Home About us Contact
|
Home About us Contact | ||
|
|
||
Dominant Strains (dominant + strain)
Selected AbstractsCoexistence of a sulphate-reducing Desulfovibrio species and the dehalorespiring Desulfitobacterium frappieri TCE1 in defined chemostat cultures grown with various combinations of sulphate and tetrachloroetheneENVIRONMENTAL MICROBIOLOGY, Issue 2 2001Oliver Drzyzga A two-member co-culture consisting of the dehalorespiring Desulfitobacterium frappieri TCE1 and the sulphate-reducing Desulfovibrio sp. strain SULF1 was obtained via anaerobic enrichment from soil contaminated with tetrachloroethene (PCE). In this co-culture, PCE dechlorination to cis -dichloroethene was due to the activity of the dehalorespiring bacterium only. Chemostat experiments with lactate as the primary electron donor for both strains along with varying sulphate and PCE concentrations showed that the sulphate-reducing strain outnumbered the dehalogenating strain at relatively high ratios of sulphate/PCE. Stable co-cultures with both organisms present at similar cell densities were observed when both electron acceptors were supplied in the reservoir medium in nearly equimolar amounts. In the presence of low sulphate/PCE ratios, the Desulfitobacterium sp. became the numerically dominant strain within the chemostat co-culture. Surprisingly, in the absence of sulphate, strain SULF1 did not disappear completely from the co-culture despite the fact that there was no electron acceptor provided with the medium to be used by this sulphate reducer. Therefore, we propose a syntrophic association between the sulphate-reducing and the dehalorespiring bacteria via interspecies hydrogen transfer. The sulphate reducer was able to sustain growth in the chemostat co-culture by fermenting lactate and using the dehalogenating bacterium as a ,biological electron acceptor'. This is the first report describing growth of a sulphate-reducing bacterium in a defined two-member continuous culture by syntrophically coupling the electron and hydrogen transfer to a dehalorespiring bacterium. [source] The diversity of Listeria monocytogenes strains from 10 Icelandic sheep farmsJOURNAL OF APPLIED MICROBIOLOGY, Issue 5 2004K.B. Gudmundsdottir Abstract Aims:, The purpose of this study was to examine the diversity of Listeria monocytogenes strains from healthy sheep, winter feed and environment of sheep farms in Iceland. Methods and Results:, A total of 104 L. monocytogenes isolates from animals, winter feed and environment on 10 Icelandic sheep farms were compared by serotyping, ribotyping, and pulsed-field gel electrophoresis with ApaI and AscI. The isolates were divided into 24 genotypes, all identified as serovars 1/2a, 1/2b, or 4b. Nine genotypes were detected on more than one farm. On three of the farms there seemed to be a dominant strain of L. monocytogenes. Isolates from incidents of listeriosis in animals occurring on two of the farms belonged to the genotype most commonly found on the particular farm. Nine of the 24 genotypes found on the sheep farms have been associated with disease in animals and/or humans elsewhere in Iceland. Conclusions:, Certain strains of L. monocytogenes seem to be widely distributed on Icelandic sheep farms. On some farms there appears to be a dominant strain of L. monocytogenes. Incidents of listeriosis in animals may tend to be associated with strains commonly found on the farm. Significance and Impact of the Study:, This study demonstrates the diversity of L. monocytogenes present in healthy sheep and their environment. [source] Microbiota analysis of Caspian Sea yogurt, a ropy fermented milk circulated in JapanANIMAL SCIENCE JOURNAL, Issue 2 2009Kenji UCHIDA ABSTRACT We analyzed the microbiota of domestic ropy fermented milk, Caspian Sea yogurt (or ,kasupikai yohguruto' in Japanese), circulated in Japan. We collected six varieties from five localities. Lactococcus (L) lactis ssp. cremoris was isolated from all samples as the dominant strain at levels of 108,109 CFU/g. We show this strain produces an extracellular polysaccharide (EPS) that causes the unique characteristic viscosity of the product. From analysis of the RAPD pattern of 60 bacterial isolates from the six samples, we found that 59 strains from a total of 60 isolates were identical and produced this viscosity. Furthermore, PFGE analysis of representative strains from each sample indicated that the isolates could be classified into four subgroups. This suggests these L. lactis ssp. cremoris strains found in Caspian Sea yogurt may have been slightly mutated during subculture in Japan. In addition, Lactobacillus (L.) sakei ssp. sakei were isolated from three samples; L. plantarum, Gluconoacetobacter sacchari and Acetobacter aceti were isolated from two samples; and L. paracasei, L. kefiri, Leuconostoc (Leu.) mesenteroides were isolated from one sample. [source] Saccharomyces cerevisiae wine yeast populations in a cold region in Argentinean Patagonia.JOURNAL OF APPLIED MICROBIOLOGY, Issue 4 2002A study at different fermentation scales Aims: To study the diversity and dynamics of indigenous Saccharomyces wine populations during Malbec spontaneous fermentation, a representative Patagonian red wine, at both industrial and laboratory scale. Methods and Results: Two molecular techniques, including restriction fragment length polymorphism of mitochondrial (mt) DNA and polymorphism of amplified , interspersed element sequences, were used for characterization of indigenous yeasts at strain level. The mtDNA restriction patterns showed the major discriminative power; however, by combining the two molecular approaches it was possible to distinguish a larger number of strains and, therefore, draw more representative conclusions about