DIT review - Micro 1

Question 1

What is the function of lipoteichoic acid, and is it found in gram + or gram - bacteria

Answer 1

Gram positive

• Lipoteichoic acid (contained within peptidoglycan layer)
  
  • Induce cytokines (IL-1, IL-6, TNF-a)

Question 2

Which bacteria, + or -, contain outer membrane

What is the function of the outer membrane

Answer 2

Gram negative

• Contains lipopolysaccharide (LPS) endotoxin
  
  • LPS induces cytokines
  • Vs. Gram (+) which induce cytokines via lipotechoic acid

Question 3

What is the periplasmic space

Is it in gram + or gram - bacteria

What is located here?

Answer 3

• Periplasmic space
  
  • Between inner and outer membrane
  • Gram -
  • Location of beta-lactamases

Question 4

What is the Quellung reaction

Answer 4

• Can determine if a capsule is present via Quellung reaction
  
  • Add anti-capsular serum to bacteria
  • If capsule is present, it will appear swollen under a microscope

Question 5

Which 2 bacterial species are spore-forming

Answer 5

Bacillus and Clostridium species

Question 6

What do you call a piece of genetic material seperate from chromosomal DNA in a bacteria?

Answer 6

Plasmid

Question 7

Describe genetic transfer via transformation

Answer 7

· DNA is released from a lysed cell and then naked DNA is taken up by a living bacterium

· DNA fragment incorporated into chromosomal DNA

· Adding deoxyribonuclease to environment will degrade naked DNA in the medium à no transformation seen

· Feature of SHiN bacteria:

o Strep pneumo, H. influenza type B, Neisseria

Question 8

Describe genetic transfer via transposition

Answer 8

· Segment of DNA that can self-excise and relocate (to different part of chromosome, to different chromosome, or to plasmid)

· Can transfer antibiotic resistance

Question 9

Describe genetic transfer via conjucation

Answer 9

· One way transfer of chromosomal or plasmid DNA

· Donor cell F factor DNA codes for sex pilus

· Bacteria that lack F factor serve as recipient cell

Question 10

Describe genetic transfer via transduction

Answer 10

· Transfer of DNA by bacteriophage (virus that infects bacteria)

Question 11

Compare generalized transduction vs. specialized transduction

Answer 11

• Generalized transduction = a “packaging” event
  
  • Lytic phage infects bacterium, leading to cleavage of bacterial DNA
  • Parts of bacterial chromosomal DNA become packaged in phage capsid
  • Phage infects another bacterium, transferring these genes
• Specialized transduction = an “excision” event
  
  • Lysogenic phage infects bacterium
  • Viral DNA incorporates into bacterial chromosome
  • When phage DNA is excised, flanking bacterial genes may be excised with it
  • DNA is packaged into phage capsid and can infect other bacterium

Question 12

What are the reasons that each of the following bacteria do not gram-stain well:

• Treponema
• Mycobacteria
• Mycoplasma
• Legionella
• Rickettsia
• Chlamydia

Answer 12

• Treponema – too thin
• Mycobacteria – cell wall has high lipid content
• Mycoplasma – no cell wall
• Legionella, Rickettsia, Chlamydia – intracellular
  
  • Chlamydia also lack classic peptidoglycan because of decreased muramic acid

Question 13

Which bacteria use Giemsa stain

Answer 13

• Chlamydia, Borrelia, Rickettsia, Trypanosomes, Plasmodium

Question 14

Which bacteria use periodic acid schiff (PAS) stain

Answer 14

• Stains glycogen and mucopolysaccharides
• Used to diagnose Whipple disease (Tropheryma whipplei)

Question 15

Which bacteria use Ziehl-Neelson stain

Answer 15

Aka carbol fushin stain

• Acid-fast bacteria
• Mycobacteria, Nocardia

Question 16

Which pathogen uses india ink stain

Answer 16

• Cryptococcus neoformans (not a bacteria)

Question 17

Which pathogens use silver stain

Answer 17

• Legionella
• Helicobacter pylori
• Fungi (e.g. Coccidiodides, Pneumocystis jiroveci)

Question 18

What are the 3 main effects of endotoxin

Answer 18

(1) Macrophage activation
(2) Complement activation
(3) Tissue factor activation

Question 19

Endotoxin-mediated macrophage activation causes production of what substances, which leads to what presentation?

Answer 19

• Production of IL-1 and IL-6
  
  • Fever
• Production of TNF-a
  
  • Fever and hypotension
• Production of nitric oxide
  
  • Hypotension

Question 20

Endotoxin-mediaed complement activation has what effect?

Answer 20

• C3a
  
  • Histamine release à hypotension and edema
• C5a
  
  • Histamine release à hypotension and edema
  • Neutrophil chemotaxis

Question 21

Endotoxin-mediated tissue factor activation has what effect?

Answer 21

• Activation of coagulation cascade
  
  • DIC

Question 22

Can vaccines be formed against endotoxins or exotoxins and why?

