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Prokaryotes – Microbiology Outline Notes

By at September 19, 2012 | 9:10 am | Print

Microbiology

Prokaryotes

I. Prokaryotic cells – bacteria and archaea

A. No nucleus or organelles

1.  Eukaryotes (animals, plants, fungi, protists) have a nucleus and organelles

B. Structure of Bacteria

1. External Structures

a. Appendages – flagella, pili, fimbriae

b. Glycocalyx – capsule, slime layer

2. Cell Envelope

a. Cell wall

b. Cell Membrane

3. Internal Structures

a. Cytoplasm, chromosome, plasmid, ribosomes, inclusions

C. External Structures

1. Flagella – provide movement

a. 3 parts – filament, hook and basal body

b. Rotates like a propeller

c. Arrangement

1) Monotrichous

2) Lophotrichous

3) Amphitrichous

4) Peritrichous

d. Chemotaxis – movement in response to chemicals

1) Positive – move toward chemical (food)

2) Negative – move away from harmful chemical

3) Receptors in cell membrane bind chemicals & affect flagella

2. Fimbria

a. Don’t produce movement

b. Used to adhere to cells and other surfaces

c. gonococcus (gonorrhea) adheres to epithelium of urethra

 


3. Pilus – “sex pilus”

a. Used for conjugation in gram-negative bacteria (“mating”)

4. Glycocalyx – “coating” on bacterial cell

a. Slime layer – protects against dehydration and loss of nutrients

1. ex) sticky slime captures nutrients (sugar); plaque on teeth

b. Capsule – thick mucus covering

1. Resist phagocytosis by WBC’s, increases pathogenicity

D. Cell Envelopes

1. Cell Walls

a. Gram positive

b. Gram negative

c. Non-typical cell walls

2. Cell Membranes

 

3. Periplasmic space

a. Between cell wall and cell membrane

E. Cell Walls

1. Surrounds the cell membrane

2. Protects (osmotic pressure), maintains shape, anchors flagella

3. Clinically

a. Contributes to pathogenicity & stimulate immune response

1) Endotoxins – lipids in gram negative walls

2) Teichoic acid – proteins in gram positive cell walls

b. Target for some antibiotics, disinfectants

4. Composed of Peptidoglycan (a.k.a. murein)

a. Peptido – polypeptide (chains of amino acids)

b. Glycan – sugars (2 repeating monosaccharides)

1) N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)

c. Wall is composed of repeating units of sugars attached by polypeptides

d. Cell walls differ in gram-positive and gram-negative bacteria

e. NOTE

1) Penicillin disrupts polypeptides

2) Lysozyme (enzyme) in tears/saliva disrupts glycan

3) Results in cell lysis

 

F. Gram Positive Cell Walls

1. Thick layer of peptidoglycan (20-80 nm)

2. Teichoic acid is bound to peptidoglycan

a. Teichoic acid is made of alcohol (glycerol or ribitol) and phosphate

b. 2 types of Teichoic acid

1) Wall Teichoic acid – bound to peptidoglycan on surface

2) Lipoteichoic acid – linked to plasma membrane

c. Functions

1) Regulate cation flow, growth, wall protection

2) Antigenic specificity – makes bacteria unique; what our immune                                                             system responds to

3. Usually cell wall and cell membrane are pressed together leaving only thin

to no periplasmic space

G. Gram Negative Cell Walls

1. Two Layers

a. Outer membrane

b. Peptidoglycan layer (1-3 nm)

 


2. Outer membrane – similar to cell membrane but has special lipids

a. Makes gram negative more resistant to disinfectants and dyes; harder to kill

than gram positive bacteria

b. Alcohol based compounds can dissolve outer layer

c. Lipopolysaccharides (LPS) are lipids on outer membranes that have

polysaccharides attached to them on outer surface.

1) Block host defenses and serve as receptors

2) Toxic when released during infection

a) Endotoxins

d. Lipoproteins

1) Anchor the outer membrane to the peptidoglycan layer.

e. Porins

1) Proteins that form channels for the entry and exit of solutes through the

                                    outer membrane of the gram-negative cell wall. 

