#Strept Flashcards
Define viridans Streptococci
Alpha hemolytic Strept
Which group(s) of Strept are beta hemolytic?
Beta hemolytic strept: groups A and B
Alpha hemolytic strept can be further classified as optochin positive or negative. Which Strept spp fall into either category?
Optochin positive: Streptococcus pneumoniae
Optochin negative: Viridans streptococci
If you observe gamma hemolysis on a Strept plate and you conduct a PYR test, what bacteria are indicated by a +ve or -ve result?
Gamma hemolysis: either enterococcus (if PYR +ve) or non-enterococcus Strept spp (if PYR -ve)
Describe one characteristic of each of the classes of Strept (Groups A, B, C, D, F and G)
◦Group A Streptococcus (GAS): most common clinical infection
◦Group B Streptococcus: important pathogen in neonates
◦Group C: mostly zoonotic
◦Group D: mostly enterococci
◦Group F: Streptococcus anginosus or S. milleri group
◦Group G: typically found in animals
The main bacteria in Group A Strept is ___
This bacteria is responsible for two general types of infection, suppurative and non-suppurative. Describe each.
Group A Strept: Same thing as Strept pyogenes
Suppurative – pus producing; pharyngitis and skin infections
Non suppurative – more immunologically mediated; rheumatic fever and rheumatic heart disease, acute glomerulonephritis
The main virulence factor in Group A Strept is ___ which is strongly antiphagocytic
M protein: very antiphygocytic (way of escaping immunity) - binds serum proteins (e.g. factor H) that inhibit activation of alternative complement components
Also elicits opsonic antibodies
The M protein also helps Strept to adhere to the host cells. Which particular cells does the protein bind to?
How is the M protein implicated in cardiac complications resulting from previous Strept infection?
Binds numerous serum proteins and CD46 on keratinocytes
Certain types can generate antibodies that react with cardiac myosin and sarcolemma
M protein sticks out of the membrane and at the end of the protein is where there is genetic diversity
Antibodies will be specific to any particular M protein
M protein binds to keratinocytes and causes skin and soft tissue infections
Some M proteins can develop antibodies that can cross react with cardiac myosin (attack cardiac tissue) and sarcolemma
Name two other virulence factors for Strept (hint: these are part of Strept’s structure i.e. not secreted)
Capsule and surface adhesins
**the capsule is made of hyaluronic acid, is non-immunogenic and anti-phagocytic**
Describe the functions of the following surface adhesins:
◦Lipoteichoic acid
◦M protein
◦Protein F
◦Lipoteichoic acid – binding to host cells
◦M protein – bind to keratinocytes
◦Protein F – bind to fibronectin and mucosal cells** (Strept throat mediated by protein F mucosal binding)
___ and ___ are two hemolysins produced by Strept
Hemolysins (RBC lysis):
◦Streptolysin O (antibodies to this suggest previous infection)
◦Streptolysin S
Describe how Streptococcal pyrogenic exotoxins contribute to virulence in Streptococcus
◦SpeA, SpeC
◦Encoded by bacteriophages
◦Superantigens (cause cytokine storm and dramatic immune response)
◦Responsible for characteristic features of Scarlet Fever and Streptococcal Toxic Shock Syndrome
◦HLA dependent response**
◦SpeB
Describe the function of the following enzymes in Strept virulence:
◦DNAses
◦Hyaluronidase
◦Streptokinase
◦DNAses
◦Hyaluronidase
◦Streptokinase: Degrades fibrin and used as a medication (clot busters)
How does Strept evade the innate immune response?
◦C5a peptidase: disrupts complement activity
◦SpeB: cleaves IgG
Where on/in the body does one get colonized with Strept?
How is Strept transmitted from person to person?
Multiple episodes of transient colonization of oropharynx and skin
Transmitted person to person via oral secretions or contact with skin lesions
Suppurative diseases caused by Strept include ___ manifesting as Scarlet fever, and pneumonia, which is uncommon
Skin diseases causes by Strept include Impetigo, ___ (form of cellulitis), necrotizing fasciitis and ____ syndrome
Suppurative diseases caused by Strept include pharyngitis manifesting as Scarlet fever, and pneumonia, which is uncommon
Skin diseases causes by Strept include impetigo, erysipelas, necrotizing fasciitis and Streptococcal toxic shock syndrome
What are the clinical features of pharyngitis (esp those that point to a bacterial infection and NOT a viral infection)?
