Selected Yeast Isolates Research Articles

Selection of Pectinolytic Yeast from Liberica Green Coffee Beans (Coffea liberica)

Liberica coffee has an inferior quality when compared to arabica and robusta coffee. This flavour can be improved through a fermentation process involving indigenous microbes, one of which is a group of pectinolytic yeasts. Therefore, this study aimed to obtain yeast isolates with pectinolytic activity. Green bean samples were used for yeast isolation using YEPD agar media. Selected yeast isolates were screened for their pectinolytic activity semi-quantitatively using the well-diffusion method and quantitatively using the dinitrosalicylic acid (DNS) method. A total of six yeast isolates with different colony morphological characters were obtained and referred to as isolates Y1, Y2, Y3, Y4, Y5, and Y6. The isolates suspected to produce pectinase enzyme due to a clear zone around the well are Y2, Y3, Y4, and Y5. Y5 had the highest pectinolytic index, 022 and 0,73 on the second and fifth days of incubation, respectively. The four selected isolates were then screened quantitatively and showed that Y2 had the highest pectinase enzyme activity with a value of 12,66 ± 0,17 U/mL. The results showed that four yeast isolates from Liberica green coffee beans had pectinolytic activity with the highest enzyme activity found in Y2.

Selection of Starter from Decaying Oranges and Pineapple for Bioethanol Production

Screening of yeasts for bioethanol production is an important aspect of industrial microbiology and biotechnology. Optimal yeast nutrition also requires availability of nutrients allowing for growth and ethanol production and ability to withstand the increasing concentration of the medium during fermentation. This study seeks to use appropriate methods to isolate, characterize and identify yeasts isolates with essential attributes for bioethanol production. Microbiological and Physicochemical assessment of the isolated strains was carried out on yeast maintenance media for the determination of ethanol, temperature and salt tolerance ability, growth at different pH and temperature, chloramphenicol and nalidixic acid test, determination of killer toxins production capacity of yeast, nitrate and carbon assimilation and sugar fermentation tests were carried out to select the best starter for production.
 Fifteen yeasts were isolated belonging to the genera Saccharomyces, Candida, Rhodotorula, Kluvyreomyces, Trichosporon, Pichia. S. cerevisae and K. marxianus showed efficient physico-chemical attributes. Proximate analysis of fruits juice showed a moisture content between 81.83 – 86.37%, crude protein 1.33 – 2.00%, Ash 0.73 – 0.83%, carbohydrate 11.87 – 15.67% and Ether 0.1 – 0.5%. The total sugar ranged from 1.83 – 13.17, equal mixture of oranges and pineapple juice showed a sugar content of 15 which reduced during fermentation while the alcohol content increased. Organisms were able to tolerate a percentage of 4-30% ethanol content, tolerating 15% sodium chloride which is an index of osmotolerance. At higher concentration, growth reduced, organisms produced catalase, reduced nitrate and showed a variation in utilization of different sugars.
 At the end of the screening, S. cerevisiae and K. marxianus showed the best attribute essential for bioethanol production and were chosen as starters. The ability of the selected yeast isolates to produce Killer toxins against E. coli showed a negative result. Antibiotic sensitivity test was carried out on the selected yeast isolates using chloramphenicol and nalidixic and the two organisms were resistant to the antibiotics tested.
 The ability of the organisms to grow in changing environmental conditions and ethanol tolerance are attributes essential for production while Saccharomyces cerevisiae showed the highest attribute followed by Kluveromyces marxinus. This study concluded that Saccharomyces cerevisiae can be employed as starter in the industry for the production of bioethanol and in the conversion of agricultural waste to wealth.

