Gram Positive Cocci: Identification of Human Staphylococcal and Streptococcal Pathogens

A complete set of vocabulary flashcards covering identification tests, characteristics, and virulence factors of human staphylococcal and streptococcal pathogens.

Catalase Test

A diagnostic test used to differentiate Staphylococcus species (positive) from Streptococcus species (negative) based on the production of effervescence when mixed with $3\%$ hydrogen peroxide ($H_2O_2$).

Slide Coagulase Test

A test that detects bound coagulase ("clumping factor") by mixing bacteria with normal saline solution (NSS) and rabbit's plasma to produce a white fibrin clot within 1 minute.

Tube Coagulase Test

A test that detects free coagulase ("coagulase-reactive factor") by incubating bacterial cells with $0.5\,\text{mL}$ ($500\,\mu\text{L}$) rabbit's plasma in a water bath at $35^\circ\text{C}-37^\circ\text{C}$, reading for clot formation at 30 minutes, 4 hours, and 16-18 hours.

Mannitol Fermentation Test

A selective and differential test using Mannitol Salt Agar (containing $7.5\%-10\%$ NaCl and phenol red indicator) where mannitol fermenters produce yellow colonies/agar (e.g., Staphylococcus aureus) while non-fermenters remain red.

DNase Test

A test (also known as the Thermonuclease Test) used to identify organisms like Staphylococcus aureus and Serratia marcescens, producing clear or pink zones around colonies using methyl green, toluidine blue, or dilute HCl.

Staphylococcus epidermidis

A coagulase-negative staphylococcal species that is the most common cause of hospital-acquired UTIs and prosthetic device infections, characterized by biofilm production, gamma hemolysis, Novobiocin sensitivity, and phosphatase positivity.

Staphylococcus saprophyticus

A coagulase-negative staphylococcal species that causes urinary tract infections such as pyelonephritis and cystitis in sexually active young women, characterized by Novobiocin resistance and phosphatase negativity.

Staphylococcus lugdunensis

A virulent coagulase-negative staphylococcus that can mimic S. aureus infections, cause infective endocarditis and septic shock, contains the mecA gene, and is positive for slide coagulase, negative for tube coagulase, and positive for PYR.

Methicillin-Resistant Staphylococcus aureus (MRSA)

A strain of S. aureus resistant to penicillin due to the mecA gene altering penicillin-binding protein (PBP), requiring vancomycin as the treatment of choice.

D-test

A modified double disk diffusion test using $15\,\mu\text{g}$ Erythromycin and $2\,\mu\text{g}$ Clindamycin to detect inducible clindamycin resistance, shown by a flattening of the clindamycin inhibition zone adjacent to erythromycin (forming a D-shape).

Modified Oxidase Test

A presumptive test used to differentiate Micrococcus species (positive, dark-blue end product) from Staphylococcus species (negative) by detecting cytochrome C using tetramethyl-p-phenylenediamine dichloride in DMSO.

Alpha (\alpha) Hemolysis

Incomplete or partial hemolysis of red blood cells on blood agar, causing a greenish or brownish discoloration surrounding the colony (e.g., Streptococcus pneumoniae, Viridans Streptococci).

Beta (\beta) Hemolysis

Complete lysis of red blood cells surrounding a colony on blood agar, resulting in a clear, colorless zone (e.g., Streptococcus pyogenes, Streptococcus agalactiae).

Brown's Classification

A classification system created by J.H. Brown that categorizes streptococci into Alpha, Beta, Gamma, and Alpha Prime based on their patterns of hemolysis on Blood Agar.

Lancefield Classification

A system created by Rebecca Lancefield that classifies streptococci into serological Groups (Group A through G) based on the extraction of group-specific C carbohydrate antigens from the cell wall.

M protein

The major cell surface antigen and primary virulence factor of Streptococcus pyogenes (emm protein) that functions by preventing phagocytosis.

Streptolysin O

An oxygen-labile extracellular toxin produced by Streptococcus pyogenes that lyses leukocytes and red blood cells under anaerobic conditions and is highly immunogenic.

Streptolysin S

An oxygen-stable extracellular hemolysin produced by Streptococcus pyogenes that is active under aerobic conditions, lyses leukocytes, and is non-immunogenic or weakly immunogenic.

Dick's Test

A skin susceptibility test for Scarlet fever where a positive result is demonstrated by redness at the injection site.

Schultz-Charlton Test

A diagnostic reaction (also called Blanche Phenomenon) used to determine if a rash is caused by Streptococcus pyogenes, indicated by a positive fading or gradual disappearance of the redness.

PYR Hydrolysis Test

A presumptive diagnostic test for Group A streptococci and Group D enterococci based on the hydrolysis of L-pyrrolidonyl-\beta-naphthylamide, yielding a red or orange color upon reagent addition.

Streptococcus agalactiae

Group B Streptococcus, a major cause of invasive neonatal disease and the number one leading cause of neonatal meningitis.

CAMP Test

A presumptive test for Streptococcus agalactiae that demonstrates synergistic hemolysis when cultured near a Staphylococcus aureus streak on blood agar, forming a characteristic arrowhead-shaped zone of hemolysis.

Hippurate Hydrolysis Test

A test detecting hippuricase activity in Streptococcus agalactiae, which hydrolyzes sodium hippurate to benzoic acid (detected by ferric chloride) and glycine (detected by ninhydrin reagent to yield a purple color).

Streptococcus anginosus

A Group F streptococcal species found as normal flora in the oropharynx and urogenital tract, noted for producing a distinctive sweet odor of honeysuckle or butterscotch.

Bile Solubility Test

A test that differentiates Streptococcus pneumoniae (positive) from other alpha-hemolytic streptococci by using $10\%$ or $2\%$ sodium deoxycholate reagent to cause lysis/clearing of colonies.

Neufeld-Quellung Reaction

The most specific and rapid method for identifying Streptococcus pneumoniae, using anti-pneumococcal serum and methylene blue to make the bacterial capsule appear swollen under microscopy.

Enterococcus

A genus of Gram-positive cocci (commonly E. faecalis and E. faecium) characterized by positive results for PYR, $6.5\%$ NaCl growth, and Bile Esculin hydrolysis, with inherent resistance to bacitracin and penicillin-cephalosporin.