Streptococcaceae and Other Related Genera Flashcards
When comparing staph and strep colonies, what are the differences?
- Staph is opaque
- Strep is “transparent” (or at least not as opaque)
Alpha (or gamma) hemolytic Streps
- Group D
- S. pneumoniae
- Enterococcus sp.
- Alpha Strep (not Group D)
Beta hemolytic Streps
- Group A
- Group B
- Group D (rarely beta hemolytic)
- Enterococcus spp. (rarely beta hemolytic)
- Beta Strep (not Group A, B, or D)
S. pneumoniae characteristic features on a plate
- Colonies are often depressed in center (autolysis) or mucoid (encapsulated)
Throat cultures (strep screens) must be incubated ____?
Anaerobically
Streptolysin O is ____ ____
Oxygen labile
Streptolysin S is ____ ____
Oxygen stable
Principle of the Lancefield grouping test
Grouped by “C substance” in cell wall
Streptococci
- Catalase (pos/neg)
Catalase negative
Bile Esculin hydrolysis
- Principle
To determin an organism’s ability to hydrolyze esculin to esculetin in presence of bile. Esculetin reacts w/ Fe citrate in medium to form black ppt
Bile Esculin agar
- What do pos/neg tests look like?
Pos: blackening of medium
Neg: no blackening
LAP
- Principle
To determine organism’s ability to produce the enzyme leucine aminopeptidase, which will hydrolyze leucine-a-naphthylamide disk
LAP
- What do pos/neg tests look like?
Pos: red
Weak pos: pink
Neg: yellow
- 5% NaCl
- Principle
To determine an organism’s ability to grow in a high salt environment (6.5%)
- 5% NaCl
- What do pos/neg tests look like?
Pos: turbid
Neg: clear, no change
PYR
- Principle
To determine an organism’s ability to produce the enzyme pyrrolidonyl peptidase
PYR
- What do pos/neg tests look like?
Pos: red
Neg: no color change
Optochin susceptibility test
- Principle
To determine an organism’s susceptibility to the chemical optochin (ethylhydrocupreine hydrochloride)
Optochin susceptibility test
- What do pos/neg tests look like?
Pos: zone of inhibition >= 14 mm
Neg: no zone of inhibition
Bile solubility
- Principle
To determine the ability of organisms to lyse in presence of bile salt (sodium desoxycholate)
- Plate and tube method
Bile solubility
- What do pos/neg tests look like?
Plate
- Pos: disintegration of colony under desoxycholate drop (flat hemolyzed area remains)
- Neg: no visible change under desoxycholate drop
Tube
- Pos: clearing of “test” but “control” remains turbid (cloudy)
- Neg: both tubes (“test” and “control”) remain turbid (cloudy)
Quellung test
- Principle
To determine the ability of the organism’s capusle Ags to bind to known Abs forming a precipitate. Visualized w/ the addition of methylene blue to the slide
Quellung test
- What do pos/neg tests look like?
Pos: capsule looks opaque and appears to enlarge around dark blue-stained cell
Neg: no appearance of a clear, enlarged halo surrounding stained cell
Bacitracin
- Principle
To detect an oganism’s susceptibility to the anitmicrobial agent bacitracin. Filter paper disks impregnated w/ bacitracin are sued to determine susceptibility or resistance
Bacitracin
- What do pos/neg tests look like?
Pos: zone of inhibition
Neg: no zone of inhibiton
CAMP test
- Principle
To detect presence of CAMP factor produced by certain organisms that will enhance the beta-hemolytic activity of S. aureus on SBA
Sodium Hippurate
- Principle
Hippuric acid is hydrolyzed to benzoic acid and glycine by hippuricase. Glycine end product is detected by addition of ninhydrin reagent
Sodium Hippurate
- What do pos/neg tests look like?
Pos: dark blue to purple color
Neg: no color change
Other grouping tools for determining Streptococcus and Enterococcus
- Ag testing (in/direct)
- Fluorescent Ab (esp. Group A)
- Kit systems (API, Vitek, etc.)
Latex agglutination
- Principle
To dtect certain Ags or Abs in a variety of bodily fluids (blood, saliva, urine, CSF). Sample to be tested is sent to the lab where it’s mixed w/ latex beads coated w/ a specific Ag or Ab.
Coagglutination
- Principle
Method used for organism identification using specific, known commercial Abs taht have been attached to a dead bacterium, most often Staphylococcus. Dead Staphylococcus act similarly to a latex bead, allowing Ag-Ab reaction to be visible to the naked eye
Coagglutination
- What do pos/neg tests look like?
Pos: visible agglutination w/in 1-2 minutes
Neg: remain smooth
2 types of Ag testing for Streptococcus and Enterococcus sp.
Latex agglutination and coagglutination
Who is/are PYR positive?
- Group A
- Enterococcus spp.
Who is/are NaHippurate positive?
- Group B
Who is bacitracin susceptible?
Group A
What Strep are LAP positive?
All of them we work with in the lab
What test did we use coagglutination on in the lab?
Group B
Who is/are quellung test positive?
S. pneumoniae