Streptococci Flashcards
How do streptococci differ from staphylococci on gram stain?
Strep- gram + chains
Staph- gram + clusters
Are streptococci catalase positive?
No
Certain species of streptococci can either completely or partially hemolyze RBCs. The streptococci are divided into 3 groups based on their specific hemolytic ability, what are these 3 groups?
Alpha- partially lyse RBCs (green zone around colony)
Beta- completely lyse RBCs (clear zone around colony)
Gamma- non-hemolytic
Streptococci can be classified based on the antigenic characteristics of the C carbohydrate (Lancefield antigen), what 2 pathogenic species of the streptococcal genus do not have Lancefield antigens?
Streptococcus pneumoniae
Strep Viridans
Streptococci can be classified based on the antigenic characteristics of the C carbohydrate (Lancefield antigen), what pathogenic species of Strep has Lancefield group A antigen?
Streptococcus pyogenes
What diseases are caused by Streptococcus pyogenes?
Strep throat (pharyngitis)
Skin infections (erysipelas, cellulitis, impetigo, necrotizing fasciitis)
Scarlet fever
Toxic shock-like syndrome
Acute rheumatic fever
Post streptococcal glomerulonephritis
What components of the streptococcal cell wall are antigenic?
C-carbohydrate (Lancefield antigen)
M protein (major virulence factor)
What is the function of M protein?
Inhibits phagocytosis
Inhibits complement activation
Immunity to streptococci infection is based on development of antibodies directed against which protein?
M protein (protection is M-type specific)
What cells are destroyed by streptolysin O?
RBCs
Neutrophils
What is the mechanism of action of the streptococcal enzyme streptokinase?
Activates plasmin which breaks up fibrin
In addition to scarlet fever, what syndrome is mediated by Exotoxin A?
Streptococcal toxic shock syndrome
What diseases caused by group A Strep directly result from local invasion and/or exotoxin release?
Strep throat
Skin infection
Scarlet fever
Toxic shock like syndrome
What diseases caused by group A strep are a direct result of delayed antibody mediated responses?
Acute rheumatic fever
Post streptococcal glomerulonephritis
What test should be ordered to diagnose streptococcal pharyngitis?
RADT- rapid antigen detection test
A 9 year old child presents with red swollen tonsils and pharynx, and purulent tonsils. A RADT is negative. What is your next step in management?
Throat culture- RADT has high specificity, but only moderate sensitivity
Antibiotic therapy of streptococcal pharyngitis is directed primarily at preventing what complication?
Acute rheumatic fever
Skin infections caused by group A Strep can range from folliculitis, pyoderma, cellulitis, erysipelas, and impetigo. These infections can also be caused by S. aureus, thus, what type of therapy should be initiated?
Penicillinase resistant penicillin (dicloxacillin)
Erysipelas is a superficial bacterial infection of the skin most often caused by beta-hemolytic group A streptococci (Streptococcus pyogenes). It involves the lymphatics of the superficial dermis. Describe the rash associated with this condition.
Bright red
Well demarcated border
Impetigo is a superficial skin infection caused by inoculation of streptococci through scratches or other breaks in the skin. Describe the rash associated with this condition.
Honey crusted plaques, often found around the mouth
Detail the clinical findings of scarlet fever.
Sandpaper-like scarlet rash which begins on the neck, moves to the trunk, and finally to the extremities.
Strawbery tounge
Fever
Define exanthem.
Diffuse rash
What disease refers to necrotizing fasciitis of the genital region?
Fournier gangrene
How do you treat severe Streptococcal pyogenes infections?
High doses of penicillin
Clindamycin- inhibits bacterial ribosome which shuts down protein production
What are the 6 major manifestations of acute rheumatic fever?
Fever
Arthritis
Myocarditis
Subcutaenous nodules
Erythema marginatum
Chorea
Are group B strep hemolytic?
Yes, beta-hemolytic
What is another name for group B streptococci?
Streptococcus agalactiae
What diseases are caused by group B strep?
Neonatal: meningitis, pneuomnia, sepsis
Neonates with meningitis do not present with the classic sign seen in adults, a stiff neck. What organisms must be covered if you suspect meningitis in the newborn?
Streptococcus agalactiae
E. coli
Listeria monocytogenes
Two bacteria cause meningitis later in life after maternal antibodies given to the fetus wane and prior to new antibody formation. What are these bacteria?
Neisseria meningitidis (Meningococcus)
Haemophilus influenzae
What 2 diseases are caused by Viridans group streptococci?
Dental infections- S. mutans
Endocarditis- S. sanguinis
Contrast the endocarditis due to Viridans group strep to that due to Staph.
Viridians group- subacute bacterial endocariditis (SBE), pt develops low grade fevers, fatigue, anemia, heart murmur
Staph- abrupt onset of chills, spiking fever, and rapid valve destruction
Group D streptococci were divided into two groups for many years: Group D enterococci and Group D nonenterococci. This classification was changed because recent DNA and rRNA homology studies demonstrated that enterococci are not closely related to other streptococci. How has this altered the classification of group D streptococci?
Many former group D streptococci have been reclassified and placed in the genus Enterococcus
What are the primary pathogenic enterococci?
Enterococcus faecalis
Enterococcus faecium
Enterococci are identified in the lab based on unique characterisitcs. What are these characterisitcs?
Grow well in 6.5% NaCl
Grow well in 40% bile
Hydrolyze esculin
Group D organisms share several features with enterococci, including the group D antigen. How do they differ based on their ability to grow in different solutions?
Group D strep can not grow in 6.5% NaCl
Both can grow in 40% bile
What diseases are commonly caused by enterococci?
UTIs
Biliary tract infections
Bacteremia
Subacute bacterial endocariditis
Streptococcus bovis is associated with what malignancy?
Colon cancer
What Lancefield antigen is associated with Viridans group streptococci?
None
What diseases are commonly caused by pneumococcus?
Adults: meningitis, pneumonaie, sinusitis
Children: otitis media
(Most common cause of these infections)
What is the major virulence factor of pneumococcus?
Polysaccharide capsule- protects organism from phagocytosis
How can you distinguish between Strep viridans and pneumococcus when both are alpha hemolytic, gram + cocci?
Viridans- optochin insensitive
Streptococcus pneumoniae- optochin sensitive
What is the most common cause of pneumonaie in adults?
Strep pneumoniae
What does a CXR show in a patient with pneumoniae?
Consolidation
What bug is the most common cause of bacterial meningitis in adults?
Streptococcus pneumoniae
Contrast the bacitracin sensitivity of group A and B strep.
Group A- bacitracin sensitive
Group B- bacitracin resistant
Do Viridans group Strep have a capsule?
No
What is the Lancefield group of S. bovis?
Group D
What region of the body are Enterococci part of the normal flora?
GI tract
Which alpha hemolytic Strep are bile soluble/insoluble?
Bile soluble- S. pneumoniae
Bile insoluble- Viridians group strep
