Day 2.1 Micro Flashcards
What part of the bacteria stains with crystal violet?
Peptidoglycan layer.
Gram+ have big peptidoglycan layer, so they turn purple (violet)
What are the acute phase cytokines?
IL-1
IL-6
TNF-alpha
Where are Beta-lactamases located?
In the periplasm (space) of gram-neg bacteria. B-lactamases break down Abx like penicillin
What bacteria are encapsulated?
Some Killers Have Nice Shiny Bodies: Strep pneumonia Klebsiella Hemohilus influenza B Neisseria Salmonella B (gp B strep)
How do you test for encapsulated bacteria?
+ quelling reaction
Capsule swells with anti-capsular Ab.
(Doesn’t swell w/o Ab bc capsule protects)
The capsule serves an the Ag in which vaccines?
Pneumococcal (Pneumovax)
HiB
Meningiococcal
These vaccines are all derived from capsular Ag
What are the spore-forming bacteria
Only gram+ rods do this:
Bacillus (anthrax, B. cereus)
Clostridium (perfringens, tetani, botulinum)
Coxiella burnetti (Q fever)
Where is the DNA for Abx-resistance proteins (e.g. B-lactamase) found?
On plasmids. Not part of regular genome.
How does Endotoxin (lipid A) cause septic shock?
It activates macrophages, which release NO. NO causes vasodilation, which leads to hypotension and septic shock.
Where is endotoxin (LPS) found?
On the cell wall of gram-neg bactera, and in one gram+ bacteria: Listeria monocytogenes.
How does endotoxin (LPS) cause anaphylactic shock?
It activates the complement pathway, which causes C3a activation. C3a causes basophils and mast cells to degranulate and rls histamine, which causes vasodilation, hypotension, and edema.
What does C5a cause?
Neutrophil chemotaxis
Which are secreted, endotoxins or exotoxins?
Exotoxins are secreted. Endotoxin (LPS) is part of the cell wall.
Which needs a lower dose in order to be fatal, endo or exotoxin?
Exotoxin is the more fatal, meaning it needs only a small amt to be toxic. The toxicity of endotoxin is low, meaning it needs a higher dose to be toxic.
What are superantigens?
Exotoxins (secreted toxins)- bind directly to MHC-II and TCR simultaneously, activating lg numbers of Tcells to stimulate rls of IFN-gamma and IL-2.
S. aureus and S. pyogenes (gp A) have a lot of them.
What are the S. aureus superantigens (exotoxins)?
alpha-toxin - hemolysis
beta-toxin - sphingomyelinase
gamma-toxin (proteins A, B, C) - A + B = hemolysin (hemolysis), B + C = leukocidin (destroys leukocytes)
Enterotoxins A-E - food poisoning-vom/D
TSST-1 - rls cytokines - TSS
Epidermolytic/exfoliative - epithel cell lysis-scalded skin syndr
What are the Strep pyogenes (Gp A Strep) superantigens (exotoxins)?
Streptolysin O - hemolysis (O2 labile)
Streptolysin S - hemolysis (O2 stabile)
Erythrogenic /pyrogenic toxins - skin rash, fever of scarlet fever
What do ADP-ribosylating A-B toxins do?
Interfere w host cell fn
B (binding) part binds to a receptor on host cell surf, enabling endocytosis of the toxin.
A (active) part attaches and ADP-ribosyl to host cell protein (ADP ribosylation), altering protein fn
What are the pathogens with ADP ribosylating A-B toxins?
C. diptheriae
V. cholera
E.coli (ETEC)
B. pertussis
How does the ADP ribosylating toxin of Corynebacterium diptheria work?
Inactivates EF-2 (elongation factor), causes pharyngitis and pseudomembrane (gray) in throat. Don’t scrape or will get into blood and kill pt.
How does the ADP ribosylating A-B toxin of Vibrio cholera work?
ADP ribosylation of Gs protein stim’s adenylate cyclase, causes incrsd pumping of Cl- into gut and decrsd Na+ absorption. H20 follows salt in gut, causing voluminous rice-water diarrhea
How does the ADP ribosylating A-B toxin of ETEC work?
Heat-labile toxin stim’s adenylate cyclase
Heat-stabile toxin stim’s guanylate cyclase
both cause watery diarrhea
Labile like Air (A = adenylate)
Stabile like Ground (G = guanylate)
How does the ADP ribosylating A-B toxin of Bordetella pertussis work?
