Microbiology Strx and Fnxn Flashcards
What is a microbe?
Bacteria (prokaryote)
Protozoa (eukaryote)
Fungi (eukaryote)
Viruses (neither prokaryotic nor eukaryotic)
Prokaryote
Bacterial Strx
Bacterial Strx ctd.
Rods
Aka “bacillus”
Two bacilli together – Diplobacilli
Chains of bacilli are called streptobacilli
Other arrangements are called “palisades”
Side by side/ “X” “V” or “Y” figures
Cocci
Spirochete: Flexible undulating corkscrew
Spirillum: RIGID corkscrew shape
Bacterial Strx properties
Inner workings
Flagella and pili (fimbriae)
Capsule
Cytoplasmic membrane
Cell envelope
Gram positive
Gram negative
The Gram stain
Mesosome
Plasmid DNA
PK locomotion
Flagella & pilli
Whatever is external on bacteria is HIGHLY ANTIGENIC
Flagella -some have >1.
Used by bacteria for locomotion.
Composed of flagellin.
Different arrangements of flagella:
Monotrichous (Vibrio cholerae)
Lophotrichous (Bartonella bacilliformis)
Amphitrichous (Spirillum serpens)
Peritrichous (Escherichia coli)
Recognition of flagella helps determine which antimicrobial to use
The Flagellar Motor
Made of the protein flagellin and consists of a filament and basal region. The basal region has a hook and a basal body which has a rod and rings. Gram positive organisms have 2 rings, one in the cell wall and one in the cell membrane. Gram negative organisms have 4 rings, 2 in the cell wall and 2 in the cell membrane.
Pili (Fimbriae)
The Capsule
Some have these. Those that can…
A slimy outer coating not found in all bacteria.
Usually a complex of high molecular weight polysaccharides.
A.k.a. Slime or glycocalyx (generally more loosely associated – adherence properties).
Special Note: BIOFILMS.
Can be antiphagocytic - resistant to macrophage cells that would try to engulf it.
Cytoplasmic membrane
Peptidogycan
Gram Positive and Gram Negative Bacterial Cell Envelopes
The Gram Stain
The gram stain procedure was originally developed by the Danish physician Hans Christian Gram (no kidding) to differentiate pneumococci (Streptococcus pneumoniae) from Klebsiella pneumoniae.
The difference between gram-positive and gram-negative bacteria is in the permeability of the cell wall to “purple colored iodine-dye complexes” when treated with the decolorizing solvent.
Gram-positive bacteria retain purple iodine-dye complexes after the treatment with the decolorizing agent, gram-negative bacteria do not retain complexes when decolorized. Safranin is used after decolorization treatment to “counterstain” gram-negatives.
Gram Stain Process
Works due to diff in peptidoglycan in bacterial cell walls
Bacteria are heat fixed to a slide.
Crystal violet is added – all cells stain blue.
Iodine fixes the stain into the bacterial cell.
Alcohol decolorizes gram negative bacteria. Gram positives remain blue/purple.
Safranin (counterstain) stains the gram negative bacteria a pink color.
Gram Positives
Found only in the gram + cell wall are:
- Teichoic acids / Teichuronic acids*
- Lipoteichoic acid (LTA)*
- Polysaccharides*
Teichoic Acid.
A water soluble polymer of ribitol or glycerol residues joined by phosphodiester linkages.
Teichuronic Acid.
Similar to teichoic acid, but made in phosphate-limiting conditions.
Lipoteichoic Acid (LTA).
Lipid attached to Teichoic Acid – Adhesin!
Polysaccharides.
Most likely composites of sugars released from teichoic and teichuronic acid.
Gram Negatives
Found only in the gram negative cell wall are:
Lipoproteins
Periplasmic space
Outer membrane
Lipopolysaccharide
Periplasmic space
A gel-like matrix between the cytoplasmic membrane and the outer membrane
Contains enzymes for nutrient breakdown and substrate binding proteins, including penicillin binding proteins.
Lipoprotein
Cross-links outer membrane to peptidoglycan
In the periplasmic space
Outer Membrane
A phospholipid bilayer containing lipopolysaccharides (later) Contains porins (non-specific pore proteins), anchor proteins and transport proteins. Protects the cell from hydrolytic enzymes.
Lipopolysaccharide (LPS)
Made of Lipid A (a complex lipid) covalently attached to a polysaccharide with core and terminal repeat units.
LPS (Lipid A) = endotoxin. It is extremely toxic to animals.
The lipid portion of LPS is attached to the outer membrane by hydrophobic bonds.
The polysaccharide chain of repeating units is called the O-antigen, is exposed to the outside of the cell, and is antigenic.
The Mycoplasma (and Ureaplasma)
The smallest free-living organisms.
NO CELL WALL!
That means no peptidoglycan.
Bacterial stains don’t work well.
The only barrier is the cytoplasmic membrane.
Membranes contain sterols – required for growth (not synthesized by the bacterium).
Many mycoplasmal pathogens exhibit filamentous or flask-shaped appearances and display prominent and specialized polar tip organelles that mediate attachment to host target cells.
Acid fast bacteria
Mycobacteria (and Nocardia).