3. Peptidoglycan layer – gram negative cell walls

a. Thin and within periplasmic space

 

H. Non-typical Cell Walls

1. Mycobacterium have peptidoglycan and stain gram +, but primarily composed

of a thick, waxy lipid called mycolic acid.

a. Mycolic acid – contributes to pathogenicity

b. Resistant to chemicals and dyes

1) Acid-fast stain used

2. Mycoplasmas – lack cell walls

a. Membranes have sterols that make it stable; resist lysis

I. Cell Membranes

1. Located beneath cell wall

2. Phospholipid bilayer with proteins embedded throughout

3. Functions

a. Regulate transport via selective permeability

b. Enzymes for energy reactions

c. Secretion of toxins and enzymes to environment

d. Enzymes for synthesis of molecules for cell envelope

J. Cell Cytoplasm

1. 70-80% water

2. Nutrients – sugars, amino acids, electrolytes, etc

3. Bacterial Chromosome, Plasmids, Ribosomes, Granules

K. Bacterial Chromosome

1. Heredity information for cell regulation

2. Singular circular strand of DNA

3. No nucleus; Chromosome located in area called Nucleoid

4. Genes are located along length of chromosome; recipes to make proteins

L. Plasmids

1. Circular pieces of DNA; contain a few dozen genes

2. Duplicated during bacterial reproduction and passed on to offspring

3. Not necessary for bacterial survival

4. Carry adaptive genes for survival such as             drug resistance genes.

a. Antibiotic resistant bacteria

5. Used in genetic engineering

M. Ribosomes

1. Site of protein synthesis

2. Composed of rRNA and protein

3. Prokaryote ribosomes are rated as 70s

a. Composed of 2 subunits, 50s and 30s

b. S rating is based on weight and size

4. Eukaryotic ribosomes are 80s

a. 2 subunits of 60s and 40s

N. Inclusions

1. Membrane structures for storing nutrients that are used in time of need

a. Glycogen and B-hydroxybutyrate (ketone)

O. Bacterial Endospores (a.k.a. spores)

1. Dormant structures produced by Bacillus, Clostridium, and Sporosarcina

2. Highly resistant to harsh conditions; can survive millions of years

a. Heating, drying, freezing, radiation, chemicals

3. Medical significance

a. Resist normal disinfectants, soaps, boiling water

b. Inhabit dirt and dust

c. Easily contaminate open wounds; infection in clinical settings

d. Food poisoning; C. botulinum

3. 2 phase life cycle

a. Vegetative cell – metabolically active and growing

b. Endospore – dormant, high resistance for long-term survival

4. Sporulation – process of vegetative cell forming an endospore

a. Triggered environmentally; usually due to depletion of nutrients (amino acids)

P. Endospore Formation (Sporulation)

1. Sporangium formation

a. Stimulated vegetative cell converts to spore producing cell called sporangium

1) Chromosome is duplicated

2) 2 new structures are formed each with a chromosome

a. Sporangium and Forespore

3) Sporangium engulfs Forespore

b. Sporangium adds protective layers around forespore

c. Mature endospore (protected and dormant) is released from sporangium

Q. Germination of Endospore

1. Favorable conditions trigger germination; water and nutrient

2. Activated enzymes digest protective layers

3. Reverts back to vegetative cell (active bacterium)

II. Bacterial Shapes, Arrangements and Sizes

A. Shapes

1. Coccus – round, ball-shaped

2. Bacillus – rod-shaped

a. Coccobacillus – short, plump rod

b. Vibrio – curved rod

3. Spiral

a. Spirillum – rigid spiral-shaped, corkscrew

a. Spirochete – more flexible, spring-like shape

1) ex. Treponema pallidum – syphyllis

*Pleomorphism – cells in a single species vary in shape

B. Arrangement

1. Cocci

a. Diplococci – 2 cells

b. Tetracocci­ – 4 cells

c. Streptococci – chains of cells, a few to hundreds

d. Staphylococci – irregular clusters of cells

e. Sarcina – organized cubital packets of 8

 

