Department of Biology

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Browsing Department of Biology by Author "A.Gashe Berhanu (PhD)"

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    Amylase Production by Bacillus Species Isolated from Fermenting Tef and Kocho
    (Addis Ababa University, 1993-06) Fikru Lealem; A.Gashe Berhanu (PhD)
    Amylase producing bacterial strains associated with kocho and tef fermentation were isolated. The strain from fermenting kocho was identified as Bacillus subtilis while the strain from fermenting tef was identified as Bacillus licheniformis. Conditions for the productions of amylases were investigated. The bacterial strains secreted amylase into a liquid medium containing 1% soluble starch. When starch was replaced by disaccharide and monosaccharide, amylase production was reduced. Amylase production was higher with unfermented kocho compared to other native straches. Of the nitrogen sources tested, the greatest growth and amylase production were obtained with 0.5% peptone. The most appropriate metal salt for amylase production was found to be 0.02% MgS04. 7H20· Amylase was produced over a wide pH range (4.5 to 9.5 for Bacillus subtilis and 5 to 10 for Bacillus licheniformis with the maximum activity between pH 6 and 8. Amylase produci ton was greater at temperatures from 18 to 24 (room temperature) at 72 hour of cultivation. The amylases which were found to be extracellular were optimally active at 400 C and pH 5.6. Bacillus licheniformis T 31 amylase was also active at pH 8. The amylases of both organisms retained 100% activities for 1 hour at 60oC. These enzymes were stable in the pH range of 5.5-8.5. MgS04,CaC12 and BaC12 were found to stimulate amylase activity. The amylases were stable in 0.5 M NaCl with 64% -78% of their original activities being. retained after 24h. In addition to amylase, Bacillus subtilis also produced pullulanse. Using chromatographic analysis, glucose, maltose and maltotriose were detected as products of hydrolysis .
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    Ear Infections : Etiologic Agents Isolated from Patients Visiting Two Hospitals in Addis Ababa and their Susceptibilities to Antimicrobials
    (Addis Ababa University, 1994-06) Asmelash Tsehaye; A.Gashe Berhanu (PhD)
    Infonnation pertaining to the etiologic agents responsible for ear infection are absent in Ethiopia. Therefore, this study was initiated to identify the causative agents together with their sensitivities to antimicrobials. Microbiological samples were collected from 389 ears of 355 patients attending the E. N. T. clinics of two Hospitals (Addis Ababa). Four hundred and twenty (98.4%) bacterial strains and 7 (1.6%) fungi were isolated. Gram-negative bacteria were most frequently encountered. Of these 60.4% were members of the family Enterobacteriaceae. Of all the isolates, Proteu spp. (25.5%), Pseudomonas aentginosa (13.1%), Staphylococcus aureus (12.7%), and Klebsiella spp. (9%) were common. All bacterial strains were tested for their susceptibility to antibiotics following a standardized method. Ampicillin, tetracyclline, penicillin, and cephalothin were the least effective antimicrobials in their respective order. Pseudomonas aentginosa was the predominantly resistant organism to several antibiotics (all strains were resistant to one or more antibiotics, 93 % resistant to four or more antibiotics, and 71 % resistant to six or more antibiotics). Strains of Proteus mirabilis were resistant to tetracyclline in 97% and Staphylococcus aureus was resistant to penicillin G in 82 %. This study has showen the polymicrobial etiology of ear infections with P. mirabilis being the dominating organism. Gentamycin and carbenicillin were among the effective agents agaist most of the bacterial isolates.
