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1.
The mechanism of resistance to gentamicin and tobramycin in a clinical isolate ofAcinetobacter baumannii, in which aminoglycoside-modifying enzymes were not detected, was investigated. For increase of the resistance gene product, DNA prepared from theA. baumannii isolate was cloned into pUC18 and introduced intoEscherichia coli by transformation. Gentamicin-resistant transformants were screened for aminoglycoside-modifying enzymes. This approach identified two genes encoding AAC(3) and AAD(2) activity, respectively. To determine whether both genes are expressed in the hostAcinetobacter strain, we extracted total cellular RNA from this strain, and Northern blots were hybridized with the cloned AAC(3) and AAD(2) structural genes. mRNA transcribed from the AAC(3) gene alone was detected. This shows that cloning a functional resistance gene is not sufficient in itself to investigate mechanisms of resistance in bacterial strains without detectable aminoglycoside-modifying activity. Furthermore, this study suggests a potential limitation of antibiotic resistance gene probes for studying mechanisms of resistance. 相似文献
2.
Abstract A thermophilic Lactobacillus , isolate VB183, was tested for comparative glucose and pentose utilization. The possible adverse effect of high concentrations of metabolic end products on cell yield was lessened or eliminated by using low substrate concentrations. Possible growth due to intracellular reserve material, was counteracted by starving the cells for 90 min before being used as inoculant. Isolate VB183 exhibited a higher growth rate on glucose (μ= 1.08 h−1 ) than on ribose (μ= 0.76 h−1 ). L. salivarius was included as a pentose non-fermenting control and showed no significant difference between growth on basal medium with and without ribose. VB183 was also found to utilize l (+)-arabinose but not d (−)-arabinose, stressing the importance of the isomer of the sugars tested. 相似文献
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4.
G. J. Steyn 《Cryobiology》1993,30(6)
Cryoprotective agents were evaluated to find the optimal concentration of the cryoprotectant and most suitable combination of solution and cryoprotectant. A cryoprotective agent composed of 4% glucose and 9% glycerol yielded the best results. It was established that the optimal freezing rate is dependent on the composition of the cryoprotective agent. Maximal survival of catfish spermatozoa (60%) occurs at 5°C min-1 and faster and slower freezing rates result in poor survival or no survival at all. Incorporation of an isothermal holding period into the freezing rate led to remarkable increase (20-30%) in sperm survival when Me2SO was present in the cryoprotective agent. Cryoprotective agents containing glucose also showed improved survival when a three phase freezing rate was used. These results lead to the conclusion that the presence of an isothermal holding period in the freezing rate is beneficial for the cryoprotective action of Me2SO and glucose. 相似文献
5.
Cloning and expression in Escherichia coli of a recA homologue from Mycobacterium tuberculosis. 总被引:1,自引:0,他引:1
A 3.8 kb PstI fragment of Mycobacterium tuberculosis was cloned in a recA-deleted Escherichia coli by selecting transformants with increased EMS resistance. The cloned fragment restored homologous recombination in Hfr crosses and conferred resistance to long wave (302 nm) but not short wave (254 nm) UV light. E. coli containing the 3.8 kb PstI fragment produced a 38-40 kDa protein which cross-reacted with antibodies raised against the E. coli RecA protein. The cloned DNA thus probably encodes a RecA homologue. 相似文献
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7.
Production of sterigmatocystin by Aspergillus versicolor and Bipolaris sorokiniana on semisynthetic liquid and solid media. 总被引:4,自引:4,他引:0
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Higher yields of sterigmatocystin were obtained with Aspergillus versicolor than with Bipolaris sorokiniana both in liquid and on solid media. The optimum temperature for sterigmatocystin production by A. versicolor was 27 to 29 degrees C and 23 degrees C for B. sorokiniana. In liquid shake cultures, production of sterigmatocystin by B. sorokiniana was negligible, whereas maximal production by A. versicolor was 210 mg/liter. On solid substrates, the highest yields (8 g/kg) were obtained with A. versicolor on still cultures of whole corn supplemented with Soytone. 相似文献
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Anna F. Feller Oliver M. Selz Matthew D. McGee Joana I. Meier Salome Mwaiko Ole Seehausen 《Ecology and evolution》2020,10(14):7445-7462
The East African cichlid radiations are characterized by repeated and rapid diversification into many distinct species with different ecological specializations and by a history of hybridization events between nonsister species. Such hybridization might provide important fuel for adaptive radiation. Interspecific hybrids can have extreme trait values or novel trait combinations and such transgressive phenotypes may allow some hybrids to explore ecological niches neither of the parental species could tap into. Here, we investigate the potential of second‐generation (F2) hybrids between two generalist cichlid species from Lake Malawi to exploit a resource neither parental species is specialized on: feeding by sifting sand. Some of the F2 hybrids phenotypically resembled fish of species that are specialized on sand sifting. We combined experimental behavioral and morphometric approaches to test whether the F2 hybrids are transgressive in both morphology and behavior related to sand sifting. We then performed a quantitative trait loci (QTL) analysis using RADseq markers to investigate the genetic architecture of morphological and behavioral traits. We show that transgression is present in several morphological traits, that novel trait combinations occur, and we observe transgressive trait values in sand sifting behavior in some of the F2 hybrids. Moreover, we find QTLs for morphology and for sand sifting behavior, suggesting the existence of some loci with moderate to large effects. We demonstrate that hybridization has the potential to rapidly generate novel and ecologically relevant phenotypes that may be suited to a niche neither of the parental species occupies. Interspecific hybridization may thereby contribute to the rapid generation of ecological diversity in cichlid radiations. 相似文献
10.
Salome Dürr Borna Müller Silvia Alonso Jan Hattendorf Cláudio J. M. Laisse Paul D. van Helden Jakob Zinsstag 《PLoS neglected tropical diseases》2013,7(8)
Tuberculosis (TB) is one of the most devastating infectious diseases worldwide. Whilst global burden estimates for M. tuberculosis infection (MtTB) are well established, accurate data on the contribution of zoonotic TB (zTB) caused by M. bovis or M. caprae to human TB are scarce. The association of M. bovis infection with extrapulmonary tuberculosis has been suggested repeatedly, though there is little scientific evidence available to support this relationship. The present study aimed to determine globally the occurrence of extrapulmonary TB and the primary site (i.e. primary body location affected) of zTB in comparison with MtTB, based on previously published reports. A systematic literature review was conducted in 32 different bibliographic databases, selecting reports on zTB written in English, French, German, Spanish or Portuguese. Data from 27 reports from Africa, America, Europe and the Western Pacific Region were extracted for analyses. Low income countries, in Africa and South-East Asia, were highly underrepresented in the dataset. The median proportion of extrapulmonary TB cases was significantly increased among zTB in comparison with data from registries of Europe and USA, reporting mainly MtTB cases (47% versus 22% in Europe, 73% versus 30% in the USA). These findings were confirmed by analyses of eight studies reporting on the proportions of extrapulmonary TB in comparable populations of zTB and MtTB cases (median 63% versus 22%). Also, disparities of primary sites of extrapulmonary TB between zTB and MtTB were detected. Our findings, based on global data, confirm the widely suggested association between zTB and extrapulmonary disease. Different disability weights for zTB and MtTB should be considered and we recommend separate burden estimates for the two diseases. 相似文献