Increases cAMP by inhibiting Gi (Inhibits the inhibitor). Causes whooping cough. Inhibits chemokine receptor, causing lymphocytosis (increased lymphocytes)
When C. diptheria inactivates EF-2, this can interfere with protein synthesis in which cells?
Heart cells and nerve cells
What does the toxin of C. perfringens do?
alpha toxin- it’s a lecithinase that acts as a phospholipase to cleave cell membranes
causes gas gangrene
What does the toxin of C. tetani do?
Tetanospasmin
Blocks rls of inhibitory NTs GABA and Glycine.
Causes lockjaw
What drugs potentiate GABA?
Benzos and Barbituates.
GABA is the main inhibitory NT of the brain, so potentiating it means slowing down the brain.
What does the toxin of C. botulinum do?
Blocks rls of ACh, causing anti-cholinergic symptoms, CNA paralysis (esp cranial nerves) and floppy baby flaccid paralysis.
Spores in canned food and honey, don’t give to kids <1 yo
What does the toxin of B. anthracis do?
Includes edema factor, which is itself an adenylate cyclase- so it increases cAMP. (Without the Gprotein first)
What does the toxin of Shigella do?
Shiga toxin cleaves host cell rRNA, inactivating the 60S eukaryotic ribosome. Also enhances cytokine rls, causing HUS.
Shiga toxin is also md by E.coli
What does the toxin of S. pyogenes (Gp A Strep) do?
Streptolysin O- it’s a hemolysin.
It serves as the Ag for ASO Ab, which is used to dx rheumatic fever.
Also Streptolysin S and erythrogenic and pyrogenic toxins.
What toxins induce cAMP?
Vibrio cholera toxin (permanently activates Gs
Pertussis toxin (permanently inactivates Gi)
E. coli (ETEC) heat-labile toxin
B. anthracis (includes edema factor, which is an adenylate cyclase)
What causes scarlet fever? What are the toxins?
S. pyogenes (Gp A strep)- erythrogenic toxin (red skin) and pyrogenic toxin (fever)
What neurotransmitters does Tetanus toxin block?
GABA and Glycine (inhibitory NTs)
Which pathogens are intracellular?
Rickettsia and Chlamydia
Stay inside bc it’s Really Cold.
Also Legionella is primarily intracellular
What organisms are too thin to be gram stained?
Treponema
Use darkfield microscopy and fluorescent Ab staining instead
What organisms have a high lipid content and therefore do not gram stain well?
Mycobacteria.
Use acid-fast (Ziehl-Neelson) stain instead
What organisms have no cell wall and therefore do not gram stain well?
Mycoplasma
What stains with Giemsa?
Borrelia, Plasmodium, trypanosomes, Chlamydia
What stains with India Ink?
C. neoformans.
What is congo red stain used for?
Amyloid
What is silver stain used for?
Fungi
Legionella
What media does H. influenza need to grow?
Chocolate agar with factors V (NAD+) and X (hematin)
What agar is M. tuberculosis grown on?
Lowenstein-Jensen agar
takes 3-4 wks to grow
What is MacConkey’s agar made of?
Bile salts, crystal violet (these kill gram+)
Lactose, Neutral red (gram-neg lactose fermenters take up both of these, making colonies pink)
What agar is E. coli grown on?
MacConkey’s (pink colonies) or
EMB eosin-methyline blue (blue-black colonies with metallic sheen)
What agar is fungi grown on
Sabourad’s agar
In what environment does Pseudomonas (aeruginosa) love to grow?
Aerobe (needs air) and loves moist environment: hot tub (folliculitis) sweaty shoes contact lenses burn victims
At which point on the bacterial growth curve does spore formation occur?
At the end of the stationary phase, when nutrients are almost depleted.
What are the 4 methods of bacterial DNA exchg?
- Transformation (take up from env)
- Conjugation (with pilus)
- Transduciton (phages)
- Transposition (jump from plasmid to chromosome)
Which bacteria can undergo transformation (take up DNA from env)
SHiN:
S. pneumoniae
H. influenza B
Neisseria
Staph are gram+ and catalase+, meaning they make catalase. What does catalase do?
Degrades H2O2 into O2 and H2O.
H2O2 is usually converted by myeloperoxidase to a microbicide. Staph prevents this by getting rid of the H2O2 in the first place.
