Bacterial Cell Structure

Eukaryotes v. Prokaryotes

Eukaryotes: comparmentalized
Prokaryotes: simple, efficient, etc

Essential Components of Prokaryotes

Cytosol, Nucleolus, Ribosomes, Cytoplasmic membrane, cell wall

Non-essential components of Prokaryotes

Pilus/fimbria, Flagellum, Plasmid, Granule, Capsule/Glycocalyx, Spore
These are involved in virulence of the bacteria


site of metabolic rxns, reserve granules, nucleoid, ribosomes, mRNA


Contains bacterial chromosome.
contains no nuclear membrane, contains 2-4 per cell depending on growth rate.

Bacterial chromosomes

Large single/double-stranded DNA, supercoiled

Bacterial Ribosome

70S (30S + 50S)
Target for antibacterial drugs

Bacterial Cytoplasmic Membrane

phospholipid bilayer, contains no sterols (except mycoplasma --> walking pneumonia), Site of electron transport and energy production

Bacterial Cell Well

protects, gives shape, this is what gives bacterial their Gram stain (positive v negative), target for antibiotics
Exception: mycoplasma pneumoniae does not have a cell wall

Gram (+) vs Gram (-)

Murein Layer: Gram pos has a very thick cell wall, 20x more than Gram neg
Teichoic Acid: present in gram pos
Outer membrane: present in gram neg
Periplasm: present in gram neg
Susceptibility to penicillin/lysozyme: high in gram pos

What is Peptidoglycan called?

Murein. Linking of amino acids.
Only found in prokaryotes.

Gram-positive Cell Wall

Thick peptidoglycan layer, Teichoic acid linked to muerin, Lipoteichoic acid anchored in cell membrane
Resistant to many enzymes except lysozyme

Periplasmic space/gel

Thin murein layer found only in gram negative bacteria.
Contains enzymes

Outer membrane

Found only in gram negative bacteria.
Transmembrane proteins and porins
Lipopolysaccharides found on the outer layer, functions as antigens

What are the components of Lipopolisaccharides?

Found ONLY in Gram neg. Also called an endotoxin.
Endotoxin: toxin that is part of the cell, typically only released when cell is lysed.
LipidA: Toxic aspect of the lipopolisaccharide in all Gram neg bacteria.
Core: unusual carbohydrate residues
O Antigen

Examples of Gram (+) pathogens

Staphylococcus aureus: Skin infections, endocarditis, food poisoning

Examples of Gram (-) pathogens

E. Coli: UTI, Meningitis, GI tract infections

Examples of cell that will not stain

Mycoplasma: no cell wall
Spirochetes: too thin to be seen (although Gram neg)
Mycobacterium: waxy cell wall, dyes won't go through

Cell walls of Mycobacterium

Major determinant of virulence, composed of peptidoglycan + complex lipids.
Unique cell wall that is responsible for resistance to drying and chemical disinfectants, common antibiotics, osmotic lysis via complement deposition, lethal oxidation --> surviva

Describe Acid Fast Stain?

Used to stain Mycobacterium.
Add heat + fuschin --> turns pink.
Adding acid alcohol and methylene blue counterdye won't change color of the stained cell.

Shape of Bacillus

Rod. Ex: E. coli

Shape of Coccus

Circle; Ex: staph aureus

Shape of Spirochete

Spiral; Ex: Treponema Pallidum

Shape of Coccobacillus

Short rod; Ex: Haemophilus influenzae

Shape of Vibrio

Curved rod; Ex: Vibrio Cholerae

Gram(+) cocci in clusters


Gram (+) cocci in chain


Gram (-) rods

E. coli

Gram (+) diplococci

Streptococcus pneumonia...


Small circular extra-chromosomal (episomal) DNA - nonessential; dsDNA; often codes for virulence factors, antibiotics resistance, and self-transmission

What are Pili (fimbriae)?

Hair-like porjections of cell, composed of pilin.
Common pili: around the cell, important to adhesion to host cell surface
Sex pilus: connection between another cell, transfer DNA


Motility and Chemotaxis
Monotrichous/polar: single polar flagellum
Lophotrichous: multiple flagella, same spot
Peritrichous: all around the cell

Components of Flagella Apparatus

Basal body: protein organized as rings, between cell membrane and cell wall, Hook, Filament (made of flagella)

Components of Spirochetes

Motility: movements of endoflagellar filaments.
Endoflagellar filaments surround cytoplasm. Outer and inner membranes present.
Gram (-), but poor stain, too thin

Important Spirochetes

Borrelia burgdoferi: Lyme disease

Capsule/Slime Layer

Outside cell wall
Also called glycocalyx, made of polysaccharides
Well defined = Capsule
Less defined = slime layer
Virulence factors: attachment to surfaces, protection against phagocytic engulfment

What is Biofilm?

Kind of like a giant capsule made of polysaccharide, protects bacteria, very hard to eliminate pathogen with antibiotics b/c difficult to access. Slimy. Can reach your heart/bowels.
65% of hospital infections caused by Biofilm

Functions of Bacterial Envelop?

Cytoplasmic membrane + cell wall + external structures.
Maintains Structure
Allows for Host interaction
Results in antiobitic sensitivity/resistance

What is a spore?

Dormant for of a bacterial cell
Occurs during starvation --> sporulation. Returns to growing state/vegetative form when nutrients available --> germination. Resistant to environmental stressors. Found only in Gram(+).

Important examples of spores?

Bacillus anthracis (anthrax).
Clostridium Tetani (tetanus).

What makes up a spore?

Coat made of keratin-like protein, Cortex made of peptidoglycan-like, Core made of calcium dipicolinate and protects DNA.

What is Beta Hemolysis?

Full Hemolysis

What is Alpha Hemolysis?

Incomplete Hemolysis

What is Gamma Hemolysis?

No Hemolysis