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    Lignocellulosics for Cellulase and Fungal Biomass Production
    (Addis Ababa University, 1994-06) Kebede Amaha; A.Gashe Berhanu (PhD)
    The effects of teff straw (Eragrostis tett) or corn stalk (Zea mays) on cellulase and biomass production by Trichoderma sp. BDCC-1, Penicillium sp. BDCC-2 and Cladosporium sp. BDCC-3 were studied and compared with those of cellulosic substrates. In Trichoderma sp. both teff straw and corn stalk were found to be superior to filter paper for inducing B-GDase as well as for improving fungal biomass production. CMCase and FPase productions were, however, lower on these substrates than they were on filter paper. In Cladosporium sp. teff straw and corn stalk were found to be better than CMC for inducing both CMCase and FPase. However, no B-GDase activity was detected when only these lignocellulosics were used in the media. It's biomass production was also relatively lower on these substrates as compared to that it produced on 1% CMC. Penicillium sp. produced relatively large amounts of biomass, CMCase, FPase and B-GDase on 2% corn stalk as compared to those it produced on 2% CMC. Lye- and 2% NaOH-pretreatments were generally effective in improving biomass production in the test fungi. But their effect on CMCase, FPase and B-GDase production was not similar for the three fungi. There was, however, no significant difference between Lye- and 2% NaOH-pretreatment in their performance on biomass and cellulase production. 65-80% of the polysaccharides of alkali-treated teff straw and corn stalk were hydrolysed to reducing sugars in 72 hours using culture filtrate of Trichoderma sp. BDCC-1 which consisted of 1.7 IU/ml of FPase. The hydrolysates were found to support good growth of Candida utilis BDCC-25 (16.7-24.8mg dry wt./100ml) and Saccharomyces cerevisiae BDCC-24 (14.6-15.6mg dry wt./100ml). The yields of yeast biomass produced on these hydrolysates were higher than those produced on D-glucose (0.02%). It was, therefore, concluded that teff straw and corn stalk could provide cheap substrates for mold biomass production as well as for single-cell protein production if they are pretreated with Lye.
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    A Preliminary Survey of Salmonellae in Cattle Slaughtered at Tile Addis Ababa and Dire Dai'ia Abattoirs
    (Addis Ababa University, 1983-06) Ayalew Sahlu; A.Gashe Berhanu (PhD)
    In an attempt to assess the incidence of Salmonellae in apparently healthy cattle slaughtered at the Addis Ababa and Dire Dawa abattoirs, a total of 1571 organ samples were collected, out of which 971 were obtained from the former and 600 from the latter. The 971 samples from Addis Ababa abattoirs included 315 spleen, 303 mesenteric lymph node and 353 small intestine samples and these yielded 16 (5.1%), 10 (3.3%) and 8 (2.3:') strains of Salmonellae, respectively. The remaining 600 samples collected from cattle slaughtered at the Dire Dawa abattoir were 200 spleen, 200 mesenteric lymph node and 200 small intestine samples and from these 14 (7/1,),3(1.5%) and 8 (4%) strains of Salmonellae \~ere isolated, respec tively. From this finding the incidence of Salmonellae in the cattle slaughtered at the Addis Ababa and Dire Dawa abattoirs was found to be 5.1% and 7% respectively. No significant difference was observed ( p~ 0.05). Serogrouping of the 59 Salmonella isolates recovered from the 1571 samples showed that, \~i th 24 (40.7%) strains, group D was the most frequent serogroup, to be followed by C1 with 13 (22%) strains, B with 11 (18.6%), C 2 with 6 (10.2')1,) and E with 5 (8.5%). A comparision of the relative frequency of the serogroups in the samples from the two abattoirs also revealed that the most frequent sero['.roup Vias D. The relative incidence of the rest of the serogroups was, however, found to be variable. Of the two culture media used viz., Desoxycholate Citrate Agar and Brilliant Green l>1acConkey Agar, the former was found to be slightly superior in supporting the growth of more strains, both in number ffild type, of Salmonellae encountered in this work
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    Reaction Studies of a Select Group of Sorghuh Lines to Le; F Streak Disease (Xanthohonas Holcicola)
    (Addis Ababa University, 1984-05) Andenow Yeshi; A.Gashe Berhanu (PhD)
