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Clinical Bacteriology > (M) Lab: Biochemical Identification of Bacteria (Part 2) > Flashcards

(M) Lab: Biochemical Identification of Bacteria (Part 2) Flashcards

BIOCHEMICAL IDENTIFICATION FOR GRAM-POSITIVE COCCI

1
Q
  • 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
A

Catalase Test

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2
Q

Catalase Test

Reporting/Interpretation: Effervescence

A

Reporting: POSITIVE for catalase test
Interpret: Staphylococcus

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3
Q

Catalase Test

Reporting/Interpretation: No effervescence

A

Reporting: NEGATIVE for catalase test
Interpret: Streptococcus

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4
Q
  • 2nd test if positive for catalase
  • Determines species
  • Identifies the most medically important pathogen under Staph: S. aureus
A

Coagulase Test

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5
Q
  • 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
A

S. aureus

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6
Q

Coagulase Test

Positive results?

Reporting and Interpretation

A

Reporting:Within 4 hours: medium will clot, solidify, gel-like, or will turn cloudy
Interpret: S. aureus

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7
Q

Coagulase Test

Lysis or dissolution of clot, causing a false-negative result

A

Staphylokinase

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8
Q

T or F: Even after 4 hours, there is still no clotting, we should report it as negative immediately.

A

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
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9
Q
  • Follow-up for coagulase-negative
  • Novobiocin is an antimicrobial agent (AMA) that inhibits one spp of Staph: S. epidermidis
A

Novobiocin Susceptibility Test

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10
Q

Novobiocin Susceptibility Test

  • Susceptible to novobiocin, confirmed by the presence of a ZOI measuring >16mm
A

S. epidermidis

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11
Q

Novobiocin Susceptibility Test

  • Resistant, with ZOI <16mm
A

S. saprophyticus

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12
Q
  • 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
A

Bacitracin Susceptibility Test

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13
Q

Bacitracin Susceptibility Test

____ susceptibility to Taxo A is demonstrated by any size of ZOI

A

S. pyogenes

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14
Q

Bacitracin Susceptibility Test

If no ZOI, then the organism is?

A

Taxo A resistant

It is not Group A Strep, but is beta-hemolytic.

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15
Q
  • Follow-up if Taxo A-negative
  • Identifies Group B Strep also known as S. agalactiae
A

CAMP Test

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16
Q

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

A

S. agalactiae

17
Q

Study the procedures for CAMP test.

A

Go bestie :]

18
Q
  • For gamma hemolytic
  • Identifies Group D streptococci, which includes, those that test positive for bile esculin
A

Bile Esculin Hydrolysis

19
Q
  • They can resist bile and can hydrolyze esculin present in the medium: Bile Esculin Agar (BEA) demonstrated by a blackening of the medium
A

Group D Enterococci
Group D Non-enterococci

20
Q

T or F: The blackening of BEA is not due to pigment, but due to hemolysis.

A

T

21
Q
  • For gamma hemolytic
  • Differentiates enterococci from non-enterococci
A

Salt Tolerance Test

22
Q

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
A

Enterococci

23
Q

Salt Tolerance Test

  • Non-halophilic resulting in a clear solution after inoculation
A

Non-enterococci

24
Q
  • Also called Taxo P → inhibits alpha-hemolytic strep: S. pneumoniae
A

Optochin Susceptibility Test

25
Q

Optochin Susceptibility Test

  • Susceptible demonstrated by a ZOI >14mm
A

S. pneumoniae

26
Q

Optochin Susceptibility Test

  • Resistant which is demonstrated by a ZOI <14mm
A

Viridans

27
Q
  • 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
A

Biochemical Identification for Gram-Positive Cocci

Clinical Bacteriology (33 decks)

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