Bacteriology 1 : Bacterial Morphology & Taxonomy Flashcards
Name the bacterial cell envelope from outer to in
-capsule (k antigen): outer gelatinous layer
-Outer membrane = LPS (o antigen) only present in gram (-)
-cell wall = peptidoglycan
-inner cell membrane
-Glycocalyx: adhesion, biofilm
Bacterial cell structure for cytoplasmic structure
-nucleoid
-plasmid
-ribosome (16S rRNA)
-endospore ( extraordinary resistance)
Appendages
-flagella (H antigen)
-endoflagella: in spirochetes (twisting or flexing)
-fimbriae: short hair-like bristles- aid in biofilm, adhesion
-Pili: sex pilus for DNA transfer
Only what type of bacteria has LPS and what is it also called?
Negative bacteria
-O antigen
the outer membrane of bacteria can be composed of LPS (O antigen)
Bacterial cell structure
-Gram positive vs. Gram negative
gram positive
-capsule/ transmembrane protein/ cytoplasmic membrane/ cell wall peptidoglycan
-teichoic acid Gram (+) bacteria cell structure is composed primarily of peptidoglycan containing teichoic acid
-lipoteichoic acid
-lipoprotein
-wall-ass. Proteins
gram negative
-capsule/ transmembrane protein/ cytoplasmic membrane/ cell wall peptidoglycan
-LPS
-outer membrane
-periplasm
-outer membrane proteins
-secretion apparatus
-Muriel lipoprotein
Which type of bacteria are characterized by the presence of two membranes? How do these membranes differ?
Gram (-)
-a cytoplasmic (inner) And an outer membrane
-the outer membrane carries LPS
The periplasmic space is found in which bacteria and made up of what?
Gram (-)
Contains hydrolytic enzymes and binding proteins for nutrient uptake
Which antigen can induce an immune response?
ALL antigens can induce an immune response. Antigen O (outer membrane- LPS) would be the most severe.
ANTIGENS
-K = capsule
-O = outer membrane (LPS) in gram (-)
-H = flagella: swimming-like motility/locomotion
Gram (+) bacteria cell structure is composed primarily of
Peptidoglycan containing teichoic acid
How is the outer membrane of a Gram (-) bacteria distinct from the inner membrane?
Carries lipopolysaccharides
Peptidoglycan Cell wall of bacteria
-found in
-shape
-structure
- gram (-) and (+)
(peptidoglycan in gram (+) contain teichoic acid)
-helical shape
-long repeating N-acetylgucosamine (NAG), N-acetylmuramic acid (NAM), and carbohydrate backbone (sugar)
-(NAG) and (NAM) are connected by alternating D and L amino acids. These peptide chains are connected by a peptide inter-bridge (pentapeptide bridge) to other carbohydrate backbones
-helical shape! the pentapeptide bridges are connected together by a tetrapeptide (transpeptidase; also called penicillin binding protein) this will form rigid cell walls
What forms the rigid cell walls in the peptidoglycan structure?
The rigid cell walls of bacteria are formed primarily through the cross-linking of peptidoglycan strands.
Transpeptidase are responsible for catalyzing the formation of the peptide cross-links between peptidoglycan strands.
The cross-links = the peptide inter-bridge
B-lactam antibiotics
penicillin
-bind to inhibit the transpeptidase enzyme reaction that Links chains of NAG (G)-NAM (M) polymers together.
catalyzes the peptide inter-bridge formation
Vancomycin antibiotic
Binds to NAG-NAM- peptide precursor at the D-ala-D-ala terminus. This blocks its incorporation into the peptidoglycan chain (Transglycosylation) and prevents cross-linking (Transpeptidation)
By binding here, Vancomycin prevents two critical enzymatic steps:
Transglycosylation: The enzyme responsible for adding the NAG-NAM-peptide precursor to the growing peptidoglycan chain is blocked, preventing polymerization.
