Streptococci Flashcards
Group A Strep:
Streptococcus pyogenes (Group A Strep)
Group B Strep
Streptococcus agalactiae (Group B Strep)
Streptococci catalase:
Catalase negative
Streptococci media:
Requires complex media
Streptococci oxygen requirement:
Prefers anaerobic or carbon dioxide atmosphere
Streptococci morphology:
Gram-positive Cocci in pairs and chains
Features that distinguish S. pneumoniae from Enterococcus
P.I.C.S
Production of pneumolysin
Inhibited by Optochin - tested by placing a disc on agar
Capsule
Soluble in the presence of bile
Streptococci hemolysis:
beta hemolytic: GAS, GBS, anginosus, groups C and G
alpha hemolytic: enterococci, viridans, anginosus, S. pneumoniae
Describe the process of Lancefield typing of Streptococci.
Latex Agglutination Assay:
Beaded, individual antibodies are added to a carbohydrate on the surface of the colonies on agar
If there is a carbohydrate-specific interaction, there is clumping specific to the Lancefield group
What determines the Lancefield group of streptococci?
Group specific carbohydrates carried on the surface of streptococcus organisms
5 Laboratory techniques for identification of streptococcus organisms:
Hemolysis
Catalase Test
PYR Test PYR (L-pyrrolidonyl-ß- naphthylamide)
Streptolysin O Antibody Detection
Lancefield Typing
Purpose of the PYR Test PYR.
Quick spot test for detection of pyrrolidonyl peptidase enzyme and the identification of Enterococcus and Group A strep
Purpose of the Streptolysin O Antibody Detection
test.
Useful for confirming a diagnosis of rheumatic fever following production of antibodies to Streptolysin O 3-4 weeks after initial exposure to S. pyogenes
What are the 6 of Streptococcus pyogenes infections discussed in lecture?
S.A.I.N.T.E
Scarlet Fever Acute pharyngitis Impetigo Necrotizing Fasciitis Toxic Shock-like Syndrome Erysipelas
How is acute pharyngitis caused by S. pyogenes transmitted?
Via respiratory droplets
Acute pharyngitis caused by S. pyogenes presents very similarly to what infection?
Acute viral pharyngitis
Classic symptoms of acute pharyngitis caused by S. pyogenes
Fever
Sore throat
Headache
Cervical lymphadenopathy (swollen lymph nodes), Peritonsillar exudate
Name the 2 clinical hallmarks of Erysipelas.
Spreading erythema and lesions often with well demarcated edge on the face (or legs)
Fever and lymphadenopathy with accompanying streptococcal pharyngitis
Name the clinical hallmarks of Impetigo.
Pyoderma - small, pus-filled lesions
Pustules with yellow crust form on the face or extremities
State the demographic most affected by impetigo and the reason why.
Affects young children, usually in the warm months and as a result of poor hygiene
How does one contract impetigo?
Associated with trauma / insect bites
How does one contract scarlet fever?
Complication of streptococcal pharyngitis
5 Hallmark features of Scarlet Fever:
Fine, red, and rough-textured rash, but not on face followed by desquamation
Circumoral pallor
Sore throat - exudate over tonsillar area of throat
Fever
Bright red tongue with a “strawberry” appearance
Hallmark features of Necrotizing Fasciitis:
Occurs deep in the subcutaneous tissues and spreads along the fascial planes.
Extensive destruction of the muscle and fat
(flesh-eating)
Systemic toxicity
Hallmark features of Toxic Shock-like Syndrome:
Multisystem organ failure (heart, respiratory tract, kidney)
Cultures are positive for group A strep
What infection may accompany Necrotizing Fasciitis?
Toxic Shock-like Syndrome
What virulence factor causes Toxic Shock-like Syndrome?
Streptococcal pyrogenic exotoxins (SPE)
Name two diseases that occur as sequelae to streptococcal infections
Rheumatic Fever
Acute Glomerulonephritis
4 Hallmark features of Rheumatic Fever:
F.E.N.A
Non-suppurative inflammatory disease
Fever, carditis, subcutaneous nodules, chorea, polyarthritis
Aschoff bodies - characteristic cardiac lesions and valvular damage
Endocarditis later in life
4 Hallmark features of Acute Glomerulonephritis:
Edema, hypertension, hematuria, proteinuria
Immune-complex deposits in the glomeruli seen on kidney biopsy
Why are Strep infections (i.e. streptococcal pharyngitis) treated?
To prevent post-streptococcal sequelae
Rheumatic Fever occurs following what streptococcal infection?
1-5 weeks after strep pharyngitis
Acute Glomerulonephritis occurs following what streptococcal infection?