S. aureus is gram+ catalase+ coagulase+. What does coagulase do?
Coagulase converts fibrinogen to fibrin. This makes it easy for S. aureus to hide in blood clots (since it helps make fibrin)
What gram+ bacteria is found as diplococci?
S. pneumonia
What are the Coag-neg staph?
S. epidermidis
S. saprophyticus
What strep are alpha-hemolytic?
S. pneumonia and Viridans group (S. mutans)
What bacteria causes endocarditis, esp in drug users
S. epidermis (coag-neg)
What bacteria cause subacute bacterial endocarditis?
Coag-neg S. epidermis
Enterococci
Viridans group (S. sanguis)
What bacteria causes dental caries?
S. mutans (viridans group)
What diseases can be caused by S. aureus?
Inflam dz: Skin/wound infection Organ abscess Respi infection/pneumonia Bacteremia/sepsis UTI Endocarditis, meningitis, osteomyelitis, septic arthritis
Toxin-mediated dz:
TSS (TSST-1 toxin)
Scalded skin syndrome (epidermolytic/exfoliative toxin)
Gastroenteritis/food poisoning (enterotoxins)
What is Protein A?
Virulence factor of S. aureus.
Binds to the Fc region of IgG, preventing opsonization (complement fixation) and phagocytosis.
Is S. aureus ever normal flora?
Yes, in nose!
Who should get the pneumococcal vaccine? (Against S. pneumonia)
>65 yo Asplenic Sickle cell anemia HIV+ Hx of chronic lung dz (COPD, asthma)
What skin infections can be caused by both S. pyogenes and S. aureus?
Folliculitis
Celluitis (deep skin infection)
Impetigo (skin vessicles around mouth, rupture and make thick yellow weeping crusted lesions- honeycomb lesion)
What does S. pyogenes (Gp A Strep) cause?
Proliferative/pyogenic dz: pharyngitis endocarditis skin infections necrotizing fasciitis bacteremia, sepsis
Toxin-mediated dz:
Scarlet fever
TSS
Autoimm Ab-mediated (but initiated by S. pyogenes):
Acute glomerulonephritis
Rheumatic fever
What bacterial virulence factor does S. pyogenes (Gp A Strep) have?
M protein- helps prevent phagocytosis
What organisms cause neonatal death?
Group B Strep (S. agalactiae)
E. coli
Listeria
(These can all cause meningitis in newborns)
What is the most common organism in the large intestine?
Bacteroides fragilis (obligate anaerobe)
What are the obligate anaerobes?
Clostridiium
Bacteroides
Acintomyces
What is the Rx for obligate anaerobes?
Metronizadole or Clindamycin
What organism causes acute endocarditis?
S. aureus
What organism causes mastitis of breast?
S. aureus
What bacteria is common in neonates bc it’s normal vag flora in 25% of women?
Group B Strep (S. agalactiae)
What can Gp B Strep cause in neonates?
Meningitis
Sepsis
Pneumonia
Most common cause of meningitis?
S. pneumonia
Most common cause of osteomyelitis?
S. aureus
Cause of cellulitis?
S. pyogenes or S. aureus
Cause of otits media in children
S. pneumonia
Pharyngitis which leads to glomerulonephritis is cause by which organism?
Group A Strep (S. pyogenes)
Food-poisoning w vom that resolves quickly
Caused by S. aureus (ingested enterotoxins)
S. pneumonia is the most common cause of what 4 things?
MOPS: Meningitis Otitis media in kids Pneumonia Sinusitis
All of these are protected by IgA (IgA is in mucus) normally, but S. pneumonia is an IgA protease.
15% of colon cancer pts are colonized with which bacteria?
Strep bovis (Gp D strep)
What is the treatment for Diptheria?
Diptheria anti-toxin (Ab)
Penicillin
Dpt vaccine
C. diff produces pseudomembranous coliits. What is a pseudomembrane of the gut?
Necrosis of gut epithelium, with exudate, fibrin, and leukocytes
How do you dx C. diff?
Look for C. diff toxin in stool
What is the Rx for C. diff?
Metronidazole (oral or IV)
Vancomycin (oral)- this is the only time Vanc can be given orally. When given orally it will be metabolized and not go systemically. Here, that’s okay bc you just want it in gut. Also, the oral dose is not nephrotoxic bc it doesn’t go systemic, so it’s okay for pts w renal dz
Nocardia and Acintomyces: both are gram+ filamentous branching rods. Are they aerobic or anaerobic?
Acintomyces = anaerobic Nocardia = aerobic