Tannin-Tolerant Saccharomyces cerevisiae Isolated from Traditional Fermented Tea (Miang) of Northern Thailand and Its Feasible Applications

This study evaluated the ability of a yeast strain isolated from traditional fermented tea leaves (Camellia sinensis var. assamica), Miang from northern Thailand, to grow and produce ethanol in the presence of tannin. Among 43 Miang samples, 25 yeast isolates displayed gas-forming character in the presence of 1% (w/v) tannin, but only ML1-1 and ML1-2 isolates were confirmed as ethanol-producing yeast capable of tannin tolerance. These isolates were further identified to be Pichia occidentalis and Saccharomyces cerevisiae, respectively, based on D1/D2 domain sequence analysis. S. cerevisiae ML1-2 was selected for further studies and exhibited growth at 20–35 °C, pH 4–7, and tolerance to high sugar concentrations of up to 350 g/L. Supplementation of 1% (w/v) tannin had no effect on sugar utilization and ethanol production, while delayed sugar consumption and ethanol production were observed in the reference strain S. cerevisiae TISTR 5088. However, 5 and 10% (w/v) tannin showed inhibitory effects on the growth and ethanol production of the selected yeast isolates. During the fermentation under high tannin conditions derived by mixing Java plum fruit with ground seed, S. cerevisiae ML1-2 showed significant advantages in growth and enhanced the content of ethanol, polyphenols, tannin, and flavonoids compared to S. cerevisiae TISTR 5088. This indicated its potential for high-tannin substrate-based bioconversion for the production of either fuel ethanol or functional alcoholic beverages.

The synergistic effect of titanium dioxide nanoparticles and yeast isolated from fermented foods in reduction of aflatoxin B1.

The presence of aflatoxins in food products can lead to health risks in human societies. Therefore, in the present study, the effect of yeast strains isolated from fermented products and titanium dioxide nanoparticles (TiO2-NPs) was studied on aflatoxin reduction. Yeast strains were isolated from fermented products such as sweet fruits and dairy products and identified using biochemical, ascospore (testing by culture medium optimization V8 which is called V8NLF), and molecular methods. The probiotic activity of four selected yeasts was evaluated. Then, the effect of selected yeast isolates and TiO2-NPs on reducing aflatoxin B1 (AFB1) in the medium was studied by measuring AFB1 using ELISA and HPLC. The results of biochemical and molecular identification experiments indicate that the selected strain (Y1) is Saccharomyces cerevisiae. The selected strains showed good tolerance to different concentrations of bile salt, pH, and NaCl, indicating appropriate probiotic activity. It also showed antimicrobial activity against Escherichia coli, Shigella dysenteriae, and Salmonella typhimurium. Selected strain and TiO2-NPs showed AFB1 reducing activity in the medium and when combined, showed synergistic effects in reducing AFB1. TiO2-NPs in combination with selected yeast strains have a high ability to remove AFB1 from the medium and, therefore, can be used for future studies.

Screening Ethanol-Producing Yeast Origin from Pineapple Honey Ananas comosus (L.) Merr var Quenn

The availability of fossil-based fuels will gradually decrease while the amount required increases. This has prompted research to find alternative energy sources, including bioethanol. Bioethanol, as an alternative energy source, can be used as a transportation fuel better than fossil-based fuels because ethanol has a high octane number, laminar velocity and heat of vaporisation. Meanwhile, the level of carbon and hydrocarbon emissions is low so it can increase combustion efficiency in vehicles. In addition, the use of bioethanol as fuel is environmentally friendly and renewable. Ethanol can be produced through a fermentation process using ethanol-producing yeast. Pineapple honey is known for its high sugar and other nutrient content, so it is supposed that many types of yeast can grow well in it. This study aims to isolation and screening of bioethanol-producing yeast from Pineapple Honey. This study was carried out by yeast isolation method, primary yeast screening, secondary yeast screening, and characterisation of selected yeast isolates. Data on ethanol production by yeast isolates were analysed by ANOVA with α=0.05 using the R studio program. This primary isolation and screening phase found eight yeast isolates capable of fermenting glucose and producing acid and gas in the test medium. Test ethanol production in DPE medium with 18% glucose content on all isolates showed that all isolates could produce ethanol with a range of 4.20-10.35%. Isolates of IK4 showed the highest ethanol production ability (10.35%) (p<0.5%) in significant contrast to the other seven isolates. Based on macroscopic and microscopic morphological characterisations, IKM 4 isolates show similarities to the genus Saccharomyces
 Keywords: ethanol, pineapple, yeasts

In Vitro Characterization and Identification of Potential Probiotic Yeasts Isolated from Fermented Dairy and Non-Dairy Food Products.

