Wk 1 Clinical Bacteriology Flashcards
What is darkfield microscopy used for?
When organism is difficult to see with bright field
Borrelia, Treponema, Mycoplasma
Gram stain examples
What color are acid fast negative and positive bacteria?
negative = blue
positive = red
What do mycobacterium species cell walls contain?
mycolic acids, fatty acids, and lipids
-they are acid-fast positive
What are non-acid fast bacteria counter stained with?
Methylene blue
What does hemolysis on blood agar look like?
What are 2 types of non-selective media?
- tryptic soy broth - widely used to isolate bacteria
- thioglycolate broth - can differentiate b/w species based on O2 requirements
3-anaerobic bacteria (like Gram-positive spore formers)
3 types of selective and differential media
- CNA agar - selects for Gram-positive bacteria (Colistin and** N**alidixic acid inhibit Gram-negative bacteria) (Gram + Staphylococcus, Streptococcus)
- MacConkey agar - selects Gram-negative, lactose, bile salts inhibit Gram + bacteria (differentiates lactose fermenters (pink) vs non-lactose fermenters (not pink)
- Thayer-Martin media - chocolate agar supplemented w/ antibiotics (used to culture and isolate Neisseria sp), Vancomycin kills Gram-positives, Trimethroprim and Colistin kill most Gram-negative organisms except Neisseria) - think Neisseria sp. with this!!
Common clinically important anaerobes
What are 3 biochemical tests?
- Catalase test
- Coagulase test
- Oxidase test
Catalase test
Coagulase Test
Oxidase Test
Oxidative-Fermentation test
TSI
=triple sugar iron
Agglutination tests
What are 5 serologic tests
Antigensoftheorganismintissues or body fluids
* Antibodiesinpatient’sserum
Tests:
1. Agglutination (rapid)
2. Enzyme immunoassay (ELISA)
3. immunofluorescence (IF)
4. Immunohistochemistry (IHC)
5. Western blot
Review
Most common staphylococcus
-are catalase positive
S. aureus
S. epidermidis
S. saprophyticus
Staphylococcus aureus
- Catalase positive
- Coagulase positive
- β-Hemolytic
MRSA (Methicillin-Resistant S. aureus)
- Highly antibiotic resistant=SUPER BUG
- Resistant to the penicillinase-stable penicillins (methicillin, nafcillin, and oxacillin) and all beta-lactam drugs
- Altered penicillin-binding protein PBP2A encoded by mecA
Staphylococcus epidermidis
- Non-hemolytic
- Catalase positive
- Coagulase negative
- Novobiocin sensitive
- Normal skin flora (epidermis=skin)
- Contaminates blood cultures
- Skin/wound infections
- Biofilms on plastic devices: catheters, prostheses (hip implant, heart valve)
Staphylococcus saprophyticus
*Gram-positive
Catalase positive
* Coagulase negative
* Novobiocin resistant
- Normal flora of female genital tract
- Urinary tract infection or Uncomplicated cystitis, second most common cause
- Peritonitis
Streptococcus and Enterococcus
- S. pyogenes (Group A Strep)
- S. agalactiae (Group B Strep)
- S. pneumoniae (pneumococcus)
- Viridans Streptococci group
- Enterococcus species
Streptococcus classification
Streptococcus agalactiae (Group B Streptococcus)
- Catalase negative
- β-hemolytic
- Narrow zone of hemolysis
- Bacitracin resistant
- Lancefield Group B
- Polysaccharide capsule is a significant virulence factor
- Colonizes genital and lower GI tracts of 10-40% of women; also found in oropharynx, upper GI
- Pregnant women screened at 36-38 weeks for
GBS - Intrapartum penicillin prophylaxis if positive
Streptococcus pyogenes (Group A Streptococcus, GAS)
- Group A Strep, human-restricted pathogen
- β-hemolytic
- Bacitracin sensitive
- Differentiate from other β-hemolytic streptococci
- Lancefield Group A
- Virulence factors
– Capsule
– M protein: Antiphagocytic, inhibits complement
– Enzymes for tissue invasion: Streptolysin, DNAses,
Streptokinase (dissolves clots)
– Superantigens
S. pyogenes (Group A Streptococcus)
- Pyogenic
- Pharyngitis*
- Impetigo (honey crusted lesions) * Cellulitis
- Scarlet fever (strawberry tongue)
- Bacteremia, toxic shock-like syndrome
- Necrotizing fasciitis
Streptococcus pneumoniae (pneumococcus)
- Lancet-shaped diplococcus * No Lancefield group
- α hemolytic (partial)
- Optochin sensitive
- Differentiate from α-hemolytic Viridans Streptococci
- Bile soluble
- Autolysin activated by bile
- Meningitis, otitis media, pneumonia, sinusitis
(MOPS)
- Meningitis, otitis media, pneumonia, sinusitis
