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Microbiology > L17: Intro to Micro, Classification and Identification > Flashcards

L17: Intro to Micro, Classification and Identification Flashcards

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Biology 101 flashcards
1
Q

Out of the microbes, what can be seen using light microscopy, what requires electron microscopy

A
  • Viruses typically are seen by electron microscopy only, some can be seen under light microscopy
  • Bacteria (scale of 0.1-10 microns), protozoa and fungi can be seen with light microscope
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2
Q

Are fungi and parasites (helminths and protozoa) eukaryotes or prokaryotes?

A
  • Both are eukaryotes
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3
Q

What ribosomes do bacteria carry?

A
  • 70S
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4
Q

Methods for detecting bacterial in clinical samples?

A
  • Microscopy, bacterial antigens, bacterial nucleic acids, metabolic properties (what do they use), biochemical tests, human antibody response via ELISA, WB and immunostaining
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5
Q

What features are used to classify bacteria?

A
  1. ) Visible features: shape, spore formation, gram reaction
  2. ) Nutrition: media, anaerobic/aerobic, temp for growth
  3. ) End products: enzymes or toxins
  4. ) Surface molecules: unique molecules
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6
Q

Shapes of bacteria

A
  • Cocci (spherical)
  • Bacilli (rods – straight or curved)
  • Spirochetes (spiral)
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7
Q

Describe cytology of bacteria

A
  1. ) Plasma membrane is lipid bilayer without sterols – where e- transport takes place
  2. ) Cell wall composed of peptidoglycan
  3. ) Appendages: pili (“spikes”) or flagella (“tails”)
  4. ) Capsule
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8
Q

2 major classifications of bacterial via staining – describe each, what color do they stain?

A
  1. ) Gram pos: plasma membrane surrounded by peptidoglycan layer – stains P for purple
  2. ) Gram neg: plasma membrane surrounded by peptidoglycan layer (thinner than G+) surrounded by outer membrane **periplasmic space between PM and outer membrane with Pglycan layer inside – stains reddish/pink (depending on counter stain)
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9
Q

What are acid fast bacteria, which genus?

A
  • Bacteria with complex cell envelope containing mycolic acid (LC BCFA) with thick waxy membrane layer. Retain carbol fuchsin dye even after strong acid decolorization process
  • Bacteria = mycobacteria (mnemonic = myco) and nocardia
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10
Q

Why are acid fast bacteria complex, slow growing and also hard to get rid of?

A
  • Mycolic acid impedes entry of chemicals and lysosomal enzymes leading to this phenomenon
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11
Q

Structure of acid fast bacteria wall – describe unique structures

A
  • similar to G+ as they have PM with overlying peptidoglycan – no outer membrane
  • Peptidoglycan has mycolic acid (waxy), arabinogalactans bound to mycolic acid and lipoarabinomannan (LAM) that confers structure and viability to organism
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12
Q

What of acid fast bacteria trigger the immune system?

A
  • LAM (lipoarabinomannan) related to LPS. Binds TLRs and triggers TNF production
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13
Q

Gram stain process

A
  1. ) Crystal violet
  2. ) Gram iodine (to precipitate the crystal violet and cause it to stick)
  3. ) Decolorizer via etoh or acetone (washes out crystal violet if G-)
  4. ) Safranin red
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14
Q

Describe the structure of peptidoglycan

A
  • linear alternating chain of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) via beta-1,4-linkage
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15
Q

Where is the lysozyme cleavage site on peptidoglycan?

A
  • the beta-1,4-linkage between N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
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16
Q

What effect does peptidoglycan have on the immune system?

A
  • Proinflammatory: fixes complement, binds TLR, triggers TNF production via NF-kB
17
Q

Describe the structure of the bacterial gram-positive envelope

A
  • PM with outer peptidoglycan layer
  • Lipoteichoic acid associated with PM into peptidoglycan layer
  • Teichoic acid that is peptidoglycan associated only
18
Q

What are the bacterial gram-positive envelope virulence factors?

A
  • teichoic and lipoteichoic acid
19
Q

Describe the structure of the bacterial gram-negative envelope

A
  • PM, periplasmic space with peptidoglycan layer, outer membrane
  • Outer membrane: rich in porins, other structural and transport proteins – it is asymmetric phospholipid bilayer with inner leaflet containing phospholipids and outer layer with unique LPS (lipopolysaccharide)
  • Peptidoglycan layer with lipoproteins
20
Q

True / False. Gram-negative bacteria are associated with LPS

A
  • True. In outer leaflet of outer membrane
21
Q

Lipoteichoic acid and teichoic acid are associated with gram-negative bacteria

A
  • False, only with gram-positive
22
Q

What recognizes LPS in the human immune system? Response?