◦Fever
◦Absence of cough
◦Purulent exudate – pus on tonsils
◦Cervical lymphadenopathy
How do you Dx Strept and what is the best course of treatment?
Dx: Rapid Strept test
**won’t be necessary if pt has symptoms of a viral thing
If strept Ag test is negative but they’re symptomatic, do a culture. If culture is +ve, give antibiotics. If –ve, no treatment. Most folks get better w/o antibiotics but we treat b/c prevention of non-suppurative cmplxns
Also responsive to Penicillin. Macrolides or clindamycin for penicillin allergy
Describe the condition below and what causes it
Scarlet fever
** Uncommon manifestation of acute infection (usually pharyngitis)
Manifestation of SpeA or SpeC
Rash begins on trunk
Capillary fragility:
◦Accentuated in skin folds
◦Petechiae elicited with blood pressure cuff
Subsequent desquamation
Describe the condition below and what causes it
Erysipelas: Form of cellulitis
Highly characteristic of β-hemolytic Streptococcus
Bright erythema
Edema
Sharp raised edges
Regional lymphadenopathy
Systemic symptoms
Clinical symptoms to look for when suspecting Strept mediated necrotizing fasciitis include ___, septic shock in association with cellulitis, ___ bullae and dishwater drainage
◦Pain out of proportion for clinical findings
◦Septic shock in association with cellulitis
◦Hemorrhagic bullae
◦Dishwater drainage (if the bullae pop and it looks like dirty dishwater)
Streptococcal toxic shock syndrome is due to ___ and results in multi-organ system dysfunction, rash, fever, hypotension and shock
Streptococcal toxic shock syndrome is due to pyognic exotoxins (SpeA and SpeC) and results in multi-organ system dysfunction, rash, fever, hypotension and shock
How does Strept infection lead to rheumatic fever and acute glomerulonephritis?
Rheumatic fever and rheumatic heart disease
◦Molecular mimicry – specific M proteins have epitopes shared with cardiac antigens
◦Infiltration of T lymphocytes into heart tissue, inflammatory cytokines, cardiac valve lesions
◦Associated with certain HLA-DR alleles
Acute glomerulonephritis
◦Likely due to deposition of immune complexes in kidney
◦Activation of enzymes that damage glomerular basement membrane, with protein loss and decreased renal function
Acute rheumatic fever has several major criteria, including: ___ ,carditis, ___, erythema marginatum, ___
Minor criteria include arthralgia, fever, elevated ___ or ESR, ___ degree heart block
Acute Rheumatic fever:
Clinical syndrome
◦Major criteria (2 or 1 plus 2 minor)
◦Polyarthritis, carditis, chorea, erythema marginatum, subcutaneous nodules (remember JONES from Sketchy)
◦Minor criteria
◦Arthralgia, fever, elevated C-reactive protein or ESR, 1st degree heart block
◦Evidence of recent infection
Culture, antigen or serology (can use ASO)
Sydenham’s chorea can be described as ___
Molecular M protein mimicry in the brain (not cardiac but the disease is essentially the same. This one is pretty much irreversible)
◦St. Vitus’ Dance
◦Rapid, uncoordinated movements
◦Primarily face, hands, feet
◦More common in females
◦Molecular mimicry
Describe the treatment of rheumatic fever
◦Symptomatic therapy with aspirin or corticosteroids
◦Primary prevention: treatment of pharyngitis
◦Secondary prevention: benzathine penicillin G monthly or oral penicillin daily
Post Streptococcal glomerulonephritis is characterized by ___, hypertension, proteinuria, microscopic hematuria, ___
◦Edema
◦Hypertension
◦Proteinuria, microscopic hematuria
◦Acute renal failure
**mainly pediatric disease**
There’s only organism in Group B Strept and that is ___
How does this bug cause disease in neonates? (i.e. in which 2 places does it colonize to allow for this to happen?)
Streptococcus agalactiae
Normally colonizes gastrointestinal and female genital tracts
(see below for more info)
Strept anginosis belongs to Strept anginosis group which also includes which two other Strept spp?
What type of hemolysis do these bugs display?
The main pathology caused by this Strept group is ___
S. anginosis, S. constellatus, S. intermedius
Can display β-hemolysis, α-hemolysis or γ-hemolysis
Have unusual propensity to cause abscess: Liver, brain, periodontal
Which group of Strept shares the feature of alpha or gamma hemolysis and colonizes mucosal surfaces but not the skin?
