Introduction to Microbiology Flashcards
What are the sizes of Viruses and Bacteria, and what type of microscope is used to view them?
Viruses (0.03-0.3 microns; Electron-light microscope)
Bacteria (0.1-10 microns; Light microscope)
Unique Features: Viruses
Smallest infectious particles
Require host for replication
Unique Features: Bacteria
Simple unicellular organisms
Prokaryotes
Unique Features: Fungi
More complex
Eukaryotes
Unicellular (yeast) or filamentous (mold)
Unique Features: Parasites
Most complex
Eukaryotes
Unicellular to multicellular
What is unique about prokaryotes compared to eukaryotes?
- No nucleus
- Single, double-stranded, circular DNA chromosome (Haploid)
- Smaller ribosome (70s)
- Mesh-like peptidoglycan cell wall
Classification of Bacteria (4 things)
- Visible features (shape, spore formation, gram reaction)
- Nutrition (growth media, aerobic vs anaerobic, temperature for optimal growth)
- End products (production of specific enzymes/toxins)
- Surface molecules (antigen composition)
***Currently developing a more rigid classification system by nucleic acid analysis (PCR, nucleic acid homology, and gene probes)
What are the shapes of Cocci, Bacilli, and Spirochetes?
Cocci (spherical)
Bacilli (rod; straight or curved)
Spirochetes (spiral)
Are gram positive or gram negative cell walls more simple?
Gram Positive
Do gram positive or negative cells stain purple?
Positive (Purple = Positive)
Where is the peptidoglycan layer found?
Internal to the capsule (if present) and external to the cytoplasmic membrane (not found in Mycoplasma and Chlamydia)
Functions of peptidoglycan
Provide protection
Determines shape
Unique to bacteria; both gram positive and gram negative have it
Structure of Peptidoglycan
- Linear chain of alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) with tetra peptide crosslinks
- Linked via B-1,4 linkages
Where does lysozyme from endothelial cells attack bacteria?
At the B-1,4 linkages of the peptidoglycan layer
Proinflammatory effects of Peptidoglycan
Fixes Complement
Binds pattern recognition receptors (e.g. Toll-like receptors)
Triggers TNF production
Unique features of gram-positive envelope
- Thick layer of peptidoglycan (many layers w/ extensive crosslinking)
- Teichoic Acid (PG associated; PM associated (Lipoteichoic Acid, LTA))
- Various proteins and lipids which differ between bacteria
What are the functions of Teichoic Acid and LTA?
Promote attachment of bacteria to other bacteria or host cells (virulence factors)
Unique features of gram-negative envelope
- Greatly reduced peptidoglycan
- PG (peptidoglycan) is within the periplasmic space
- Surrounded by an OUTER MEMBRANE rich in porins and endotoxin/LPS (lipopolysaccharide; important pathogen-associated molecular pattern)
Structure of outer membrane of gram-negative envelope
- “Stiff canvas sack”
- Maintains structure/permeability barrier
- Rich in porins (allow diffusino of hydrophilic molecules less than 700 Da through)
- Structural and transport/secretory proteins
- Asymmetric phospholipid bilayer
Inner leaflet vs outer leaflet of Outer Membrane of gram-negative envelope
Inner leaflet contains phospholipids
Outer leaflet contains LPS (creates asymmetry of membrane)
What are the 3 subunits of LPS/Endotoxin?
Lipid A, Core Polysaccharide, O Antigen
Lipid A
- Responsible for endotoxin activity of LPS*
- Fatty acids anchor it into outer membrane
Core Polysaccharide
- Branched polysaccharide of 9 to 12 sugars
- Required for bacterial structure and viability
O Antigen
- Long, linear polysaccharide of repeating saccharide units of 4 to 7 sugars/unit
- **Helps to classify specific serotypes bacteria due to VARIATION
- Missing in Neisseria (LOS)
How does LPS/Endotoxin cause inflammation/septic shock?
Binds CD14 and TLR4 on phagocytes/APCs, which activates the immune system and causes transcription of proinflammatory cytokines (TNF, IL-1, IL-6)
Acid-fast Bacteria Characteristics
- Complex cell envelope
- Mycolic acids (long, branched chain fatty acids) covalently bound to the peptidoglycan via a polysaccharide
- Other mycolic acid-containing compounds as well as complex lipids form a thick waxy membranous layer outside of the peptidoglycan
Examples of Acid-Fast Bacteria
Mycobacteria, Nocardia, and Corynebacteria
Weakly-stained bacteria
Legionella
Cell wall too thin to be visible
Treponema, Leptospira
Wall-less bacteria
Mycoplasma
Gram Stain Steps
- Crystal Violet
- Gram Iodine
- Decolorizer (Alcohol or Acetone)
- Safranin Red
Acid-Fast Stain Steps
- Stain all bacteria red by carbol fuchsin
- Acid alcohol added to remove stain from everything except those that are Acid-Fast
- Methylene blue used to counter-stain and label other bacteria
Acid Fast Cell Wall
- Waxy outer wall found on Mycobacteria and Nocardia
- Outermost layer is rich in mycolic acids, which causes a very SLOW GROWING bacteria
Acid Fast Structure
***Similar to Gram Positive
(Inner plasma membrane overlaid with peptidoglycan and no outer membrane)
-Contains Lipoarabinomannan (LAM), Arabinogalactans, and Mycolic Acid
Lipoarabinomannan (LAM)
Functionall related to LPS (structure, viability, activates immune system)
Arabinogalactans
Branched polysaccharides that bind to mycolic acid
Mycolic Acid
60-90 carbons
-WAXY
Pili/Fimbrae (two functions)
- Common or somatic (involved in attachment to epithelial cells; usually called adhesins, lectins, evasins, or aggressins)
- Sex - only one per cell (involved in gene transfer; usually a plasmid)
Important antigen associated with Flagella
H-Antigen
Flagella function
Locomotion; can be located at one or both poles
-Important VIRULENCE FACTOR (if removed, more difficult to cause infection)
Important Qualities of Capsule
- Can be present on both gram positive and negative
- Called slime layer or glycocalyx
- Hydrophilic
- Aides in protection from immune system (ANTIPHAGOCYTIC, poorly antigenic, major VIRULENCE FACTOR)
- Needed to survive in host, not in culture
- **Capsule + protein conjugate serves as antigen for many vaccines
Biofilm
An organized community of microbial cells that has a capsule/slime layer over the entire population
Quellung reaction
Used to detect encapsulated bacteria
How are encapsulated bacteria cleared from the body?
Opsonized and cleared by the spleen
Endospores
Only formed by Gram POSITIVE bacteria in harsh environmental conditions (e.g. low nutrition)
- Bacteria convert to vegetative state
- Gives rise to a single bacteria when conditions are favorable
Endospore Characteristics
- Dehydrated, multishelled structure
- Contains a complete copy of the chromosome
- Has minimum proteins and ribosomes
- High concentration of calcium bound to DIPCOLINIC ACID
- Inner membrane, two peptidoglycan layers, and an outer keratin-like protein coat
- Multiple coats make it resistant to many treatments*
Endospores: Human pathology
-Can be aerosolized (airborne, bioterrorism)
-Difficult to manage in hospital settings, as they can withstand extreme pH, temperature (boiling), radiation, attack by enzymes and chemicals
-Can exist for centuries
Sterilization: Autoclave, 120 degrees C at high pressure for over 20 mins, 70% EtOH, 10% bleach and water
