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PoD Test 1 > Microbial Cell Structure, Classification and Bacterial Virulence > Flashcards

Microbial Cell Structure, Classification and Bacterial Virulence Flashcards

1
Q

What is a virulence factor?

A

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

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2
Q

What are pili?

A

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

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3
Q

What is a capsule (glycocalyx)?

A

Varies from thick vixcous layer to thin amorphous slime layers

Usually polysaccharide, confers resistance to phagocytosis

Gives colony a smooth or shiny appearance

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4
Q

What are cytoplasmic inclusion bodies?

A

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

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5
Q

What type of ribosome is associated with bacterial protein synthesis?

A

70S ribosomes

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6
Q

What is an endospore?

A

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

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7
Q

What is the bacterial cell envelope?

A

Plasma membrane + cell wall + intervening material

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8
Q

What are the functions of the bacterial cell envelope?

A

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

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9
Q

What is the Gram stain?

A

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

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10
Q

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

A

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

Teichoic acid, lipoteichoic acid

Plasma membrane

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11
Q

What is peptidoglycan?

A

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

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12
Q

What are the functions and biological activities of peptidoglycan?

A

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

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13
Q

What are teichoic acids?

A

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

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14
Q

What are Lipoteichoic acids?

A

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

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15
Q

What are the functions of TAs and LTAs?

A

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

I.e. kind of virulence factor

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16
Q

What are the functions of the plasma or inner membrane?

A

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

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17
Q

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

A

Unique outer membrane which contains lipopolysaccharide (LPS)

Thin peptidoglycan overlying plasma membrane

Periplasmic space

Inner (plasma) membrane

18
Q

Where is lipopolysaccharide (LPS) located?

A

Outer leaflet of the outer membrane of gram negative bacteria

19
Q

What is lipopolysaccharide (LPS)?

A

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

20
Q

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

A

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

21
Q

What are the biological effects of LPS?

A

Induce synthesis of IL-1, TNF and other cytokines

Complement and coagulation cascades are activated

22
Q

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

A

Sleep

Fever

Leukopenia

Hypoglycemia

Hypotension

Shock

DIC and organ failure (severe)

23
Q

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

A

Porins - channels

Barun lipoprotein - covalently anchors the outer membrane to peptidoglycan

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

24
Q

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

A

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

25
Q

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

A

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

26
Q

What are four phenotypic methods of classification for bacteria?

A

Morphology

Cell structure

Biochemical typing

Serotyping (antibodies to specific antigen)

27
Q

What are three genotypic methods of classification for bacteria?

A

DNA hybridization (Southern Blotting)

Plasmid analysis

DNA sequence analysis

28
Q

What are archaebacteria?

A

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

29
Q

What family do most pathogens belong to?

A

Eubacteria

30
Q

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

A

Pili (fimbriae)

Adhesins - surface proteins

Biofilms

31
Q

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

A

Bacterial surface proteins called invasins induce rearrangements in the actin cytoskeletons

This causes the formation of pseudopod-like structures which mediate bacterial engulfment

32
Q

How do some bacteria survive phagocytosis?

A

Produce catalse + SOD and have lysozyme resistant cell walls

33
Q

How do bacteria escape phagocytic vesicles following ingestion by phagocytes?

A

They have numerous advantages associated with an intracellular existence

Bacterial protein either forms a pore or disrupts the vesicle membrane to allow escape

34
Q

What are three strategies developed by bacteria to acquire iron?

A

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

35
Q

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

A

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

36
Q

What are exotoxins and three types of them?

A

Exotoxins are toxic bacterial proteins, many of which are secreted into the medium

AB toxins

Pore-formers (hemolyisns)

Superantigens

37
Q

What are AB toxins?

A

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

38
Q

What is the action of pore former toxins?

A

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

39
Q

What is the action of phospholipase?

A

Enzymatically removes the charged head of phospholipids

This acts to destabilize the cell membrane, also resulting in cell lysis

40
Q

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

A

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

41
Q

What is the cause of septic shock?

A

Bacterial products hyperactivate the complement cascade leading to shock/hypotension, DIC and organ failure

Toxin is active and recognized when bacterium is lysed

PoD Test 1 (31 decks)

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