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Microbiology > Unit 1: Intro to Micro > Flashcards

Unit 1: Intro to Micro Flashcards

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Biology 101 flashcards
1
Q

____________ = categorization of organisms into taxonomic groups

A

Classification

Includes:
Morphologic properties
Biochemical and physiological properties
Genetic properties

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2
Q

______________ = Naming of an organism according to its characteristics

A

Nomenclature

Binomial: genus and species (eg - Escherichia coli)

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3
Q

____________ = Use of a classification scheme to isolate and identify organisms

A

Identification

This is the major focus of a clinical microbiology laboratory

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4
Q

Size of bacteria

A

Most range from 0.5-2.0 µm in diameter/width. Length can vary.

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5
Q

Bacterial shapes

A 
Coccus = balls
Bacillus = rods
Coccobacillus = between ball and rod
Vibrio = comma shaped
Spirochete = tight spiral
Spirilla = loose spiral
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6
Q

Bacteria defined as _______________ have no defined shape

A

Pleomorphic

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7
Q

The characteristic arrangements that bacteria can assume depends on ….

A

The plane of division

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8
Q

A cell that divides in one plane gives rise to short or long chains described as:

A

Diplo- (pair) or Strepto- (chain)

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9
Q

If you see gram negative diplococci, think:

A

Neisseria gonorrhoeae

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10
Q

A cell that divides in two or more planes gives rise to clusters or packets described as:

A

Staphylo- (grapelike cluster)
Tetras (packets of 4 cells)
Sarcoma (packets of 8 cells)

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11
Q

Bacterial cell membranes are similar to eukaryotic cell membranes except:

A

They do not contain sterols

EXCEPTION: aerobic bacteria b/c sterols require O2 for synthesis

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12
Q

Functions of the cell membrane

A
  • Selective permeability and transport of solutes
  • Secretion of proteins
  • Housing enzymes and carrier molecules
  • Electron transport and oxidative phosphorylation
  • Housing receptors and other proteins of the chemo tactic and sensory transduction systems
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13
Q

Semi-rigid structure outside of the cell membrane, found in most bacterial species

A

Cell wall

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14
Q

Most the structures of the bacterial cell wall are classified as …

A

Virulence factors

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15
Q

Functions of the cell wall…

A
  • Maintenance of cell shape
  • Prevent osmotic lysis
  • Environmental protection
  • Anchor for external structures
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16
Q

What is peptidoglycan?

A

Repeating disaccharide cross-linked by tetrapeptides
• N-acetylglucosame (NAG)
• N-acetylmuramic acid (NAM)
• Tetrapeptide linkage between NAMs (the specific peptides vary among species)

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17
Q

Mechanisms for interfering with peptidoglycan synthesis/structure

A
  1. Secretion of various antimicrobial compounds

2. Secretion of lysozyme (found in egg whites, various secretions, and in the granules of PMNs)

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18
Q

Antibiotics that target the cell wall are known as:

A

Cell wall inhibitors

These can only affect cells that are actively growing (eg synthesizing peptidoglycan)

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19
Q

The enzyme ________, found in tears, saliva, and mucus, degrades the glycine backbone of peptidoglycan.

A

Lysozyme

Weakens the integrity of the cell wall, even in bacteria that are not actively growing.

Lysozyme is used in the lab to aid in lysis of bacterial cells.

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20
Q

The thickness of the peptidoglycan layer within the cell wall ranges from:

A

1-2 sheets to 40+ sheets

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21
Q

Classification of most bacteria into these two groups depends on the thickness of the peptidoglycan layer:

A

Thin peptidoglycan layer = gram negative
(Ex. E. coli, Bordatella pertussis, Salmonella typhi…)

Thick peptidoglycan layer = gram positive
(Ex. Staphylococcus aureus, Strep pneumo, Clostridium botulinum…)

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22
Q

Color for gram-positive bacteria

A

Gram-positive cells (thick peptidoglycan) retain the primary stain (crystal violet) and stain purple

(Think Positive = Purple)

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23
Q

Color for gram-negative bacteria

A

Gram-negative cells (thin peptidoglycan) retain the counter stain (safranin) and stain RED.

