Microbial Cell Structure, Classification and Bacterial Virulence

Question 1

What is a virulence factor?

Answer 1

Component of a microbial cell or virus which enhances its ability to cause disease

Question 2

What are pili?

Answer 2

Thin, rigid appendages composed of proteins called pilins; allow cells to adhere to host cell or other bacterial cell surfaces

Question 3

What is a capsule (glycocalyx)?

Answer 3

Varies from thick vixcous layer to thin amorphous slime layers

Usually polysaccharide, confers resistance to phagocytosis

Gives colony a smooth or shiny appearance

Question 4

What are cytoplasmic inclusion bodies?

Answer 4

Sites where nutrient macromolecules (usually polysaccharides) are stored as large, microscopically visible complexes

Question 5

What type of ribosome is associated with bacterial protein synthesis?

Answer 5

70S ribosomes

Question 6

What is an endospore?

Answer 6

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

Question 7

What is the bacterial cell envelope?

Answer 7

Plasma membrane + cell wall + intervening material

Question 8

What are the functions of the bacterial cell envelope?

Answer 8

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

Question 9

What is the Gram stain?

Answer 9

Staining method used to differentiate bacteria into two major groups based on their reaction (Gram positive or Gram negative)

Question 10

What are the key features of a gram positive cell envelope?

Answer 10

Thick, multilayered peptidoglycan overlaying plasma membrane (responsible for blue color)

Teichoic acid, lipoteichoic acid

Plasma membrane

Question 11

What is peptidoglycan?

Answer 11

Complex macromolecule consisting of glycan polymers which are cross-linked by peptide chains

Question 12

What are the functions and biological activities of peptidoglycan?

Answer 12

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

Question 13

What are teichoic acids?

Answer 13

Water-soluble polymers of either ribitol phosphate or glycerol phosphate that are covalently linked to peptidoglycan

Question 14

What are Lipoteichoic acids?

Answer 14

Teichoic acids which terminate in a fatty acid that serves to anchor the molecule in the plasma membrane

Question 15

What are the functions of TAs and LTAs?

Answer 15

Common surface antigens that promote attachment to specific receptors on cell surfaces

I.e. kind of virulence factor

Question 16

What are the functions of the plasma or inner membrane?

Answer 16

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

Question 17

What are the key features of a gram-negative cell envelope?

Answer 17

Unique outer membrane which contains lipopolysaccharide (LPS)

Thin peptidoglycan overlying plasma membrane

Periplasmic space

Inner (plasma) membrane

Question 18

Where is lipopolysaccharide (LPS) located?

Answer 18

Outer leaflet of the outer membrane of gram negative bacteria

Question 19

What is lipopolysaccharide (LPS)?

Answer 19

Amphipathic macromolecule consisting of three covalently linked sections: Lipid A, Core, and O Antigen

Question 20

What is the function of each of the three sections of LPS?

Answer 20

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

Question 21

What are the biological effects of LPS?

Answer 21

Induce synthesis of IL-1, TNF and other cytokines

Complement and coagulation cascades are activated

Question 22

What are possible clinical manifestations of LPS in the bloodstream (during bacteremia)?

Answer 22

Sleep

Fever

Leukopenia

Hypoglycemia

Hypotension

Shock

DIC and organ failure (severe)

Question 23

Besides LPS, what are three other outer membrane structures found within gram-negative bacterial envelopes?

Answer 23

Porins - channels

Barun lipoprotein - covalently anchors the outer membrane to peptidoglycan

Omp proteins - stabilize the outer membrane and act as specific receptors

Question 24

What are the functions of the outer membrane in gram negative bacteria?

Answer 24

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

Question 25

What is located within the periplasmic space of G(-) bacteria?

Answer 25

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

Question 26

What are four phenotypic methods of classification for bacteria?

Answer 26

Morphology Cell structure Biochemical typing Serotyping (antibodies to specific antigen)

Question 27

What are three genotypic methods of classification for bacteria?

Answer 27

DNA hybridization (Southern Blotting) Plasmid analysis DNA sequence analysis

Question 28

What are archaebacteria?

Answer 28

Lack a true peptidoglycan layer and include thermophiles, halophiles and methanogens

Question 29

What family do most pathogens belong to?

Answer 29

Eubacteria

Question 30

What bacterial structures are involved in the successful colonization of host surfaces?

Answer 30

Pili (fimbriae) Adhesins - surface proteins Biofilms

Question 31

How do bacteria enter cells that are not naturally phagocytic (induced phagocytosis)?

Answer 31

Bacterial surface proteins called invasins induce rearrangements in the actin cytoskeletons This causes the formation of pseudopod-like structures which mediate bacterial engulfment

Question 32

How do some bacteria survive phagocytosis?

Answer 32

Produce catalse + SOD and have lysozyme resistant cell walls

Question 33

How do bacteria escape phagocytic vesicles following ingestion by phagocytes?

Answer 33

They have numerous advantages associated with an intracellular existence Bacterial protein either forms a pore or disrupts the vesicle membrane to allow escape

Question 34

What are three strategies developed by bacteria to acquire iron?

Answer 34

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

Question 35

What are two mechanisms by which bacteria evade complement and antibody response?

Answer 35

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

Question 36

What are exotoxins and three types of them?

Answer 36

Exotoxins are toxic bacterial proteins, many of which are secreted into the medium AB toxins Pore-formers (hemolyisns) Superantigens

Question 37

What are AB toxins?

Answer 37

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

Question 38

What is the action of pore former toxins?

Answer 38

Acts to lyse the cell by permitting rapid water entry in response to the osmotic gradient

Question 39

What is the action of phospholipase?

Answer 39

Enzymatically removes the charged head of phospholipids This acts to destabilize the cell membrane, also resulting in cell lysis

Question 40

What are two mechanisms by which pathogens cause host disease by perturbing host defenses?

Answer 40

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

Question 41

What is the cause of septic shock?

Answer 41

Bacterial products hyperactivate the complement cascade leading to shock/hypotension, DIC and organ failure Toxin is active and recognized when bacterium is lysed