微生物學(xué)英文題庫(kù)(已修改)

　

【正文】 IntroductionMicrobes are a diverse group of organisms that can be divided into the viruses, unicellular groups (Archaea, Eubacteria, protista, some fungi and some chlorophyta) and a small number of organisms with a simple multicellular structure (the large fungi and chlorophyta).Microbiology: the science (logos) of small (micro) life (bios). The study of living things so small that they cannot be seen with the naked eye.The threedomain system is a biological classification introduced by Carl Woese that divides cellular life forms into archaea, bacteria, and eukaryote domains. In particular, it emphasizes the separation of prokaryotes into two groups, originally called Eubacteria (now Bacteria) and Archaebacteria (now Archaea).Microorganisms were first visualized by Antoni van Leeuwenhoek (1632–1723), a Dutch cloth merchant and an expert lens grinder.The first proof of the involvement of bacteria in disease and the definitive proof of the germ theory of disease came from the German Robert Koch.Koch’s postulates:1, The microorganism must be present in every instance of the disease and absent from healthy individuals.2, The microorganism must be capable of being isolated and grown in pure culture.3 ,When the microorganism is inoculated into a healthy host, the same disease condition must result.4, The same microorganism must be reisolated from the experimentally infected host.Chapter oneFungi include yeasts, molds, and mushrooms.Viruses are noncellular organisms。 they are intracellular parasites of animals, plants, or bacteria. 1, The Prokaryotes can be divided into two kingdoms, Bacteria and Archaea. The classification was first proposed by Woese based on the differences in 16S rRNA sequence.2, Prokaryotic microorganism（原核微生物）: It is an singlecelled organism which doesn’t have a nuclear membrane outside the cell nucleus and only has the bare DNA called as the nuclear area.3, Many bacteria are shaped like long rods twisted into spirals or helices。 they are called spirilla （螺旋菌）if rigid and spirochetes (螺旋體) when flexible.4, Capsules (莢膜) and slime layers (粘液層) usually are posed of polysaccharides (多糖), but they may be constructed of other materials.5, Gram staining procedure(革蘭氏染色的步驟)In the first step of the Gramstaining procedure, the smear is stained with the basic dye crystal violet, the primary stain. It is followed by treatment with an iodine solution functioning as a mordant. That is, the iodine increases the interaction between the cell and the dye so that the cell is stained more strongly. The smear is next decolorized by washing with ethanol or acetone. This step generates the differential aspect of the Gram stain。 grampositive bacteria retain the crystal violet, whereas gramnegative bacteria lose their crystal violet and bee colorless. Finally, the smear is counterstained with a simple, basic dye different in color from crystal violet. Safranin, the most mon counterstain, colors gramnegative bacteria pink to red and leaves grampositive bacteria dark purple. 6, The Mechanism of Gram Staining （革蘭氏染色的機(jī)制）Although several explanations have been given for the Gramstain reaction results, it seems likely that the difference between grampositive and gramnegative bacteria is due to the physical nature of their cell walls. If the cell wall is removed from grampositive bacteria, they bee gram negative. The peptidoglycan itself is not stained。 instead it seems to act as a permeability barrier preventing loss of crystal violet. During the procedure the bacteria are first stained with crystal violet and next treated with iodine to promote dye retention. When grampositive bacteria then are decolorized with ethanol, the alcohol is thought to shrink the pores of the thick peptidoglycan. Thus the dyeiodine plex is retained during the short decolorization step and the bacteria remain purple. In contrast, gramnegative peptidoglycan is very thin, not as highly crosslinked, and has larger pores. Alcohol treatment also may extract enough lipid from the gramnegative wall to increase its porosity further. For these reasons, alcohol more readily removes the purple crystal violetiodine plex from gramnegative bacteria. 簡(jiǎn)而言之，不同細(xì)菌的染色差異（G+或G）是由于細(xì)胞壁化學(xué)成分的差異而引起了物理特性（脫色能力）的不同。具體而言：通過(guò)初染和媒染后，在細(xì)胞膜內(nèi)形成了不溶于水的結(jié)晶與碘的復(fù)合物。G+菌由于細(xì)胞壁厚，肽聚糖網(wǎng)層次多而交聯(lián)緊密，并且不含類脂，故以乙醇脫色時(shí)不會(huì)溶出縫隙，反而使肽聚糖網(wǎng)孔收縮，使染料滯留在細(xì)胞壁內(nèi)而使其染上紫色；反之，G菌由于細(xì)胞壁薄，外膜層類脂含量高，肽聚糖層薄和交聯(lián)度差，當(dāng)