This study is about the isolation of yeast from fermented dairy and non-dairy products as well as the characterization of their survival in in vitro digestion conditions and tolerance to bile salts. Promising strains were selected to further investigate their probiotic properties, including cell surface properties (autoaggregation, hydrophobicity and coaggregation), physiological properties (adhesion to the HT-29 cell line and cholesterol lowering), antimicrobial activities, bile salt hydrolysis, exopolysaccharide (EPS) producing capability, heat resistance and resistance to six antibiotics. The selected yeast isolates demonstrated remarkable survivability in an acidic environment. The reduction caused by in vitro digestion conditions ranged from 0.7 to 2.1 Log10. Bile salt tolerance increased with the extension in the incubation period, which ranged from 69.2% to 91.1% after 24 h. The ability of the 12 selected isolates to remove cholesterol varied from 41.6% to 96.5%, and all yeast strains exhibited a capability to hydrolyse screened bile salts. All the selected isolates exhibited heat resistance, hydrophobicity, strong coaggregation, autoaggregation after 24 h, robust antimicrobial activity and EPS production. The ability to adhere to the HT-29 cell line was within an average of 6.3 Log10 CFU/mL after 2 h. Based on ITS/5.8S ribosomal DNA sequencing, 12 yeast isolates were identified as 1 strain for each Candida albicans and Saccharomyces cerevisiae and 10 strains for Pichia kudriavzevii.

Reduction of the Fusarium Mycotoxins: Deoxynivalenol, Nivalenol and Zearalenone by Selected Non-Conventional Yeast Strains in Wheat Grains and Bread.

Mycotoxins, toxic secondary metabolites produced by fungi, are important contaminants in food and agricultural industries around the world. These toxins have a multidirectional toxic effect on living organisms, causing damage to the kidneys and liver, and disrupting the functions of the digestive tract and the immune system. In recent years, much attention has been paid to the biological control of pathogens and the mycotoxins they produce. In this study, selected yeasts were used to reduce the occurrence of deoxynivalenol (DON), nivalenol (NIV), and zearalenone (ZEA) produced by Fusarium culmorum, F. graminearum, and F. poae on wheat grain and bread. In a laboratory experiment, an effective reduction in the content of DON, NIV, and ZEA was observed in bread prepared by baking with the addition of an inoculum of the test yeast, ranging from 16.4% to 33.4%, 18.5% to 36.2% and 14.3% to 35.4%, respectively. These results indicate that the selected yeast isolates can be used in practice as efficient mycotoxin decontamination agents in the food industry.

Investigation of probiotic potential of yeasts isolated from sourdoughs from different regions of Turkey

Abstract In this study, 14 yeast cultures from 62 isolates from traditional sourdoughs collected from 6 different regions of Turkey were selected by FT-IR identification and characterised to reveal their probiotic properties. Four yeast strains were genotypically identified and compared with FT-IR identification. In all analyses, it was observed that mostly Saccaromyces cerevisiae strain exhibited high hydrophobicity, auto-aggregation feature, and all yeast isolates in this study showed tolerance to 0.3%, even salt concentration. In addition, all yeast strains were susceptible to anti-yeasts agents, although they were resistant to all antibiotics used in the study. All selected yeast isolates exhibited high antimicrobial activity against the Staphylococcus aureus. In conclusion, this study investigated the potential probiotic properties of yeast strains isolated from sourdough.

The growth rate of inulinolytic yeast isolates from yum (Pachyrhizus erosus L.) and their inulinase production capability

Inulinase (EC. 3.2.1.7) is a hydrolytic enzyme that hydrolyze inulin into fructose. This enzyme was very important in the high fructose syrup industry. Microbes producing inulinase can be isolated from various sources, among others from various types of tuber that contain inulin. The isolation of inulinolytic yeast from yum (Pachyrhizus erosus L.) obtained two potential isolates. Research on the growth rate of the two potential yeast isolates in producing inulinase is necessary to understand the pattern of the yeast growth and its ability to produce inulinase. The parameters observed in this study were specific growth rate (µ), generation time (g) and inulinase activity of two selected yeast isolates B2 and B3. The results showed that the specific growth rate (µ) of B2 isolate was 0.11 hours with generation time (g) 6.12 hours, whereas for B3 isolates the specific growth rate (µ ) was 0.21 hour and generation time 3.29 hours. The inulinase activity from yeast isolates B2 and B3 were 0.294 IU and 0.235 IU, respectively.

