Microbiology

Question 1

Poor gram staining

Answer 1

These Rascals May Microscopically Lack Color
Treponema (darkfield)
Rickettsia
Mycobacteria
Mycoplasma (no cell wall)
Legionella (intracellular - silver stain)
Chlamydia (intracellular, lacks muramic acid)

Remember: GS detects peptidoglycan in cell wall

Question 2

Wright-Giemsa stain

Answer 2

Borrelia
Chlamydia
Plasmodium
Trypanosomes (T. brucei - sleeping sickness, T. cruzi - Chagas)

Question 3

PAS (periodic acid-Schiff)

Answer 3

Stains glycogen, mucopolysaccharides

• Tropheryma whippelii (PAS-pos foamy macrophages)
• GSDs
• apha1 anti-trypsin
• adenocardinomas (mucin secreting)
• mycosis fungiodes and Sezary sydrome (cutaneous T cell lymphoma, incr mucopolysaccharides in affected T cells)

Question 4

Ziehl-Neelson (carbolfuchsin, methylene blue counter-stain)

Answer 4

Acid-fast organisms (lots of mycolic fatty acid, stains red, resist decoloration with acid)

• Mycobacterium: TB, leprae, kansasii, avium-intracelliulare
• Nocardia: contains mycolic acids, too! weakly acid-fast

Question 5

India ink

Answer 5

Cryptococcus neoformans

- mucicarmine stains thick polysaccharide capsule red

Question 6

Silver stain

Answer 6

• Fungi (e.g. Pneumocystis: dark disk-shaped yeast)
• Legionella: facultative intracellular GNR, charcoal yeast extract
• Bartonella: Cat scratch disease

Question 7

Chocolate agar with V and X

Answer 7

H. flu

V = NAD+, X = hematin

Question 8

Thayer-Martin (VPN/VCN) media

Answer 8

Neisseria gonorrhoeae (and meningitidis, but don’t really need to abx becuase usually growing from sterile fluid)

Chocolate agar with abx: V = vancomycin (inh GPs), P = polymyxin/C = colistin (inh other GNs), N = nystatin (inh fungi)

Question 9

Chocolate agar, plain

Answer 9

N. meningitidis

Question 10

Tellurite plate, Loffler’s media

Answer 10

Corynebacterium diphtheriae

• Non-spore forming gram-pos aerobic rod with red/blue granules
• Growth like “chinese letters”
• ABCDEFG: ADP ribsyl, beta-prophage, Coryne, Dip, EF-2, Elek test for toxin, Granules

Question 11

Lowenstein-Jensen agar

Answer 11

Mycobacterium tuberculosis

Question 12

Eaton’s agar

Answer 12

Mycoplasma pneumoniae

Question 13

Pink colonies on MacConkey’s agar

Answer 13

Lactose-fermenting organisms

• Citrobacter (slow)
• Klebsiella (fast)
• E. coli (fast)
• Enterobacter (fast)
• Serratia (slow)

Question 14

Green colonies on eosin-methylene blue agar

Answer 14

E. coli

Question 15

Charcoal yeast agar buffered with cysteine iron

Answer 15

Legionella

Question 16

Sabouraud’s agar

Answer 16

Fungi (e.g. dermatophytes)

Question 17

Obligate aerobes

Answer 17

Nagging Pests Must Breathe

• Nocardia (branching partially acid fast GP)
• Pseudomonas (GNR, lactose-, oxidase+)
• Myobacterium tuberculosis
• Bacillus (GPR)

Question 18

Obligate anaerobes

Answer 18

Can’t Breathe Air

• Clostridium (GPR, spore-forming)
• Bacteriodes (GN non-spore forming)
• Actinomyces (branching, non-acid fast GP)

Question 19

Bordet-Gengou agar

Answer 19

Potato agar

- Bordetella pertussis (GN “cocciod” rod)

Question 20

Obligate intracellular

Answer 20

Stay inside bc it’s Really Cold. Can’t make own ATP

• Rickettsia
• Chlamydia

Question 21

Falcultative intracellular

Answer 21

Some Nasty Bugs May Live FacultativeLY

• Salmonella
• Neisseria
• Brucella
• Mycobacterium
• Listeria
• Francisella
• Legionella
• Yersinia pestis

Question 22

Encapsulated bacteria

Answer 22

SHiN SKiS

• Strep pneumo
• H. flu
• Niesseria meningitidis
• Salmonella
• Klebsiella
• Strep agalactiae (GBS)

Caution:

• Asplenic
• B cell immune deficiency

Question 23

Catalase positive

Answer 23

SSPACEL for your “cats”

• S. aureus
• Serratia (+lactose, slow)
• Pseudomonas (-lactose, +oxidase)
• Aspergillus
• Candida
• E. coli
• Listeria

