Microbial Cell Structure, Classification and Bacterial Virulence Flashcards
What is a virulence factor?
Component of a microbial cell or virus which enhances its ability to cause disease
What are pili?
Thin, rigid appendages composed of proteins called pilins; allow cells to adhere to host cell or other bacterial cell surfaces
What is a capsule (glycocalyx)?
Varies from thick vixcous layer to thin amorphous slime layers
Usually polysaccharide, confers resistance to phagocytosis
Gives colony a smooth or shiny appearance
What are cytoplasmic inclusion bodies?
Sites where nutrient macromolecules (usually polysaccharides) are stored as large, microscopically visible complexes
What type of ribosome is associated with bacterial protein synthesis?
70S ribosomes
What is an endospore?
Heat resistant, dehydrated multi-layered cells that are rich in calcium dipicolinate; formed within the cell by a process called sporulation
Germinate into growing cells when adverse conditions wane
What is the bacterial cell envelope?
Plasma membrane + cell wall + intervening material
What are the functions of the bacterial cell envelope?
Structural rigidity and packaging of cytoplasmic contents
Permeability barrier
Metabolic uptake
Energy production (via PM)
Attachment to host cells
Escape from immune recognition (capsule)
Antibiotic target
What is the Gram stain?
Staining method used to differentiate bacteria into two major groups based on their reaction (Gram positive or Gram negative)
What are the key features of a gram positive cell envelope?
Thick, multilayered peptidoglycan overlaying plasma membrane (responsible for blue color)
Teichoic acid, lipoteichoic acid
Plasma membrane
What is peptidoglycan?
Complex macromolecule consisting of glycan polymers which are cross-linked by peptide chains
What are the functions and biological activities of peptidoglycan?
Allows diffusion of small molecules to the plasma membrane
Confers Rigidity and shape to the bacterial cell
Interferes with phagocytosis and is mitogenic
Muramyl dipeptide(MDP): adjuvant, pyrogen, and somnagen
What are teichoic acids?
Water-soluble polymers of either ribitol phosphate or glycerol phosphate that are covalently linked to peptidoglycan
What are Lipoteichoic acids?
Teichoic acids which terminate in a fatty acid that serves to anchor the molecule in the plasma membrane
What are the functions of TAs and LTAs?
Common surface antigens that promote attachment to specific receptors on cell surfaces
I.e. kind of virulence factor
What are the functions of the plasma or inner membrane?
Permeases required for active transport of nutrients
Respiratory chain enzymes and proton pumps
Sites for the synthesis of peptidoglycan and outer membrane components
MDP - product of peptidoglycan degredation
What are the key features of a gram-negative cell envelope?
Unique outer membrane which contains lipopolysaccharide (LPS)
Thin peptidoglycan overlying plasma membrane
Periplasmic space
Inner (plasma) membrane
Where is lipopolysaccharide (LPS) located?
Outer leaflet of the outer membrane of gram negative bacteria
What is lipopolysaccharide (LPS)?
Amphipathic macromolecule consisting of three covalently linked sections: Lipid A, Core, and O Antigen
What is the function of each of the three sections of LPS?
Lipid A - responsible for endotoxic activity, anchors LPS to outer leaflet
Core Polysaccharide - essential for LPS structure and bacterial viability
O antigen - basis for serotypes of bacterial strains
What are the biological effects of LPS?
Induce synthesis of IL-1, TNF and other cytokines
Complement and coagulation cascades are activated
What are possible clinical manifestations of LPS in the bloodstream (during bacteremia)?
Sleep
Fever
Leukopenia
Hypoglycemia
Hypotension
Shock
DIC and organ failure (severe)
Besides LPS, what are three other outer membrane structures found within gram-negative bacterial envelopes?
Porins - channels
Barun lipoprotein - covalently anchors the outer membrane to peptidoglycan
Omp proteins - stabilize the outer membrane and act as specific receptors
What are the functions of the outer membrane in gram negative bacteria?
Maintain structural rigidity
Permeability barrier
Protects peptidoglycan and plasma membrane
Sieve for small water-soluble molecules
Sites for host cell and phage attachment
Possesses LPS and other molecules that serve as molecular signals to host organism
What is located within the periplasmic space of G(-) bacteria?
Variety of hydrolytic enzymes including proteases, lipases, nucleases
Pathogens can also have collagenases, hyaluronidas and beta-lactamases which help the organism invade tissue or escape treatment
What are four phenotypic methods of classification for bacteria?
Morphology
Cell structure
Biochemical typing
Serotyping (antibodies to specific antigen)
What are three genotypic methods of classification for bacteria?
DNA hybridization (Southern Blotting)
Plasmid analysis
DNA sequence analysis
What are archaebacteria?
Lack a true peptidoglycan layer and include thermophiles, halophiles and methanogens
What family do most pathogens belong to?
Eubacteria
What bacterial structures are involved in the successful colonization of host surfaces?
Pili (fimbriae)
Adhesins - surface proteins
Biofilms
How do bacteria enter cells that are not naturally phagocytic (induced phagocytosis)?
Bacterial surface proteins called invasins induce rearrangements in the actin cytoskeletons
This causes the formation of pseudopod-like structures which mediate bacterial engulfment
How do some bacteria survive phagocytosis?
Produce catalse + SOD and have lysozyme resistant cell walls
How do bacteria escape phagocytic vesicles following ingestion by phagocytes?
They have numerous advantages associated with an intracellular existence
Bacterial protein either forms a pore or disrupts the vesicle membrane to allow escape
What are three strategies developed by bacteria to acquire iron?
Sideophores/enterobactins chelate iron effectively and bring it inside the cell
Some bacteria have receptors for transferrin, lactoferrin, etc.
Cytotoxins which damage/kill host cells act to liberate intracellular nutrients, including iron
What are two mechanisms by which bacteria evade complement and antibody response?
Capsules and slime layers - covers bacterial surface and helps bacterial cell evade the complement system and phagocytes
Antigenic switching: H1/H2 pilus switching in Salmonella and antigen variation in treponemes
What are exotoxins and three types of them?
Exotoxins are toxic bacterial proteins, many of which are secreted into the medium
AB toxins
Pore-formers (hemolyisns)
Superantigens
What are AB toxins?
Have separate activ A and binding B subunits, variant forms have one molecule of each or 5 binding subunits
Toxin entry can be through membrane translocation or endocytosis
Some act by ADP ribosylating a target protein, eliminating its activity
What is the action of pore former toxins?
Acts to lyse the cell by permitting rapid water entry in response to the osmotic gradient
What is the action of phospholipase?
Enzymatically removes the charged head of phospholipids
This acts to destabilize the cell membrane, also resulting in cell lysis
What are two mechanisms by which pathogens cause host disease by perturbing host defenses?
Autoimmune activation - produces proteins or polysaccharides which produce antigenic determinants that are cross reactive to host products
Elaboration of superantigens - prominent in toxic shock, superantigen binds to both MHC Class II and T cell receptors, resulting in hyperactivation of immune system
What is the cause of septic shock?
Bacterial products hyperactivate the complement cascade leading to shock/hypotension, DIC and organ failure
Toxin is active and recognized when bacterium is lysed
