Microbial Structure and Function Flashcards
Four types of microbes
Bacteria (prokaryote)
Protozoa (eukaryote)
Fungi (eukaryote)
Viruses (neither prokaryotic nor eukaryotic)
Bacterial structures (2 basic shapes, 4 others)
Two basic shapes: Rod Cocci Other shapes: Spirochetes Spirillum Diplococci Diplobacilli
Prokaryote versus eukaryote: genetic material
Chromosome: single circular; paired linear
Chromosome location: nucleoid (no membrane); nucleus (membrane present)
Nucleolus: absent; present
Extrachromosomal DNA: plasmid; mitochondria and chloroplast
Prokaryote versus eukaryote: site of cellular respiration and ribosomes
Cell membrane (don’t have organelles); mitochondria
Prokaryote versus eukaryote: ribosomes
30S & 50S /70S (structurally same but different proteins – antibiotic target** bacterial protein synthesis); 40S & 60S /80S in cytoplasm (70S in organelles)
Prokaryote versus eukaryote: locomotion and adhesion
Rotating flagella and gliding; Undulating flagella and cilia , and also amoeboid movement
Sex or attachment pili (fimbriae) – important for attachment to cells in body and for bacterial genetic exchange; absent
Rods
Bacilli
Two bacilli together – Diplobacilli
Streptobacilli
Chains of bacilli
Staphlococci
Clumps
Palisades
Side by side arrangements of bacilli/ “X” “V” or “Y” figures
Cocci group arrangements
Single, diplo, tetrad, chains, clumps, cubical
Structure: spirochete versus spirillum
Spirochete: Flexible undulating corkscrew
Spirillum: RIGID corkscrew shape
Inner workings of the bacteria
Flagella and pili
Capsul
Cytoplasmic membrane
Cell envelope*
How many chromosomes do bacteria have?
One chromosome (nucleoid), tightly packed
What is the mesosome?
Chromosomal DNA attached to the bacterial membrane invaginated into the cell at the site of bacterial division. Controversial topic.
What is plasmid DNA? How is it passed on and was is its importance to the cell?
A self-replicating unit of DNA distinct from the chromosome.
Much smaller than the bacterial chromosome but contains important genetic information
Ie plasmids are usually associated with antibiotic resistance genes
Plasmids are passed on as bacteria divide/grow, but are also sometimes mobile – can transfer from one bacteria to another (usually within same species, but not always, ie streptococcal transfers to staphylococcal)
Ribosomes and Granules
Where are ribosomes distributed in the cell?
No ER, so ribosomes are found throughout the cytoplasm, and often attached to the membrane
External features of bacteria and immunology
External membranes and structures of bacteria (such as flagelli and cell walls) are highly antigenic – our immune cells make antibodies to recognize, target and destroy them.
What are the different arrangements of flagella?
Not so important
Monotrichous (Vibrio cholerae)
Lophotrichous (Bartonella bacilliformis)
Amphitrichous (Spirillum serpens)
Peritrichous (Escherichia coli)
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.
Types of pili (fimbriae)
Shorter and finer than flagella.
Two types:
1. Adherence pili – attach bacteria to surfaces.
2. Sex pili – important in bacterial conjugation; found in some gram negative bacteria.
– Pili are generally a big part of infectiousness: the ability to attach/congregate/colonize and transferring antibiotic resistance
What is the capsule? What structures does it form?
A slimy outer coating not found in all bacteria.
Usually a complex of high molecular weight polysaccharides.
A.k.a. Slime layer or glycocalyx (generally more loosely associated – adherence properties).
Can be antiphagocytic: evading macrophages
Special Note: BIOFILMS.
Hip replacement– some bacteria like to produce a biolfilm on the artificial hip disease
Cytoplasmic membrane
Phospholipid bilayer (selectively permeable) that encloses the bacterial cytoplasm
Imbedded with proteins.
Site of nutrient transport in/out.
Site of respiration.
Peptidoglycan
Part of bacterial cell walls – another site of antibiotic action because unique to each bacteria
60-90% of gram positive cell wall, much less in gram negatives.
Determines staining properties
What is peptidoglycan monomer made of?
All bacteria have NAM-NAG (N-acetyl glucose amine bonded to N-acetyl neuramic acid? )
NAM has a tetrapeptide tail (depends on species)
How is peptidoglycan arranged?
Alternating monomer and tetrapeptide, cross-linked
Depending on species, cross-linking either by another peptide or directly to each other
What is the action of penicillin?
Penicillin inhibits the cross linking of peptidoglycan in the cell wall.
Cell lyses because osmotic pressure in cell high, the uncross-linked cell wall structure is not strong enough
Antibiotics than inhibit peptidoglycan cross linking are less effective in gram negative bacteria because less cross linking occuring. And some can’t get by the envelope anyway.
What structures do gram positive and gram negative cell envelopes BOTH have?
BOTH have cytoplasmic/bacterial membranes.
BOTH have Peptidoglycan.
Which has more peptidoglycan, gram + or -? Which has periplasmic space?
Gram positive has much more peptidoglycan
Gram negative has periplasmic space
Structure and features of the Gram positive cell wall.
What are the structures found ONLY in gram positive cell walls?
Lots of peptidoglycan on top of cytoplasmic membrane.