Question 24

Urease positive

Answer 24

PUNCH-KSS

• Proteus
• Ureaplasma
• Nocardia
• Cryptococcus
• H. pylori
• Klebsiella
• Staph sap
• Staph epi

Question 25

Pigment producers 1. yellow "sulfur" granules 2. yellow/honey-colored pigment 3. blue-green pigment 4. reg pigment

Answer 25

1. Actinomyces israelii 2. S. aureus 3. Pseudomonas aeruginosa 4. Serratia marcescens

Question 26

Select virulence factors: 1. Protein A 2. IgA protease 3. M protein

Answer 26

1. S. aureus 2. SHiN (S. pneumo, H. flu, Neisseria) 3. GAS/S. agalactiae

Question 27

Exotoxins that inhibit protein synthesis

Answer 27

1. Diptheria toxin (C. diptheriae): inhibits protein synthesis; A subunit ADP ribosylates EF-2 inhibiting mRNA translation; B subunit binds to heart and neural tissue 2. Exotoxin A (Pseudomonas): similar to (1) but targets liver, ADP ribosylates and inhibits EF-2 3. Shiga toxin (Shigella): inactivates 60S ribosome, cleaving rRNA; leads to dysentery, cytokine release, HUS 4. Shiga-like toxin (EHEC--O157:H7, EIEC): same as Shigella, inactivates 60S ribosome; causes HUS but does NOT invade

Question 28

Exotoxins that increase fluid secretion

Answer 28

1. Heat-stable toxin (Yersinia): incr cGMP, decr NaCl and H20 reabs; Yersinia invades and causes watery diarrhea 2. Heat-stable toxin (ETEC): incr cGMP, decr NaCl and H20 reabs 3. Heat-labile toxin (ETEC): similary to choleragen; incr cAMP, incr Cl- secretion and H20 efflux 4. Cholera toxin (Vibrio cholerae): incr cAMP via permanent Gs activation, incr NaCl secretion; "rice water diarrhea," death from dehydration! 5. B. cereus toxin: also similar to choleragen 6. Edema factor (Bacillus anthracis): mimics adenylate cyclas, incr cAMP, which impairs neutrophil/macrophage phagocytic function and disrupts water homeostasis.

Question 29

Inhibit phagocytic ability

Answer 29

``` Pertussis toxin (Bordetella pertussis) - A subunit activates membrane G protein to activate adenylate cyclase, incr cAMP ```

Question 30

Bordetella pertussis toxins

Answer 30

1. Pertussis toxin: B subunit Binds, A subunit incr cAMP and inhibits phagocytosis 2. Extracytoplasmic adenylate cyclase: similar to anthrax EF, impairs phagocyte chemotaxis and phagocytosis 3. Filmentous hemagglutinin: allows binding to ciliated epithelial cells 4. Tracheal cytotoxin: damages respiratory epithelial cells

Question 31

Neurotoxins

Answer 31

1. Tetanus toxin (C. tetani): cleaves SNARE protein, preventing inhibitory NT (GABA, Gly) release 2. Botulinum toxin (C. botulinum): cleaves SNARE, inhibits stimulatory ACh release from NMJ leading to flaccid paralysis

Question 32

Lyse cell membranes

Answer 32

1. Alpha toxin/lecithinase (Clostridum perfringens): hydrolyses lecithin in cell membranes causing cell death --> tissue destruction and gas gangrene 2. Streptolysin O (S. pyogenes): Lyses RBCs [think beta hemolysis!]

Question 33

Pyrogenic toxins/superantigens causing shock

Answer 33

1. Exotoxin A (Strep pyogenes/GAS) 2. Toxic shock syndrome toxin-1 (S. aureus) Both activate endogenous mediators of shock. Bring MHC II and TCR closer together to cause overwhelming release of IFN-gamma and IL-2. IFN-gamma from Th1 cells activate macrophages to release TNF-alpha and IL-1

Question 34

Functions of S. pyogenes toxins 1. Hemolysins/streptolysin O and S 2. Streptokinase 3. DNAases 4. Hyaluronidase 5. NADase

Answer 34

1. Lyses RBCs 2. Activates plasminogen to lyse fibrin clots 3. Hydrolyzes DNA 4. Breaks down proteoglycans 5. Hydrolyzes NAD

Question 35

Most common causes of aseptic meningitis

Answer 35

Coxsackie Echovirus Mumps virus

Question 35

Functions of S. aureus toxins 1. Lipases 2. PCNases 3. Staphylokinase 4. Leukocidin 5. Exfoliatin 6. Complement-binding factors

Answer 35

1. Hydrolyzes lipids 2. Destroys PCNs 3. Activates plasminogen to lyse fibrin clots 4. Lyses WBCs 5. Epithelial cell lysis 6. Cripples host complement defense