Introduction to Microbiology Lecture Notes PDF

 By Dr: Rania Abdelazeem Tawfeek PHD of Microbiology and Immunology, Faculty of Pharmacy, Assiut University Introduction to Microbiology  ILOs Define the scope of Medical Microbiology: Bacteriology, Virology, Mycology, and Immunology. Recall microorganis...

 By Dr: Rania Abdelazeem Tawfeek PHD of Microbiology and Immunology, Faculty of Pharmacy, Assiut University Introduction to Microbiology  ILOs Define the scope of Medical Microbiology: Bacteriology, Virology, Mycology, and Immunology. Recall microorganisms that cause infectious diseases and their properties. Outline the difference between microorganisms: Prokaryotic /Eukaryotic. Define microbiological nomenclature Bacterial structure  Medical microbiology Is the study of microorganisms causing infectious diseases of humans and the human reactions to such infections. In other words, it deals with etiology, pathogenesis, laboratory diagnosis, specific treatment, and control of infection (immunization). Medical Microbiology: Includes: Bacteriology, Virology, Mycology, Immunology and Parasitology.  Microorganisms that cause infectious diseases are: Too small to be seen with the naked eye. Exist as single cells (unicellular) or in multiple cells (multicellular). They include some eukaryotes, prokaryotes, viruses and prions.  Cellular organisms are broadly classified as prokaryotic or eukaryotic. Prokaryotic organisms include bacteria. Eukaryotic organisms include fungi, protozoa, and helminths as well as humans. Prokaryotic and eukaryotic cell structure Properties of medically important microorganisms  Microbiological nomenclature: In Microbiology the binominal system of nomenclature is accepted where each species has a generic (genus) and a specific (species) name. The genus name is written with a capital letter, and the species name – with a lowercase letter. The names should be italicized in text. Once the complete name of a microorganism has been written out once, the genus name can be abbreviated to just the capital letter.  Bacterial examples: the anthrax bacillus – Bacillus anthracis (B. anthracis). the tetanus bacillus – Clostridium tetani (C. tetani). Fungal example: Candida albicans (C. albicans) Viruses are not named so. Bacteriology  Bacteriology Bacteria are widely distributed in nature, and according to their habitat and way of living they are described as: A. Saprophytic bacteria: live on inanimate material; in the soil, in water, in dust, in the air, on clothes or on dead bodies and decaying organic matter. B. Parasitic bacteria: live on or in the body of living creatures. Parasitic bacteria are classified into: 1. Pathogenic bacteria cause disease in man or animals or plants. 2. Commensal bacteria live on or in the body without exerting a harmful effect. Some of these commensals may be potentially pathogenic (opportunistic) and may cause disease if the body resistance is lowered by any means.  Morphological Study of Bacteria: Microscopic examination is usually the first step taken for the identification of an unknown bacterium. The morphological features of importance are the size, shape, arrangement, and structure. This is carried out by examination of fresh preparations OR fixed and stained preparations. 1- Size of the Bacterial Cell: The majority of bacteria fall within the general dimensions of 0.75 to 4 um. 2- Shape of the Bacterial Cell: They are unicellular structures which may occur as: – Cylindrical (rod-shaped or bacilli) e.g., E. coli – Spherical (cocci or coccoid) forms e.g., Staphylococci. – Coma-shaped (vibrios) e.g., Vibrio cholera – Many twists (spiral) e.g., spirochaetes. Shape of bacterial cell  3- Arrangement: When the bacterial cell divides, the two daughter cells may at once separate, or they may remain attached to one another by the cell membrane. It may be: ▪ Cocci in clusters e.g., Staphylococci ▪ Cocci in pairs (diplococci) e.g., Pneumococci ▪ Cocci in chains e.g., Streptococci ▪ Bacilli parallel to each other or at angle e.g., Corynebacterium diphtheria Arrangement of bacteria  Bacterial structure Four main essential components of the bacterial cell present in all species; cell wall, cell or cytoplasmic membrane, cytoplasm, and nucleoid.  