(M) Lab: Biochemical Identification of Bacteria (Part 2) Flashcards
BIOCHEMICAL IDENTIFICATION FOR GRAM-POSITIVE COCCI
- First test done for G(+) cocci
- Determines the genus
- (+) Staphylococcus releases a catalase enzyme seen upon the addition of 3% H2O2 resulting in a large bubble formation or the presence of effervescence
Catalase Test
Catalase Test
Reporting/Interpretation: Effervescence
Reporting: POSITIVE for catalase test
Interpret: Staphylococcus
Catalase Test
Reporting/Interpretation: No effervescence
Reporting: NEGATIVE for catalase test
Interpret: Streptococcus
- 2nd test if positive for catalase
- Determines species
- Identifies the most medically important pathogen under Staph: S. aureus
Coagulase Test
- Releases coagulase that acts as its defense mechanism
- The release is demonstrated when organism is cultured in its required medium: commercially prepared EDTA or citrated rabbit’s plasma
- Do tilt tube method to confirm changes in consistency
S. aureus
Coagulase Test
Positive results?
Reporting and Interpretation
Reporting:Within 4 hours: medium will clot, solidify, gel-like, or will turn cloudy
Interpret: S. aureus
Coagulase Test
Lysis or dissolution of clot, causing a false-negative result
Staphylokinase
T or F: Even after 4 hours, there is still no clotting, we should report it as negative immediately.
F (further incubate for 24 hours)
- If there is clotting: interpret as S. aureus
- If there is no clotting: interpret as not S. aureus, report it as Coagulase-negative Staphylococcus
- Follow-up for coagulase-negative
- Novobiocin is an antimicrobial agent (AMA) that inhibits one spp of Staph: S. epidermidis
Novobiocin Susceptibility Test
Novobiocin Susceptibility Test
- Susceptible to novobiocin, confirmed by the presence of a ZOI measuring >16mm
S. epidermidis
Novobiocin Susceptibility Test
- Resistant, with ZOI <16mm
S. saprophyticus
- Also called Taxo A
- Even at a low amount of Taxo A (0.04 units), it can inhibit Group A Strep or S. pyogenes, the very important beta-hemolytic streptococcus
Bacitracin Susceptibility Test
Bacitracin Susceptibility Test
____ susceptibility to Taxo A is demonstrated by any size of ZOI
S. pyogenes
Bacitracin Susceptibility Test
If no ZOI, then the organism is?
Taxo A resistant
It is not Group A Strep, but is beta-hemolytic.
- Follow-up if Taxo A-negative
- Identifies Group B Strep also known as S. agalactiae
CAMP Test
CAMP Test
Releases a Christie-Atkins-Munch-Peters (CAMP) factor that enhances the beta-hemolysis of GBS when the bacteria is inoculation with another beta-hemolytic bacteria, usually S. aureus
S. agalactiae
Study the procedures for CAMP test.
Go bestie :]
- For gamma hemolytic
- Identifies Group D streptococci, which includes, those that test positive for bile esculin
Bile Esculin Hydrolysis
- They can resist bile and can hydrolyze esculin present in the medium: Bile Esculin Agar (BEA) demonstrated by a blackening of the medium
Group D Enterococci
Group D Non-enterococci
T or F: The blackening of BEA is not due to pigment, but due to hemolysis.
T
- For gamma hemolytic
- Differentiates enterococci from non-enterococci
Salt Tolerance Test
Salt Tolerance Test
- Said to be halophilc → they grow at high salt concentration, specifically at 6.5% NaCl, which is demonstrated by the presence of turbidity
Enterococci
Salt Tolerance Test
- Non-halophilic resulting in a clear solution after inoculation
Non-enterococci
- Also called Taxo P → inhibits alpha-hemolytic strep: S. pneumoniae
Optochin Susceptibility Test
Optochin Susceptibility Test
- Susceptible demonstrated by a ZOI >14mm
S. pneumoniae
Optochin Susceptibility Test
- Resistant which is demonstrated by a ZOI <14mm
Viridans
- These are done routinely for G(+) cocci
- More on follow-up tests since you have to wait for the results of the prior tests before moving on to the next
- Usually takes 2-3 days before you can give genus and spp, especially if it is under the Strep group
Biochemical Identification for Gram-Positive Cocci
