Staphylococci & Streptococci Flashcards
What is included in the staphy species?
S. aureus (coagulase +)
What is included in the strepto species?
- S. pyogenes
- S. pneumoniae
- group B strepto
What are the gram + cocci?
- staphylococcus
- streptococcus
- enterococcus
What are the characteristics of staphylococci?
- gram + cocci that occurs in -> single, pairs, short chains, clusters
- catalase +
- faculative anaerobes
What are the characteristics of steptococci?
- gram + cocci that occurs in -> pairs, short & long chains
- catalase -, faculative anaerobes
What do leukocidins do?
lyses white cells
What do hemolysins do?
lyses red blood cells
What is the catalase test?
- catalyzes conversion of hydrogen peroxide into water & hydrogen gas
- postive test = bubble formation
- negative test = no change
What is a coagulase test?
- forms a fibrin clot
- postive test = clot formation
- negative test = no change
What is mannitol salt agar?
- selective for staph
- pink to yellow indicates a change in pH
What are the S. aureus virulence factors?
- leukocidin
- protein A
- teichoice acids
- coagulase
- hemolysins
What are the characteristics of S. aureus enterotoxin?
- GI tract
- exotoxin
- acid & heat resistant
- causes food poisoning 1-8 hours after ingestion
What are the characteristics of S. aureus exfoliating toxin?
- causes staph scalded skin syndrome
- red skin color (erythema) & desquamation
- primarily occurs in infants
What are the characteristics of S. aureus toxic shock syndrome?
- causes toxic shock -> hypotension
- primarily seen in women -> associated with tampon use
What are the characteristics of S. aureus penton-valentine leukocidin?
- causes cell lysis by punching holes in cell membranes & inducing apoptosis via caspases
- necrotic lesions in skin & mucosa
What are the toxins of S aureus?
- enterotoxin
- exfoliative toxin
- toxic shock syndrome
- oanton-valentine leukocidin
What is the diagnosis for S aureus?
- catalase & coagulase +
- grows on MSA and turns yellow
- beta-hemolytic
What is the treatment for S. aureus?
vancomycin for MRSA
What is the Lancefield classification for strep?
- group A strep. pyyogens
- group B -> strep. agalactiae
What are the virulence factors for S pyogenes?
- streptolysins
- erythrogenic toxin -> super Ag
- exotoxin A -> toxic shock syndrome
- exotoxin B -> necrotizing fascitis
- capsule
- M protein -> mimics host Ags
- protein F
- protein G
- C-polysaccharide -> basis of Lancefield classification
What is the pathogenesis of S. pyogenes in respiratory infections?
- inhaled via F protein
- produces M protein
- streptolysin damages epithelial tissue
- targets people 5-15 years old
What are the suppurative diseases of S. pyogenes?
- pharyngitis -> mediated by streptolysins; sore throat, malaise, fever
- scarlet fever -> strawberry tongue & rash
- strep toxic shock
- cellulitis
- necrotizing fascitis
What are the non-suppurative diseases of S. pyogenes?
- rheumatic fever -> mediated by protein M; type 3 hypersensitivity
- glomerulonephritis -> antibody- Ag complexes in glomeruli (type 3 hypersensitivity); occurs 10 days after infection
Which exotoxin is associated with necrotizing fascitis & which with toxic shock syndrome?
- necrotizing fascitis -> exotoxin B
- toxic shock syndrome -> exotoxin A
What are the virulence factors of S. agalactiae?
- capsule
- cell wall
- enzymes
What are the diseases of S. agalactiae?
presents as neonatal infections
* puerperal sepsis
* septicemia
* pneumonia
* meningitis
How is S pyogenes diagnosed?
- beta-hemolytic -> small white colonies & large hemolytic area
- bacitracin sensitive
- rapid test
How is S agalactiae diagnosed?
- beta-hemolytic -> large colonies & small hemolytic area
- bacitracin resistant
What are the characteristics of S pneumoniae?
- oval/ lancet shaped
- diplococci
What are the virulence factors of S pneumoniae?
capsule
What are the clinical diseases associated with S pneumoniae?
- pneumonia
- sinusitis
- otitis media
- bacteremia
- meniingitis
How is S. pneumoniae diagnosed?
alpha-hemolytic