A
  • Binds CD14 and TLR 4 on phagocytes and APCs

- Response = inflammation, potentially leading to septic shock via TNF, IL-1 and IL-6 – all via NF-kappa B signalling

23
Q

Describe structure of LPS(aka endotoxin) – function of structures

A
  • 3 subunits: lipid A, core polysaccharide, O antigen
  • Lipid A: anchored to outer membrane via fatty acids, responsible for endotoxin activity
  • Core polysaccharide: sugars required for structure and viability of bacterial cell
  • O ontigen: long linear polysaccharide repeating subunits
24
Q

Of the LPS structure, what is missing in Neisseria?

A
  • O antigen
25
Q

Are all bacteria gram positive and negative?

A
  • No. Legionella are weakly-stained bacteria. Treponema and leptospira have a cell wall that is too thin to be visible. Mycoplasma are wall-less. Acid fast Mycobacterium with waxy membrane.
26
Q

Two types of bacterial appendages – describe, function?

A
  1. ) Pili/fimbrae: pilin protein which forms tube with small core found on both G+ and G- bacteria. Two functional types = somatic (common) and sex. Somatic used to attach to epithelial cells. Sex (only 1 per cell) involved in gene transfer (plasmid etc.)
  2. ) Flagella: helical protein structures anchored to PM responsible for locomotion
27
Q

What are the O, K and H bacterial antigens? Which bacteria are each associated with – G+ or G-?

A
  • O: LPS / endotoxin containing polysaccharide in G negative bacteria
  • K: capsule surrounding some G positive or negative bacteria
  • H: flagella in some G positive or negative bacteria
28
Q

What is a bacterial capsule? Function? In what bacterial type?

A
  • Loose polysacc or protein layer surrounding bacteria
  • Protection from immune system (poorly antigenic, antiphagocytic, virulence factor)
  • In some G+ and G-
29
Q

How are encapsulated bacteria tested for in lab?

A
  • Quellung reaction – look for capsule to swell when anticapsular AB added
30
Q

Function of spleen in regards to encapsulated bacteria?

A
  • Cleared by phagocytes in spleen through opsonization
31
Q

Why are asplenic pts more likely to get encapsulated bacterial infections?

A
  • Phagocytes in spleen help clear encapsulated bacteria through opsonization
32
Q

What are endospores? What bacteria form them? Describe structure? Relevance?

A
  • Under harsh environmental conditions, bacteria convert from vegetative (actively metabolizing an dividing) to dormant/spore state, where they give rise to single bacteria through germination process.
  • Produced by some G+ bacteria
  • Free endospore is released from environment, is a dehydrated multishelled structure containing complete copy of c/s, minimum concentration of proteins and ribosomes and high concentration of calcium bound to dipicolinic acid. Inner membrane with two peptidoglycan layers and outer keratin-like protein coat
  • Aerosolized, found in wide environmental range withstanding extreme pH, high temp, radiation etc, exist for centuries, require 120 deg C autoclave at high pressure for more than 20 minutes
33
Q

Chemical unique to identification of bacterial endospores

A
  • Dipicolinic acid
34
Q

A pt presents with flulike illness (fever, chills, headache, cough, myalgias and chest pain). Analysis of sputum sample by phase-contrast microscopy reveals intracellular spherical forms of about 8 micron diameter with a single nucleus. Causative agent of infection is likely a
A. Virus
B. Fungus
C. Bacterium

A
  • No nuclei in bacterium. Likely causative agent is fungus. No viruses seen under light microscopy.
35
Q

Acid fast bacteria contain peptidoglycan in their cell wall – True / False.

A
  • True. These are most similar to gram positive – unique mycolic acid too
36
Q

Endotoxin is a component of
A. Gram-positive bacteria only
B. Gram-negative bacteria only
C. Gram-positive and negative bacteria

A
  • Only gram-negative bacteria
37
Q

Which of the following is a virulence factor that inhibits phagocytosis by macrophages? Flagella, pili, capsule, endospore or teichoic acid?

A
  • Capsule

Microbiology (16 decks)

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