BSC 361 - Illinois State University
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
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