Bacteria Are Prokaryotes

BSC 361 January 28,2013 Bacteriology

Bacteria are Prokaryotes No membrane bound organelles: No nuclear membrane No mitochondria or chloroplasts Endosymbiant theory suggests that mitochondria and chloroplasts evolved from internalized bacteria Circular (usually) chromosome Considered haploid, but multiple copies of genes may be present during rapid genome replication. Reproduce by binary fission

Characterized by cell shape, cell wall structure and biochemical/physiological features Shapes: Cocci-spheres Bacilli-rods Spirillia-cork-screw shape Pleomorphic-shape varies Coccobacilli-football or coffee bean shape

Cell wall structure-uses Gram stain Gram + Has single membrane (cytoplasmic membrane) Thick cell wall Peptidoglycan, teichoic acid, lipoteichoic acid Peptidoglycan comprises alternating linkages of N- acetyl-glucosamine and N-acetyl-muramic acid NAM has amino acid chain Forms linear strands which are cross-linked by bond formation between short amino acid chains

Gram - Has two sets of cell membranes (cytoplasmic and outer) Area between two membranes is periplasmic space Outer leaflet of outer membrane is largely composed of Lipopolysaccharide (LPS) or Lipooligosaccharide (LOS)

Has very thin cell wall between membranes

Cell features: LPS/LOS basically the same molecule with one exception LOS lacks O-antigen Structure:Lipid A, core, O-antigen (LPS only) Lipid A-inflammatory portion of molecule Causes host tissue damage Core, carbohydrates that can bind host receptors (LOS) O-antigen, provides protection against complement Also involved in binding and persistence

Fimbria (or pili)-long filamentous, protein structures that extend from cell Used for adherence or conjugation Heteropolymers, but made mostly of a repeating units of structural proteins called fimbrial subunits Adhesins can be present along shaft or only at end of fimbriae Fimbriae are hollow, helical structures

Capsule-polysaccharide Coats bacteria to prevent strong immune response Can also be used in adherence and persistence

Biofilm-slime coat Increases resistance to chemotherapeutic agents and protects from host immune defenses Similar to capsule, but usually only produced when bacteria are present in large numbers Quorum sensing-genetic regulation via cell density Cells produce small, soluble molecule called autoinducer Autoinducer passes freely through bacterial cells High level of autoinducer signals many cells in vicinity Transcriptional activator is triggered

Flagella-cell motility Spiral structure-similar to a corkscrew Allows bacteria to spread quickly Generally linked to sensor mechanism Chemotaxis-movement directed by chemical gradients Positive or negative Change in tumble vs straight Toxins-molecules that cause damage to host Can be direct or indirect Direct-toxin causes damage Indirect-host immune response causes damage Many are excreted from cells

Spores-dormant "seed" of bacteria Germinate under favorable growth conditions Produced by Gram+ only Some are very stable for long periods of time Antibacterial agents Bacteriostatic-stops division, but bacteria are still alive Bacteriocidal-kills bacterial cells May very according to concentration and organism Antibiotics-three main modes of action Inhibit cell wall synthesis Inhibit protein synthesis Inhibit nucleic acid synthesis

Classes- Beta-lactams-penicillin, ampicillin, amoxicillin Bind to penicillin-binding proteins in cytoplasmic membrane Inhibit peptidoglycan crosslinking Vancomycin- Binds to D-alanine, D-alanine termini of amino side groups Inhibits peptidoglycan crosslinking Bacitracin Inhibits transport of peptidoglycan precursors Aminoglycosides-streptomycin, kanamycin, gentamycin Bind irreversibly to 30S subunit of ribosome Tetracyclines Inhibit binding of tRNA to 30S/mRNA complex Chloramphenicol Binds to 50S ribosome subunit,cross reacts with bone marrow Macrolides-erythromycin Reversibly bind to 50S subunit Quinolones- Inhibit DNA supercoiling by interacting with gyrase Rifampin Inhibits transcription by binding RNA polymerase

Antibiotic resistance-modes of activity Degrade or change antibiotic Beta-lactamase Chloramphenicol acetyltransferase (CAT) Change recognized molecule Vancomycin resistance Quinolone Aminoglycosides Prevent antibiotic entry-cytoplasmic antibiotics Tet pump Aminoglycosides