Transpeptidation: This step, in which transpeptidase enzymes cross-link peptidoglycan strands, is also blocked because Vancomycin prevents access to the D-Ala-D-Ala dipeptide.
INHIBITING CELL WALL SYNTHESIS (peptidoglycan)
To build the cell wall, these NAG-NAM chains are linked together, and then cross-linked by peptide chains through the action of enzymes like transglycosylases (for polymer elongation) and transpeptidases (for cross-linking).
SUMMARY
Vancomycin:
Binds to D-Ala-D-Ala on peptidoglycan precursors.
Inhibits both transglycosylation (polymer assembly) and transpeptidation (cross-linking).
Results in a weakened cell wall and cell lysis.
Bacitracin:
Inhibits bactoprenol recycling, stopping the transport of NAG-NAM precursors across the membrane.
Blocks peptidoglycan synthesis at an early stage.
Cycloserine:
Inhibits the synthesis of D-Ala-D-Ala dipeptides, preventing the formation of peptide side chains in peptidoglycan.
Affects early precursor formation, leading to defective cell wall synthesis.
Bacitracin antibiotic
Inhibits the recycling of BPP (the lipoprotein that translocates NAM-NAG precursors across the inner membrane to the outer surface where cell wall synthesis occurs)
-prevents the precursor from reaching its destination.
SUMMARY
Vancomycin:
Binds to D-Ala-D-Ala on peptidoglycan precursors.
Inhibits both transglycosylation (polymer assembly) and transpeptidation (cross-linking).
Results in a weakened cell wall and cell lysis.
Bacitracin:
Inhibits bactoprenol recycling, stopping the transport of NAG-NAM precursors across the membrane.
Blocks peptidoglycan synthesis at an early stage.
Cycloserine:
Inhibits the synthesis of D-Ala-D-Ala dipeptides, preventing the formation of peptide side chains in peptidoglycan.
Affects early precursor formation, leading to defective cell wall synthesis.
Cycloserine antibiotic
Inhibits the synthesis of the D-ala-D-ala dipeptide
Cycloserine inhibits the synthesis of the D-alanine-D-alanine dipeptide, which is essential for peptidoglycan cross-linking.
Blocking cell wall synthesis (peptidoglycan)
Cycloserine is a structural analog of D-alanine and interferes with the early stages of peptidoglycan synthesis. By blocking these enzymes, cycloserine prevents the formation of the D-Ala-D-Ala dipeptide, which is essential for building the peptide side chains of NAM in peptidoglycan.
SUMMARY
Vancomycin:
Binds to D-Ala-D-Ala on peptidoglycan precursors.
Inhibits both transglycosylation (polymer assembly) and transpeptidation (cross-linking).
Results in a weakened cell wall and cell lysis.
Bacitracin:
Inhibits bactoprenol recycling, stopping the transport of NAG-NAM precursors across the membrane.
Blocks peptidoglycan synthesis at an early stage.
Cycloserine:
Inhibits the synthesis of D-Ala-D-Ala dipeptides, preventing the formation of peptide side chains in peptidoglycan.
Affects early precursor formation, leading to defective cell wall synthesis.
Is a LPS (lipopolysaccharide) an endotoxin or exotoxin?
Endotoxin: they have it inside/cell membrane
Therefore when Gram-negative bacteria die and their cell walls break apart, endotoxins are released into the surrounding environment.
Many of the periodontal pathogens are what type of bacteria
Gram (-)
-What are the 3 domains that make up LPS (Lipopolysaccharide)?
-What do LPS do?
-Where do most of the detrimental biological activities of LPS reside?
-lipid A = anchored in the outer membrane of gram (-)
-core polysaccharide = extended This middle region connects the O-antigen to the lipid A portion.
-O-antigen side-chain =extended; how we differentiate between/w diff bacterias. The O-antigen is composed of repeating units of sugar molecules (polysaccharides), which can vary greatly between different bacterial strains.
LPS- cause disease, stabilize outer membrane, contribute to the attachment to the surface, biofilm formation.
