Bacterial Cells: Structure/Function

Describe Eukaryotic Cells
- Cells from Mammalian organisms
- Includes algae, fungi, protozoa
- Composed of a plasma membrane, cytoplasm, centrioles, and the membrane bound organelles: mitochondria, ER, golgi, and the nucleus
Describe Prokaryotic Cells
- Includes the 300 different types of bacteria
- Composed of a cell wall, membrane, cytoplasm, ribosomes, and a nucleoid
- All are unicellular
- Have cytochromes in place of mitochondria
What is a capsule and its function?
- The capsule is a polysaccharide outer cover that some bacteria have
- It is used for attachment to the host cell
- Represents a determinant of pathogenicity
- It makes it hard for neutrophils to engulf it
What is the function of pilli?
- Most gram negative bacteria use pilli to transfer DNA from one bacteria to another (a sex organ)
- Also for attachment
What are the 3 types of bacteria and what color do they stain?
1. Gram + has a thick peptidoglycan layer that stains bluish/purple in crystal violet
2. Gram - has a thin peptidoglycan layer that stains red/pink in safranin
3. Acid fast (Mycobacterium) has a cell wall with mycolic acid
What is the periplasmic space?
In Gram - bacteria, the space between the cytoplasmic membrane and the outer membrane and the between the outer membrane and the cell wall. It is filled with toxins.
Bacterial Nomenclature
Binomial: genus + species
Define Species
Strains with a high degree of overall similarities that differ fromother strains
Define genus
A collection of similar species
What 3 things can the nomenclature indicate?
1. Morphology
2. Discoverer
3. Disease association
Why is bacterial classification important?
Because it
A. Facilitates proper lab identification of clinical isolates
B. Necessary for determining etiology of infectious diseases
C. Essential to nomenclature
How is phylogenetic relatedness determined?
By comparison of the 16S rRNA sequences
What is the average diameter and length of bacteria?
0.2 - 2.0 um in diameter and 2 - 8 um in length
Wht are the 3 shapes of bacteria?
1. Cocci - spherical
2. Bacilli - elongated
3. Spirochetes - spiral
What shapes can bacteria take duing reproduction?
1. Diplococci (pairs)
2. Streptococci (chains)
3. Staphylococci (clusters)
What type of bacteria are the Neisseria genus? (N. gonorrhea, N. sicca, N. meningitis)
Gram Negative Diplococci
What type of bacteria are Streptococcus pneumoniae?
Gram Positive Diplocci
Are all streptococci gram negative or positive?
Gram positive
What are 2 examples of a single bacillus associated with disease?
1. E. Coli - diarrhea, septicemia, UTI
2. Pseudonomas auruginosa - cystic fibrosis, burn trauma
What are 2 exampls of coccobacilli that are associated with disease?
1. Bordetella pertussis - whooping cough
2. Hemophilus influenza - childhood meningitis
What is an example of a Vibrio bacteria?
Vibrio cholera - profuse diarrhea
What are 2 examples of a disease associated Spirochete?
1. Borellia burgdorferi - Lyme Disease
2. Treponema pallidum - Syphillis
What agar is good to use to grow bacteria that has demanding requirements?
Blood agar
What agar is good to use for acidic bacteria like Neisseria?
Chocolate agar
What is chocolate agar?
heated blood agar (heat denatures the Hb)
What agar is used to isolate gram negative bacteria?
EMB agar
What is EMB agar?
Eosin Methylene Blue on agar that does not allow growth of gram positive bacteria
What is useful about growth agar?
isolate colonies so we can study metabolic activities, other associated function, and color changes
What is Klebsiella?
- a genus of gram negative, oxidase negative, rod shaped bacteria that lives in the GI tract and causes UTI and pneumonia.
- when grown on nutrient agar, forms mucoid cultures
What are proteus species?
- Live in the GI tract and cause kidney infection (pyelonephritis)
- form mucoid cultures
Why do mucoid cultures present?
Due to overproduction of capsule
What colors do E. coli, staph, and strep appear in colony isolation?
