Streptococcus, Enterococcus, and similar organisms Flashcards
Characteristics of Streptococcus, Enterococcus, and similar organisms
Gram-positive cocci in pairs or chains, Catalase and Oxidase negative, Facultative anaerobe
Classification of Streptococcus based on Rebecca Lancefield grouping
All except S. pneumoniae and Viridans group
Most common infection caused in human is caused by
Enterococcus
Pyogenic classification according to Academic/Bergey’s
Grows at 37°C only: S. pyogenes, S. agalactiae
Viridans classification according to Academic/Bergey’s
Grows at 37°C and 45°C: S. mutans, S. mitis
Lactic classification according to Academic/Bergey’s
Grows at 10°C and 37°C: S. lactis
Enterococcus classification according to Academic/Bergey’s
Grows at 10°C, 37°C, and 45°C: E. faecalis
Lancefield Grouping: Pyogenic
Group A: S. pyogenes
Lancefield Grouping: Viridans
Group B: S. agalactiae
Lancefield Grouping: Lactic
Group C, G: S. dysgalactiae, S. equi
Lancefield Grouping: Enterococcus
Group D: Enterococci
Smith and Brown Hemolysis: Pyogenic
Alpha-hemolytic: S. pneumoniae
Smith and Brown Hemolysis: Viridans
Beta-hemolytic: S. pyogenes, S. agalactiae
Smith and Brown Hemolysis: Gamma-hemolytic
Gamma-hemolytic: S. bovis
Group A Streptococcus species
Streptococcus pyogenes
Pathogenic features of S. pyogenes
Always pathogenic, M protein (responsible for sequelae and binds Factor H), Protein F (epithelial cell attachment via fibronectin binding), Hyaluronic acid (inhibits phagocytosis), C5a peptidase (destroys chemotactic factors)
Characteristic that is oxygen labile, Antigenic, Subsurface hemolysis (stab)
Streptolysin O
Characteristics that is oxygen stable, Non-antigenic, Surface hemolysis (streak)
Streptolysin S
Other enzymes and toxins of S. pyogenes
DNase, Streptokinase (dissolves clots), Hyaluronidase, Pyrogenic exotoxin (causes Scarlet fever, erysipelas)
Causative agent of acute pharyngitis, impetigo, cellulitis, erysipelas, necrotizing fasciitis, bacteremia, pneumonia, scarlet fever, streptococcal toxic shock syndrome
S. pyogenes
Post-streptococcal sequelae of S. pyogenes
Rheumatic fever, Acute glomerulonephritis (Bright’s disease)
Critical value in wounds
Presence of S. pyogenes
Diagnostic tests 0.040 U Bacitracin (Taxo A sensitive), PYR test (+, cinnamaldehyde), ASO titer, Dick’s test (susceptibility, reddish reaction), Schulz-Charlton test (immunity, anti-toxin)
S. pyogenes
Rheumatic fever mechanism
Antibody cross-reactivity of M protein to heart muscle (M protein Class I)
Acute glomerulonephritis mechanism
Deposition of antigen-antibody complexes in glomeruli (M protein Class I or II)
Signs and symptoms of Rheumatic fever
Fever, endocarditis, subcutaneous nodules, polyarthritis
Signs and symptoms of Acute Glomerulonephritis
Edema, hypertension, hematuria, proteinuria (Bright’s disease, HS Type III)
Group B Streptococcus species
Streptococcus agalactiae
Normal flora percentage for S. agalactiae
10-30% of women
Key infections caused by S. agalactiae
Neonatal meningitis, sepsis, pneumonia, respiratory distress, lethargy
Virulence factor for S. agalactiae
Capsule, Activation of complement
Laboratory diagnosis of S. agalactiae
CAMP test, Hippurate test (+), LIM, Todd-Hewitt, Granada, Carrot medium, CSF latex agglutination
Group C Streptococcus species
Streptococcus dysgalactiae subsp. equisimilis and others
Normal flora locations for Group C Streptococcus
Skin, nasopharynx, GI, genital tract
Infections caused by Group C Streptococcus
Pharyngitis, impetigo, necrotizing fasciitis, osteomyelitis, endocarditis, rheumatic fever, AGN
Hemolysis type for Group C Streptococcus
β-Hemolytic
Group D Enterococcus species
Enterococcus faecalis, Enterococcus faecium
Virulence factors for Enterococcus spp.
Biofilms, Adhesins, Cytolysin, Hemolysin, Peptide inhibitors
Infections caused by Enterococcus spp.
UTI, bacteremia, wound infections, abdominal region infections
Lab tests for Enterococcus spp.
Positive in Bile esculin, 6.5% NaCl tolerance, and PYRase; grows on Enterococcosel agar
Streptococcus pneumoniae morphology
Encapsulated bullet/lancet-shaped diplococci
Infections caused by S. pneumoniae
Meningitis, CA-Pneumonia, Otitis media, Endocarditis
Lab tests for S. pneumoniae
Optochin sensitive, Bile solubility, Neufeld quelling, CSF latex agglutination, Urine antigen test
Colony morphology of S. pneumoniae
Alpha-hemolytic, mucoidal, umbilicate colonies
Viridans Streptococci normal flora
Oral cavity, GI tract, female genitals
Infections caused by Viridans Streptococci
Subacute endocarditis (S. sanguis), pneumonia, bacteremia, meningitis (S. salivarius), dental caries (S. mutans, S. sobrinus)
Lab features of Viridans Streptococci
Alpha-hemolytic, butterscotch smell on CAP, LAP positive, PYR negative
Gemella haemolysans morphology
Decolorizes easily, may appear as Gram-negative cocci
Infections caused by Gemella haemolysans
Endocarditis, meningitis, brain abscess, ocular infections, septic arthritis, osteomyelitis
Hemolysis type of Gemella haemolysans
Alpha or Non-hemolytic
Abiotrophia and Granulicatella spp. requirements
Cysteine and pyridoxal (Vitamin B6)
Lab features for Abiotrophia/Granulicatella spp.
Do not grow on BAP; use CAP with pyridoxal disk, cross-streak with S. aureus, or supplemented Vitamin B6
Aerococcus urinae infections
UTI
Lab features of Aerococcus urinae
Positive in Hippurate and 6.5% NaCl tolerance; Negative in Bile esculin and PYR
Leuconostoc and Pediococcus features
Low virulence, intrinsic vancomycin resistance
Infections caused by Leuconostoc/Pediococcus spp.
Bacteremia, UTI, wounds, isolated from sterile fluids
Lab feature differentiating Leuconostoc and Pediococcus
Pediococcus is LAP positive, Leuconostoc is LAP negative
Helcococcus spp. infections
Bacteremia, empyema, prosthetic joint infections, skin/soft tissue infections (mostly foot infections)
Lab features of Helcococcus spp.
Lipophilic, Vancomycin sensitive, PYR positive, LAP negative
