Lecture 1: Morphology and Cell Structure of Microorganisms PDF

Lecture 1 Morphology and cell structure of microorganisms Dr. Mouna Hossni Elgadhafi MBChB MSC Medical Microbiology/Immunology Morphology and cell structure of microorganism 1- Difference between eukaryotic and prokaryotic cells...

Lecture 1 Morphology and cell structure of microorganisms Dr. Mouna Hossni Elgadhafi MBChB MSC Medical Microbiology/Immunology Morphology and cell structure of microorganism 1- Difference between eukaryotic and prokaryotic cells 2-bacterial cells structure Comparison of medically important organisms  Exercise Compare between Prokaryotic& Eukaryotic Characteristic Prokaryotic Eukaryotic 1) Nucleus No Yes 2) Size 0.05-10µm 10-100µm 3) Nuclear Yes No membrane (Nucleus) (Nucleoid)  Characteristic Prokaryotic Eukaryotic 4) Membrane- bound organelles Mitochondria ▪ Present Absent Golgi apparatus ▪ Endoplasmic ▪ reticulum  Characteristic Prokaryotic Eukaryotic 5) Chromosome One Number (circular) Multiple (linear) 70S 80S 6) Ribosome (30S-50S) (40S -60S) Characteristic Prokaryotic Eukaryotic Present EXCEPT Absent 7) Cell wall Mycoplasma Fungi (Chitin) 8) Cell membran No sterols EXCEPT in mycoplasma Has sterols Characteristic Prokaryotic Eukaryotic Binary fission Mitosis 9) Division Morphology and cell structure of microorganism Shape ,size and arrangement and of bacteria Bactria are classified by shape into three basic groups : Cocci Bacilli Spiral Some bacteria are variable in shape are said to be pleomorphic (many shaped) Arrangement  The smallest bacteria (Chlamydia and Rickettsia) are just 0.1 to 0.2 μm in diameter, whereas larger bacteria may be many microns in length. Most species, however, are approximately 1 μm in diameter and are therefore visible with the use of the light microscope,. In comparison, animal and plant cells are much larger, ranging from 7 μm (the diameter of a red blood cell) to several feet (the length of certain nerve cells)  Different between Macroscopic and Microscopic appearance of bacteria: Macroscopic Microscopic appearance appearance Bacterial cells structure (essential component and non essential component) Essential components: Non-essential: Cell wall Capsule Cytoplasmic membrane flagella Nuclear material pili Ribosomes Plasmides Mesosomes Inclusions , metachromatic granules Bacterial structure Cell wall Capsule Spore Cell Membrane Inclusion bodies Nucleoid Flagellum Ribosome Plasmid Mesosome Pili  Bacterial cells structure Intracytoplasmic Structures Cell Wall bacterial ribosome cytoplasmic membrane nucleoid. Plasmids External Structures capsules, Fimbriae (pili) Flagella  Structure of bacteria Intracytoplasmic Structures Cell wall The cell wall is the outermost component common to all bacteria except (Mycoplasma species which are bounded by a cell membrane not a cell wall ) Some bacteria have surface features external to the cell wall such as capsule , flagella and pili which are less common components and are discussed next. The cell wall is located external to the cytoplasmic membrane and composed of Peptidoglycan  cell wall Rigidity Cell (Peptidoglycan) membrane Comparison of cell walls of gram positive and gram negative bacteria : Component Gram positive cell Gram negative cell Peptidoglycan Thicker; multilayer Thinner; single layer Teichoic acids Yes No lipopolysaccharide No Yes  1- Cell Wall. Gram-positive and Gram-negative cell wall : Gram-Positive Bacteria wall : Peptidoglycan (murein): is complex component surround the cytoplasmic membranes. Thick (50-80%), multilayered and consist of glycan chains of NAG (N-acetyl glucosamine) & NAM (N-acetyl muremic acid) cross Linked by peptide bridge by the action of transpeptidase enzyme. Teichoic acids: are located in the outer layer of the gram positive cell wall extend from it they are composed of polymers Fibers of glycerol phosphate or polyribitol phosphate cross linked to the peptidoglycan and extend from it. Lipoteichoic acid: Polymers of glycerol teichoic acid penetrate the peptidoglycan layer and covalently linked to the lipid in cytoplasmic membrane.  Composition Of cell Wall Glycosidic bond (Transglycosidase) Alternating repeating unit NAM NAG NAM NAG Transpeptidase NAM NAG NAM NAG Peptidoglycans  Composition NAM NAG NAM NAG NAM NAG NAM NAG NAM NAG NAM NAG NAM NAG NAM NAG NAM NAG NAM NAG NAM NAG NAM NAG  Gram-Negative Bacteria : Peptidoglycan: Thin layer (5-10%) Periplasmic space: there is a gap present between cell wall and cell membrane. It can be observed in the gram-negative bacteria under electron , which is the site of Enzymes involved in transport, degradation, synthesis & virulence factors (collagenases,, proteases, and β-lactamase). Outer membrane: asymmetric bilayer structure. The inner side contains phospholipids normally found in bacterial membranes & the outer