L14 Basic Biology of Bacteria Maulik 2024 PDF

Microbiology BMF VI grant from us i Basic Biology of Bacteria important s Malabika Maulik, PhD Clinical Assistant Professor 1 Assigned Reading Medical Microbiology, 9th edition, (2020) Murray et al: Parts of Chapter 12. Sherris Medical Microbiology, 7th edition, (2018): Parts of Chapter 1. 2 Learnin...

Microbiology BMF VI grant from us i Basic Biology of Bacteria important s Malabika Maulik, PhD Clinical Assistant Professor 1 Assigned Reading Medical Microbiology, 9th edition, (2020) Murray et al: Parts of Chapter 12. Sherris Medical Microbiology, 7th edition, (2018): Parts of Chapter 1. 2 Learning Objectives After this lecture students will be able to: 1. Develop a vocabulary relevant to the cell biology of bacterial pathogens. 2. Contrast prokaryotic from eukaryotic cell biology and ultrastructure. 3. Describe in detail the major ultrastructural components of the bacterial cell and their major functions. 4. Relate macromolecular biosynthesis to antibacterial drug mechanisms of action using β-lactam antibiotics as a model. Introduction to Prokaryotes LO1  All bacteria exhibit prokaryotic cell ultrastructure, and are therefore very simple with regard to cell organization. They are unicellular, smaller than eukaryotes (1-10 µm) possess a rigid cell wall composed of peptidoglycan (Mycoplasma spp. are the exception). The prokaryotic bacterial cell. (Reproduced with permission from Willey JM: Prescott, Harley, & Klein’s Microbiology, 7th ed. New York, NY: McGraw Hill; 2008.) Introduction to Prokaryotes  Physiologically, they may be  chemotrophic or phototrophic with regard to energy sources,  autotrophic or heterotrophic with regard to carbon sources,  lithotrophic or organotrophic with regard to electron sources, aerobic, facultative, or anaerobic with regard to their relationship with molecular oxygen. The vast majority reproduce primarily by transverse binary fission; however, a few also form endospores (e.g., Bacillus spp. and Clostridium spp.) Exhibit budding, or undergo hyphal fragmentation (e.g., Streptomyces spp.). Reproduction is always asexual (i.e., haploid only). LO1 L1 Bacterial Morphology LO1 Gross morphology simple observation of organisms with the aid of a microscope. Most important parameters are cell size, shape, and grouping. Most bacteria range in size from about 1.0-10.0 µm in diameter or length. Possible cellular shapes include: a. Coccus (cocci)-spherical b. Bacillus (bacilli)-cylindrical rod. c. Coccobacillus (coccobacilli)-ovoid rod. d. Vibrio-bent rod. e. Fusiform-elliptical rod. f. Spirillum (spirilla)-rigid helical rod. g. Spirochete-flexible helical rod. h. Filaments-filamentous rod. i. Pleomorphic-variable. Fig. 12.3B, Murray et al. Morphology of bacteria. LO1 Bacterial Morphology LO1 Grouping results when cellular separation is delayed by one or more generations after cellular division and is dependent on the plane of division. Possibilities for cocci include: a. Micrococci-single. b. Diplococci-pairs. c. Streptococci-chains. d. Staphylococci-grape-like clusters. e. Tetrads-packets of four. f. Sarcina-cubical packets of eight. Possibilities for bacilli include: a. Single rods. b. Diplobacilli-pairs. c. Streptobacilli-chains. Note: Microscopic observation of endospores, capsulation, flagella, and cytoplasmic inclusions require specialized and often complex (i.e., more than one stain) staining procedures and are therefore considered ultrastructural rather than morphological. Prokaryotic Ultrastructure LO1 includes the cytoplasm, cytoplasmic organelles, cell envelope, and appendages. a. It is best observed using transmission electron microscopy of thinsectioned cells. b. Very simple and similar among all prokaryotes, regardless of cell morphology. Gram reactivity is much more important than morphology with regard to the physiology and pathogenicity of the organism, and is a function solely of bacterial cell envelope ultrastructure. Prokaryotic vs eukaryotic LO2 Prokaryote – without true nucleus Cell wall- peptidoglycan * Cell membrane-lipopolysaccharide * Single, circular chromosome