General Biology

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Browsing General Biology by Author "Abegaz Berhanu (PhD)"

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    Aerobic Heterotrophic Bacterial Flor1ff one of Shalla Hot Springs
    (Addis Ababa University, 1991-06) Kibret Mulugeta; Abegaz Berhanu (PhD)
    Four sites in one of the hot springs of Shalla were selected for the study. The water from the sites merge to form a stream lqhich forms a temperature gradient. In this sttldy four' media were compared for the cuI ti vation and isolation of aerobic heterotrophic bacteria. The pH of the hot spring was 8.7 with a temperature of 96-560C. The formulated media were adjusted to pH values of 7.0-13.0. However,high counts of bacteria (lxl03-7xl01 cfu/ml) was only registered when the pH lqas adjusted between 8.0 and 9.0. A medium containing normal concentration of Trypton Soya Agar (TSA) was effective in supporting the growth of bacteria than a medium containing onequarter strength of TSA or supplement of tl'ace minerals. Replacing trace minerals ld th hot spring water improved the total number of bacteria growing and also the number of isolates. Thermophiles were numerous (lxl03-7xl01 cfu/ml) than thermotolerants (2xl02-2xlOI cfu/ml) at all si tes. The population of Bacillus brevis, Bacillus sphaericus, Bacillus stearothermophilus and Hicrococcus sp. was found to be low at lOlqer environmental temperatures than at higher environmental temperatures. In the course of this study a total of 44 microorganisms were isolated and characterized. Twenty nine were identified. to the species level and were found to be members of genus Bacillus. Three isolates were Gr~n-positive cocci identified to the genus level - Micrococcus. The remaining 12 isolates were either Gram-positive, filamentous or non-filamentous rods which need a detailed biochemical analysis for identification. To identify if any of the isolates may have industrial applications, they were checked for production of amylase and protease. Fifteen of the isolates produced protease, 18 amylase and eleven produced both amylase and protease.
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    Assesment of Conorrhoea and Syphilis in Patients Attending Clinics For Sexually Transmitted Diseases in Addis Ababa
    (Addis Ababa University, 1993-05) Meless Hailu; Abegaz Berhanu (PhD); Gebreyohanne Afeworki (PhD)
    In this study a total of 754 individuals were involved. The study population was divided into 3 ~roups: a/200 (27%) pre~nant women, b/l05 (14%) students, and c/449 (59%) patients attending clinics for STDs. Blood samples collected from all members of the study population, were examined for syphilitic infection. A seroprevalence of 13%, 11.2% and 21.6% were found among pregnant "homen, students and STD patients by both RPR and TPHA respectively. The validity of RPR as a screening test was determined using sensitivity, specificity, percentage of positive predictive value and efficiency. Strong positives and positives by the RPR test can be considered as positive for syphilis. Only weak positives require retesting. Endocervical and urethral (male) discharge samples, collected from 233 STD patients in addition to the blood samples, were examined for the presence of Neisseria I{onorrhoeae. The organism was isolated from 68 (29.2%) sub.i ects. Among the isolates, PPNC strains comprised 48 (70%) of the samples. PPNC strains Were resistant to penicillin (100%), ampicillin (96%). bactrim (91%) and kanamycin (22%). Of the nonPPNG strains 25% were resistant to pencillin. 20% to ampicillin, 40% to bactrim and 15% to kanmycin. Both groups were, however. sensitive to erythromycin, tetracycline, chloramphenicol and ceftriaxone.
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    Lactic Acid Bacteria of Fermentlng Tef Dough and Fermented Kocho and Their Inhibitory Effect on Certain Food -Borne Pathogens or Spoilage Organisms
    (Addis Ababa University, 1992-06) Nigatu Ayele; Abegaz Berhanu (PhD)
    Lactic acid fermentation is the commonest and inexpensive traditional household food manufacturing method. "Injera" and "Kocho" are two major Ethiopian lactic acid fermented foods. Injera is a pancake-like bread baked from "Tef" (Eragrostis tef) or other cereals' flour fermented for two to three days. Kocho is a product of "Ensete" plant (Ensete ventricosum) pitfermented for few weeks to several months. It is then baked and consumed Members of the Enterobacteriaceae family initiate tef dough fermentation. They lower the pH from about 6.3 to 4.7. Lactic acid bacteria(LAB)- Leuconostoc, Lactobacillus, streptococcus and Pediococcus species succeed and further lower the pH to or below 4.00. Species of Bacillus degrade the starch. Kocho fermentation was found to be initiated by Leuconostoc spp. and the other LAB follow to lower the pH. A properly fermented kocho has a pH of 4-4.5 and contains a large number of LAB. Yeasts and molds were also common at lower pH values in both foods. Lactic acid bacteria were known to prevent food-borne pathogens and spoilage bacteria from growing in fermenting foods using their antibiotic metabolites. Nevertheless, inhibitory effect of fermenting tef or fermented kocho on such undesirable organisms was not known. Hence, in this study effect of these two acidic foods and also their components in broth on certain disease-causing and spoilage bacteria was determined. The results showed that tef dough began inhibition after 30 h of fermentation (pH 4.7). This period had maximum nutrient availability and best inhibitory activity among all fermentation periods in tef. Fermented kocho (pH 4.3) was inhibitory except for B. cereus. It also inhibited best at lower concentrations but higher pH values among all agents employed. Spent media from the LAB inhibited growth of most test bacteria where Streptococcus spp. did the best amongst the group. The pH decline as a result of introducing acetic and/or lactic acid to broth was much higher than anyone of the other agents. Therefore, the inhibitory activity of the foods or the LAB was due to antibiotics elaborated-by the LAB and some species of Bacillus. Heat treatment of tef dough or kocho extract also seemed to have a promotion effect on antimicrobial potency of the extracts. Sporeforming bacteria, yeasts and molds survived baking temperature, but much lowered to low populations. Furthermore, tef dough fermented upto properly fermented kocho (to about pH 30-48 4.3) h (pH 4. 1-4 • 7 ) and both baked before consumption were found as safe foods from food-borne infections and spoilage bacteria. Further studies on these two foods and their micro flora were recommended.
