Streptococci and Enterococci: Sore Throats, and Beyond!

Chapter 12 Streptococci and Enterococci: Sore Throats, and Beyond!

1. How would you classify Enterococci?  Enterococci are γ hemolytic (not hemolytic), group D streptococci i. Group D refers to serological reactivity

2. What are the two common patterns of infection with S. pyogenes/Group A Streptococci? Who is most affected?  GAS infections usually present as acute pharyngitis or pyoderma  Children under 3 are most affected

3. How does S. pyogenes bind to mucous membranes? What does the virulence factor M protein bind besides fibrinogen?  Several adhesins are used by Group A Strep: i. lipotichoic acid binds to fibronectin ii. Protein F attaches to fibronectin iii. M protein attaches to fibrinogen [fltim-FLTAM]  M proteins bind host complement control proteins, inhibiting the complement cascade i. Their fibrinogen binding also interferes with the alternative pathway

4. What other enzymes can S. pyogenes use to cause disease (2)?  Streptokinase breaks down clots: binds to plasminogen to convert plasminogen to plasmin, which in turn degrades fibrin, the main component of blood clots  Streptolysins S and O lyse host cells with pores—> β hemolysis

5. What is the capsule of S. pyogenes made of? How does the microbe break it down?  GAS use a hyaluronic acid capsule to evade the immune system, however it must be digested by its hyaluronidase in order for the microbe to cause infection

6. What is responsible for causing scarlet fever?  The streptococcal pyrogenic exotoxins A, B, and C are superantigens that cause scarlet fever

7. Describe the course of acute rheumatic fever. How can it be prevented?  Manifestations of acute rheumatic fever appear 1 to 4 weeks after streptococcal pharyngitis, and features carditis, polyarthritis, chorea, subcutaneous nodules, and erythema marginatum—weird ring rashes on the trunk and limbs  Acute rheumatic fever can be prevented within 9 days after the onset of sore throat, with a 10 day antibiotic course of penicillin which must be completed

8. Describe acute post-streptococcal glomerulonephritis. How can it be prevented?  Acute post-streptococcal glomerulonephritis follows pharyngitis OR pyodermal infection. It is caused by only a few M serotypes of S. pyogenes  It can’t be. Antibiotic treatment does not alter the risk of APSGN, because the disease is due to antigen-antibody deposition on the GBM, not attack 9. What are some treatment alternatives to penicillin?  Although there is no resistance to penicillin, a single injection of benzathine penicillin can be used instead i. Breaks the rule and so far no absolutely resistance has been documented  Erythromycin and other macrolide antibiotics are appropriate when the patient is allergic

10. What kind of hemolysis do group B streptococci cause? What is the only reason to fear them?  Group B streptococci are β-hemolytic [the B is for Baby]  Pregnant women need to be screened at 35 to 37 weeks gestation, because group B streptococci frequently cause neonatal sepsis and meningitis

11. What are the three major bacteria from Groups C, G, and F? How can they be dangerous?  S. mutans, S. sanguis, and S.milleri are viridans (α-hemolytic)  S. mutans and S. sanguis can cause rare endocarditis in people with defective heart valves  S. milleri can cause polymicrobial abcesses [millet, like TB’s milliary disemination]

12. What makes infection dangerous when it’s caused by Enterococci/group D streptococci/E. faecalis and E. faecium?  These enterococci have a strong propensity for developing drug resistance i. Penicillins are only bacteriostatic in Enterococci ii. Cephalosporins are not active in Enterococci iii. Enterococci also are intrinsically resistant to aminoglycosides

13. How can Enterococci be erradicated? Dr M: “I wouldn’t worry about treating at this point”  A combination of B-lactam and aminoglycoside is effective for treating Enterococci  As are Dalfopristin—quinupristin: effective against E. faecium only  Linezolid: effective against both E. faecalis and E. faecium  Daptomycin: effective against both