In Vitro Evaluation of Probiotic Properties of Indigenous Yeasts Isolated from Nigerian Fermented Food Products

Probiotics are living microbial food supplements which beneficially affect the host by improving the intestinal microbial balance. Before an organism can be designated as probiotic there are certain criteria that must be fulfilled. These include acid and bile tolerance, antimicrobial activity, ability to co-aggregate, hydrophobicity etc. One hundred and eighty one indigenous yeast isolates recovered from various fermented food products of Nigeria were characterized and grouped using phenotypic methods. Forty two selected yeast isolates were identified using molecular method which involved sequencing of D1 and D2 domain of the large subunit of ribosomal DNA. Then nine indigenous Saccharomyces cerevisiae were evaluated for their probiotic characteristics such as acid and bile tolerance, transit in simulated gastric and intestinal juices, autoaggregation and hydrophobicity. Saccharomyces cerevisiae SC10 was included as a positive control. The S. cerevisiae were able to grow in the presence of acidic medium with pH as low as 2 and 3. In the minimum inhibitory concentration test with 0-1% ox bile, all the S. cerevisiae tested were able to grow. The growth for 3% bile tolerance test ranged from 4.81 to 5.35 log cfu/ml. These isolates were able to survive in simulated gastro-intestinal transit. All the yeast isolates exhibited bile salt deconjugation activity against sodium glycodeoxycholate and were able to grow in the presence of all other bile salts investigated. Autoaggregation ability (an adhesive property) of the indigenous yeast isolates ranged from 89.80% for S. cerevisiae BK19 to 99.91% for S. cerevisiae OB03. The native yeast isolates also exhibited high percentage hydrophobicity, another adhesive property of probiotics. The values obtained ranged from 31.62 to 83.45% for isolates AG23A and OB 17. These observations indicate that the native yeast isolates from Nigerian fermented foods have the potential of being use as probiotics for making functional foods.

Screening of Indigenous Yeast From Different Ecological Region of Kathmandu Valley and Its Application in Wine Production

Objectives: The aim of the study was to isolate and screen the potent yeast from the air for implementing new yeast in wine fermentation.
 Methods: In this study, 35 air samples collected in sterile grape juice in glass jar and left over for four days exposure for the growth of yeast from different locations around the Kathmandu Valley. Yeasts were screened by culturing on selective Ethanol Sulfite Agar (ESA) media at 30°C for 2-3 days in Microbiology Lab of Pinnacle College. Yeast isolates were characterized based on colony morphology, microscopic characteristics, Fermentative capacity, Hydrogen sulfide production. Selected yeast isolates were subjected to ethanol fermentation and tested for alcohol tolerance capacity. Wine quality was assessed by sensory evaluation.
 Results: Of 35 samples, only 20 yeast isolates were isolated. Among these isolates, the variation in colony characteristics along with oval and ellipsoidal microscopic appearance was observed. All the isolates were able to ferment major sugars such as glucose, fructose and sucrose, but few could not ferment galactose and maltose, while none-fermented lactose and xylose. Here, isolates showing no H2S (L29, L34) and mild H2S producer (isolate L31) were subjected to ethanol fermentation. Also, Comparative analysis was made by using commercial standard wine yeast (STAN). Rapid fermentation of grape juice with initial 21 0Brix was observed in L31 isolate, which produced 12.99% v/v alcohol with titratable acidity (TA) 5.25 g/L, followed by L29 strain with 11.99%v/v alcohol and 4.5 g/L TA which were higher than STAN (10.99% alcohol). These isolates specified as Ethanol tolerance up to 13%v/v, while none of them were able to grow at 15% v/v ethanol concentration and 45°C temperature. However, significant growth was observed at pH 3 along with sugar tolerance capacity at 30 0Brix. The wine produced by these isolates was found to be remarkably different among each other. While the sensory analysis of wine led to isolate L31 being congenial to tasters.
 Conclusion: L31 isolate was found to be efficient and advantageous for wine production indicating its industrial application.

