intro to medical micro

Question 1

what are the organisms that make up medical microbiology?

Answer 1

• viruses
• bacteria
• fungi
• parasites

Question 2

gram + bacteria examples

Answer 2

• staph
• strep
• enterococci
• bacillus
• cornynebacteria
• actinomyces

Question 3

gram - bacteria examples

Answer 3

• enterobacteriaceae

Question 4

bacterial morphologies

Answer 4

• cocci
• bacilli
• coccobacilli
• spirochetes
• comma
• individual cells, pairs, chains, or clusters

Question 5

bacterial size (average)

Answer 5

1-2µM in diameter

Question 6

cell envelope structure

Answer 6

gram +

• cytoplasmic (inner) membrane
• peptidoglycan cell wall

gram -

• cytoplasmic (inner) membrane
• peptidoglycan cell wall + periplasm
• outer membrane

Question 7

cell envelope functions

Answer 7

• surround cytosol
• protect from environmental threats
• cellular functions that happen in organelles in eukaryotes (like metabolism)

Question 8

cytoplasmic membrane structure

Answer 8

• lipid bilayer
• integral and peripheral proteins
• no sterols (except mycoplasma)

Question 9

cytoplasmic membrane function

Answer 9

• permeability barrier
• ETC
• export of membrane and secreted proteins
• cell wall component biosynthesis
• partitioning of daughter cells during division

Question 10

cell wall function

Answer 10

• gives cells shape
• protection against osmotic lysis
• mycoplasma does not have a cell wall

Question 11

cell wall structure

Answer 11

thick (+) or thin (-) peptidoglycan layer

Question 12

peptidoglycan structure

Answer 12

• N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) disaccharides linked in long polymers
• Peptides of alternating L and D AAs extending from sugars
• Cross-linking of 3rd AA from one peptide to the terminal (usually 4th) AA of another peptide, often via gly residues

Question 13

peptidoglycan synthesis

Answer 13

• Penicillin binding proteins add peptide side chains to the sugar polymers and add cross-linking glycines
• synthesis inhibited by B-lactams and vanco
• polymer cleaved into NAGA-NAMA disaccharides by lysozyme

Question 14

gram stain process and results

Answer 14

1. stain with crystal violet dye
2. iodine (mordant) cross links crystal violet
3. alcohol wash decolorizes gram (-)
4. counterstain with safranin

gram (+) are stained purple
gram (-) are counterstained pink/red

Question 15

teichoic acids

Answer 15

• components of the gram (+) cell envelope
• long polymers of glycerol phosphate or ribitol phosphate with sugars and AAs
• attached to cell wall or cytoplasmic membrane (lipoteichoic acids)
• function: adhesins – help bacteria stick to surfaces

Question 16

gram (-) outer membrane structure

Answer 16

• inner leaflet = phospholipids

- outer leaflet = lipopolysaccharide

Question 17

lipopolysaccharide structure

Answer 17

inner -> outer

• Lipid A: phosphorylated diglucosamine with 5-7 saturated fatty acids. Forms a tight barrier.
• Core polysaccharide: 7-9 sugars (including weird ones like KDO and heptose)
• O-antigen: polysaccharide chain made of repeating units of 3-5 sugar residues with up to 40 total. Not present in all gram (-). Initially resists complement deposition (serum resistance) but recognized by specific antibodies with repeated exposure

Question 18

physiological effects of LPS for the human host

Answer 18

effects caused by lipid A

low dose:

• fever
• complement activation
• stimulation of B cells and MΦ
• activates acute phase response

high dose:

• septic shock
• hypotension
• circulatory shock
• disseminated intravascular coagulation
• multiple organ failure
• death

Question 19

mechanism of LPS toxicity

Answer 19

1. LPS-binding protein (LBP) binds LPS
2. Bound complex interacts with monocyte/MΦ CD14 receptors
3. LBP-CD14 activates TLRs
4. Pro-inflammatory cytokine production (IL-1B, TNF-a)
5. Inflammatory response: fever, increased adherence of leukocytes to endothelial surfaces (WBCs move from blood stream to infected tissues), septic shock syndrome