Gram-Positive Catalase-Negative Cocci – Vocabulary Flashcards

A set of curated vocabulary flashcards covering classifications, virulence factors, laboratory tests, diseases, and distinctive properties of Streptococcus, Enterococcus, and related catalase-negative Gram-positive cocci for exam preparation.

Streptococci

Gram-positive, catalase-negative cocci that grow in chains or pairs; many are normal flora but include important human pathogens.

Enterococci

Former Group D streptococci; hardy intestinal flora that cause opportunistic UTIs, wound infections, and bacteremia; notable for intrinsic drug resistance.

Catalase-Negative

Biochemical characteristic of streptococci and enterococci distinguishing them from staphylococci, which are catalase-positive.

Lancefield Classification

Serogrouping method based on C-carbohydrate antigens in the cell wall; mainly used for β-hemolytic streptococci (Groups A–V).

Bergey’s (Academic) Classification

System that groups streptococci by temperature growth ranges and hemolysis patterns (Pyrogenic, Viridans, Enterococcus, Lactic).

Smith & Brown Classification

Scheme that categorizes streptococci by hemolysis on blood agar: α (partial), β (complete), γ (none).

Alpha Hemolysis

Partial hemolysis on blood agar producing a green discoloration around colonies.

Beta Hemolysis

Complete lysis of red cells on blood agar showing a clear zone surrounding colonies.

Gamma Hemolysis

No hemolysis on blood agar; agar around colonies remains unchanged.

Group A Streptococcus (GAS)

Streptococcus pyogenes; β-hemolytic pathogen of humans transmitted via respiratory droplets.

Streptococcus pyogenes

Principal GAS species; causes pharyngitis, scarlet fever, skin infections, rheumatic fever, and more.

M Protein

Major virulence factor of S. pyogenes that resists phagocytosis and mediates adherence; encoded by emm genes.

Streptolysin O

Oxygen-labile hemolysin of S. pyogenes; antigenic, basis of ASO titer for recent infection.

Streptolysin S

Oxygen-stable, non-immunogenic hemolysin of S. pyogenes responsible for surface β-hemolysis.

DNase (Streptococcal)

Enzyme that lowers exudate viscosity, promoting spread; produced in four types (A–D).

Streptokinase

Fibrinolytic enzyme of GAS that activates plasminogen and dissolves clots.

Hyaluronidase

“Spreading factor” enzyme that degrades connective-tissue hyaluronic acid.

Streptococcal Pyrogenic Exotoxins (Spe)

Superantigen toxins (Spe A, B, C, F) linked to scarlet fever and toxic shock syndrome.

Scarlet Fever

Erythematous sand-paper rash illness from Spe toxins; classic ‘strawberry tongue’.

Rheumatic Fever

Post-streptococcal inflammatory disease involving heart, joints, and CNS due to antigenic mimicry.

Acute Glomerulonephritis

Immune-complex kidney damage following GAS skin or throat infection.

Bacitracin (Taxo A) Test

Disk diffusion screen where GAS is characteristically susceptible (any inhibition zone).

PYR Test

Rapid color test for pyrrolidonyl arylamidase; positive in GAS and enterococci (cherry-red color).

Group B Streptococcus (GBS)

Streptococcus agalactiae; β-hemolytic colonizer of genital and GI tracts; major neonatal pathogen.

Streptococcus agalactiae

GBS species causing early- and late-onset neonatal sepsis/meningitis and adult obstetric infections.

GBS Capsule

Polysaccharide capsule containing sialic acid that inhibits complement and phagocytosis.

CAMP Test

Synergy hemolysis test where GBS produces arrow-head β-lysis near S. aureus β-lysin.

Hippurate Hydrolysis Test

Biochemical assay detecting hippuricase; purple color signifies positive result for GBS.

Early-Onset GBS Disease

Neonatal infection <7 days old, presenting as pneumonia or sepsis acquired vertically from mother.

Late-Onset GBS Disease

Neonatal infection ≥7 days–3 months, typically meningitis; linked to maternal vaginal carriage.

Group C Streptococci

Animal-associated β-hemolytic species (e.g., S. dysgalactiae subsp. equisimilis) occasionally infecting humans.

Group D Streptococci

Serogroup including enterococci and non-enterococcal S. bovis group; grow in bile and hydrolyze esculin.

Enterococcus faecalis

Most common enterococcal isolate; causes nosocomial UTIs, bacteremia, and endocarditis.

Bile Esculin Test

Medium that selects with 40 % bile and detects esculin hydrolysis; blackening indicates positive result.

6.5 % NaCl Broth Test

Salt tolerance assay; enterococci grow (turbidity) whereas S. bovis group does not.

Optochin Susceptibility

Disk test where S. pneumoniae is inhibited by ≤5 µg optochin (≥14 mm zone).

Streptococcus pneumoniae

Lancet-shaped diplococcus causing pneumonia, meningitis, otitis media; α-hemolytic and bile soluble.

Pneumococcal Capsule

Principal virulence factor of S. pneumoniae; antiphagocytic polysaccharide basis for vaccines.

Bile Solubility Test

Clearing of culture in presence of bile salts due to autolysin; positive for S. pneumoniae.

Neufeld-Quellung Reaction

Microscopic capsular swelling when pneumococci are mixed with specific antiserum; used for serotyping.

Viridans Streptococci

Heterogeneous α-hemolytic streptococci lacking Lancefield antigens; normal oral flora, major cause of subacute endocarditis.

Leucine Aminopeptidase (LAP) Test

Enzyme assay turning red; positive for most streptococci and enterococci, negative in Aerococcus and Leuconostoc.

Voges-Proskauer (VP) Test

Detects acetoin production; positive in S. anginosus, S. bovis, and S. mutans groups.

Abiotrophia/Granulicatella

Pyridoxal-dependent, nutritionally variant streptococci causing endocarditis; satellite growth on blood agar.

Aerococcus

Catalase-weak Gram-positive cocci in clusters/tetrads; airborne; causes UTIs/endocarditis; grows in 6.5 % NaCl.

Leuconostoc

Vancomycin-resistant Gram-positive cocci from plants and dairy; opportunistic infections in immunocompromised hosts.

Pediococcus

Vancomycin-resistant cocci forming tetrads/clusters; BE and LAP positive; associated with abdominal surgery patients.

Necrotizing Fasciitis

Rapidly progressive soft-tissue infection; Type 2 form caused solely by GAS (‘flesh-eating disease’).

Streptococcal Toxic Shock Syndrome

Systemic illness with multiorgan failure due to GAS SpeA toxin; high mortality.

Penicillin

Drug of choice for most streptococcal infections; erythromycin used if allergic.

ASO Titer

Serologic test measuring antibodies to streptolysin O; indicates recent GAS infection.

CAMP Factor

Extracellular protein of GBS that enhances β-lysin hemolysis produced by Staphylococcus aureus.

Tellurite Tolerance

Growth property used to identify Enterococcus faecalis on media containing tellurite.

Capsular Serotypes (GBS)

Ten polysaccharide types (Ia, Ib, II–IX) determined by latex agglutination; relevant for epidemiology.

PCV13 Vaccine

13-valent pneumococcal conjugate vaccine for routine immunization of children under 5 years.