Chapter 15: Streptococci Flashcards
What are the general characteristics of streptococci and enterococci?
Gram-positive cocci, catalase negative, pairs or chains, facultative anaerobes, aerotolerant anaerobes, grow best on enriched media with blood or serum, do not grow well on TSA.
Catalase reactions can be false positive if taken from growth media containing blood.
What is the Lancefield classification?
A system used to classify streptococci based on carbohydrate composition of antigens found on the bacteria’s cell wall.
What are the types of hemolysis observed on sheep blood agar?
- Alpha (α) hemolysis
- Beta (β) hemolysis
- Gamma (γ) hemolysis
What is the significance of streptococci commonly isolated in the clinical lab?
They are important in diagnosing and treating various infections, including pharyngitis, skin infections, and invasive diseases.
What are the virulence factors of S. pyogenes (Group A)?
- M protein
- Fibronectin-binding protein (Protein F)
- Lipoteichoic acid
- Capsule
- Streptolysin O
- Streptolysin S
- Hyaluronidase
- Streptococcal pyrogenic exotoxins (SPEs)
What is the primary clinical manifestation of S. pyogenes?
Pharyngitis and tonsillitis (strep throat).
What are the clinical infections associated with S. pyogenes?
- Scarlet fever
- Skin infections (impetigo, erysipelas, cellulitis)
- Necrotizing fasciitis
- Streptococcal toxic shock syndrome
- Post-streptococcal sequelae (rheumatic fever, acute glomerulonephritis)
What is the role of streptolysin O in S. pyogenes?
Responsible for hemolysis on blood agar plates, active under anaerobic conditions, destroys white blood cells, platelets, and other tissues.
What is the transmission route for early onset S. agalactiae infections in newborns?
Vertical transmission from mother during birth.
What are the major serotypes of S. agalactiae?
- Ia
- Ib
- II
What types of infections can S. pneumoniae cause?
- Pneumonia
- Sinusitis
- Otitis media
- Bacteremia
- Meningitis
- Endocarditis
- Peritonitis
What is the characteristic morphology of S. pneumoniae colonies on blood agar?
Large zone of alpha-hemolysis, round, glistening, wet, mucoid, dome-shaped.
What is the treatment for S. agalactiae infections?
Ampicillin with or without an aminoglycoside.
What differentiates Group D streptococci from Enterococcus?
Enterococcus is resistant to penicillin, while Group D is generally susceptible.
What are the virulence factors of Enterococcus?
- Surface adhesion proteins
- Extracellular serine protease
- Gelatinase
What is the function of the capsule in S. pneumoniae?
Prevents phagocytosis, making the bacterium more virulent.
Fill in the blank: The major end product of fermentation in streptococci is _______.
lactic acid
True or False: S. pyogenes can cause necrotizing fasciitis.
True
What test is used for direct antigen testing of Group A streptococci?
Bacitracin susceptibility test.
What is the role of hyaluronidase in S. pyogenes?
It breaks down connective tissue, aiding in the spread of the infection.
What is the characteristic appearance of Enterococcus in laboratory diagnosis?
Weak bubbling in catalase test, can grow under extreme conditions like bile, salt, or alkaline pH.
What is Enterococcus resistant to?
Penicillin
Group D is generally susceptible.
What test is used to separate Group D from Enterococcus?
PYR Test
What type of reaction does Enterococcus show in a catalase test?
Weak bubbling (pseudocatalase reaction)
