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microbiology basics 2


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Where is beta-lactamase in bacteria? What does it do?
Beta-lactamases are found in the periplasm of gram negative bacteria. The enzyme hydrolyzes beta-lactam antibiotics, conferring resistance.
Which gram-positive organism lacks a polysaccharide capsule and has a capsule made of something else?
Bacillus anthracis - has D-glutamate instead of polysaccharide
What are spores made of and what do they do?
Keratin-like coat, dipicolinic acid. Provide resistanceto dehydration, heat and chemicals
What helps organisms adhere to indwelling catheters?
The glycocalyx (composed of polysaccharide)
What is the major surface antigen of gram-positive cell walls and what does it do?
Teichoic acid - unique to gram-positive bacteria. Induces TNF and IL-1
What is specific to gram-negative bacterial cell membranes?
Endotoxin/LPS (lipopolysaccharide)
Describe the four phases of bacterial growth.
1) Lag phase of metabolic activity without division. 2) Log phase of rapid cell division. 3) Stationary phase in which nutrient depletion slows growth. 4) Death due to prolonged nutrient depletion and buildup of waste products.
What are exotoxins and endotoxin chemically?
Exotoxins are polypeptides, while endotoxins are lipopolysaccharides.
Where do bacteria keep their exotoxin or endotoxin genes?
Exotoxin genes on plasmids or bacteriophages; endotoxin genes on bacterial chromosomes.
Which is more fatal – exotoxin or endotoxin?
Exotoxin is highly fatal (~1 microgram), while you need 100’s of micrograms for endotoxin to prove lethal.
Which has greater heat stability – endotoxin or exotoxin?
Endotoxin – stable at 100°C for 1 hour, while endotoxin is rapidly destroyed at 60°C (EXCEPT Staph enterotoxin)
True or False: We can vaccinate against exotoxins and endotoxins.
False: We do have toxoids vaccines against exotoxins for diseases like tetanus, botulism and diphtheria, but there are no vaccines against endotoxins.
Which bugs have Exotoxin that acts by ADP ribosylation?
Corynebacterium diphtheriae (which then inactivates EF-2). Also Escherichia coli, Vibrio cholerae, and Bordetalla pertussis (all these then stimulate adenylate cyclase).
Which bug has exotoxin that blocks the release of acetylcholine? What symptoms does that cause?
Clostridium botulinum. Anticholinergic symptoms, CNS paralysis, floppy baby, and a wrinkle-free forehead if injected!!
Which bug has exotoxin that blocks glycine release? What does that cause?
Clostridium tetani. Causes “lockjaw”.
How does Staph aureus cause toxic shock syndrome?
The toxin is a superantigen that binds to MHC II protein and T-cell receptor à induces IL-1 and IL-2 à TSS
How could bacterial infection cause disseminated intravascular coagulation?
Endotoxin can activate Hageman factor --> initiates coagulation cascade --> DIC
How could bacterial infection cause hypotension?
Endotoxin activates macrophages to release nitric oxide (--> vasodilationà hypotension); can also activate alternate complement pathway C3a, --> hypotension (N.B. also edema).
How does bacterial infection cause fever?
Endotoxin activates macrophages to release IL-1 and TNF --> fever.
Gram Stain Limitations: --- are too thin to be visualized. Use darkfield microscopy and fluorescent antibody staining instead.
Gram Stain Limitations: --- lack a cell wall
Gram Stain Limitations: --- stain with silver
Legionella pneumophila
What are the two Neisseria species?
N. meningitidis, N. gonorrhoeae
How are the Neisseria species differentiated?
MeninGococci ferment Maltose & Glucose; Gonococci ferment only Glucose
Pigment-producing Bacteria: --- produces a yellow pigment
Staphylococcus aureus (Latin aureus = gold)
Pigment-producing Bacteria: --- produces a blue-green pigment
Pseudomonas aeruginosa
Pigment-producing Bacteria: --- produces a red pigment
Serratia marcescens (think red marachino cherry)
IgA proteases allow organisms to⬦
⬦ colonize mucosal surfaces
Name 4 organisms with IgA proteases
Strep pneumoniae, N. meningitidis, N. gonorhoeae, H. influenzae
What are the lab steps for ID'ing Staphylococcus aureus?
1st gram stain --> get purple/blue cocci (= positive); 2nd catalase test --> positive (staphylococcus clusters); 3rd coagulase test --> positive (differentiates S. aureus from the coagulase-negative S. epidermidis and S. saprophyticus)
What are the 4 types of gram-postive rods?
Corynebacterium, Listeria, Bacillus, Clostridium
When do you test for bacitracin sensitivity or resistance?
For beta-hemolytic strep. Bacitracin-sensitive --> Group A beta-hemolytic Strep pyogenes. Bacitracin-resistant --> Group B (Bad!) beta-hemolytic Strep agalactiae
Name 4 laboratory features of Streptococcus pneumoniae
alpha hemolytic (green – partial hemolysis), positive Quellung reaction, optochin-sensitive, and bile-soluble
When would you do the optochin test?
When you have alpha hemolytic strep
Once you see gram-negative rods under the microscope, what is your next diagnostic test?
test lactose fermentation
What are the 3 fast lactose fermenters:
Klebsiella, E. coli, and Enterobacter
How do you distinguish among lactose non-fermenters?
Perform an oxidase test
Which are oxidase-positive?
Which are oxidase-negative?
Shigella, Salmonella, or Proteus
What are the gram-negative cocci?
What are the gram-negative coccoid rods?
H. influenzae, Pasteurella, Brucella, Bordetella pertussis
Which gram negative coccoid requires factors V and X for growth?
H. flu
Use chocolate agar and factors V & X for ---
Hemophilus influenzae
Factor V has --- and Factor X has ---
NAD, hematin
Thayer-Martin (VCN) media to culture ---
Neisseria gonorrhoeae
Bordet-Gengou (potato) agar to culture ---
Bordetella pertussis
Tellurite plate, Loffler's medium, blood agar for ---
Corynebacterium diphtheriae
Lowenstein-Jensen agar for growing ---
Mycobacterium tuberculosis
Pink colonies on MacConkey's agar are ---
Lactose-fermenting enterics (Klebsiella, Eschericihia, or Enterobacter
Charcoal yeast extract agar buffered with increased iron and cysteine to grow ---
Legionella pneumophila
Sabouraud's agar to culture ---

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