Probiotic potential of Saccharomyces cerevisiae and Kluyveromyces marxianus isolated from West African spontaneously fermented cereal and milk products.

The yeast species Saccharomyces cerevisiae and Kluyveromyces marxianus are associated with fermentation of West African indigenous foods. The aim of this study was to characterize potential probiotic properties of S. cerevisiae and K. marxianus isolates from the West African milk products lait caillé and nunu and a cereal-based product mawè. The strains (14 in total) were identified by 26S rRNA gene sequencing and characterized for survival at gastrointestinal stress (bile salts and low pH) and adhesion to Caco-2 intestinal epithelial cells. Selected yeast isolates were tested for their effect on the transepithelial electrical resistance (TEER), using the intestinal epithelial cell line Caco-2 and for maintenance of intracellular pH (pHi ) during perfusion with gastrointestinal pH (3.5 and 6.5). All tested yeasts were able to grow in bile salts in a strain-dependent manner, exhibiting a maximum specific growth rate (μmax ) of 0.58-1.50 h-1 . At pH 2.5, slow growth was observed for the isolates from mawè (μmax of 0.06-0.80 h-1 ), whereas growth of yeasts from other sources was mostly inhibited. Yeast adhesion to Caco-2 cells was strain specific and varied between 8.0% and 36.2%. Selected strains of S. cerevisiae and K. marxianus were able to maintain the pHi homeostasis at gastrointestinal pH and to increase TEER across the Caco-2 monolayers, indicating their potential to improve intestinal barrier functions. Based on overall results, strains of K. marxianus and S. cerevisiae from mawè exhibited the highest probiotic potential and might be recommended for further development as starter cultures in West African fermented products.

Isolation, Identification and Heavy Metal Biosorption Assessment of Yeast Isolates Indigenous to Abandoned Mine Sites of Itogon Benguet, Philippines

Water samples collected from abandoned mining sites in Itogon, Benguet, Philippines were screened for metal resistant microorganisms, in particular yeasts that will be used to remove toxic metals such as Zn, Cu, Pb, Cr and Ni from aqueous media. Among the five yeast strains selected and five heavy metals tested, Nodulisporium sp. exhibited the highest removal efficiency of 80% and biosorption capacity of 56.7 mg g-1 for Pb. This was based on the model equation for each metal that was generated to derive optimum response for removal efficiency. The metal accumulation potential for all selected yeast isolates was generally higher at the lower initial metal concentration of 25 mg L-1, indicating rapid metal absorbing ability of the isolate and that adsorption sites in the biomass are taking up available metal ions more quickly. An increased removal capability was observed when the best isolate was applied in a semi-continuous treatment system thru an Aerobic Cascading Filter Bed Baffled Reactor (ACFBBR). The reactor design including the packing material remarkably enhanced the contact between the yeast biomass and Pb contaminated wastewater resulting in a much greater biosorption capacity of 170.14 mg g-1 as compared to the biosorption of 56.7 mg g-1 achieved during the batch adsorption experiment.

GREEN SYNTHESIS AND CHARACTERIZATION OF MARINE YEAST-MEDIATED SILVER AND ZINC OXIDE NANOPARTICLES AND ASSESSMENT OF THEIR ANTIOXIDANT ACTIVITY

Objective: The present study focuses on the synthesis of silver and zinc oxide (ZnO) nanoparticles from marine yeasts, isolated from the sediments of the Bay of Bengal, Bakkhali coast, West Bengal, and India.Methods: The marine sediment samples were diluted through serial diution and cultured onto yeast malt agar medium by the spread plate method. The selected yeast isolates were screened for the biosynthesis of silver and ZnO nanoparticles. Characterization of both the nanoparticles was done by applying ultraviolet (UV)-visible spectroscopy, atomic force microscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy.Results: A total of five marine yeasts isolates were able to synthesize silver and ZnO nanoparticles as evidence of the color change. Optical density was measured in UV-spectrometer at different time interval for the conformation of production of nanoparticles. The size of silver nanoparticle was 31.78 nm and ZnO nanoparticle was 86.27 nm. The synthesized nanoparticles are then used for antioxidant assays.Conclusions: We are concluding that marine yeast isolates SAG1 and SAG2 both are potential marine yeast isolates which can synthesize both the silver and ZnO nanoparticles. They also showed good antioxidant activity.