Teicoic acid in cell wall and cytoplasmic membrane (called lipoteicoic acids) also unique to gram positive
– found within the peptidoglycan layer as well as extending vertically from the extracellular space, through peptidoglycan, into the cytoplasmic membrane
Found only in the gram positive cell wall are**:
Teichoic acids / Teichuronic acids: Water soluble polymers of ribitol or glycerol residues joined by phosphodiester linkages
Lipoteichoic acid (LTA): Lipid attached to Teichoic Acid – Adhesin/anchors to the cytoplasmic membrane!
Polysaccharides: Most likely composites of sugars released from teichoic and teichuronic acid
What is the difference between teichoic acid and teichuronic acid?
Teichuronic acid is made in phosphate-limiting conditions.
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.
General structure of the gram negative cell wall?
Gram negative envelope composed of:
Outermembrane with LPS and pores that allow components to get down to cytoplasmic membrane (to be transported in)
Periplasmic space
Peptidoglycan (smaller component with smaller amount of cross linking)
Lipoproteins (not in gram +’s)
What are the structures found ONLY in gram negative cell walls?
Found only in the gram negative cell wall are:
- Lipoproteins: Cross-links outer membrane to peptidoglycan in the periplasmic space
- 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 (ones that do the cross linking).
- Outer membrane: A phospholipid bilayer that protects the cell from hydrolytic enzymes.
Contains lipopolysaccharides, porins (non-specific pore proteins), anchor proteins and transport proteins. - Lipopolysaccharide (LPS): Part of the outer membrane
Lipopolysaccharides (LPS) in gram negative bacteria.
Where is it found?
What is it made of? Which component is unique to each species and which is conserved across species?
Part of the outer membrane
Made of:
Lipid A (a complex lipid) covalently attached to a polysaccharide with core and terminal repeat units.
LPS (Lipid A) is called 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.
Lipid A (endotoxin) is conserved, the O-antigen is unique to each species.
Which component of the gram negative cell wall is antigenic?
Lipids aren’t that antigenic – body’s response is mainly to the O-antigen, not Lipid A
*Remember, Lipid A is the same across species, whereas the polysaccharide chain that makes up O-antigen is unique to each
Which type of cell wall (gram + or -) is more difficult for large antibiotics to penetrate?
Much harder to get antiobiotics through Gram negative cell walls because of its layers – outer envelope, periplasmic space, peptidoglycan, cytoplasmic membrane
ie antibiotic that targets bacterial protein synth:
Sometimes so large, they only work on gram pos because cant get into gram neg
The gram stain: differences between gram positive and gram negative
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 because the thicker peptidoglycan/more cross-linking ensures that the fixed dye complexes that formed can’t get out.
Gram-negative bacteria do not retain complexes when decolorized.
Safranin is used after decolorization treatment to counterstain gram-negatives red.
The gram stain process
Bacteria are heat fixed to a slide.
Crystal violet is added – all cells stain blue.
Iodine (mordant) fixes the stain into the bacterial cell – stain molecule forms a large complex.
Alcohol (takes away phospholipids) decolorizes gram negative bacteria. Gram positives remain blue/purple because the greater cross linking doesn’t allow the big stain molecules to wash off.
Safranin stains the gram negative bacteria a pink color.
Colors of gram positive versus gram negative
Gram + = blue/purple
Gram - = pink
What are my Mycoplasma (and Ureaplasma) know for?
The smallest free-living organisms.
NO CELL WALL! That means no peptidoglycan so bacterial stains don’t work well. The only barrier is the cytoplasmic membrane.
Membranes contain sterols – required for growth (not synthesized by the bacterium).
The cousin to Mycoplasma
Don’t stain positive or negative, different stain
Only cause certain diseases – usually respiratory system (ie asthma)
If you know it’s in this family, have the lab run an acid fast stain
Don’t have Lipid A (no endotoxins associated)
Morphology of mycoplasmal pathogens
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 (cousin of Mycoplama) and Nocardia
Contain small amounts of peptidoglycan. Contain large amounts of glycolipids. - Lipoarabinomannan (LAM). - Mycolic acids (60% large portion of the cell wall). - Make the cell walls impermeable.
Acid fast staining
Acid fast staining involves staining with red carbolfuchsin and destaining with acid alcohol. Only acid-fast bacteria will retain the stain after the decolorizing step.
Don’t have Lipid A (no endotoxins associated)
Protein secretion systems
In addition to cell walls and cell envelopes, most bacteria have protein secretion systems. Gram negatives have six classes; Gram positives have an additional class Play a major role in bacteria interacting with their environment and helping to determine their pathogenicity.
What type of system they have depends on the genes within the bacteria and can be extremely important to the pathogenesis of the bacteria
Structure of protein secretion systems
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.
**Secretion systems are important – remember which bacteria have injectisome – how toxins enter host cells
What is the function of injectosomes?
Injectisomes – when the bacteria approaches another cell, it can inject things (usually harmful) into that other cells (ie toxins)
Unique to the individual strains
What is the function of protein secretion systems?
- Transport proteins and/or nucleic acids (T4SS) to the outside of the cell, periplasm, or inside host cells.
Transported proteins can be surface proteins like adhesins (help adhere to host cells) or toxins which modify host cell physiology causing pathological consequences.
Endospores
-Made by Bacillus and Clostridium species in nutrient-limiting conditions (i.e. starvation).
-Highly resistant to heat, desiccation, and chemical damage.
-Reasons for heat resistance:
Dehydration.
Calcium dipicolinate in the core (5-15% of the spore dry weight)
**Component of the spore, NOT the bacterial cell wall
