Cellulase production and activity in a species ofCladosporium

ACladosporium species produced large amounts of cellulase enzyme components when grown in shake-culture with medium containing carboxymethylcellulose. There was significantly less activity when Avicel, filter paper or cotton were used as substrates. KNO₃ was better than NH₄Cl or urea for the production of cellulase. Tween 80 at 0.1% (w/v) increased the production of cellulase by 1.5 to 4.5-fold. All the cellulase components were optimally active in the assay at pH 5.0 and 60°C.     

Invasion of tissue culture cells by diarrhoeagenic strains of Escherichia coli which lack the enteroinvasive inv gene

Abstract Invasive Escherichia coli strains of certain serotypes invade by the same mechanism as the Shigella sp. It has been proposed that invasion of epithelial cells by EPEC strains may also occur; this is a previously overlooked property. In the present study E. coli strains isolated from patients with diarrhoea or ulcerative colitis, lacking the inv plasmid mediating classical invasion, but hybridizing with probes for different adhesins, were analyzed for their ability to invade HeLa and Caco-2 cells. The majority of strains invaded Caco-2 cells to a higher extent than HeLa cells. Adhesion to Caco-2 cells was a prerequisite for subsequent invasion of the cells but EAF, eae , EAgg and other known virulence factors were not sufficient to mediate invasion. In 8/9 E. coli strains invasion was enhanced after growth under iron restriction. Growth during anaerobic conditions did not influence subsequent invasion by E. coli strains whereas 6/9 strains had their invasive ability significantly decreased after growth in the presence of 1% glucose. The invasive process was inhibited by mannose but not by lactose, fucose or galactose. Our data indicate that strains of E. coli may invade Caco-2 cells by novel mechanisms which require adhesion to the cells but which differ from those of Salmonella sp., Yersinia sp., Shigella sp. and classical enteroinvasive E. coli .     

Effect of heat treatment on the antimicrobial properties of tef dough,injera, kocho and aradisame and the fate of selected pathogens

A known population from each of a 24h culture of Bacillus cereus, Pseudomonas aeruginosa, Salmonella spp., Shigella spp., Klebsiella spp. and Staphylococcus aureus was inoculated into tef flour–water/kocho–water mixtures in screw-capped flasks and allowed to ferment for 30h at room temperature (18–21°C). The flasks were then heat-treated. Cultures of the test bacteria were inoculated into tubes containing graded volumes of 30-h-fermented tef dough/kocho extracts which had been heat-treated at 45, 61 and 80°C in assay broth containing aqueous extracts from injera and aradisame. They were incubated for 24h at 32°C and optical densities determined. Populations of the major indigenous bacteria, yeasts and moulds in fermented tef dough (30h), kocho samples, injera and aradisame were determined from other control portions of the same samples. Higher temperature (80°C) heat-treatment promoted the inhibitory potential of extracts from doughs of both foods as compared with lower temperature heat-treatments (45 and 61°C). Asporogenous test bacteria were affected more than the spore-formers. Better efficacy of extracts from injera and aradisame suggested improved antimicrobial properties of the baked products than in doughs. Heat of baking inactivated all vegetative cells although spores of B.cereus, the yeasts and moulds survived the heat (100°C) applied for 5min. The c.f.u./g of food for B. cereus was below the disease-causing level (0.5×101 and 1.5×103, in injera and aradisame, respectively). Actual baking temperatures in homes are higher than the ones used here; if post-baking contamination is minimized or prevented, the products would be microbiologically safe with respect to the asporogenous pathogens when served fresh. Further studies on aflatoxins and improved storage conditions for kocho are recommended.     

Effect of heat treatment on the antimicrobial properties of tef dough, injera, kocho and aradisame and the fate of selected pathogens

A known population from each of a 24h culture of Bacillus cereus, Pseudomonas aeruginosa, Salmonella spp., Shigella spp., Klebsiella spp. and Staphylococcus aureus was inoculated into tef flour–water/kocho–water mixtures in screw-capped flasks and allowed to ferment for 30h at room temperature (18–21°C). The flasks were then heat-treated. Cultures of the test bacteria were inoculated into tubes containing graded volumes of 30-h-fermented tef dough/kocho extracts which had been heat-treated at 45, 61 and 80°C in assay broth containing aqueous extracts from injera and aradisame. They were incubated for 24h at 32°C and optical densities determined. Populations of the major indigenous bacteria, yeasts and moulds in fermented tef dough (30h), kocho samples, injera and aradisame were determined from other control portions of the same samples. Higher temperature (80°C) heat-treatment promoted the inhibitory potential of extracts from doughs of both foods as compared with lower temperature heat-treatments (45 and 61°C). Asporogenous test bacteria were affected more than the spore-formers. Better efficacy of extracts from injera and aradisame suggested improved antimicrobial properties of the baked products than in doughs. Heat of baking inactivated all vegetative cells although spores of B.cereus, the yeasts and moulds survived the heat (100°C) applied for 5min. The c.f.u./g of food for B. cereus was below the disease-causing level (0.5×101 and 1.5×103, in injera and aradisame, respectively). Actual baking temperatures in homes are higher than the ones used here; if post-baking contamination is minimized or prevented, the products would be microbiologically safe with respect to the asporogenous pathogens when served fresh. Further studies on aflatoxins and improved storage conditions for kocho are recommended.     

