineense could be important sources of bactericidal compounds against M. tuberculosis and could probably be promising candidates that can be further investigated.

Characterization of Mexican Coriander (Eryngium foetidum) Essential Oil and Its Inactivation of Listeria monocytogenes In Vitro and during Mild Thermal Pasteurization of Pineapple Juice

The aim of this work was to characterize the essential oil (EO) of Eryngium foetidum (EfEO) and assess its activity toward Listeria monocytogenes in broth and during thermal inactivation of the pathogen in pineapple juice. In this respect, EfEO was chemically characterized, and its antilisteria potential in broth as a function of pH, cell load, and EfEO concentration was assessed through a central composite design. Furthermore, the inactivation kinetics of L. monocytogenes in the juice were assessed by combining EfEO and low pasteurization temperatures. A total of 81 compounds were identified from EfEO. The reduction of pH and cell load increased EO activity. The use of only 15 ppm of EfEO during pasteurization of pineapple juice at 60°C reduced the time required for a 4-log reduction in L. monocytogenes CFU/ml by 74.9% (i.e., from 8.5 to 2.1 min) compared with treatment without EfEO. It could be concluded that EfEO activity toward L. monocytogenes increases with the reduction of pH and that it can be used at sublethal concentrations in combination with low temperatures in pineapple juice pasteurization. This study demonstrates that EO-assisted pasteurization is a promising strategy for the reduction of thermal impact during juice production. EfEO is easily available and compatible with many juices and is thus promising for industrial application.

Antifungal properties of selected lactic acid bacteria and application in the biological control of ochratoxin A producing fungi during cocoa fermentation

Thirteen Lactic acid bacteria strains isolated from fermenting cocoa and seven reference strains were used in order to assess their antifungal properties towards three ochratoxin A (OTA) producing fungi (Aspergillus carbonarius, Aspergillus niger and Aspergillus ochraceus). Furthermore, two of the isolates strains (A19 and A21) identified as belonging to the genus of Pediococcus as well as Lactobacillus plantarum B4496, Lactobacillus brevis 207 and Lactobacillus sanfranciscensis BB12 showed interesting in vitro broad antifungal activities towards the three ochratoxin-producing fungi with inhibition percentages ranging from 15% to 66.7%. Treatment of cell-free supernatant at 100°C affected antifungal activity suggesting that the main compounds responsible for this activity were of proteic nature, and hence could be bacteriocins. Application of isolate A19 in cocoa fermentation as starter inhibited the growth of each of the OTA-producing species. At the end of fermentation in boxes inoculated with A19, A. niger was not detectable while A. carbonarius concentration was found to be 2 Log CFU/g of wet beans. The assessment of the ochratoxin produced during fermentation of cocoa inoculated with A. carbonarius indicated that the use of isolate A19 as starter could reduce their level of growth so as to have only a toxin production of 0.0012 ± 0.0005 μg/kg after 40 days of storage, while this was 2.45 ± 0.35 μg/kg of fermented and dried cocoa beans in the absence of A19. This work is a contribution for the application of biological control of OTA-producing fungi during cocoa production.

Possible Use of Wood Ash and Compost for Improving Acid Tropical Soils

Infertility of acid soils is a major limitation to crop production on highly weathered and leached soils throughout the world. The main characteristics of these soils are their low pH, low levels of organic matter, Ca, Mg, P, or Mo deficiency, Al or Mn toxicity, or both, and very low mineralization and nitrification rates. Lime is generally recommended to correct soil acidity, but lime is unaffordable for resource-poor farmers in the tropics. Many alternatives have been proposed, and among them products from organic waste materials, e.g., composts, have proven to be an efficient alternative to the use of lime. Wood ash is a potential source of trace elements, nutrients, and lime. Wood ash could be used as an additive to fertilizer, and wood ash admixture to organic wastes prior to composting is known to improve compost quality and may reduce the amount of compost required to raise the pH to suitable levels. Wood ash compost as a liming agent as a replacement for lime could potentially aid in remediating acidity and base deficiency as well as boosting the soil microbial pool in tropical agricultural soils.

First Insight into the Current Prevalence of Bovine Tuberculosis in Cattle Slaughtered in Cameroon: the Case of Main Abattoirs of Yaoundé and Douala

Aim: The aim of this study was to evaluate the current prevalence of bovine tuberculosis at Yaounde and Douala abattoirs. Study Design: Many investigations confirmed that bovine tuberculosis is prevalent in cattle destined for consumption in Cameroon but the magnitude and the distribution of animal tuberculosis in the country are unknown. Place and Duration of Study: Sampling was made during routine meat inspection, in the Yaounde and Douala abattoirs located in the Central and Littoral regions of Cameroon respectively. Sampling was successively carried out from November 2010 to April 2011. Sample processing (culture, acid-fast staining and spoligotyping) was made at

In vitro and in vivo anti-Helicobacter/Campylobacter activity of the aqueous extract of Enantia chlorantha.

The aqueous extract of Enantia chlorantha Oliver (Annonaceae) stem bark, a plant widely used in Cameroon for the traditional treatment of gastritis and stomach problems, was assessed for in vitro and in vivo anti-Helicobacter/Campylobacter properties using the well diffusion assay, agar dilution assay, and killing rate determination. The in vitro activity was dose-dependent, and the same antimicrobial parameters (MAQ = 0.63 mg; MIC = 0.39 mg/mL; MBC = 1.56 mg/mL; ET100 = 8 h) were obtained for both H. pylori and C. jejuni/coli. When the plasma active principle concentration equivalence was determined in vitro using plasma from rats exposed to a single dose (3000 mg/kg) of the extract, the peak absorption of E. chlorantha active principle against H. pylori occurred at 2 h. Plasma activity was nil 8 h after extract administration. The in vivo H. pylori eradication potency of the extract was assessed using mice infected with H. pylori. Antral mucus sample cultures from mice treated with E. chlorantha extract (500 and 1000 mg/kg for 3 days) did not yield any growth. The results suggest that in addition to its in vitro activity, E. chlorantha water extract also possesses in vivo antibiotic effects against H. pylori.

Circulating vaccine-derived polioviruses in the Extreme North region of Cameroon

BACKGROUND The World Health Organization (WHO) poliovirus eradication program includes careful surveillance of acute-flaccid paralysis (AFP) and mass and routine immunization with oral polio vaccine (OPV). In populations with low vaccine coverage, the live-attenuated Sabin strains, OPV types 1, 2 and 3, can evolve into virulent vaccine-derived polioviruses (VDPVs) and circulate in the community. Until recently, circulating VDPVs (cVDPVs) had not been reported in Cameroon despite the fact that VDPV2 outbreaks have occurred in nearby countries. OBJECTIVES This study aimed to characterize virus isolates from four AFP patients infected with cVDPV2 in the Extreme North region of Cameroon in 2013. STUDY DESIGN The complete VP1 region of the four VDPV strains was sequenced and the relationships with cVDPVs from neighboring countries were investigated. RESULTS All four patients were infected by cVDPV2 strains showing 1.2-2.0% nucleotide difference compared to the reference Sabin 2 VP1 sequence. Phylogenetic analysis indicated that the VDPV strains were genetically linked to cVDPV2 lineages of the recent Chad cVDPV2 outbreak. CONCLUSIONS The circulation of pathogenic VDPVs suggests that there are localized immunization gaps in some districts like Makary, Mada and Kolofata in Cameroon. To avoid poliomyelitis outbreaks in Cameroon, especially in the districts close to neighboring countries with ongoing cVDPV outbreaks, high polio vaccine coverage is essential.