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Lec.1 Dr. Inas Khalifa Al-Sharquie 2012-2013 Bacteriology Introduction to Microbiology Learning Outcomes: At the end of this lecture, the students should be able to: 1. Sate the general characteristics of microorganisms: Procaryotic / Eucaryotic and viruses. 2. Describe the bacterial structure and composition in comparison with eukaryotic cells (e.g., nucleoid and cytoplasm). Microbiology: Is the science that studies a great variety of living organisms that are too small for us to see without of microscope- the microbes, or microorganisms, and that exist as single cells or cell clusters; it also includes viruses, which are microscopic but not cellular. Microorganisms have a tremendous impact on all life and the physical and chemical makeup of our planet. They are responsible for cycling the chemical elements essential for life, including carbon, nitrogen, sulfur, hydrogen, and oxygen; more photosynthesis is carried out by microorganisms than by green plants. Humans also have an intimate relationship with microorganisms; more than 90% of the cells in our bodies are microbes. Important features of Microbes: Microbes that cause human infectious diseases belong to five major groups of organisms: bacteria, fungi, protozoa, helminthes, and viruses. These microbes have many important characteristics features shown in Table 1-1, but the most significant one is that bacteria, fungi, protozoa and helminthes are cellular whereas 1 Lec.1 Dr. Inas Khalifa Al-Sharquie 2012-2013 viruses are not but can replicate only within cells. This difference is based on the following criteria: 1- Structure: Cells have nucleus, while viruses are not cells and do not have a nucleus. 2- Method of replication: Cells replicate either by binary fission (e.g., bacteria) or by mitosis (e.g., fungi). In contrast, viruses disassemble, produce many copies of their nucleic acid and protein, and then reassemble into multiple progeny viruses. 3- Nature of the nucleic acid: All cells contain both DNA and RNA, whereas viruses contain either DNA or RNA, but not both. Table 1-1 Comparison of Medically important Organisms Discovery of Microorganisms & germ theory -Antony van Leewenhock (1632-1723) who invented the first microscope (50-300x), was first to accurately observe and describe microorganisms. 2 Lec.1 Dr. Inas Khalifa Al-Sharquie 2012-2013 - The French chemist and microbiologist Louis Pasteur, the English surgeon Joseph Lister, and the German physician Robert Koch are given much of the credit for development and acceptance of the germ theory, the theory that certain diseases are caused by the invasion of the body by microorganisms. Cell structure Historically, it was the microscope that first revealed the presence of bacteria, the secrets of cell structure. Today, it remains a powerful tool in cell biology. Optical Methods 1- The light microscope: Several types of light microscopes are commonly used in microbiology: 1) Bright-Field Microscope: These microscopes generally employ a 100-power objective lens with a 10-power ocular lens, thus magnifying the specimen 1000 times. 2) Phase Contrast Microscope: The phase contrast microscope was developed to improve contrast differences between cells and the surrounding medium, making it possible to see living cells without staining them; with bright-field microscopes, killed and stained preparations must be used. 3) Dark-Field Microscope: Is a light microscope in which the lighting system has been modified to reach the specimen from the sides only. 4) Fluorescence Microscope: Is used to visualize specimens that fluoresce, which is the ability to absorb short wavelengths of light (ultraviolet) and give off light at a longer wavelength (visible). 3 Lec.1 Dr. Inas Khalifa Al-Sharquie 2012-2013 5) Differential Interference Contrast (DIC) Microscope: Microscopes employ a polarizer to produce polarized light. The polarized light beam passes through a prism that generates two distinct beams; these beams pass through the specimen and enter the objective lens where they are recombined into a single beam. Because of slight differences in refractive index of the substances each beam passed through, the combined beams are not totally in phase but instead create an interference effect, which intensifies subtle differences in cell structure. 2- The electron microscope: The superior resolution of the electron microscope is due to the fact that electrons have a much shorter wavelength than the photons of white light so it enlarges objects up to 0.01-0.2 Mm. 1) Transmission electron M. (TEM) 2) Scanning electron M. (SEM). 3- Confocal Scanning Laser Microscope: couples a laser light source to a light microscope to get 3D image 4- Scanning Probe Microscopes: measure surface features by moving a sharp probe over the object's surface. Eukaryotes and Prokaryotes Cells have evolved into two fundamentally different types, eukaryotic (Fungi and Protozoa) and prokaryotic (e.g., Bacteria). Eukaryotes and prokaryotes are organisms because they contain all of enzymes required for the replication and possess the biologic equipment necessary for the production of metabolic energy so they are distinguished form viruses which depend upon host cells for their necessary functions. 4 Lec.1 Dr. Inas Khalifa Al-Sharquie 2012-2013 Bacterial cell structure 1- The Nucleoid The prokaryotic cells have nucleoid filled with DNA fibrils, which equivalent to the eukaryotic nucleus and can be seen in light microscope. Prokaryotes generally possess only a single circular chromosome. Since there is no nuclear membrane, the chromosome is bound to a specific site on the cell membrane - the mesosome, this attachment plays a role in the separation of the two sister chromosomes following replication. The number of copies of these chromosomes in a cell depends on the growth conditions. Bacterial nucleoid contains no nuclear membrane and no histones, there is little resemblance to the eukaryotic nucleus. (Figures 1A, B, and 2). 2. Cytoplasmic structure The prokaryotic cell, in contrast to the eukaryotic cell, is not compartmentalized. Nuclear membranes, endoplasmic reticulum, Golgi body, phagosomes, lysosomes and mitochondria are not present, so the electron transport enzymes are located in cell membrane instead of mitochondria (Figures 1A, B, and 2). The bacterial cytoplasm contains several different types of granules that serve as storage areas for nutrients and stain with certain dyes. When the source of nitrogen, sulfur or phosphorus is limited or when the pH is low, excess carbon in the medium is converted to starch and glycogen. These granular are then used as carbon source when protein nucleic acid synthesis is resume. For example, volutin granules is a reserve of high energy stored and it stains red with methylene blue dye, so then it appears as a metachromatic granules that are present in Corynebacterium diphtheria. 5 Lec.1 Dr. Inas Khalifa Al-Sharquie 2012-2013 Bacterial ribosomes are the site of protein synthesis as in eukaryotic cells, but they differ from eukaryotic ribosomes in size and chemical composition. The bacterial one is smaller than eukaryotic ribosome. Bacterial Plasmids are extrachromosomal, double-stranded, circular DNA molecules that are capable of replicating independently of the bacterial chromosomes (Figure 3). A 6 Lec.1 Dr. Inas Khalifa Al-Sharquie 2012-2013 B Figure 1: The prototype bacterial cell 7 Lec.1 Dr. Inas Khalifa Al-Sharquie 2012-2013 Figure 2: An animal cell Figure 3: Bacterial Plasmid 8 Lec.1 Dr. Inas Khalifa Al-Sharquie 2012-2013 Summary • Bacteria, Fungi, Protozoa and viruses are the agents of human infectious diseases • There are two fundamentally two types of cells: Prokaryotes & Eukaryotes. • Viruses are not cells and do not have a nucleus. • Eukaryotes have membrane-bound organelles • Eukaryotes may be multicellular with highly specialized cells • Certain structures are unique to eukaryotes Main References: 1. Jawetz, Melnick and Adelberg’s Medical Microbiology (Brooks, Butel,Morse), 2010. 2. Review of Medical Microbiology and Immunology, 12th Edition, (2012). 9