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63 Cards in this Set
- Front
- Back
How does strep appear on gram stain (other than positive)?
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Lines up like a strip (whereas staph clusters together)
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Difference between alpha and beta hemolytic
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alpha: can only partially lyse RBCs, leaving a greenish discoloration of culture medium around colony
beta: completely lyse RBCs, leaving a clear zone of hemolysis around the colony. |
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What is another term for gamma hemolytic?
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non-hemolytic (they don't actually lyse RBCs)
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Strep are classified based on antigenic characteristics of the ___________
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C carbohydrate, aka Lancefield antigen. Given letter names A, -S
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Streptococcus pyogenes also called
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Group A beta-hemolytic strep
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What diseases does streptococcus pyogenes cause?
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Direct invasion/toxin:
skin infections, strep throat, scarlet fever, toxic shock syndrome Antibody-mediated: rheumatic fever, post-streptococcal glomerulonephritis |
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Components of strep pyogenes cell wall that are antigenic (2)
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1) C Carbohydrate/lancefield antigen
2) M protein: major virulence factor for group A strep. Inhibits activation of complement, but plasma cells secrete antibodies against it. |
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Enzymes of group A strep contributing to pathogenicity
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1) Streptolysin O (oxygen labile - inactivated by oxygen): destroys blood cells. ASO antibodies to this develop
2) Streptolysis S (oxygen stable). Also causes beta-hemolysis 3) pyrogenic/erythrogenic exotoxin: found only in a few strains, but can cause scarlet fever 4) toxic shock syndrome toxin |
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Streptokinase:
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activates proteolytic enzyme plasmin that breaks up fibrin blood clots
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Difference between streptolysin O and S
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1) Streptolysin O (oxygen labile - inactivated by oxygen): destroys blood cells. ASO antibodies to this develop
2) Streptolysis S (oxygen stable). Also causes beta-hemolysis. Non antigenic |
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4 types of disease caused by group A strep (either local invasion and/or exotoxin release)
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1) Strep pharyngitis
2) Strep skin infections 3) Scarlet fever 4) Strep toxic shock syndrome |
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2 delayed antibody mediated diseases caused by group A beta hemolytic strep
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1) Rheumatic fever
2) Acute post-strep Glomerulonephritis |
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Streptococcal pharyngitis: signs and symptoms
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red swolen tonsils and pharynx, purulent exudate, high temp, swolen lymph nodes. Lasts 5 days. Give antibiotics (penicillin)
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Treatment of skin infections and why
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penicillinase resistant penicillin like dicloxacillin, which covers both group A beta-hemolytic strep and staph aureus
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strep infection of dermis only
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erysipelas (almost always caused by strep, not staph)
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pustule usually on extremity or face that breaks down after 4-6 days to form a crus
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pyoderma
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necrotizing fasciitis caused by what kind of strep?
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group A beta hemolytic strep (Strep pyogenes) with M proteins that block phagocytosis, allowing bacteria to move rapidly through the tissue. Strep enter through a break and then follow path along the fascia.
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form of necrotizing fasciitis involving male genital area and perineum, often caused by mixed organisms but can be caused by Strep pyogenes.
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fournier's gangrene
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scarlet fever: what is special about the strep that causes it?
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group A beta-hemolytic strep actually produce a toxin (pyrogenic/erythrogenic toxin) that produces fever and rash.
The toxin comes from a phage. |
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How to treat severe strep pyogenes infections?
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high dose penicillin and clindamycin (Strep pyogenes remains sensitive to penicillin, and clindamycin inhibits bacterial ribosome and thus shuts down protein synthesis of pyrogenic toxin and M protein)
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When does rheumatic fever happen?
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After untreated beta-hemolytic group A strep pharyngitis (NOT skin infection)
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6 symptoms of rheumatic fever
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1) Fever
2) Myocarditis 3) Joint swelling (arthritis) 4) Chorea - begins 2-3 weeks after. Aka St Vitus' Dance 5) Subcutaneous nodules 6) Rash - erythema marginatum 10-20 years post infection - may develop permanent heart damage. |
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rheumatic fever is __________ mediated
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antibody
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How to prevent further damage to the heart after rheumatic fever?
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prophylactic penicillin therapy to prevent future beta-hemolytic group A strep infections (that would elicit more of the antibodies that recognize heart proteins too)
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Symptoms of acute post-strep glomerulonephritis
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Antibody-mediated inflammatory disease of kidney glomeruli.
Retention of water (puffy face), dark urine (due to hematuria - blood in urine), high blood pressure |
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acute post-strep glomerulonephritis : cause
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occurs after strep infection of pharynx OR skin by nephritogenic strains of beta-hemolytic group A strep.
Antigens from this induce antibody response. Resulting complexes travel to kidneys and get depositied in glomerular basement membrane, leading to local glomerular destruction in kidney. |
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Group B Strep: significance
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Dangerous during pregnancy. Think B for Baby.
Cause neonatal meningitis, pneumonia, sepsis. |
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3 most common pathogens associated with meningitis in infants <3 months of age
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1) E coli
2) Group B strep 3) Listeria monocytogenes |
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What 2 bacteria can cause meningitis later in life when maternal antibodies wane and new fetal antibodies develop?
