L17: Intro to Micro, Classification and Identification 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
2
Q
Are fungi and parasites (helminths and protozoa) eukaryotes or prokaryotes?
A
- Both are eukaryotes
3
Q
What ribosomes do bacteria carry?
A
- 70S
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
5
Q
What features are used to classify bacteria?
A
- ) Visible features: shape, spore formation, gram reaction
- ) Nutrition: media, anaerobic/aerobic, temp for growth
- ) End products: enzymes or toxins
- ) Surface molecules: unique molecules
6
Q
Shapes of bacteria
A
- Cocci (spherical)
- Bacilli (rods – straight or curved)
- Spirochetes (spiral)
7
Q
Describe cytology of bacteria
A
- ) Plasma membrane is lipid bilayer without sterols – where e- transport takes place
- ) Cell wall composed of peptidoglycan
- ) Appendages: pili (“spikes”) or flagella (“tails”)
- ) Capsule
8
Q
2 major classifications of bacterial via staining – describe each, what color do they stain?
A
- ) Gram pos: plasma membrane surrounded by peptidoglycan layer – stains P for purple
- ) 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)
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
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
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
12
Q
What of acid fast bacteria trigger the immune system?
A
- LAM (lipoarabinomannan) related to LPS. Binds TLRs and triggers TNF production
13
Q
Gram stain process
A
- ) Crystal violet
- ) Gram iodine (to precipitate the crystal violet and cause it to stick)
- ) Decolorizer via etoh or acetone (washes out crystal violet if G-)
- ) Safranin red
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
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)
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
Are all bacteria gram positive and negative?
- 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
Two types of bacterial appendages – describe, function?
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
What are the O, K and H bacterial antigens? Which bacteria are each associated with – G+ or G-?
- 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
What is a bacterial capsule? Function? In what bacterial type?
- Loose polysacc or protein layer surrounding bacteria
- Protection from immune system (poorly antigenic, antiphagocytic, virulence factor)
- In some G+ and G-
29
How are encapsulated bacteria tested for in lab?
- Quellung reaction – look for capsule to swell when anticapsular AB added
30
Function of spleen in regards to encapsulated bacteria?
- Cleared by phagocytes in spleen through opsonization
31
Why are asplenic pts more likely to get encapsulated bacterial infections?
- Phagocytes in spleen help clear encapsulated bacteria through opsonization
32
What are endospores? What bacteria form them? Describe structure? Relevance?
- 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
Chemical unique to identification of bacterial endospores
- Dipicolinic acid
34
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
- No nuclei in bacterium. Likely causative agent is fungus. No viruses seen under light microscopy.
35
Acid fast bacteria contain peptidoglycan in their cell wall – True / False.
- True. These are most similar to gram positive – unique mycolic acid too
36
Endotoxin is a component of
A. Gram-positive bacteria only
B. Gram-negative bacteria only
C. Gram-positive and negative bacteria
- Only gram-negative bacteria
37
Which of the following is a virulence factor that inhibits phagocytosis by macrophages? Flagella, pili, capsule, endospore or teichoic acid?
- Capsule