Viral diversity and diversification of major non-structural genes vif, vpr, vpu, tat exon 1 and rev exon 1 during primary HIV-1 subtype C infection

To assess the level of intra-patient diversity and evolution of HIV-1C non-structural genes in primary infection, viral quasispecies obtained by single genome amplification (SGA) at multiple sampling timepoints up to 500 days post-seroconversion (p/s) were analyzed. The mean intra-patient diversity was 0.11% (95% CI; 0.02 to 0.20) for vif, 0.23% (95% CI; 0.08 to 0.38) for vpr, 0.35% (95% CI; -0.05 to 0.75) for vpu, 0.18% (95% CI; 0.01 to 0.35) for tat exon 1 and 0.30% (95% CI; 0.02 to 0.58) for rev exon 1 during the time period 0 to 90 days p/s. The intra-patient diversity increased gradually in all non-structural genes over the first year of HIV-1 infection, which was evident from the vif mean intra-patient diversity of 0.46% (95% CI; 0.28 to 0.64), vpr 0.44% (95% CI; 0.24 to 0.64), vpu 0.84% (95% CI; 0.55 to 1.13), tat exon 1 0.35% (95% CI; 0.14 to 0.56 ) and rev exon 1 0.42% (95% CI; 0.18 to 0.66) during the time period of 181 to 500 days p/s. There was a statistically significant increase in viral diversity for vif (p = 0.013) and vpu (p = 0.002). No associations between levels of viral diversity within the non-structural genes and HIV-1 RNA load during primary infection were found. The study details the dynamics of the non-structural viral genes during the early stages of HIV-1C infection.     

Production of alkaline protease by an alkaliphilic bacteria isolated from an alkaline soda lake

A new alkaliphilic strain of Microbacterium producing an alkaline protease was isolated from an alkaline soda lake in Ethiopia. High level of protease activity was produced in the presence of glucose and sucrose as carbon sources. The optimum temperature and pH for activity were 65°C and 9.5-11.5 respectively. Above 50°C, Ca²⁺ was required for enzyme activity and stability. At 55 and 60°C it retained 100 and 85% of its original activity respectively after 1 h incubation. The enzyme was stable over the pH range of 5-12. This revised version was published online in November 2006 with corrections to the Cover Date.     

Production of alkaline xylanase by an alkaliphilic Bacillus sp. isolated from an alkalinesoda lake

An alkaline xylanase-producing alkaliphilic Bacillus sp. AR-009 was isolated from analkaline soda lake in Ethiopia. The enzyme was optimally active at pH 9 and was stable over abroad pH range. The optimum temperature for xylanase activity, assayed at pH 9, was60°–65°C. Measured at pH 8 and 9, the enzyme had good stability at 55° and60°C. At both pH values, over 80% of its original activity was retained after heating for2·5 h at 55°C. At 60°C, the enzyme maintained 63% of its original activity after2·5 h incubation while at pH 9 it retained 54% of its original activity after 1 h heating. Theseproperties qualify the enzyme to be novel and potentially important for application in someindustrial processes.     

Amylase production by a Gram-positive bacterium isolated from fermenting tef (Eragrostis tef)

Bacillus sp. A-001, which produced large amounts of amylase, was isolated from fermenting tef ( Eragrostis tef ) on tryptone soya agar supplemented with 1% starch. The organism grew between pH 4.5 and 10.5 with an optimum at 7–7.5. Growth occurred between 20 and 55°C but the optimum was about 35–40°C. At optimum medium pH (7.5) and a temperature of 35°C the organism entered the stationary phase after about 72 h and amylase production was at its highest (9.6 units ml^-1) at this time. Enzyme activity was optimal at pH 5.5 and 40°C and showed good thermal stability; it required 110 min to lose 50% of its activity at 70°C. The enzyme hydrolysed native starch (flour from tef, corn and kocho) to various oligosaccharides, including maltotriose, maltose and glucose.     

Spoilage organisms of kocho

Summary Ensette (Ensette ventricosum) is one of the leading staple crops in Ethiopia andc. 5 to 6 million people depend directly on it as their main source of food. Emphasis in being given to this plant because it is fairly drought resistant. Kocho, an acidic fermented starchy product, is derived from pulverized ensette pseudostems and tubers. The acidic product, once removed from fermentation pits, becomes easily contaminated and spoilt by micro-organisms and, as a consequence of their activities, a substantial amount of the product is thrown away. Prior knowledge of the spoilage organisms is essential before shelf life of the food can be improved; hence, this research was conducted to identify the most common spoilage organisms of kocho. Isolation, biochemical characterization and naming of organisms were performed following standard microbiological procedures. Results indicate that the food is easily attacked by fungi, of whichPenicillium sp. stands out as the most prominent;Trichoderma sp. andChaetomium sp. were also abundant.Aspergillus sp. andFusarium sp. were also isolated occasionally. Of the bacterial species,Leuconostoc sp.,Pseudomonas sp.,Bacillus sp. andErwinia sp. were isolated from a slimy sample of ocho. Yeasts were also found in association with slimy ocho. Whether the attack on the food was of fungal or bacterial origin, discoloration of the product was a common occurence. The principal organisms responsible for kocho spoilage have been identified and ways of preventing or delaying their activities is being studied.

