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1、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 sc
2、ience (logos) of small (micro) life (bios). The study of living things so small that they cannot be seen with the naked eye.The three-domain system is a biological classification introduced by Carl Woese that divides cellular life forms into archaea, bacteria, and eukaryote domains. In particular, i
3、t 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 (16321723), a Dutch cloth merchant and an expert lens grinder.The first proof of the involvement of
4、bacteria in disease and the definitive proof of the germ theory of disease came from the German Robert Koch.Kochs 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 p
5、ure culture.3 ,When the microorganism is inoculated into a healthy host, the same disease condition must result.4, The same microorganism must be re-isolated from the experimentally infected host.Chapter oneFungi include yeasts, molds, and mushrooms.Viruses are noncellular organisms; they are intra-
6、cellular 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 single-celled organism which doesn
7、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 (螺旋体) when flexible.4, Capsules (荚膜) and slime layers (粘液层) usual
8、ly are composed of polysaccharides (多糖), but they may be constructed of other materials.5, Gram staining procedure(革兰氏染色的步骤)In the first step of the Gram-staining procedure, the smear is stained with the basic dye crystal violet, the primary stain. It is followed by treatment with an iodine solution
9、 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; gram-positive bacteria ret
10、ain the crystal violet, whereas gram-negative bacteria lose their crystal violet and become colorless. Finally, the smear is counterstained with a simple, basic dye different in color from crystal violet. Safranin, the most common counterstain, colors gram-negative bacteria pink to red and leaves gr
11、am-positive bacteria dark purple. 6, The Mechanism of Gram Staining （革兰氏染色的机制）Although several explanations have been given for the Gramstain reaction results, it seems likely that the difference between gram-positive and gram-negative bacteria is due to the physical nature of their cell walls. If t
12、he cell wall is removed from grampositive bacteria, they become 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 i
13、odine to promote dye retention. When gram-positive bacteria then are decolorized with ethanol, the alcohol is thought to shrink the pores of the thick peptidoglycan. Thus the dye-iodine complex is retained during the short decolorization step and the bacteria remain purple. In contrast, gram-negativ
14、e peptidoglycan is very thin, not as highly cross-linked, 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 violet-iodine complex from gram-negative bac
15、teria. 简而言之，不同细菌的染色差异（G+或G-）是由于细胞壁化学成分的差异而引起了物理特性（脱色能力）的不同。具体而言：通过初染和媒染后，在细胞膜内形成了不溶于水的结晶与碘的复合物。G+菌由于细胞壁厚，肽聚糖网层次多而交联紧密，并且不含类脂，故以乙醇脱色时不会溶出缝隙，反而使肽聚糖网孔收缩，使染料滞留在细胞壁内而使其染上紫色；反之，G-菌由于细胞壁薄，外膜层类脂含量高，肽聚糖层薄和交联度差，当遇到乙醇时，以类脂为主的的外膜迅速溶解，这时薄而松散的肽聚糖网不能阻挡结晶紫与碘的复合物的溶出，故细胞退成无色。再经番红等红色染料复染时，就使G-菌呈现红色，而G+菌仍保留紫色或紫红色。图示革兰氏
16、阳性菌和革兰氏阴性菌细胞壁结构。试述革兰氏阳性菌和革兰氏阴性菌肽聚糖单体的异同点。（1）四肽尾的第3个氨基酸不是L-lys，而是被内消旋二氨基二酸（m-DAP）所代替（2）没有特殊的肽桥，其前后两个单体间的连接仅通过甲四肽尾的第4个氨基酸-D-Ala的羧基与乙四肽尾的第3个氨基酸-m-DAP的氨基直接相连。Endospore(芽孢)：某些细菌在其生长发育后期，在细胞内形成一个圆形或椭圆形、厚壁、含水量极低、抗逆性极强的休眠体，称为芽孢。芽孢的结构：Endospore-forming process (芽孢的形成过程)鞭毛（flagellum）的结构分为基体、钩形鞘和螺旋丝; 革兰氏阴性菌（G-）基体由L、P、S、M四个环构成; 革兰氏阴性菌（G+）基体由2个环构成。The systemic taxa of mocroorganisms follow the systemic taxa built by Lin