Think Negative = Red

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24
Q

The three main types of cell walls found in bacteria:

A

Gram-negative
Gram-positive
Acid-fast

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25
Q

Characteristics of acid-fast bacteria

A
  • Their cell wall still contains peptidoglycan
  • They have a unique cell wall structure different from both gram (+) and gram (-) bacterial cells
  • These bacteria do not stain using gram stains
26
Q

Gram (-) cell walls contain 1-2 layers of peptidoglycan plus the following structures:

A

Outer membrane
• LPS (or LOS)
• Trimeric poring
• Lipoprotein

Periplasmic space

27
Q

Outer membrane of gram negative cell walls

A

External to the peptidoglycan layer

Is a bi-layer
• Inner Layer is identical to the cell membrane
• Outer layer of the outer membrane is composed primarily of lipopolysaccharide (LPS)

28
Q

The outer portion of LPS is referred to as…

A

O-antigen

Long, linear repeating units of carbohydrates (*LOS = short, branched)

Species and even strain specific

Serves as attachment site (sticky carb that binds to host cells) - show to inhibit phagocytosis

Highly variable and immunogenicity - used to identify bacterial strains

29
Q

Core polysaccharide

A

Branched polysaccharide containing 9-12 sugars

Connects lipid A to the O antigen within the LPS

Essentially just a bridge between lipid A and O antigen

30
Q

Lipid A

A

Embedded in the outer membrane, has toxin activity

Heat stable

B cell mitogen

Induces production of cytokines and inflammatory mediators

RESPONSIBLE FOR BACTERIAL SEPSIS

31
Q

Portion of the LPS responsible for bacterial sepsis

A

Lipid A

32
Q

Portion of the outer membrane that serves as an attachment site to host cells

A

O antigen

33
Q

Connection between LPS and bacterial septic shock

A

LPS can directly activate complement (via alternative pathway)

LPS can bind to receptors on various cells, causing release of cytokines and other pro-inflammatory mediators, ultimately resulting in symptoms of septic shock

34
Q

The outer membrane of gram-negative cell walls contains __________ protein channels called ____________.

A

Trimeric protein channels called porins

Non-specific channels allowing water and small molecules across the outer membrane

Controls transport of substances into/out of the cell

35
Q

_____________ is the most abundant protein of gram-negative cells

A

Lipoprotein

Functions to stabilize the outer membrane and anchors the outer membrane to the peptidoglycan layer

36
Q

What is the periplasmic space?

A

Lies between the outer membrane and the cell membrane in gram-negative cell walls

Houses the thin peptidoglycan layer, transport proteins, and a variety of hydrolytic enzymes

Some bacteria concentrate antibiotic hydrolases here, which leads to resistance

37
Q

Gram-positive cell walls contain a thick peptidoglycan layer along with one or both of the following structures that provide elasticity and stability:

A

Wall teichoic acids (WTA) - anchored to the peptidoglycan itself

Lipoteichoic acids (LTA) - anchored to the cell membrane (go all the way through)

38
Q

Two main functions of WTA and LTA that increase the virulence of gram-positive organisms:

A

They function as adhesions (structures for adherence - the first step in the invasion process)

They can, along with the peptidoglycan, initiate endotoxins-like activities when released (not as toxic as LPS but do cause an inflammatory response)

39
Q

Special features of acid-fast cell walls

A

Mycolic acid layer - polymers of long-chain fatty acids and other lipids covalently linked to peptidoglycan via arabinogalactan

Tetrameric porins (structurally different from the Trimeric porins in gram (-) cell walls) - allow passage of small hydrophilic molecules

40
Q

What gives acid-fast cell walls their waxy coat appearance?

A

The mycolic acid layer

Functions: resists desiccation, resistance to some abx, and inhibits phagocytosis

41
Q

Staining acid-fast bacteria

A

Do not stain well with gram stains due to the waxy mycolic acid layer

Primary acid-fast stain = carbol fuchsin
Counterstain = methylene blue

42
Q

Clinically important acid-fast organisms

A

Mycobacterium tuberculosis, M. leprae, M. avium-intracellulare and Nocardia asteroides

43
Q

The three major components of a flagellum:

A

Filament - composed of a self-assembling helical arrangement of flagellin protein subunits with a hollow core; includes H antigen

Hook - attaches filament to the cell surface, links to basal body

Basal body - anchors flagellum in the cell wall and cell membrane

44
Q

Purpose of a flagellum

A

Allows for motility

Average speed of a bacterium is ~50 µm/s
Helical movement
Directed motility chemotaxis

45
Q

Component of the flagellum that can be used to serotype organisms

A

H antigen

46
Q

What are pili?

