Streptococci

Question 1

Strep Pyogenes Group A Strep key features:

+ for:

virulence factor:

Answer 1

(PYR) positive

M protein virulence factor • Inhibits phagocytosis

Question 2

Strep Pyogenes Group A Strep causes 3 categories of illness

1. ) (2)
2. ) (3)
3. ) (2)

Answer 2

Infections

Pharyngitis (Strep throat) • Skin: Cellulitis/Impetigo

Toxin-mediated disease

Scarlet fever • Necrotizing fasciitis • Toxic Shock Syndrome

Immune disease

Rheumatic fever • Post-strep glomerulonephritis

Question 3

Strep Pharyngitis:

Important to identify and treat S. pyogenes Pharyngitis because:

Diagnosis:

Treatment::

Answer 3

Prevent rheumatic fever

-15-30% pharyngitis due to S. pyogenes • (Many cases viral)

Diagnosis: • Throat culture • Rapid antigen test (useful if positive)

Treatment: Penicillin, amoxicillin, cephalosporins

Question 4

S. Pyogenes Skin Infections:

Answer 4

Cellulitis and Impetigo (“honey-crusted”)

Both commonly caused by Strep but also S. Aureus •

Antibiotics need to cover Strep and Staph

Question 5

Scarlet Fever

follows:

reaction to:

symptoms:

classic finding:

Answer 5

Rash following pharyngitis

Skin reaction to erythrogenic toxin

Gene for toxin transferred by lysogenic phage

Fever, sore throat, diffuse red rash-many small papules (“sandpaper” skin) • Starts head/neck →expands to cover trunk

Classic finding: Strawberry tongue • Eventually skin desquamates • (Palms and soles are usually spared)

Question 6

2 types of Necrotizing Fasciitis & classic case

Answer 6

Type 1:

Polymicrobial • Often anaerobes (Bacteroides, Clostridium, etc.) • Occurs in diabetics, immunocompromised, post surgery

Type 2:

Group A strep (sometimes Staph) • Occurs in otherwise healthy people after skin injury

Classic case:

Minor skin trauma • Redness/warmth (can be confused with cellulitis) • Pain out of proportion!!! to exam • Fever, hypotension

Question 7

Rheumatic Fever

follows:

causes:

3 signs:

Answer 7

Follows group A strep pharyngitis infection

Streptococcus infection→ anti-strep antibodies which Cross react with tissue antigens

1.)Aschoff bodies

Cardiac nodules with inflammatory cells (granulomas) • Pathognomonic for rheumatic carditis

2.)Anitschkow’s cells

Macrophages with owl eye appearance

3.)Elevated ASO titers

Question 8

how to diagnose rheumatic fever:

Answer 8

2 major or 1 major & 2 minor

Question 9

Rheumatic Fever

clues

treatment

cardiac involvement

Answer 9

Clues:

Sore throat or URI followed by joint pain, new murmur

Treatment: Penicillin

Cardiac involvement

• Acute RF → severe valve disease, heart failure • Later (after recovery) → mitral stenosis (rarely aortic or tricuspid valves)

Question 10

Post-streptococcal GN

Answer 10

• Nephritic syndrome 2-3 weeks after GAS infection

Question 11

Strep Agalactiae Group B Strep

2 important features

Answer 11

Makes CAMP factor

Staph Aureus makes β-hemolysin • CAMP factor enhances lysis by β-hemolysis

Hydrolyzes the compound hippurate • Will alter color of hippurate test

Question 12

Strep Agalactiae Group B Strep

colonizes:

importance in pregnancy:

Answer 12

Colonizes vagina • Causes infections in newborns • Babies infected in utero or during birth • & therefore a common cause of Pneumonia, meningitis, sepsis in babies

Pregnant women screened 35-37 weeks, Women GBS (+) receive prophylaxis • Four hours prior to delivery

Penicillin, ampicillin, or cefazoli

Question 13

Strep Pneumonia

_ shape

key virulence factor

Answer 13

“Lancet shaped” gram (+) cocci •

IgA protease •

Key virulence factor: Polysaccharide capsule • Prevents phagocytosis • Basis of vaccine from capsular material • Asplenic patients at risk for sepsis • Splenectomy • Sickle cell anemia

Question 14

Strep Pneumonia causes:

Answer 14

• Lobar Pneumonia • Meningitis • Otitis Media • Sinusitis

Question 15

Viridans Group Strep

colonizes and therefore causes:

also causes subacute:

Answer 15

Normal mouth flora • Cause dental carries (Strep Mutans) •

SUBACUTE endocarditis (Strep Sanguis) • Slow onset symptoms; less sick patient • Often affects ABNORMAL valves(not as virulent as staph) • Dextran → fibrin • Requires endothelial damage • Mitral valve prolapse • Pearl: Recent dental procedure

Question 16

Enterococcus

colonizes;

infections caused:

resistant to:

best treatment:

Answer 16

• Normal colonic bacteria

Infections: • UTIs • Endocarditis (rare)

Resistant to penicillin • Vancomycin resistant enterococcus (VRE)

synergistic therapy • Vancomycin/gentamycin • Ampicillin/gentamycin

(Relatively resistant to cell wall agents • Penicillin, ampicillin, and vancomycin • Impermeable to aminoglycosides)

Question 17

Enterococcus UTIs

Answer 17

• Often hospital acquired, associated with catheters • Removal of catheter alone may cure infection • Urinalysis: NEGATIVE for nitrites like staph

Question 18

Enterococcus Endocarditis

Rare cause of:

Usually after :

__often used for empiric therapy before culture data available

___ effect of __ antibiotics

Answer 18

Rare cause of endocarditis

Usually after manipulation GU tract • TURP procedure, cystoscopy

Vancomycin/gentamycin often used for empiric therapy before culture data available

Synergistic effect of dual antibiotics

Question 19

Strep Bovis

Normal _

Rare cause _

Strongly associated with_

Answer 19

Normal colonic bacteria

Rare cause bacteremia/endocarditis

Strongly associated with colon cancer