ISOLATION AND CHARACTERIZATION OF POTENTIAL PROBIOTIC YEASTS FROM DIFFERENT SOURCES

objective The main objective of the present study is to isolate yeasts from different environmental sources to investigate their potential probiotic characteristics.Methods Appropriate in vitro assays has been conducted to examine their probiotic potentiality, such as acid and bile salt tolerance, temperature resistance, stimulated GIT tolerance, cell adhesion and cholesterol removal. All the yeast isolates were tested under in vitro conditions.Results In the present study, 20 yeast species have been isolated from different sources, screened and their desirable probiotic properties viz. pH tolerance, bile salt tolerance and thermo-tolerance have been evaluated. Screened yeast isolates treated with gastric juices showed increased survival rate above 60%. A further in vitro study investigates cholesterol removal and it showed increased cholesterol removal rate up to 92%. Exopolysaccharide production was estimated for selected yeast isolates and applications are under investigation.Conclusion Among 20 yeast isolates, 5 isolates showed increased growth under stress tolerance. It can be concluded that the screened yeast isolates LM, MR, GOI, GII2 and WI can serve as promising probiotics in various fields of food industry.Key words: Acid tolerance; bile tolerance, cholesterol removal, probiotics, yeast.

ISOLASI DAN IDENTIFIKASI KHAMIR PENGHASIL ASAM INDOL ASETAT DARI RHIZOSFER ANGGREK TANAH Pecteilis susannae (L.) Rafin

The objectives of this study were to isolate and identify yeast producing Indole-3-acetic acid from rhizosphere of terrestrial orchid Pecteilis susannae (L.) Rafin. This research commenced with the isolation of yeasts from rhizosphere of orchid P. susannae using Yeast Malt Agar (YMA) medium. Yeast isolates were selected based on growth experiment on Glucose Peptone Broth (GPB) supplemented with 200 µg/mL L-tryptophan. The IAA concentration was determined colorimetrically on spectrophotometer (OD530 nm) with Salkowsky’s reagent added to supernatant of yeast culture. Biomass (OD600 nm) and IAA production (OD530 nm) measured every 24 hours for 4 days. Identification of selected isolates carried out through macroscopic, microscopic, and biochemical properties. The results revealed that 29 isolates of yeast had been successfully isolated from rhizosphere of terrestrial orchid P. susannae (L.) Rafin, and only four isolates (K2, U5, A3 and A1) showed their capability to grow and produce high concentration of IAA on GPB. The fourth selected yeast isolates were identified as strain Saccharomyces sp.1 (K2), Saccharomyces sp.2 (U5), Cryptococcus sp.1 (A3), and Candida sp.1 (A1). Further evaluation of the selected rhizosphere yeast isolated producing IAA is necessary to be carried out to explore their potency as a source of hormone to promote plant growth.

Microbial antagonists control postharvest black rot of pineapple fruit

Incidence and severity of black rot (Chalara paradoxa (De Seyn.) Sacc.) of pineapple fruit were evaluated on fruit harvested every 2 weeks for 14 months. Rainfall did not play a major role in black rot incidence and severity. Total microbial counts on the fruit were correlated to rainfall in the month of harvest. Epiphytic antagonist microorganisms were apparently present on the pineapple fruit, as evidenced by the reduction of black rot severity when fruit were treated with pineapple fruit wash water. The most frequently isolated yeasts were able to inhibit Ceratocystis paradoxa growth in vitro and the most inhibitory isolated was Pichia guilliermondii. A mixture of five selected yeast isolates halved black rot severity compared to the control. Pichia and the yeast mixture reduced spore germination, germ tube length, and dry weight of C. paradoxa. The use of Pichia or the yeast mixture was comparable with current industry practice of holding fruit at a low temperature (8–10 °C) and fungicide. Combining the isolated Pichia or the yeast mixture with a half rate of fungicide resulted in complete control of black rot comparable to control achieved with a commercial rate of recommended fungicide. The mode of action by Pichia appeared to be competition for space and nutrients, while for the yeast mixture, mode of action appeared to be competition for space. Another possibility would be a growth inhibitor though no evidence was found to support this possibility.

