Microbiology Flashcards
Poor gram staining
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
Wright-Giemsa stain
Borrelia
Chlamydia
Plasmodium
Trypanosomes (T. brucei - sleeping sickness, T. cruzi - Chagas)
PAS (periodic acid-Schiff)
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)
Ziehl-Neelson (carbolfuchsin, methylene blue counter-stain)
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
India ink
Cryptococcus neoformans
- mucicarmine stains thick polysaccharide capsule red
Silver stain
- Fungi (e.g. Pneumocystis: dark disk-shaped yeast)
- Legionella: facultative intracellular GNR, charcoal yeast extract
- Bartonella: Cat scratch disease
Chocolate agar with V and X
H. flu
V = NAD+, X = hematin
Thayer-Martin (VPN/VCN) media
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)
Chocolate agar, plain
N. meningitidis
Tellurite plate, Loffler’s media
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
Lowenstein-Jensen agar
Mycobacterium tuberculosis
Eaton’s agar
Mycoplasma pneumoniae
Pink colonies on MacConkey’s agar
Lactose-fermenting organisms
- Citrobacter (slow)
- Klebsiella (fast)
- E. coli (fast)
- Enterobacter (fast)
- Serratia (slow)
Green colonies on eosin-methylene blue agar
E. coli
Charcoal yeast agar buffered with cysteine iron
Legionella
Sabouraud’s agar
Fungi (e.g. dermatophytes)
Obligate aerobes
Nagging Pests Must Breathe
- Nocardia (branching partially acid fast GP)
- Pseudomonas (GNR, lactose-, oxidase+)
- Myobacterium tuberculosis
- Bacillus (GPR)
Obligate anaerobes
Can’t Breathe Air
- Clostridium (GPR, spore-forming)
- Bacteriodes (GN non-spore forming)
- Actinomyces (branching, non-acid fast GP)
Bordet-Gengou agar
Potato agar
- Bordetella pertussis (GN “cocciod” rod)
Obligate intracellular
Stay inside bc it’s Really Cold. Can’t make own ATP
- Rickettsia
- Chlamydia
Falcultative intracellular
Some Nasty Bugs May Live FacultativeLY
- Salmonella
- Neisseria
- Brucella
- Mycobacterium
- Listeria
- Francisella
- Legionella
- Yersinia pestis
Encapsulated bacteria
SHiN SKiS
- Strep pneumo
- H. flu
- Niesseria meningitidis
- Salmonella
- Klebsiella
- Strep agalactiae (GBS)
Caution:
- Asplenic
- B cell immune deficiency
Catalase positive
SSPACEL for your “cats”
- S. aureus
- Serratia (+lactose, slow)
- Pseudomonas (-lactose, +oxidase)
- Aspergillus
- Candida
- E. coli
- Listeria
Urease positive
PUNCH-KSS
- Proteus
- Ureaplasma
- Nocardia
- Cryptococcus
- H. pylori
- Klebsiella
- Staph sap
- Staph epi
Pigment producers
- yellow “sulfur” granules
- yellow/honey-colored pigment
- blue-green pigment
- reg pigment
- Actinomyces israelii
- S. aureus
- Pseudomonas aeruginosa
- Serratia marcescens
Select virulence factors:
- Protein A
- IgA protease
- M protein
- S. aureus
- SHiN (S. pneumo, H. flu, Neisseria)
- GAS/S. agalactiae
Exotoxins that inhibit protein synthesis
- Diptheria toxin (C. diptheriae): inhibits protein synthesis; A subunit ADP ribosylates EF-2 inhibiting mRNA translation; B subunit binds to heart and neural tissue
- Exotoxin A (Pseudomonas): similar to (1) but targets liver, ADP ribosylates and inhibits EF-2
- Shiga toxin (Shigella): inactivates 60S ribosome, cleaving rRNA; leads to dysentery, cytokine release, HUS
- Shiga-like toxin (EHEC–O157:H7, EIEC): same as Shigella, inactivates 60S ribosome; causes HUS but does NOT invade
Exotoxins that increase fluid secretion
- Heat-stable toxin (Yersinia): incr cGMP, decr NaCl and H20 reabs; Yersinia invades and causes watery diarrhea
- Heat-stable toxin (ETEC): incr cGMP, decr NaCl and H20 reabs
- Heat-labile toxin (ETEC): similary to choleragen; incr cAMP, incr Cl- secretion and H20 efflux
- Cholera toxin (Vibrio cholerae): incr cAMP via permanent Gs activation, incr NaCl secretion; “rice water diarrhea,” death from dehydration!
- B. cereus toxin: also similar to choleragen
- Edema factor (Bacillus anthracis): mimics adenylate cyclas, incr cAMP, which impairs neutrophil/macrophage phagocytic function and disrupts water homeostasis.
Inhibit phagocytic ability
Pertussis toxin (Bordetella pertussis) - A subunit activates membrane G protein to activate adenylate cyclase, incr cAMP
Bordetella pertussis toxins
- Pertussis toxin: B subunit Binds, A subunit incr cAMP and inhibits phagocytosis
- Extracytoplasmic adenylate cyclase: similar to anthrax EF, impairs phagocyte chemotaxis and phagocytosis
- Filmentous hemagglutinin: allows binding to ciliated epithelial cells
- Tracheal cytotoxin: damages respiratory epithelial cells
Neurotoxins
- Tetanus toxin (C. tetani): cleaves SNARE protein, preventing inhibitory NT (GABA, Gly) release
- Botulinum toxin (C. botulinum): cleaves SNARE, inhibits stimulatory ACh release from NMJ leading to flaccid paralysis
Lyse cell membranes
- Alpha toxin/lecithinase (Clostridum perfringens): hydrolyses lecithin in cell membranes causing cell death –> tissue destruction and gas gangrene
- Streptolysin O (S. pyogenes): Lyses RBCs [think beta hemolysis!]
Pyrogenic toxins/superantigens causing shock
- Exotoxin A (Strep pyogenes/GAS)
- 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
Functions of S. pyogenes toxins
- Hemolysins/streptolysin O and S
- Streptokinase
- DNAases
- Hyaluronidase
- NADase
- Lyses RBCs
- Activates plasminogen to lyse fibrin clots
- Hydrolyzes DNA
- Breaks down proteoglycans
- Hydrolyzes NAD
Most common causes of aseptic meningitis
Coxsackie
Echovirus
Mumps virus
Functions of S. aureus toxins
- Lipases
- PCNases
- Staphylokinase
- Leukocidin
- Exfoliatin
- Complement-binding factors
- Hydrolyzes lipids
- Destroys PCNs
- Activates plasminogen to lyse fibrin clots
- Lyses WBCs
- Epithelial cell lysis
- Cripples host complement defense