1. E. coli - green
2. Staph - gold
3. Strep - white
What do oxidase positive bacteria possess?
cytochrome c oxidase (so they can use oxygen for energy production)
What are nucleoids
areas of DNA concentration
What kind of ribosomes do bacteria have?
What do cytoplasmic granules contain?
How do bacteria compartmentalize their long DNA
the gyrase enzyme supercoils DNA
What are the 3 components of the bacterial envelope?
1. Capsule
2. Cell Wall
3. Outer Membrane
What is the Cell Wall of Gram + bacteria composed of?
1. Peptidoglycan
2. Teichoic acid
3. Lipoteichoic acid
What is the Cell Wall of Gram - bacteria composed of?
1. Peptidoglycan
2. Periplasmic space
3. Outer membrane
4. Proteins
5. LPS
What is peptidoglycan made up of?
glycan chains of GlcNAc and MurNAc crosslinked by a peptide bridge
What is teichoic acid?
polyribitol phosphate or glycerol phosphate crosslinked to peptidoglycan. It is the major surface antigens used for serological typing. Also is a source of adherence and transport. Only in Gram +
What is lipoteichoic acid?
lipid linked teichoic acid. Only in Gram +
What is in the periplasmic space?
enzymes for transport, degradation, and synthesis. For example, phosphatases, proteases, endonucleases, binding proteins, AAs, inorganic ions, chemoreceptors, and drug resistance enzymes. It detects environmental factors and transports needed nutrients into the cell. Only in Gram -
What is the outer membrane?
phospholipids and saturated fatty acids. Gram - only. Serves as a permeability barrier and antibiotic resistance.
What are the 3 components of LPS?
1. Lipid A - an important endotoxin
2. Core - polysaccharides like KDO
3. O Antigen
What is the purpose of the cell wall?
protect the cell membrane from osmotic lysis and determine the shape and rigidity of the cell
What are the components of peptidoglycan?
Alternating residues of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) linked by B-1-4 glycosidic bonds
What are 2 factors that affect the integrity of the cell wall?
1. Beta lactam antibiotics (penicillin, cephalosporins) inhibit cell wall formation
2. Lysozyme degrades the structural integrity of the cell wall's peptidoglycan
How does penicillin inhibit cell wall formation?
By binding to transpeptidase preventing cross linkage
What distinguishes the bacterial cytoplasmic membrane with Eukaryotic membranes?
The lack of sterols
What are the 5 functions of the cytoplasmic membrane?
1. Osmotic barrier
2. Electron and Photon transport (site of ATP production)
3. Cell wall biosynthesis
4. Chemotaxis and flagella activity
5. Transport of molecules
What causes bacterial septic shock?
Lipid A (from the LPS in Gram Negative bacteria) activates macrophages that will produce abnormal amounts of cytokines (IL-1 and TNF alpha). IL-1 goes to hypothalamus and upregulates the thermostat (fever). TNF alpha goes to endothelial lining of blood vessels and increases permeability which decreases pressure (hypotension). Can also stimulate T-Cells to increase IFNy production. Depresses iron release in circulation (bacteria won't grow as fast). Regulates release of sugar (hypoglycemia).
What are 3 functions of LPS?
1. Confers a negative charge to bacteria (G- only)
2. Repels hydrophobic molecules like antibiotics, bile salts, and detergents
3. Induces fever in a bacterial infection
What is the LPS equivalent in G+ bacteria?
LTA (lipoteichoic acid)
What 2 bacterial genera characteristically create spores?
1. Bacillus (aerobes)
2. Clostridium (anaerobes)
When does sporulation occur?
When bacteria is under environmental stress (i.e. lack of nutrients, extreme temperatures) because spores resist physical and chemical conditions that are detrimental
What components of spores help them resist detrimental chemical and physical conditions?
1. Keratin is in the spore's coat making it resist chemicals
2. Calcium and dipicolinic acid contribute to heat resistance
What is the medical significance of spores?
disease dissemination
How do you destroy a spore?
Autoclaving at 121 degrees celsius for 20 min