Bacteriology: Identification of Human Staphylococcal and Streptococcal Pathogens

Flashcards covering the diagnostic tests, morphology, and characteristics of Staphylococcal and Streptococcal pathogens from the lab midterm lecture.

Staphylococcus aureus

A gram-positive coccus that produces golden yellow colonies due to cytochrome staphylotoxin and is coagulase-positive.

Staphylococcus citreus

A member of the Staphylococcus genus characterized by lemon yellow pigmentation.

Catalase Test

An initial diagnostic test using $3\%\,H_2O_2$ (hydrogen peroxide) to differentiate Staphylococci (positive, bubbles) from Streptococci (negative, no bubbles).

Staphylococcus saccharolyticus

The only member of the Staphylococcus genus that is an obligate anaerobe and non-encapsulated.

Staphylococcus albus

A synonym for Staphylococcus epidermidis, characterized by white pigment formation on Loeffler's serum slant.

Beta-hemolysis

The complete lysing of red blood cells (RBCs) on a blood agar plate.

Coagulase Test

A test used to differentiate $S. aureus$ (positive) from other Staphylococci (negative), known as Coagulase-negative Staphylococcus (CoNS).

Slide Coagulase Test

A direct testing method that detects "Clumping factor" (bound coagulase) by mixing bacteria with rabbit's plasma.

Tube Coagulase Test

A test that detects "Coagulase-reactive factor" (free coagulase) by incubating bacteria in $0.5\,mL$ of rabbit's plasma for up to 18 hours.

Mannitol Salt Agar (MSA)

A selective medium containing $7.5\%-10\%\,NaCl$ and phenol red used to detect mannitol fermentation (positive result is yellow).

DNAse test

Also known as the Thermonuclease test, it identifies $S. aureus$ by detecting the breakdown of DNA, creating a clear or pink zone around colonies.

Staphylococcus epidermidis

The most common cause of hospital-acquired UTI and prosthetic device infections; it produces biofilm and is Novobiocin sensitive (S).

Staphylococcus saprophyticus

A cause of UTI, pyelonephritis, and cystitis in sexually active young women; it is Novobiocin resistant (R).

Micrococcus

Gram-positive cocci arranged in tetrads that are obligate aerobes and test positive (blue) in the Modified Oxidase Test.

Lancefield Classification

A system developed by Rebecca Lancefield to classify Streptococci based on the extraction of C carbohydrate from their cell walls.

Streptococcus pyogenes

Group A Streptococcus (GAS) known for causing pyogenic infections and Scarlet fever; it is Bacitracin sensitive (S) and PYR positive.

Streptolysin O

An oxygen-labile, highly immunogenic extracellular product of $S. pyogenes$ that is active in reduced (anaerobic) environments.

Streptolysin S

An oxygen-stable, less immunogenic hemolysin produced by $S. pyogenes$ that is active in aerobic environments.

Dick’s Test

A skin susceptibility test for Scarlet fever where a positive result indicates redness at the site of injection.

Schultz-Charlton Test

Also called the Blanche phenomenon, it involves injecting antitoxin to see if a rash fades, confirming the rash is caused by $S. pyogenes$.

PYR Hydrolysis

A presumptive test for Group A streptococci and Group D enterococci; a positive result is indicated by a red or orange color.

Streptococcus agalactiae

Group B Streptococcus (GBS) that is a leading cause of neonatal meningitis and tests positive for CAMP and Hippurate hydrolysis.

CAMP Test

A test named after Christie, Atkins, and Munch-Petersen that detects a synergistic hemolysis effect (arrowhead zone) between GBS and $S. aureus$.

Hippurate Hydrolysis Test

A test that detects the hydrolysis of Na Hippurate to benzoic acid and glycine; a positive result with Ninhydrin reagent is purple.

Streptococcus anginosus

Group F Streptococcus that is normal flora of the oropharynx and produces a sweet odor of honeysuckle or butterscotch.

Streptococcus pneumoniae

Gram-positive, lancet-shaped diplococci known for causing community-acquired pneumonia and producing alpha-hemolysis.

Bile Solubility Test

A test used to distinguish $S. pneumoniae$ (positive, lysis/clearing) from other alpha-hemolytic streptococci using $10\%\,Na$ deoxycholate.

Neufeld-Quellung Reaction

Also called the Capsular Swelling Test, it is the most specific method for identifying pneumococcus using anti-pneumococcal serum.

Enterococcus

Gram-positive cocci identified by being positive for both PYR and $6.5\%\,NaCl$; common species include $E. faecalis$ and $E. faecium$.