Occurs after skin / respiratory infection with strep
Describe the mechanism of Acute Glomerulonephritis?
M protein antigen-antibody complexes activate complement, which results in immune-complex deposits in the glomeruli
Describe M protein’s 3 mechanisms of virulence for S. pyogenes.
Assists in binding to epidermal cells
Allows bacterial survive (Strains without M protein are avirulent)
Anti-phagocytic: Degrades complement C3b to prevent opsonization and killing by phagocytosis
Antibodies to ___ _________ activate complement and kill S. pyogenes.
Antibodies to M protein activate complement and kill the bacteria
What is the function of streptokinase?
Cleaves fibrinogen to fibrin
Facilitates S. pyogenes spread in infected tissues
What are the functions of S. pyogenes streptolysins? Name the 2 types.
Lyse RBCs and leukocytes
Cause the death of phagocytic cells
Assists in spread of bacteria in tissues
Streptolysin S and Streptolysin O
Which streptolysin does the body make antibodies for?
Streptolysin O
What clinical manifestations of strep infections are due to SPE toxins?
Strep toxic shock-like syndrome
The rash in scarlet fever “erythrogenic exotoxin”
How do SPE toxins cause disease?
They are “superantigens” that cause non-specific activation of T-cells, T cell proliferation and cytokine release leading to massive shock and organ failure.
True or false: SPE toxins are heat labile.
True
What does a Rapid Detection Test result mean?
If a Rapid Group A Detection Test is positive, in correlation with the clinical symptoms, you can be certain that the patient is infected with a Group A strep.
S. agalactiae is a common cause of _______ disease and infection in _______ women.
neonatal, pregnant
When does early onset-neonatal disease present and with what clinical manifestations?
First week of life
Presents with bacteremia, pneumonia, or meningitis
When does late onset-neonatal disease present and with what clinical manifestations?
After 1 week to 3 months of age
Presents with bacteremia and meningitis
Describe virulence of S. agalactiae and how it causes neonatal disease.
The infant has a lack of protective maternal antibody (IgG)
Sialic acid on polysaccharide capsule inhibits complement allowing organisms to multiply
How is Group B Strep Infection Prevented?
Cultures should be performed on BOTH vaginal/rectal swabs collected at 35 to 37 weeks gestation to identify if there is colonization with GBS.
If colonized, mother will receive prophylatic antibiotics to prevent infection in the baby
How can growth of GBS be selected for in culture?
Use of selective enrichment broth (LIM)
Infections caused by Group C Strep:
Associated with veterinary infections
Pharyngitis in college age patients
Sepsis
Infections caused by Group F Strep:
Associated with abscesses
Infections caused by Group G Strep:
Pharyngitis
Sepsis in neonates and elderly
Name the alpha-hemolytic streptococci
S. pneumoniae
Viridans Streptococci
Bovis Group Streptococcus
How does S. pneumoniae get into the respiratory tract to cause disease.
Normal flora of human upper respiratory tract. Usually causes disease after aspiration, so bacteria are inhaled into the lung and multiply in alveolar spaces
When is culture helpful for diagnosis of S. pneumoniae?
Culture can be helpful in patients that are immunocompromised or have severe disease, but not in patients who have community-associated pneumonia
Describe Clinical manifestations of S. pneumoniae.
Onset is abrupt
Patients usually have productive cough and chest pain (pleurisy)
_______ is the most common cause of community acquired acute bacterial pneumonia.
S. pneumoniae
What are Predisposing conditions to S. pneumoniae?
Alcoholism Diabetes mellitus Chronic lung disease Chronic renal disease Certain malignancies
What are the Streptococcus pneumoniae Virulence Factors?
Polysaccharide capsule - prevents phagocytosis
Pneumolysin - damages ciliated cells and activates the alternative complement pathway
Alpha hemolysis
Name the most important characteristic of Viridans streptococci.
Alpha or gamma hemolytic
Lacks hemolysins and toxins of beta strep
Normal flora of upper respiratory tract
Opportunistic pathogen causing sepsis, especially in neutropenic cancer patient
Important cause of endocarditis (primary presentation)
Which Viridans streptococci causes dental caries?
S. mutans is a major cause of dental caries
Major clinical manifestations of Bovis group strep?
carcinoma of colon
bacteremia, meningitis
both native and prosthetic-valve endocarditis
Name the species included in the Anginosus Group Strep
S. anginosus, S. constellatus, S. intermedius (Group C, F, G, U)
Name the major clinical infections caused by Anginosus Group Strep
Abscess formation in deep tissue (most brain abscesses)
_______ inhibits growth of S. Pneumoniae.
Optochin
Where is S. agalactiae prior to causing neonatal disease?
Maternal colonization of the vagina or rectum