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Resumen Uno de los cultivos más importantes de Etiopia es el ensette (Ensette ventricosum), ya que representa la principal fuente de alimentos para cerca de 6 millones de personas. Su cultivo está adquiriendo mucha importancia debido a que es una planta resistente a la sequía. Mediante la fermentación de tubérculos y pseudotallos de ensette pulverizados se obtiene el kocho, que es un alimento farináceo de carácter ácido. Este producto, una vez extraído de las cubas de fermentación, se contamina muy facilmente con distintos microorganismos que lo inutilizan para su consumo; perdiéndose con ello una parte importante de la producción. El estudio de los microorganismos causantes de esta destrucción del kocho es esencial para poder aumentar el periodo de conservación de este derivado. El objectivo de este trabajo ha sido la identificatión de dichos microorganismos. Los resultados obtenidos indican que el kocho es atacado muy facilmente por distintos hongos entre los cualesPenicillium sp. ha sido el más frecuente,Trichoderma sp. yChaetomium sp. tambien han sido abundantes, aíslandose ocasionalmente cepas deFusarium sp. yAspergillus sp. A partir de una muestra de kocho de consistencia viscosa se han aíslado las siguientes especies bacterianas:Leuconostoc sp.,Bacillus sp.,Pseudomonas sp., yErwinia sp.; de otra muestra de aspecto similar se han aíslado tambíen varias levaduras. Tanto si el ataque al alimento era de origen bacteriano o fúngico se producía una decoloración del producto como característica común. Una vez se han indentificado los principales organismos responsables de la degeneración del kocho se están estudiando sistemas que permitan, evitar o retrasar sus actividades.

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Résumé La banane d'Abyssinie ou ensette (Ensette ventricosum) est une des plus importantes productions vivrières d'Ethiopie, où elle constitue la principale ressource alimentaire d'environ 5 à 6 millions d'habitants. Du fait de sa bonne résistance à la sécheresse, cette plante mérite un intérêt tout particulier. Le kocho, qui est un produit de fermentation amylacé et acide, est obtenu à partir de pousses et de fruits d'ensette pulvérisés. Après avoir été recueilli dans les récipients de fermentation, le produit acide est souvent contaminé et altéré par des microorganismes, ce qui aboutit à la perte de quantités importantes. Afin d'améliorer la conservation du kocho, il est essentiel de connaître les micro-organismes contaminants. Ceux-ci ont été isolés, caractérisés biochimiquement et identifiés par les méthodes microbiologiques classiques. Les résultats ont montré que le kocho est aisément attaqué par des champignons, parmi lesquels les plus importants sont des espèces dePenicillium. Trichoderma sp. etChaetomium sp. sonts eux aussi abondants. Des espèces d'Aspergillus et deFusarium ont été isolées occasionellement Parmi les bactéries, des souches deLeuconostoc sp.,Pseudomonas sp.,Bacillus sp. etErwinia sp. ont été isolées à patir d'échantillons visqueux de kocho. Cette forme d'altération contient également des levures. Qu'elles soient d'origine fungique ou bactérienne, les altérations se manifestent par un changement de coloration du produit. Les principaux organismes responsables de la détérioration du kocho ont été identifiés, et les moyens pour prévenir leurs activités sont en cours d'étude.

     

The effect of fermentation on the growth and survival ofSalmonella typhimurium,Staphylococcus aureus,Bacillus cereus andPseudomonas aeruginosa in fermenting tef (Eragrostis tef)

Summary Growth ofSalmonella typhimurium, Staphylococcus aureus, Bacillus cereus andPseudomonas aeruginosa was inhibited when the pH of fermenting tef approached 5.0, 5.0, 5.5 and 5.0, respectively. However the test organisms grew in far more acidic conditions in broth than in fermenting tef and this is due to antimicrobial substance(s) being produced by some of the lactic acid bacteria. Except forBacillus cereus spores, all the test organisms were heat-inactivated during the baking process of the final tef injera.

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Effet de la fermentation sur la croissance et la survie de Salmonella typhimurium, Staphylococcus aureus, Bacillus cereus et Pseudomonas aeruginosa dans le tef (Eragrostis tef) en fermentation

Résumé La croissance deSalmonella typhimurium, deStaphylococcus aureus, deBacillus cereus et dePseudomonas aeruginosa est inhibée lorsque les pH du tef en fermentation approchent respectivement 5:0, 5.0, 5.5 et 5.0. Toutefois, les organismes tests croissent dans des conditiones bien plus acides que dans le tef en fermentation. Ceci est dû à des substances antimicrobiennes produites par certaines bactéries lactiques. A l'exception des spores deBacillus cereus, tous les organismes tests sont inactivés par la chaleur durant le processus de cuisson.