Where in/on the body would this bacteris typically colonize?
Viridans Streptococci
**S anginosus, mitis, mutans, salivarius- all those guys are commonly ass’d with endocarditis.
S bovis group (aka S. gallolyticus - Group D Strept) is ass’d with colon cancer (still also has that endocarditis situation going on**
**oropharynx**
Treat with penicillin or vancomycin
What are the morphological differences between Strept pneumo and Enterococcus?
Strept: gram-positive cocci arranged in pairs and chains
Enterococcus - gram-positive cocci arranged in pairs and short chains
Strept pneumo displays what type of hemolysis on blood agar? Is it optochin +ve or -ve?
Alpha hemolysis on blood agar
Susceptible to optochin (zone of inhibition around the optochin)
Solubility in bile salts
Some of the virulence factors of Strept pneumo include ___ which is antiphagocytic, ___ which destroys phagocytic cells
Other virulence factors include phosphocholine and surface adhesion proteins which do what?
Evasion of host immunity
Polysaccharide capsule-antiphagocytic
Pneumolysin-mediates destruction of phagocytic cells
**also has IgA protease that you need to know for Step
•Adherence to host surfaces
–Phosphocholine-binds to receptors on endothelial cells, leukocytes, platelets, other tissues
Surface adhesion proteins-binds to squamous epithelial cells in oropharynx
The main treatment for Strept pneumo is giving ___. What is the mechanism of resistance against this antibiotic?
Penicillin
Resistance via alteration in PBP2
Strept pneumo mediated disease occurs when the bug moves from the oropharynx to normally sterile areas. What conditions result when it moves to the following areas?
Lower airways
Paranasal sinuses
Ears
Meninges
Lower airways = pneumonia
Paranasal sinuses = sinusitis
Ears = otitis
Meninges = meningitis (direct extension from sinuses or bloodstream infection)
**Viral infection precedes bacterial infection so the bacteria end up getting trapped in certain areas**
What are the risk factors for Strept pneumo infection?
No pneumococcal vaccine
Splenectomy
Inability to form antibodies: Multiple myeloma; AIDS
Rare immune deficiencies
What are 3 epidemiological risk factors for Strept pneumo infection?
Poorly functioning polymorphonuclears PMNs:
Alcoholism
Cirrhosis of the liver
Diabetes
Glucocorticosteroid treatment
Renal insufficiency
Prior respiratory infection
Inflammatory condition
–COPD, asthma, smoking
Strept pneumo most commonly causes ___, sinusitis, ___ and meningitis
Otitis
Sinusitis
Pneumonia
Meningitis
___ is the most common bacterial isolate of otitis
When would you give antibiotics to treat this case?
Streptococcus pneumoniae is the most common bacterial isolate of otitis
If persistent fever, then reasonable antibiotic choice is amoxicillin
Most common bacterial cause of meningitis in adults is ___, the second being Neisseria
Which antibiotis would you give to treat this infection?
Most common bacterial cause of meningitis in adults is Streptococcus pneumoniae
(Second most common cause is Neisseria)
Antibiotic of choice is ceftriaxone and vancomycin
**recall that ceftriaxone has very good BBB penetration**
Which antibiotics would you use in the treatment of pneumonia due to Strept (or also atypicals)? Note if the drugs will be used in an inpatient/outpatient setting
Outpatient:
Macrolide or Doxycycline (including S. pneumoniae resistance)
Respiratory Fluoroquinolone
•NOT CIPROfloxacin due to poor S. pneumo activity**
Inpatient:
Ceftriaxone (or other Beta lactam) + atypical coverage
Respiratory FQ
There are 2 kinds of pneumococcal vaccines, Pneumovax and Prevnar. Which one is only a polysaccharide vaccine and which one is a protein conjugate?
Which of the 2 is given to adults over 65 and which one is given to chidren?
Pneumococcal polysaccharide vaccine (PPSV23 or Pneumovax): given to everyone over 65
Pneumococcal protein-conjugate vaccine (PCV13 or Prevnar 13): given to all children
Which of the following patient is at increased risk of pneumonia?
A.35 year old white male
B.35 year old African American male
C.35 year old alcoholic
D.35 year old patient on aspirin
C
Which infection does Streptococcus pneumoniae not cause?
A.Otitis
B.Skin infection
C.Meningitis
D.Pneumonia
B