A

Proteinaceous, hairlike structures with adhesions at the tips
Promote adherence to other bacteria or to host cells

47
Q

Two main types of pili?

A

Common pili (=fimbriae)

Sex pili (for conjugation)

48
Q

Common pili or fimbriae

A

Composed of pilin subunits
• Tips contain adhesions; many of these adhesions are lectins
• Lectins bind to sugars

Peritrichous arrangment - function in adhesion and “twitching” motility

49
Q

Sex pili

A

Aka conjugation pili

Produced by some gram-negative bacteria

Adherence between two cells allows for the exchange of DNA

Clinical relevance: rapid development of resistance to some abx is due in part to the transfer of resistance genes through genetic exchange mechanisms

50
Q

Polysaccharide layer outside of the cell wall; source of the K antigen

A

Glycocalyx

Commonly referred to as a capsule or slime layer

Only a few species do this

Capsule: rigid, uniform in density and thickness, closely surrounding the cell

Slime layer: loose, non-uniform, and more diffuse

51
Q

Functions of the glycocalyx

A

Often not necessary for survival but is a virulence factor

Protects from desiccation
Acts as a barrier to toxic hydrophobic molecules
Inhibits phagocytosis
Decreases PMN killing
Decreases complement-mediated cell lysis
Induces abscess formation
Promotes adherence to cells/surfaces
52
Q

Nuclear region in bacteria

A

Aka nucleoid

No nuclear membrane as in eukaryotes

Contains primarily DNA but also RNA and protein

Most bacteria have one single circular chromosome - no introns in DNA and no histones

Some bacteria have plasmids (extrachromosomal DNA)

53
Q

Bacteria can acquire ________ through various genetic exchange mechanisms

A 
Plasmids - encode for ancillary (non-essential) info including:
• Antibiotics
•Abx resistance
•Heavy metal resistance
• Toxins

Possessing these genes may increase a pathogen’s virulence (increasing ability to cause disease, evasion of immune responses)

54
Q

How are bacterial ribosomes different from eukaryotic ribosomes?

A

Consist of rRNA and protein

Bacterial ribosomes are 70s (30s and 50s subunities)

Transcription and translation are coupled

55
Q

Why do bacterial ribosomes work as targets for protein synthesis inhibitors?

A

Because these abx do not affect eukaryotic ribosomes - they are selectively toxic to either the 30s or 50s subunit of bacterial ribosomes

56
Q

Collective term for various granules, vesicles, and vacuoles within the cytoplasm

A

Inclusions or inclusion bodies

Many inclusions function as storage depots:
• Volutin granules - polymers of inorganic phosphate
• Glycogen granules - polymers of alpha-D-glucose
• PHB granules - chains of ß-hydroxybutyric acid

57
Q

A resting stage allowing an organism to survive harsh environmental conditions

A

Endospore

Often triggered due to nutrient depletion - when conditions are again favorable, the endospore will germinate, producing one vegetative cell

Each endospore contains:
• One chromosome
• Low amounts of essential proteins/ribosomes
• Peptidoglycan layer
• High concentration of calcium bound to dipicolinic acid
• Keratin spore coat

58
Q

What allows for the resistance of endospores to many chemicals, desiccation, heat, radiation, acids, disinfectants, etc?

A

Calcium dipicolinate lends to increased resistance to heat

The keratin coat is impervious to many chemicals

Can persist in the environment for months to years

59
Q

Clinically relevant genera that produce endospores?

A

Bacillus and Clostridium

Both are gram (+) - the presence of endospores in a clinical specimen narrows the DDx

The location and size of the spore varies for the different species, also aiding in identification

60
Q

Bacillus cereus has a ________ endospore

Bacillus subtilis has a ________ endospore

Clostridium tetani has a _________ endospore

A

Bacillus cereus = central endospore
Bacillus subtilis = subterminal endospore
Clostridium tetani = terminal endospore

Microbiology (6 decks)

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