Test for Streptococcus Flashcards
Presumptive test for S. pyogenes
Bacitracin susceptibility, PYR test
Principle of Bacitracin susceptibility test
Inoculate organism in media and place a 0.04 units Taxo A disk (Bacitracin)
Medium for Bacitracin susceptibility test
Supported media or BAP
Incubation for Bacitracin susceptibility test
35-37°C, 18-24 hours, 5-10% CO2
Positive QC for Bacitracin susceptibility
Zone of inhibition >10 mm (S. pyogenes, Micrococcus luteus)
Negative QC for Bacitracin susceptibility
No zone of inhibition (S. agalactiae, S. aureus)
Principle of PYR test
L-Pyrrolidonyl-β-naphthylamide + L-pyrrolidonyl arylamidase → β-naphthylamine (detected by indicator)
Medium for PYR test
Filter paper PYR disk
Reagent/Indicator for PYR test
N,N-methylamino-Cinnamaldehyde
Incubation for PYR test
22-25°C, 2 minutes
Positive QC for PYR test
Bright red color within 5 minutes (E. faecalis, S. pyogenes)
Negative QC for PYR test
No color change (S. agalactiae)
Presumptive test for Enterococci and S. bovis
Bile esculin hydrolysis
Principle of bile esculin hydrolysis test
Organisms grow in 40% bile and hydrolyze it to esculetin
Medium for bile esculin hydrolysis test
Bile esculin slant with ferric ammonium citrate (iron)
Incubation for bile esculin hydrolysis test
35-37°C, 48 hours
Positive QC for bile esculin hydrolysis
Growth + black precipitate (E. faecalis)
Negative QC for bile esculin hydrolysis
Growth but no blackening (E. coli) or no growth and no blackening (S. pyogenes)
Presumptive test for S. pneumoniae
Optochin (P disk) susceptibility test, Bile solubility test
Principle of Optochin (P disk) test
Ethylhydrocupreine hydrochloride (Taxo P disk) inhibits S. pneumoniae growth
Medium and setup for Optochin test
Organism on BAP + P disk, incubate at 35°C, 18-24 hours, 5% CO2
Positive result for Optochin test
Zone of inhibition >14 mm (S. pneumoniae)
Negative result for Optochin test
Zone of inhibition <14 mm (S. pyogenes)
Principle of Bile solubility test
S. pneumoniae’s amidase enzyme lyses its colonies in the presence of bile salts
Setup for Bile solubility test
Colony on BAP or broth culture + 10% Sodium deoxycholate, incubate at 35-37°C for 30 minutes
Positive result for Bile solubility test
Colony disintegration on agar or broth culture becomes clear (S. pneumoniae)
Negative result for Bile solubility test
Colonies remain intact or broth remains turbid (E. faecalis, Viridans)
Test that differentiates Group B Streptococcus from others
CAMP test
Factor that enhances beta-lysin hemolysis of S. aureus
CAMP factor
Positive result for CAMP test
Arrowhead hemolysis (S. agalactiae)
Negative result for CAMP test
No enhanced hemolysis/arrowhead (S. pyogenes)
Medium and incubation for CAMP test
BAP at 35-37°C for 16-18 hours
Test for presumptive identification of S. agalactiae and others
Hippurate hydrolysis test
Reaction in Hippurate hydrolysis test
Hippurate + hippuricase → glycine and benzoic acid
Positive result for Hippurate hydrolysis test
Deep purple (S. agalactiae)
Negative result for Hippurate hydrolysis test
Colorless or yellow-pink (S. pyogenes)
Incubation for Hippurate hydrolysis test
35°C for 2 hours
Test for Enterococci identification
LAP test
Reaction in LAP test
Leucine-β-naphthylamine + leucine aminopeptidase → β-naphthylamine
Positive result for LAP test
Red (E. faecalis)
Negative result for LAP test
Yellow/No color change (Aerococcus viridans)
Incubation for LAP test
22-25°C for 5 minutes
Test for differentiation between Enterococcus faecalis and Enterococcus faecium
Pyruvate test
Reaction in Pyruvate test
Ability to use Pyruvate to form acids
Positive result for Pyruvate test
Yellow (E. faecalis)
Negative result for Pyruvate test
No change or Yellow-Green/Weak (S. gallolyticus)
Incubation for Pyruvate test
35-37°C for 24-48 hours
Test for Enterococci’s ability to withstand high salinity
Salt Tolerance test
Medium for Salt Tolerance test
Heart infusion broth + 6.5% NaCl
Positive result for Salt Tolerance test
Growth, Yellow (E. faecalis)
Negative result for Salt Tolerance test
Little/no growth (S. gallolyticus)
Incubation for Salt Tolerance test
35-37°C for 24-48 hours