Extrachromosomal- plasmid 70s ribosome Flagellum- motility Eukaryote- true nucleus Nuclear membrane 80S ribosomes Many more organelles- mitochondria etc. Fig. 12.1, Murray et al. Major features of prokaryotes and eukaryotes. Table 12.1, Murray, et al. Major Characteristics of Eukaryotes and Prokaryotes (review) ftp.rtent wide Characteristic Eukaryote Prokaryote Major groups Algae, fungi, protozoa, plants, animals Bacteria, archaea Size (approximate) >5 µm 0.5-3.0 µm Nucleus Classic membrane No nuclear membrane Chromosomes Strands of DNA, multiploid genome Single, circular DNA haploid genome Mitochondria Present Absent Golgi bodies Present Absent Endoplasmic reticulum Present Absent Ribosomes (sedimentation coefficient) 80S (60S + 40S) 70S (50S + 30S) Cytoplasmic membrane Contains sterols Does not contain sterols Cell wall Is a complex structure Present for fungi, plants; containing protein, otherwise absent lipids, and peptidoglycans Reproduction Sexual and asexual Asexual (binary fission) Movement Complex flagellum, if present Simple flagellum, if present Respiration Via mitochondria Via cytoplasmic membrane Nuclear Structures Cytoplasmic Structures LO2 Prokaryotic Ultrastructural Components Intracellular Content Cytoplasm Free and bound polysomes (70S ribosomes attached to mRNA) Nucleoid (genomic DNA plus associated enzymes) Inclusion bodies Endospores (certain gram-positive species only) Cell envelope Cytoplasmic membrane (protoplast to include cytoplasmic contents absent wall) Peptidoglycan (wall) layer Outer membrane (gram-negative only) Periplasmic space (containing periplasm, gram-negative only) Appendages Flagella (if motile) Fimbriae (adhesins) Pili (conjugation) Capsules or glycocalyses (also known collectively as extracellular polysaccharide) LO3 Pilus From Wikipedia, the free encyclopedia A pilus (Latin for 'hair'; plural: pili) is a hair-like appendage found on the surface of many bacteria.The terms pilus and fimbria (Latin for 'fringe'; plural: fimbriae) can be used interchangeably, although some researchers reserve the term pilus for the appendage required for bacterial conjugation. All pili in the latter sense are primarily composed of pilin proteins, which are oligomeric. LO3 Gram + vs Gram - ve A gram-positive bacterium has a thick peptidoglycan layer that contains teichoic and lipoteichoic acids. A gram-negative bacterium has a thin peptidoglycan layer and an outer membrane that contains lipopolysaccharide, phospholipids, and proteins. Botterill isshoronous LO3 Gram-positive and Gram-negative cell walls. M, peptidoglycan or murein layer; OM, outer membrane; P, periplasmic space; PM, plasma membrane; W, Gram-positive peptidoglycan wall. (Reproduced with permission from Willey JM: Prescott, Harley, & Klein’s Microbiology, 7th ed. New York, NY: McGraw Hill; 2008.) Citation: Chapter 21 Bacteria—Basic Concepts, Ryan KJ. Sherris & Ryan's Medical Microbiology, 8th Edition; 2022. Available at: https://accessmedicine.mhmedical.com/content.aspx?bookid=3107&sectionid=260925592 Accessed: February 13, 2024 Copyright © 2024 McGraw-Hill Education. All rights reserved Use of Gram’s staining LO3 grant now just colors got Light micrograph of Staphylococcus aureus (gram positive) and Escherichia coli (gram negative). Fig. 12.3A, Murray et al. Gram-stain ultrastructure of bacteria. The crystal violet of Gram stain is precipitated by Gram iodine mordant and is trapped in the thick peptidoglycan layer in gram-positive bacteria. The decolorizer dissolves the gramnegative outer membrane and washes the crystal violet out through the thin layer of peptidoglycan. Gram-negative bacteria are visualized by the red counterstain. Important * LO3 Table 12.4, Murray, et al. Cell Envelope Characteristics of Gram-Positive and Gram-Negative Bacteria Characteristic Gram-Positive Gram-Negative Outer membrane − + Cell wall Thicker Thinner Lipopolysaccharide − + Endotoxin − + Teichoic acid Often present − Sporulation Some species − Capsule Sometimes present Sometimes present Lysozyme Sensitive Resistant Antibacterial activity of penicillin More susceptible More resistant