1. Cell Wall A. Gram-Positive Bacteria Cell Wall: Peptidoglycan layer: forms about 50% of the cell wall material. There are as many as 40 sheets of peptidoglycan in Gm +ve cell wall. It's composed of 3 layers: - A backbone of alternating N-acetyl-glucosamine and N-acetylmuramic acid. - A set of identical tetrapeptide side chains attached to the N-acetylmuramic acid. - A set of identical peptide cross bridges. Structure of Gram-positive cell wall.  Functions of peptidoglycan It gives rigid support. Protect against osmotic pressure. It confers Gram reaction. Its synthesis is inhibited by penicillins and cephalosporins and is degraded by lysozyme.  Teichoic acid layer It's a major surface component: it's a polymer of glycerol or ribitol phosphate. There are two types of teichoic acids: wall teichoic acid and membrane teichoic acid.  Functions of teichoic acid Major surface antigen in Gm +ve bacteria only. Induces TNF –α, IL-1 production. Attachment of Gram-positive bacteria to mucosal cells.  B. Gram-Negative Bacteria Cell Wall Composed of 2 layers: Inner layer of peptidoglycan which forms only 5-10% of cell wall material (there are only one or two sheets). Outer layer of lipopolysaccharides (LPS) (outer membrane)  Additionally Lipoprotein molecules cross link the peptidoglycan layer and the LPS layer. Periplasmic space: a concentrated gel-like matrix in the space between the inner cytoplasmic membrane and the bacterial outer membrane. It's the site of B-lactamases that degrade penicillins and other B-lactam drugs.  LPS Composed of 3 units: 1. A phospholipid called lipid A: responsible for the toxic effects. 2. A core polysaccharide. 3. An outer polysaccharide which is somatic, or O antigen: is used to identify certain organisms in the clinical Lab.  Functions of LPS 1. Endotoxin. It is responsible for shock; it is released only when bacterial cells are lysed. 2. Can bind specifically to receptors to activate macrophages. 3. Can nonspecifically activate B cells without the help of T cells. 4. Can be serotyped to classify bacteria. Outer membrane proteins (OMPs): OMP functions: - Attachment. - Virulence. * Porins: Porins function: Transport channels across outer membrane. Structure of Gram-negative cell wall  Functions of the cell wall 1. It's a rigid structure that maintains shape of bacteria. 2. Protects the cytoplasmic membrane from bursting in hypotonic solutions. 3. Detects the response to Gram stain. 4. Play a role in cell division. Structure of bacterial cell wall  2- Cytoplasmic membrane (inner membrane, cell membrane, or plasma membrane): It is a semipermeable double layered structure around the cytoplasm. It lies on the inside of the peptidoglycan layer of the cell wall. It is composed of phospholipid bilayer, with embedded proteins known as penicillin-binding proteins because they are targets for the β-lactam antibiotics.  Functions of cytoplasmic membrane 1. Active transport of molecules into the cell. 2. Energy generation by oxidative phosphorylation. 3. Synthesis of precursors of cell wall. 4. Secretion of enzymes and toxins. 5. It plays a role in DNA replication.  Mesosomes These are invaginations of the cytoplasmic membrane. They play a role in respiration and cell division. Mesosomes function as the origin of the transverse septum that divides the cell into 2 halves. Also, it is the binding site of the bacterial chromosome which will duplicate to provide the genetic material of each daughter cell.  3. Cytoplasm It contains the following: A. Cytoplasmic inclusion such as.: - Cytoplasmic granules (meta-polyphosphate) as a source of energy. - Glycogen granules. B. Ribosomes: 70S in size, with 30S and 50S subunits. They are the site of protein synthesis. Note: There is no rough endoplasmic reticulum in bacteria  4. Bacterial Nucleoid Bacteria contain both DNA and RNA; DNA is contained in masses or bodies within the cell (bacterial nucleoid), while RNA occurs in the surrounding cytoplasm. The bacterial nucleoid is present as single DNA duplex, from 1100-1400 bp in length, circular with no free ends.