side is composed primarily of lipopolysaccharide (LPS)  The lipopolysaccharide (LPS) of the outer membrane of the cell wall of gram negative bacteria , it is called endotoxin. It is responsible for many feature of diseases such as fever and shock especially hypotension. Its called endotoxin because it is an integral part of cell wall , in contrast to exotoxin which are secreted from the bacteria. Lipopolysaccharide LPS (endotoxin) consists of three structural sections: lipid A core polysaccharide (rough core) O antigen Lipid A is a basic component of LPS and is essential for bacterial viability. Lipid A is responsible for the endotoxin activity of LPS. The basic structure of lipid A is identical for related bacteria and is similar for all gram-negative Enterobacteriaceae. The core polysaccharide is a branched polysaccharide of 9 to 12 sugars. Most of the core region is also essential for LPS structure and bacterial viability. The core region contains an unusual sugar, 2-keto-3-deoxy-octanoate (KDO), The O antigen distinguishes serotypes (strains) of a bacterial species. For example, the O157:H7 serotype identifies the E. coli agent of hemolytic- uremic syndrome LPS structure is used to classify bacteria. The basic structure of lipid A is identical for related bacteria and is similar for all gram-negative Enterobacteriaceae Lipooligosaccharide (LOS), which is present in Neisseria species, lacks the O-antigen portion of LPS and is readily shed from the bacteria. The shorter O antigen makes Neisseria more susceptible to host-mediated complement lysis..  Gram positive/negative Teichoic acid bacteria Outer membrane (Lipopolysaccharides Lipoteichoic acid ) Porins Peptidoglycan Periplasmic space G+ve G-ve  Main Features of Exotoxin and Endotoxin Exotoxin Endotoxin Secreted by certain species of part of cell wall of gram Source gram positive and gram negative bacteria negative bacteria Chemistry Polypeptide Libopolysaccharide Toxicity High Low Clinical Various effect Fever shock effect Mode of Various mode Includes TNF and interleukin-1 action No toxoid formed and no Vaccines Toxoid used as vaccine vaccine available Typical Ex\ Sepsis by gram negative Ex \ - diphtheria diseases rods  Functions of the Cell wall 1- Cell shape and rigidity. 2-Cell division 3- Mechanical barrier 4- Selective permeability 5- Protect bacteria from external osmotic pressure 6- Surface molecules are important in attachment to other bacteria and to specific receptors on mammalian cell surfaces (adherence). Medical Significance of cell wall 7-Responsible for staining. 8- Target site of antibiotic. 9- Toxic effect. 10- Identification of bacteria.  Cell wall Deficient ❑Bacteria without Cell membrane cell wall  Cell wall Deficient 1) Naturally 2) Induced ❑ Mycoplasma ❑ Cell wall inhibitors (Sterol) ❑ Lysozyme  2) Induced Completely Partially Cell Cell membrane membrane Protoplast (+ve) L-form bacteria Spheroplast (-ve)  L-form & Mycoplasma ❑ Resist to Penicillin & Cephalosporines  2- Cytoplasmicmembrane composed of a phospholipids bilayer structure similar in microscopic appearance to that in eukaryotic cell They are chemically similar but eukaryotic membranes, contain sterols whereas prokaryotic do not have sterols. The only prokaryotic cell that have sterols in their membranes are membarne of the genus Mycoplama Functions of cytoplasmic membrane: Active transport of molecules in the cell energy production Secretion of enzymes and toxin Site of chemical reaction (contains transport proteins that allow the uptake of metabolites and the release of other substances)  Composition of cell membrane Phospholipid bilayer + Protein (No sterols ) Mesosomes Invagination of cytoplasmic membrane, important in cell division & play role in respiration (acts as mitochondria) 3- Nuclear material (nucleoid) is a DNA single, double-stranded circle that is contained in a discrete area known as the nucleoid. No Histones Function : Transfer genetic information 5- Ribosome : are the site of consists protein synthesis of 30S + 50S subunits, forming a 70S ribosome. This is unlike the eukaryotic 80S (40S + 60S) ribosome. The proteins and RNA of the bacterial ribosome are significantly different from those of eukaryotic ribosomes and are major targets for antibacterial drugs. Function :protein synthesis 3- Nuclear material (nucleoid) is a DNA single, double-stranded circle that is contained in a discrete area known as the nucleoid. No Histones Function : Transfer genetic information 5- Ribosome : are the site of consists protein synthesis of 30S + 50S subunits, forming a 70S ribosome. This is unlike the eukaryotic 80S (40S + 60S) ribosome. The proteins and RNA of the bacterial ribosome are significantly different from those of eukaryotic ribosomes and are major targets for antibacterial drug Function :protein synthesis