The use of Niger seed agar to screen for Candida dubliniensis in the clinical microbiology laboratory

Candida dubliniensis is a recently described pathogenic yeast that is closely related to C. albicans. The germ tube test is used routinely in diagnostic laboratories for the identification of C. albicans, and C. dubliniensis may also produce germ tubes under the same conditions. We evaluated a previously described method for differentiating between the two species using Niger seed agar (Staib agar). The aim was to find a useful, user-friendly and cost-effective method for use in diagnostic work. C. albicans produces only yeast cells on this medium after 24 h at 37°C, while C. dubliniensis produces extensive hyphal and pseudohyphal growth that is easily observed. Of 495 yeasts isolated in, or sent for identification to, a diagnostic mycology laboratory 9 isolates (1.8%) were found to be C. dubliniensis. The method was found to be valuable for screening yeasts before proceeding to further identification if positive for hyphal/pseudohyphal growth on Niger seed agar. This method is therefore suitable for the screening of selected yeast isolates in order to identity C. dubliniensis and will further our understanding of the clinical importance of this species.

Evaluation of CHROMagar Candida for rapid screening of clinical specimens for Candida species

CHROMagar Candida is a new differential culture medium that allows selective isolation of yeasts and simultaneously identifies colonies of Candida albicans, Candida glabrata, Candida tropicalis and Candida krusei. We evaluated this medium and compared it with a reference medium, Sabouraud glucose agar, for the presumptive identification of yeast species isolated directly on the medium from 1150 clinical specimens. A total of 731 specimens showed no growth, 299 isolates (70.2%) showed growth to the same extent on both media. Forty mixed cultures were detected on both media. More than one isolate was detected in 30 of the tested specimens on either CHROMagar (26 specimens) or Sabouraud glucose agar (four specimens). We found a sensitivity of 98.8% and a specificity of 100% for C. albicans, 66.7% and 99.8% for C. tropicalis, 100% and 100% for C. krusei, and 98% and 95.7% for C. glabrata. Regarding these results, CHROMagar Candida is recommended as a useful isolation medium capable of the presumptive identification of yeasts and better detection of mixed cultures in clinical specimens.

The relationship between soil copper content and copper resistance in yeast of an ultisol in midwestern Nigeria.

Yeast isolates were obtained from the brewer's stock of the Guinness brewery in Benin City, midwestern Nigeria, and from local sources such as mango and sugar cane. The fruits were exposed to the immediate soil environment in eleven selected sites in the Ugbowo and Ikpoba Hill areas of Benin City, Edo State of midwestern Nigeria. A total of twenty-seven yeast isolates were obtained. Fourteen isolates were identified as Saccharomyces cerevisiae and 13 as S. carlsbergensis. Analysis of resistance to copper sulphate revealed that the two brewer's yeast isolates were resistant to 3.5 mM and 4.2 mM CuSO4, respectively, while the local yeasts were resistant to higher concentrations ranging from 6.5 to 16.5 mM. The percentage copper sulphate resistance of yeast isolates obtained from Mangifera inidica ranged from 52.4 to 73.8%, while the percentage copper sulphate resistance of yeast isolates obtained from Saccharum officinarum ranged from 51.8 to 62.6%. The two brewer's yeast isolates (BY2 and BY4) had a percentage CuSO4 resistance of 32.4 and 38.5%, respectively. Comparison of soil copper concentration and copper resistance levels in selected yeast isolates indicated that the soil copper concentrations generally influenced the ability of yeasts to resist copper.