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1) neisseria meningitides
2) haemophilus influenzae |
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Characteristics of viridans group strep
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indigenous to GI tract; alpha-hemolytic (appear green on blood agar).
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viridans group strep associated with what 3 main types of infections
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1) Dental infections (s mutans)
2) Endocarditis (from dental procedures) 3) Abscesses |
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Subacute bacterial endocarditis (SBE) is caused by ______ while acute bacterial endocarditis is associated with ________
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viridans Strep or group D strep; Staph aureus
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What strep causes abscesses?
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Anginosus; Intermedius
InterMeDius and AnginoSus IMeDiately ASess for ABSCESS (if you culture a strep intermedius in blood there may be an abscess hiding in an organ - order CT) |
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What are the major Group D strep?
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Enterococci (enterococcus faecalis and faecium), Non-enterococci (strep bovis and equinus)
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Characteristics of Enterococcus (faecalis and faecium)
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Normal bowel flora that are group D strep. Alpha hemolytic.
Not too virulent but do prey on hospitalized, weak patients. Common cause of nosocomial infections. |
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What is VRE?
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vancomycin resistant enterococci (group D strep). A chromosomal transposon DNA element called vanA that modifies the terminus of peptidoglycan cell wall to have LOW AFFINITY FOR VANCOMYCIN. Can be transferred to Staph aureus!!
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Characteristics of non-enterococci Group D strep (esp Strep Bovis)
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Lives in GI tract, similar to enterococcus.
Remarkable association between this and colon cancer. BOVIS in BLOOD, look for cancer in BOWEL |
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BOVIS in BLOOD, Better Beware, CANCER in the BOWEL: what does this mean
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If Strep bovis (group D strep) is in the blood stream (bacteremia), 50% of patients will have colon cancer.
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Strep pneumoniae: characteristics
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NO lancefield antigen (so no Group). Major virulence factor is polysac capsule, which makes it hard to phagocytose.
α hemolytic |
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Major virulence factor of Strep pneumoniae
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A polysaccharide capsule that is antigenic and can be neutralized by antibodies
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What does Strep pneumoniae cause?
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bacterial pneumonia and meningitis in adults; otitis media in children.
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Pneumococcus is to Parents what group B strep is to Babies: what does this mean?
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Strep pneumoniae causes meningitis in adults while group B strep causes menigitis in children.
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what is the quellung reaction?
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lab test by which to ID encapsulated bacteria, therefore to ID pneumococcus. (Strep pneumoniae).
When S pneumoniae on a slide smear are mixed with a small amount of antiserum (serum with antibodies to capsular antigens) and methylene blue, the capsule will appear to swell, allowing for rapid ID of organism. |
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What is optochin sensitivity?
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Way to differentiate between Strep pnemoniae and Viridans (both alpha-hemolytic).
If you try to grow on optochin disc, strep pneumoniae wil be inhibited, but strep viridans will continue to grow. |
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Three main bacteria causing otitis media
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1) Strep pneumoniae (30%)
2) Haemophilus influenza (25%) 3) Moraxella catarrhalis (15-20%) |
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All Streptococci are CATALASE (POSITIVE, NEGATIVE)
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NEGATIVE
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Which Strep is sensitive to bacitracin?
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Only S.pyogenes, Group A strep is sensitive
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What is the CAMP test?
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S. aureus hemolysin and Strep agalactiae (GBS) hemolysin act synergistically
The CAMP test is a test to identify Group B β-streptococci[1][2] based on their formation of a substance (CAMP factor[3]) that enlarges the area of hemolysis formed by β-hemolysin from Staphylococcus aureus. It is frequently used to identify Listeria spp. |
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What is the esculin test?
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Liquid or solid media containing bile esculin turns black with Group D Strep (Enterococcus)
Test to ID Group D strep |
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_______ lysed in presence of bile (Na deoxycholate) - AKA bile soluble
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Pneumococci (S. pneumoniae)
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Which strep's growth is inhibited by optochin?
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Strep pneumoniae
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What is the sodium hippurate test?
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To ID S. agalactiae. (group B) They hydrolyze hippurate while other strep don't
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Cause scarlet fever in children and toxic shock syndrome in adults
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pyrogenic exotoxins
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What if Strep does not have M factor?
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It will not be virulent.
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What is ASO titer looking for?
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Clinical indicator of past S. pyogenes infection. It's looking for Antibodies to oxygen labile toxin Streptolysin O
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Most common cause of cellulitis
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Group A strep
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Mortality is highest in (strep, staph) toxic shock syndrome
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Strep
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Puerperal fever: cause
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group A strep
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Puerperal fever: symptoms
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Postpartum endometritis
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S pneumoniae: prevention
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Polyvalent vaccines composed of 23 polysaccharide types for adults
• Polyvalent vaccine composed of 7 types conjugated to protein for children—available since 2000 |
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S agalactiae: what kind of strep
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Group B (life-threatening to infant)
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Antibiotic therapy for Group D Strep/Enterococcus
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combination therapy (beta-lactam plus aminoglycoside)
. They're resistant generally |
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Strep is more associated with (community, hospital) infections while staph is more associated with (community, hospital)
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Community; hospital
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