-resident in the lipid A portion of the molecule. Lipid A is the toxic component of LPS and is responsible for the endotoxic activity seen in Gram-negative bacterial infections.
How does LPS affect the immune system and have cytotoxic properties?
LPS- interact w/ monocytes/macrophages and induce production of cytokines and inflammatory responses.
The lipid A portion of LPS is responsible for its cytotoxic properties. Here’s how it exerts harmful effects on host cells
LPS interactions w/ monocytes/macrophages lead to acute-phase inflammatory response.
Low Levels: trigger fever
High Levels: Can lead to severe outcomes like septic shock, hypotension, disseminated intravascular coagulation (DIC), and potential organ failure. (Activating the complement pathway)
Other components that can induce an immune response
-peptidoglycan, teichoic acid, lipoteichoic acid
When do you Italize the name of the microorganism?
When stating the genus and/or species.
Family: Bacteriodales
Genus: Porphyromonas
Species: P.gingivalis
Taxonomic identification by 16S rRNA gene sequencing
PCR
It’ll show known, and unknown bacterias
-old= cloning
Saliva contains an anti-bacterial enzyme called lysozyme. Which component of the bacterial cell wall is broken down by lysozyme?
Lysozyme acts on the β-1,4-glycosidic bonds between N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) in the peptidoglycan layer.
The bond between N-acetylmuramic acid and N-acetylglucosamine (NAG-NAM)
lysozyme breaks down peptidoglycan, a key component of the bacterial cell wall.
Bacterial shapes and arrangement
-coccus
-capsulated diplococci
-cocci in chains
-clusters
-bacillus
-capsulated bacillus
-flagellated bacillus
-curved bacilli
-spore-bearing bacilli
-spirochete
Endoflagella: in spirochetes (twisting or flexing motion)
P.gingivalis structure
Outer and inner components
-LPS = gram (-)
-outer/inner membrane
-capsule
-fimbriae (adhesion, biofilm, short hair-like bristles)
Virulent factors:
-Gingipains
-Hemagglutinins
-Hemolysin
Outer membrane vesicle
-THE CELL WALL+ OUTER MEMBRANE/ NOT A CELL
-NO DNA
-Gingipains
-virulence factor
P.gingivalis is found in the oral cavity
Peptidoglycan structure
-backbone
-backbone connected too
-shape
-enzyme and its role
The basic structure of peptidoglycan consists of two alternating sugars:
N-acetylglucosamine (G) and N-acetylmuramic acid (M)
These sugars form a long repeating chain, creating a carbohydrate backbone. This G-M chain is critical for the structure and strength of the bacterial cell wall.
Attached to each N-acetylmuramic acid (M) unit is a short peptide chain made up of alternating D- and L-amino acids.
This is unusual since most naturally occurring peptides use only L-amino acids, but the inclusion of D-amino acids helps make the structure more resistant to degradation by enzymes
The peptidoglycan strands are arranged in a helical shape.
Multiple strands of peptidoglycan are linked together through peptide inter-bridges (short chains of amino acids that connect the peptide side chains of adjacent strands). This creates the cross linking! A strong, mesh-like polymer that surrounds the bacterial cell, giving it mechanical strength and rigidity. This cross-linking is particularly important for maintaining the cell’s shape and protecting it. The peptide chains attached to the N-acetylmuramic acid (M) residues are cross-linked by peptide inter-bridges, typically involving four amino acids.
** Transpeptidase is an enzyme that plays a crucial role in the cross-linking process.**
It links the peptide chains attached to the N-acetylmuramic acid (M) units, creating a network that forms the rigid, protective cell wall.
This enzyme is the target of β-lactam antibiotics (such as penicillin), which inhibit its activity, leading to weak cell walls and, eventually, bacterial cell death.
Which domain of the LPS is the most detrimental?
Lipid A is the toxic component of LPS and is responsible for the endotoxic activity seen in Gram-negative bacterial infections.