Answer 22

Exotoxins

Exotoxins are antigenic and our body can form antibodies against them

Question 23

Describe the MOA of exotoxins in Clostridium Tetani and Botulinum

Answer 23

• Both are proteases that cleave SNARE (required for NT release)
• Clostridium tetani
  
  • Toxin prevents release of inhibitory (GABA and glycine) NT from Renshaw cells in spinal cord
  • Spastic paralysis, risus sardonicus, “lockjaw”
• Clostridium botulinum
  
  • Toxin prevents release of stimulatory (ACh) signals at NMJ
  • Flaccid paralysis, floppy baby

Question 24

What is the MOA of exotoxin in Corynebacterium diptheriae

Answer 24

• Inactivates elongation factor (EF-2)
• Pharyngitis with pseudomembranes in throat and severe lymphadenopathy

Question 25

MOA of Shiga and Shiga-like toxin What bacteria contains Shiga-like toxin

Answer 25

* Inactivates 60S ribosome by removing adenine from rRNA * GI mucosal damage = dysentery; HUS via enhanced cytokine release * Shiga like toxin = EHEC

Question 26

MOA of exotoxin in psuedomonas aeruginosa

Answer 26

* Inactivates elongation factor (EF-2) * Host cell death

Question 27

ETEC heat-labile vs. heat-stable exotoxin MOA

Answer 27

* Heat-labile toxin * Overactivates adenylate cyclase = increased cAMP = increased Cl- secretion in gut and H2O efflux * THINK: Labile in the Air (Adenylate cyclase) * Heat-stable toxin * Overactivates guanylate cyclase = increased cGMP = decreased reabsorption of NaCl and H2O in gut * THINK: Stable on the Ground (Guanylate cyclase) * Causes watery diarrhea * Leading cause of traveler’s diarrhea

Question 28

What are the 2 main exotoxins of bacillus anthracis

Answer 28

Edema toxin Lethal factor

Question 29

MOA of anthrax edema toxin

Answer 29

* Mimics the adenylate cyclase enzyme = increased cAMP * Edematous borders of black eschar in cutaneous anthrax

Question 30

Effect of anthrax lethal toxin

Answer 30

* Zinc-dependent protease that inhibits mitogen-activated protein kinase signaling, causing apoptosis and multisystem physiologic disruption = necrosis and black eschar

Question 31

MOA of cholera toxin

Answer 31

* Overactivates adenylate cyclase (increased cAMP) by permanently activating Gs = increased Cl- secretion in gut and H2O efflux * “Rice water” diarrhea

Question 32

MOA of Pertussis toxin

Answer 32

* Overactivates adenylate cyclase by disabling Gi, impairing phagocytosis to permit survival of microbe * Whooping cough

Question 33

MOA of alpha toxin of clostridium perfringens

Answer 33

* Alpha toxin * Phospholipase (lecithinase) that degrades tissue and cell membranes * Degradation of phospholipids à myonecrosis (“gas gangrene”) and hemolysis (“double zone” of hemolysis on blood agar)

Question 34

MOA of streptolysin O of strep pyogenes

Answer 34

* Streptolysin O * Antibodies against toxin (ASO) used to diagnose rheumatic fever * Protein that degrades cell membrane * Lyses RBCs – contributes to beta-hemolysis * Oxygen labile

Question 35

MOA of Toxic shock syndrome toxin (TSST) of staph aurues

Answer 35

* Binds to MHC II and TCR, simultaneously, outside of antigen binding site to cause overwhelming release of IL-1, IL-2, IFN-y, and TNF-a à shock * High fever, hypotension, diffuse rash

Question 36

What is the superantigen toxin of Strep pyogenes

Answer 36

Exotoxin A * Binds to MHC II and TCR, simultaneously, outside of antigen binding site to cause overwhelming release of IL-1, IL-2, IFN-y, and TNF-a à shock

Question 37

What are the gram + rods

Answer 37

Clostridium Listeria Bacillus Corynebacterium

Question 38

What color will Mannitol salt agar turn in the presence of staph aureus

Answer 38

yellow

Question 39

When is the MOA of Staph aureus virulence factor Protein A

Answer 39

Binds to Fc region of antibodies, inhibiting complement activation and phagocytosis

Question 40

Describe the presentation of scarlet fever

Answer 40

* 1) redness and swelling of tongue – strawberry tongue (chef licking strawberry) * 2) pharyngitis – red handkercheif * 3) widespread rash that spares the face – gingerbread frosted red except for face

Question 41

What substance is associated with the formation of rheumatic fever

Answer 41

M protein (highly antigenic - will create antibodies that will cross react with myosin in the heart)

Question 42

What organism is hippurate positive

Answer 42

Group B strep

Question 43

Describe the CAMP test

Answer 43

GBS will produve CAMP factor, which will enlarge the area of hemolysis formed by staph aureus

Question 44

Presentation of neonatal Group B strep

Answer 44

Meningitis Sepsis Pneumonia

Question 45

What is the virulence factor of Strep pneumo that allows it to invade mucosa

Answer 45

IgA protease

Question 46

Which vaccine is polysaccharide vs conjugate (the one for children or the one for adults)

Answer 46

Adult = only IgM response (mezzanine) * Polysaccharide vaccine Children = IgG response (ground) * Conjugate vaccine

Question 47

Presentation of Enterococcus infectin

Answer 47

do U \<3 Trees * U – UTIs * Heart – endocarditis * Tree – biliary tree infections (recall that it is insoluble in bile)

Question 48

What are the diseases associated with Strep D (Strep Bovis)

Answer 48

* Group D strep – Strep Bovis * Colonizes the gut * Can cause endocarditis * Is associated with colon cancer * Anyone who is found to have Strep D, should be screened for colon cancer