2. Bacillus

a. Diplobacilli – 2 cells

b. Streptobacilli – chains of several cells

c. Palisades – parallel arrangement of cells

C. Size

1. Most bacteria between 1 – 10 um

2. Cocci – 0.5 to 3.0 um

3. Bacilli – up to 2 um in diameter and 2-8 um in length

4. RBC – 8 um

5. Rhinovirus – .03 um (30nm)




III. Classification of Prokayotic Domains

A. Bergey’s Manual of Systematic Bacteriology

1. Reference manual divides all known prokaryotes (archaea and bacteria) into 5 volumes          based on phenetic (staining, metabolic) and phylogenetic (evolutionary relationships).

 

B. Pronunciation guide

-ae is long ī        *pneumoniae is nū-mō-nē-ī

-i is long ē          *tetani is tet-an-ē  (sometime ī as in E. coli)

-ii is ē ē              *boydii is boi-dē-ē

-aceae is ā sē ē   *rosaceae is rō-zā-sē-ē

 

C. Medically Important Classification System (and Examples)

Gram-positive

Cocci

a. Staphylococcus

1) Staphylococcus aureus

2) Skin infections, food poisoning, toxic shock syndrome

3) MRSA (methicillin-resistant Staphylococcus aureus)

 

b. Streptococcus (strep throat, cavities)

1) Streptococcus mutans – cavities

2) Streptococcus pyogenes (pī aj en ēz) – strep throat

Rods

c. Bacillus

1) Spore producing

2) Bacillus anthracis (an thrā sis) – anthrax

d. Clostridium

1) Spore producing

2) Clostridium tetani (tet an ē) – tetanus

3) C. botulinum – botulism

4. C. perfringens – food-borne diarrhea

5) C. difficile, a.k.a. C Diff

a. overuse of antibiotics, serious diarrhea

e. Listeria monocytogenes – food spoilage

f. Lactobacillus – found in mouth, intestines, vagina

g. Corynebacterium diphtheriae (kor-ī-nē-bak-tir-rē-um  dif-thir-ē-ī)

1) Diphtheria – respiratory infection

h. Mycobacterium tuberculosis, Mycobacterium leprae

i. Nocardia asteroides – pulmonary infection

j. Streptomyces – major source of antibiotics

 

Gram-Negative

Cocci

a. Neisseria gonorrhoeae (gon-or-ē-ī) – gonorrhea

b. Neisseria meningitides – meningococcal meningitis

c. Chlamydia trachomatis – STD

Rods

b. Pseudomonas

1) Pseudomonas aeruginosa – nosocomial infections, resistant to antibiotics

c. Burkholderia cepacia – contamination in hospitals

d. Escherichia coli – common enteric, most not pathogenic in intestines, can cause UTI                              1) Harmful strain is E. coli O157:H7

2) O and H refer to antigens on the cell surface and flagella, respectively

NOTE:

Strain – bacteria that differ in structure or metabolism from others of the same species.

e. Serratia marcescens – UTI and respiratory infections in hospitals

f. Salmonella enterica – salmonellosis (foodborne illness)

g. Enterobacter aerogenes (ā-raj-en-ēz) and E. cloacae (klō-ā-kī)– UTI in hospitals

h. Shigella – dysentery, severe diarrhea with blood/mucus

 

Vibrio

a. Vibrio cholerae (chol-er-ī ) – cholera

b. Campylobacter jejuni (jē-jū-nē) – foodborne disease

c. Helicobacter pylori (pī-lor-ē) – stomach ulcers

 

Spirochete

a. Treponema pallidum – syphilis

b. Borrelia burgdorferi – Lyme disease

 No Cell Walls

a. Mycoplasma pneumoniae (nū-mō-nē-ī)

b. Ureaplasma – UTI

 


 

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