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    Prevalencel of Imstitic Staphylococci Str eptococci and coliflorm (Escherichia Coli) in Threee Dairy Farhs in and Around Addis Ababa
    (Addis Ababa University, 1988-06) Tulu Girma; Abegaz Berhanu (PhD)
    Prevalence of mastitic staphylococci, streptococci & coliform species in foremilk samples of apparently healthy lactating cows was studied in 3 dairy farms. One hundred & twenty apparently healthy lactating cows were randomly selected on the basis of lactation numbers. These were 40 from Debre Zeit, 40 from Repi & 40 from Kumbi dairy farms. Pooled foremilk samples \~ere co11ected from the teats of each lactating cO\~ & totally 120 foremilk samples were collected & analysed from the 3 farms. The total mesophilic aerobic bacterial, streptococcal & staphylococcal counts & the bacterial counts of Staphylococcus & Streptococcus species were estimated using different kinds of media. The susceptibilities of 55 isolates of mastitic staphylococcal & streptococcal strains to 11 antibiotics was determined using the standard agar disc diffusion technique. The total mesophilic aerobic bacterial counts was highly variable & ranged from hundreds to mi11ions in a11 of the dairy farms. The high total mesophilic aerobic bacterial counts greater than or equal to 1 x 105 colony forming units I mi11iliter were mainly associated with high numbers of streptococcal counts. Staphylococci were regularly isolated in all foremilk samples, however, their contribution to increases in the total mesophilic aerobic bacterial count was not as significant as that of rd ' streptococci. At the 3 & subsequent lactations, the number of co\~s that had total mesophilic aerobic bacterial counts'greater than or equal to 2xl04 colony forming units/milliliter increased at Kumbi & Repi farms. At the Debre Zeit farm, with increases in lactation numbers the number of cows that had greater than or equal to lxlO 5 colony forming units/milliliter was high.Five hundred & thirty five isolates were biochemically tested from the 120 samples. Of these 312 belonged to Staphylococcus, 215 belonged to Streptococcus, 6 belonged to Micrococcus & 2 belonged to coliform. Five species & 2 subspecies of staphylococci, 7 species of streptococci & 1 coliform species were identified. Among mastitic staphylococci, Staphylococcus epidermidis was the most prevalent and was isolated from 80.8% of the foremilk samples, followed by Staphylococcus aureu~ (20%), Staphylococcus hyi~ subsp. chromogenes (12.5%), Staphylococcus hyicus subsp. hyicus (5.8%). Similarly, other Staphylococcus species were also isolated in different proportions: Staphylococcus simulans (6.7%), Staphylococcus xylosus (4.2%), Staphllococcus intermedius (0.83%) & Staphylococcus hominis/Staphylococcus w~rneri / Staphylococcus haemolyticus group (6.7%). Of the mastitic streptococcal strains, Streptococcus bovis was the most prevalent &was isolated from 40.8% of the lactating cows sampled, followed·by Streptococcus uberis (15.8%), Streptococcus dysagalactiae (14.2%), Streptococcus agalactiae (9.2%), Streptococcus faecalis (5%), Streptococcus sp. G (5.8%) & Streptococcus infrequens (0.8%). Other streptococcal strains were also isolated. Streptococcus lactis lias detected in 0.8% of the samples. Generally the frequency of isolation for Streptococcus uberis, Streptococcus dysagalactiae, Streptococcus agalactiae & Staphylococcus aureus was high during the latter lactation numbers (3, 4 & 5). Escherichia coli was not common in the herds & was detected in 1.7% of the foremilk samples from one herd only. Among 30 isolates of staphylococcal strains tested, 26.7% lIere resistant to penicillin & tetracycline. All the staphylococcal strainsliere sensitive to erythromycin, oxacillin, cephalothin, chloramphenicol, kanamycin, gentamycin, streptomycin, clindamycin & vancomycin. Of 25 isolates of streptococcal strains, resistance to oxacillin, tetracycline, kanamycin, gentamycin, streptomycin was sholin by 8, 23, 8 16 & 40% of the iso1ate~. respectively. All the streptococcal strains were sensitive to penicillin, erythromycin, cephalothin, c1indamycin, vancomycin & chloramphenicol.