    From infected sorghum leaves ~ough~ from three different place, 17 yellol'l coloured bacterial coldmies were isolated. After having conducted hypersensitivi.y, morphological, physiological and biochemical tests, including pathogenicity test using sorghum line W8 1297 as a susceptible host, only one isolate was found to be Xanthomonas ~lc~cola. the causal organism of bacterial streak disease of sorghum. Six different inoculation techniques were compared to achieve an effective method of screening together with pathogenicity test. The isolated organism induced typical symptomatic response when the rub and spray method of inoculation was used. Using the rub and spray method, 31 sorghum lines, 7 from highland (about 2000 metres), 8 from intermediate (1600-1900 metres), 15 from lowland (800_1600 metres) and sorghum WS 1297 as s control were examined for resistance to bacterial streak disease caused by .!.holcicola. High resistance to the disease was sho"m by sorghum lines 80 K 6056, Gambella 1107, 80 ~ 6088, 81 ESIP 21, 81 ESIP 25, Melkamash 79, ETS 0601, ETS 4946. Of these 75% are from lowland and 25% are from highland groups. Sorghum lines IS 9294, IS 9302, IS 9379, .81 ESIP 29, Dobbs, IS 8686, Muyra white,IS 9923 nnd'thll control \~S 1297 showed susceptible reactions. Of the susceptible sorghum lines 62,5% are from intermediate, 25% from lowland and 12.5% from highland groups. The reaction of the other lines range from moderately resistant to moderately susceptible.
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    Thermoduric & Psychrophilic Bacteria from Milk Obtained from the Addis Ababa Dairy Development -U Enterprise
    (Addis Ababa University, 1988-06) Mahari Tadesse; A.Gashe Berhanu (PhD)
    An attempt has been made in this study to isolate A identify thermoduric A psychropivilic bacteria, which are the most serious spoilage organisms, from milk obtained from tin? Addis Ababa Oairv Hovelpoment Enterprise (AADDE ). An effort was also made to trace the sources A origin of these organisms so as to prevent or at least reduce their access into milk A hence increase the shelf -life of the pasteurized milk A milk products. The standard plate count { SPG) ranged between 4 X 10? A 3 X 109 bactoria/ml for raw milk, between 6 X 10'* A 3 X 10^ for plant pasteurized milk A between 3 X 103 A 2.5 X for laboratory pasteurized milk. The high standard plate count for the plant pasteurized milk, as compared to that of the laboratory pasteurized milk, has been found to bo due to the ability of many organisms to gain access to the pasteurized milk as post pasteurization contaminants. Psychrophilic bacteria wore the most dominant organisms in both raw (98.1%) A plant pasteurized (53.0%) milk samples. Laboratory pasteurized milk, on the other hand, contained predominantly thermoduric bacte. During the course of study, bacteria belonging to 14 genera were isolated, the most dominant being: Streptococcus ( 27% ) , Staphylococcus (19,5%), micrococcus (13.9%) , Bacillus ( 12.9%) A Arthrobactor (11.3%),. Out of the 185 representative isolates identified 50% were cocci A 40% rods. As many as 16 species of bacteria belonging to 9 genera were isolated from raw milk, while 20 species of bacteria belonging to 14 gonora wore isolatcd from tho plant pasteurized milk. This indicated that bacteria , other than those found in raw milk have been introduced into the pasteurized milk as post pasteurization contaminants from the bulk tanks, fillers A their pipelines and the plastic bags that contain pasteurized milk. This fact has also been supported by data from keeping quality tests performed at different sampling sites. Sodium hydroxide ( dnOH ) A sodium carbonate ( NaC'03) , chemicals regularly used for rinsing A disinfecting utensils at the Addis Ababa hairy development Enterprise , were found to be ineffective in inactivating bacteria at concentrations as high as 1:100 at 50-90 minutes holding time. Other disinfectants tested such as Savlon , A Chlorox, on the other hand, were found to i> effective in eliminating the same group of bacteria at lower concentrations ( 3 :HOO ) at 15-30 minutes holding time. Based on this study , therefore, recommendations are made by which the Dairy Plant can improve milk handling A processing conditions A produce milk A milk products with improved shelf -life.