yeast diversity. Although a great diversity of wild Saccharomyces cerevisiae strains was observed, only nine represented more than half of the total Saccharomyces yeast biota analysed; five of these were common and took over the Malbec must fermentation in both vinifications. Conclusions: Many different indigenous S. cerevisiae strains were identified; nevertheless, the dominant strains in both industrial and laboratory vinification processes were just a few and the same. Significance and Impact of the Study: Small-scale fermentation appears to be a valuable tool in winemaking, one especially helpful in evaluating microbiological aspects of as well as possible interactions between inoculated selected strains and native strains. [source] Discrepancies between the phenotypic and genotypic characterization of Lactococcus lactis cheese isolatesLETTERS IN APPLIED MICROBIOLOGY, Issue 6 2006M. De La Plaza Abstract Aims:, The use of randomly amplified polymorphic DNA (RAPD)-PCR fingerprinting and plasmid profiles to determine at the strain level, the similarity of Lactococcus lactis isolates obtained during sampling of traditional cheeses and to verify its correspondence to the selected phenotypic characteristics. Methods and Results:, A total of 45 L. lactis isolates were genotypically analysed by RAPD-PCR fingerprinting and plasmid patterns. Phenotypic traits used to compare strains were proteolytic, acidifying, aminotransferase (aromatic and branched chain aminotransferase) and , -ketoisovalerate decarboxylase (Kivd) activities. The results show that 23 isolates could be grouped in clusters that exhibited 100% identity in both their RAPD and plasmid patterns, indicating the probable isolation of dominant strains during the cheese sampling process. However, there were phenotypic differences between isolates within the same cluster that included the loss of relevant technological properties such as proteinase activity and acidifying capacity or high variation in their amino acid converting enzyme activities. Likewise, the analysis of a specific attribute, Kivd activity, indicated that 7 of 15 isolates showed no detectable activity despite the presence of the encoding (kivd) gene. Conclusion:, Phenotypic differences found between genotypically similar strains of L. lactis strains could be linked to differences in enzymatic expression. Significance and Impact of the Study:, Phenotypic analysis of L. lactis isolates should be considered when selecting strains with new cheese flavour forming capabilities. [source] Saccharomyces cerevisiae biodiversity in spontaneous commercial fermentations of grape musts with ,adequate' and ,inadequate' assimilable-nitrogen contentLETTERS IN APPLIED MICROBIOLOGY, Issue 1 2003L. Granchi Abstract Aim: To evaluate whether intraspecific diversity of Saccharomyces cerevisiae in wine fermentations is affected by initial assimilable-nitrogen content. Methods and Results:Saccharomyces cerevisiae isolates from two spontaneous commercial wine fermentations started with adequate and inadequate nitrogen amounts were characterized by mitochondrial DNA restriction analysis. Several strains occurred in each fermentation, two strains, but not the same ones, being predominant at frequencies of about 30%. No significant differences were detected by comparing the biodiversity indices of the two fermentations. Cluster analysis demonstrated that the strain distribution was independent of nitrogen content, the two pairs of closely related dominant strains grouping into clusters at low similarity. Conclusions: The genetic variability of S. cerevisiae in wine fermentations seemed not to depend on the nitrogen availabilty in musts. Significance and Impact of the Study: Nitrogen content did not affect the genetic diversity but may have induced a ,selection effect' on S. cerevisiae strains dominating wine fermentations, with possible consequences on wine properties. [source] Drug-resistant tuberculosis: Past, present, futureRESPIROLOGY, Issue 3 2010Chen-Yuan CHIANG ABSTRACT In a population of Mycobacterium tuberculosis, random chromosomal mutation that results in genetic resistance to anti-tuberculosis (TB) drugs occurs at a relatively low frequency. Anti-TB drugs impose selection pressure so that mycobacterial mutants gradually outnumber susceptible bacilli and emerge as the dominant strains. Resistance to two or more anti-TB drugs represents cumulative results of sequential mutation. The fourth report on global anti-TB drug resistance provides the latest data on the extent of such problem in the world. The median prevalence of multi-drug-resistant TB (MDR-TB) in new TB cases was 1.6%, and in previously treated TB cases 11.7%. Of the half a million MDR-TB cases estimated to have emerged in 2006, 50% were in China and India. The optimal duration of any given combination of anti-TB drugs for treatment of MDR- and extensively drug-resistant TB (XDR-TB) has not been defined in controlled clinical trials. Standardized treatment may be feasible for MDR-TB patients not previously treated with second-line drugs, but a different strategy needs to be applied in the treatment of MDR-TB patients who have received second-line drugs before. Unfortunately, the reliability of drug susceptibility testing of most second-line anti-TB drugs is still questionable. Drug-resistant TB is not necessarily less virulent. Findings from modelling exercise warned that if MDR-TB case detection and treatment rates increase to the World Health Organization target of 70%, without simultaneously increasing MDR-TB cure rates, XDR-TB prevalence could increase exponentially. Prevention of development of drug resistance must be accorded the top priority in the era of MDR-/XDR-TB. [source] | ||||||||||