Contain small amounts of peptidoglycan.
Contain large amounts of glycolipids.
Lipoarabinomannan (LAM).
Mycolic acids (60% of the cell wall).
Make the cell walls impermeable.
DONT have lipid A (endotoxin)
Acid fast stain, not gram stain, will reveal if this is culprit
Gram negatives have six classes; Gram positives have an additional class Play a major role in bacteria interacting with their enviroment and helping to deterimine their pathogenicity.
Structure – There are some simple systems like T1SS that consist of transporters, outer membrane factors, and membrane fusion proteins; while others (T3SS, T4SS, and T6SS) involve a transmembrane structure (injectosome) which consists of more than 25 proteins.
Genes determine which secretion system.
Inject these secretions into other cells
Protein Secretion Systems
Endospores
Made by Bacillus and Clostridium (makes heat-resistant) species in nutrient-limiting conditions (i.e. starvation).
-Highly resistant to heat, desiccation, and chemical damage (innate to spore, not bacteria).
-Reasons for heat resistance:
Dehydration.
Calcium dipicolinate in the core (5-15% of the spore dry weight).
Endospore Formation
Spore Wall (Exosporium): Contains normal peptidoglycan. Will be the cell wall of the germinating bacterium.
- *Spore Coat**: Contains keratin-like proteins, very impermeable to chemicals.
- *Cortex**: The thickest part of the spore envelope – contains peptidoglycan with fewer cross-links.
- *Core**: Contains the calcium dipicolinate, and all of the nucleic acid for later growth.**
Viruses
There are 2 types of viruses:
Procaryotic viruses = Bacteriophage (upon entering, do NOT lyse cell)
Eukaryotic viruses, e.g. Animal viruses
General characteristics
Obligate intracellular parasites (need a host!)
The viral particle is DNA or RNA in a protein coat with or without a membrane
The outer coat protects the genetic material and facilitates adhesion/infection
Contains few, if any enzymes, organelles or other biosynthetic machinery.
The nucleic acids code for proteins needed for viral replication.
Enveloped Viruses:
Acquire membrane from the host.
Naked capsid viruses:
Consist of the nucleic material with a coat or capsid. …more easily transmitted.
Virues, ctd.
Viral structures/nomenclature to know:
Envelope
From host
Nucleocapsid/Capsid
Protects nucleic acids (DNA or RNA)
Capsomere
Subunit of the capsid structure.
Polyhedral/Helical
Different Capsid structures.
Viroids
Very small single-stranded circles of RNA (300-400 nucleotides).
- Cause disease in plants.
- Replication strategy unknown – probably replicate through host RNA polymerase.
- HDV is similar to a viroid.
Hepatitis D is similar to a viroid
Prions
Cause “slow virus disease”
E.g.s: Scrapie, Kuru, Creutzfeldt-Jakob disease, and “Mad Cow” disease. These diseases are subacute spongiform encephalopathies
Resistant to heat inactivation (autoclaving), radiation damage, and nucleases, e.g., DNAses and RNAses (They contain no nucleic acid)
Can be inactivated by detergents, urea, phenol, etc.
Causative agent is the prion protein: PrPSC
Prions ctd
Kuru: Human disease in cannibals in Papua New Guinea:
Mad Cow Disease (BSE):
A very real, serious problem is vCJD
For people, there’s CJD from an unknown source and vCJD – thought to be a variant form of BSE infectious for people.
PrPSC has the same protein sequence as a normal cellular protein PrPC.
The cellular protein and the prion protein have different folded conformations.
The PrPC protein is found in normal tissue and is degraded by proteases.
The PrPSC protein is NOT degraded by proteases.
Prions ctd
Fungi
General Characteristics
Eukaryotic organisms
Have cell walls for protection
Ergosterol is the dominwnt membrane sterol rather than cholesterol (impt. for therapy)
Require preformed organic compounds for growth
Fungi ctd
There are three types of fungi: yeasts, molds, and mushrooms
Some yeasts and molds produce disease
Yeasts
Yeasts
Single cell fungi
Reproduce by budding (blastoconidia)
Some strains (Candida) produce pseudohyphae
Molds
Molds
Grow in filamentous forms called hyphae
Many species produce cross walls of hyphae called septae
Nonseptate hyphae do exsist
Masses of hyphae are called mycelia
Dimorphic Fungi
Exist as yeast or yeast-like forms and filamentous forms
Form is controlled by the enviromental conditions like temperature and nutrients
Yeast form found in the body and filamentous form in the enviroment ex. Lab culture
Fungi spores
Spores
Conidia are asexual spores of molds
Arthroconidia are formed from joints in hyphae then fragmentation
Blastoconidia are yeast cell buds
Are of diagnostic value for the identification of some fungi ex, “barrel-shaped” arthrospore of Coccidiodes immitis
Parasitology
Protozoa
Single cells
Exists as trophozoites (motile form) and cysts (resting stage)
Some move by flagella ex. Giardia and some by cilia ex. Balantidum
Worms
Trematodes (flukes), cestodes (tapeworms),and nematodes (roundworms) cause disease
Infection usually involves ingestion of larval or cyst forms
Palisades of bacilli