Exotoxin production Some organisms Some organisms Summary of Ultrastructural Components LO3 Cytoplasm – water solution of endogenous mineral salts, cofactors, enzymes, metabolic intermediates, and other intracellular solutes surrounded by the cytoplasmic membrane. Referred to as a protoplast when membrane is included. Cytoplasmic organelles – functional particles within the cytoplasm including most notably ribosomes and nucleoid; some strains of certain species may have plasmids, endospores, and/or inclusion bodies. Cell envelope – cytoplasmic membrane and peptidoglycan in gram-positive organisms; cytoplasmic membrane, peptidoglycan, periplasmic space, and outer membrane in gram-negative organisms. Surface appendages-phenotypically variable structures such as flagella, fimbriae, pili, and EPSs involved in motility, adhesion, asexual mating, immune system evasion, respectively. LO4 0 Fig. 12.2A, Gram-positive cell envelope. parents Gym Downloaded from: StudentConsult (on 21 February 2008 10:48 PM) © 2005 Elsevier LO4 Fig. 12.2B, Gramnegative cell envelope. Downloaded from: StudentConsult (on 21 February 2008 10:48 PM) © 2005 Elsevier Unique Bacterial Cell Envelope Macromolecules Peptidoglycan (murein) One huge, rigid complex network composed of glycan chains covalently cross linked by short peptides which surrounds entire prokaryotic protoplast. Biosynthesis is inhibited by the β-lactam antibiotic penicillin Substrate for the hydrolytic enzyme lysozyme which degrades the glycan chain. Present in all secretory fluids (including tears, mammary milk, semen, etc). Functions as the rigid layer of the cell envelope which acts to: a. Confer cell shape. b. Protect underlying protoplast from mechanical damage. c. Protect underlying protoplast from bacteriolysis in hypotonic environments due toplasmoptysis (i.e., osmotic shock). d. Grows inward at cell midpoint to form septum during transverse binary fission (i.e.,prokaryotic cell division). LO4 Gives 1 ask.pe LO4 General structure of peptidoglycan Mesh like layer Polysaccharide polymer linked by peptide bonds The Penicillin binding proteins – ‘transpeptidase’ assembling the cell wall by crosslinking the peptidoglycan layer and reshaping the cell wall during growth and division. The cross-linking reaction is a transpeptidation FIGURE 21–6. Peptidoglycan structure. A schematic diagram of one model of peptidoglycan. Shown are the polysaccharide chains, tetrapeptide side chains, and peptide bridges. (Reproduced with permission from Willey JM: Prescott, Harley, & Klein’s Microbiology, 7th ed. New York, NY: McGraw Hill; 2008.) LO4 Penicillin, a structural analog of D-alanyl-Dalanine, therefore a competitive inhibitor of transpeptidase. Sir Alexander Fleming Peptidoglycan and therapy Polysaccharide polymer linked by peptide bonds (β 1->4) β 1->4 -> lysozyme site of action Berfimarsets Cross-linking the peptidoglycan and is the basis for the action of β-lactam and vancomycin antibiotics LO4 Teichoic and Lipoteichoic Acids LO4  polymer compounds either covalently attached to peptidoglycan (TAs) or embedded in the cytoplasmic membrane (LTAs) of gram-positive bacteria.  Highly substituted with various sugars and amino acids which confer somatic (O) serotype antigenicity and surface electronegativity to gram-positive organisms.  Important physiological roles (maintaining cell shape) and contribute to the bacterial interaction with their host. Gram-positive envelope. (Reproduced with permission from Willey JM: Prescott, Harley, & Klein’s Microbiology, 7th ed. New York, NY: McGraw Hill; 2008.) Unique Bacterial Cell Membrane Macromolecules LO4 Lipopolysaccharide  Extremely complex molecule which forms the outer leaflet of the gram-negative outer membrane with three major regions: 1. Lipid A (Endotoxin) 2. Core oligosaccharide 3. O antigen (O polysaccharide) Gram-negative infection, this substance can produce a fever and shock syndrome called Gram-negative or endotoxic shock. e gram can  Confers to unique impermeability properties to the outer membrane, thereby allowing it to act as an outer protective barrier.  Hydrophilic molecules