Intro Flashcards
Why ID important
- Common
- Diagnosable
- Communicable
- High Morbidity and mortality
- Treatable
- Newly emerging Pathogens
what 3 variables affect development of infection/disease
- Host (behavior, susceptibility, age, sex genetics, immune status)
- Environment (geography, sanitation, crowding, pollutants, social, cultural, political, economic)
- Agent (pathogenicity, prevalence, ecologic niche, tissue tropism, mechanism of immune control)
how do you do a gram stain
- Heat slide (kill/bind bacteria)
- Crystal violet (binds peptidoglycan)
- Add iodine to bind CV to gram positive cell wall
- Rinse
- add Acetone alcohol: removes stain from gram negative cells
- Rinse
- Add Safranin (counterstain)
Gram Positive vs Gram Negative structure
Gram Positive: have Teichoic acid in cell wall as well as thick peptidoglycan layer
Gram Negative: Lack Teichoic acid but have outer membrane of Endotoxin/LPS with thin peptidoglycan wall
Peptidoglycan in gram positive vs gram negative
up to 90% of cell wall in gram positive and up to 5-20% in gram negative
Appearance of Gram positive vs negative on gram stain
positive– dark purple, because they hold onto the crystal violet
Negative: due to thin peptidyglycan layer, the acetone alcohol removes the crystal violet from gram negative cells, which then stain pink with Safranin (counterstain)
Common Gram Positive cocci
Staph (clusters, pairs), Strep (pairs/chains)
Catalase +/-
common Gram negative cocci
- Neisseria- GC, meningococcus (CSF; lung)
- Moraxella - pneumonia
- Acinetobacter
Gram positive rod examples
Listeria, Clostridium
Gram negative rods
E. coli, Pseudomonas
lactose-ferment +/-
Non-staining organisms
\+/- Legionella Mycobacteria Spirochetes Rickettsia--intracellular Mycoplasma Chlamydia--intracellular
Encapsulated organisms
S. pneumoniae, H. influenzae, Neisseria meningitidis, K. pneumoniae, Bacillus anthracis
Multi-drug resistant organisms
M. tuberculosis, Ps. aeruginosa, methicillin-resistant Staph aureaus, Vancomycin-resistant enterococcus (VRE); S. pneumoniae
Bacteria producing superantigens
S. aureus, Group A Strep
Bacteria producing A-B toxins
V. cholerae, C. diphtheria
Bacteria producing “other toxins” (not A-B or superantigens)
Clostridium
Obligate intracellular organisms
Rickettsia, Chlamydia
Facultative intracelular organisms
Salmonella, Mycobacteria, Legionella
How to differentiate between gram negative rods
Lactose fermentation– most significant GNR are lactose fermentors
Pseudomonas,
Lactose Fermenting GNR
E. coli Klebsiella Enterobater Citrobacter Arizona
Non-lactose fermenting GNR
Pseudomonas aeruginosa, Salmonella, Shigella, H influenza, Acinetobater
How to distinguish E coli from other lactose fermenting GNR
Indole– E coli is the only one that is positive (except a few Klebsiella species)
Top lactose fermenting GNR
E. coli (flat), Klebsiela (mucoid), Enterobacter (mucoid)
sources of GNR
- intestine: appendix, diverticulitis, gallbladder (not Ps. aer.)
- urine: +WBC, +sxs
- lung/line (nosocomial)
Is staph coagulase positive/negative
Aureus = positive
- epidermidis (on skin) = negative
- saprophyticus (UTI)= negative
- lugdanensis = negative
Staphylococcus bacteremia
100% of S. aureus are significant;
>90% of coagulase negative staph are contaminants
Staph aureus
- carrier
- localized infection (boils, cellulitis)
- disseminated (blood, heart, joints, metastatic)
causes abscesses due to coagulase– pus!
When do you think of coagulase negative staph
plastic/metal in body (epidermidis)
2nd leading cause of UTI in sexually active females (S. saprophyticus)
hemolysis status
- alpha - green - S. pneumo, S. viridans
- beta- clear (bad; Gr. A, B, C, G Strep; S. aureus)
- gamma (none)- usually include Strept. Milleri (pus)
Bad bugs
S. aureus (incl MRSA)
Strep pneumoniae
Group A Strept
Less bad bugs
- Coag-neg/S. epidermidis
- Strep. viridans,
- Enterococcus
Wimpy bugs
P. acnes, diphtheroids
Small GPR
Listeria (risk–prego), Diptheroids, P. acnes;actinomyces
Large GPR
Clostridium, Bacillus sp.
Anaerobes
- 3% of + blood culture
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