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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