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Microbiology > Unit 1: Intro to Micro > Flashcards

Unit 1: Intro to Micro Flashcards

(60 cards)

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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
Characteristics of acid-fast bacteria
* 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
Gram (-) cell walls contain 1-2 layers of peptidoglycan plus the following structures:
Outer membrane • LPS (or LOS) • Trimeric poring • Lipoprotein Periplasmic space
27
Outer membrane of gram negative cell walls
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
The outer portion of LPS is referred to as...
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
Core polysaccharide
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
Lipid 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
Portion of the LPS responsible for bacterial sepsis
Lipid A
32
Portion of the outer membrane that serves as an attachment site to host cells
O antigen
33
Connection between LPS and bacterial septic shock
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
The outer membrane of gram-negative cell walls contains __________ protein channels called ____________.
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
_____________ is the most abundant protein of gram-negative cells
Lipoprotein Functions to stabilize the outer membrane and anchors the outer membrane to the peptidoglycan layer
36
What is the periplasmic space?
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
Gram-positive cell walls contain a thick peptidoglycan layer along with one or both of the following structures that provide elasticity and stability:
Wall teichoic acids (WTA) - anchored to the peptidoglycan itself Lipoteichoic acids (LTA) - anchored to the cell membrane (go all the way through)
38
Two main functions of WTA and LTA that increase the virulence of gram-positive organisms:
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
Special features of acid-fast cell walls
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
What gives acid-fast cell walls their waxy coat appearance?
The mycolic acid layer Functions: resists desiccation, resistance to some abx, and inhibits phagocytosis
41
Staining acid-fast bacteria
Do not stain well with gram stains due to the waxy mycolic acid layer Primary acid-fast stain = carbol fuchsin Counterstain = methylene blue
42
Clinically important acid-fast organisms
Mycobacterium tuberculosis, M. leprae, M. avium-intracellulare and Nocardia asteroides
43
The three major components of a flagellum:
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
Purpose of a flagellum
Allows for motility Average speed of a bacterium is ~50 µm/s Helical movement Directed motility chemotaxis
45
Component of the flagellum that can be used to serotype organisms
H antigen
46
What are pili?
Proteinaceous, hairlike structures with adhesions at the tips Promote adherence to other bacteria or to host cells
47
Two main types of pili?
Common pili (=fimbriae) Sex pili (for conjugation)
48
Common pili or fimbriae
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
Sex pili
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
Polysaccharide layer outside of the cell wall; source of the K antigen
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
Functions of the glycocalyx
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
Nuclear region in bacteria
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
Bacteria can acquire ________ through various genetic exchange mechanisms
``` 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
How are bacterial ribosomes different from eukaryotic ribosomes?
Consist of rRNA and protein Bacterial ribosomes are 70s (30s and 50s subunities) Transcription and translation are coupled
55
Why do bacterial ribosomes work as targets for protein synthesis inhibitors?
Because these abx do not affect eukaryotic ribosomes - they are selectively toxic to either the 30s or 50s subunit of bacterial ribosomes
56
Collective term for various granules, vesicles, and vacuoles within the cytoplasm
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
A resting stage allowing an organism to survive harsh environmental conditions
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
What allows for the resistance of endospores to many chemicals, desiccation, heat, radiation, acids, disinfectants, etc?
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
Clinically relevant genera that produce endospores?
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
Bacillus cereus has a ________ endospore Bacillus subtilis has a ________ endospore Clostridium tetani has a _________ endospore
Bacillus cereus = central endospore Bacillus subtilis = subterminal endospore Clostridium tetani = terminal endospore

Microbiology (6 decks)

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