Strep Flashcards
What is the morphological difference between Strep and Staph?
Streptococci form chains; staphylococci form “graph clusters”
What is the catalase test difference between Strep and Staph?
Streptococci are catalase negative (they will NOT bubble); staphylococcus are catalase positive
What is the species of Group A Strep?
S. pyogenes
What are the β-hemolytic Strep species and how do you distinguish them?
S. pyogenes and S. agalactiae, and GAS is bacitracin sensitive
What are the α-hemolytic Strep species and how do you distinguish them?
S. pneumoniae and Viridans, and S. pneumoniae is optochin-sensitive and has pearly colonies due to its capsule and Quellun (+)
What are the γ-hemolytic Strep species and how do you distinguish them?
Enterococcus and non-Enterococcus species; both are bile scullion (+) but Enterococcus grows in salt media
What does hyalorunate do in S. pyogenes?
It forms a protective capsule to help protect it from the immune system
What are the functions of the M-protein?
(1) Binds complement, (2) anti-opsonization; autoantibodies can form to M-proteins
What are the two invasion factors of Strep?
Hyaluronidase breaks down ECM and Streptokinase activates plasmin, dissolving the blood clots to release bacteria
What are the two major toxins from Strep?
Streptolysin O lyse erythrocytes and pyrogenic agents like erythrogenic toxin cause scarlet fever; superantigens overactivate T cells
What is a suppurative infection?
A pus-producing infection
What are some common suppurative infections caused by GAS?
Erysipelas (outermost layer, dermis); cellulitis (middle layer, dermis/sub-cu); necrotizing fasciitis; impetigo (crusty red sores around the nose)
What are some of the classic signs of scarlet fever?
Desquamating sandpaper rash, circumoral pallor, strawberry tongue, fever
What are some of the signs and causes of streptococcal toxic shock syndrome?
Hypotension, end organ damage; thought to be caused by superantigen activation
What are the organ systems usually affected by acute rheumatic fever?
Skin, joints, heart, brain
What are three of the five criteria for ARF?
Pancarditis, polyarthritis, subcutaneous nodules, erythema marginatum, Sydenham chorea
What is the common renal complication of GAS infection?
Post-streptococcal glomerulonephritis (PSGN), which is caused by antibody complex deposition
What are the four categories of β-lactams?
Penicillins, cephalosporins, carbapenams, and monobactams
What is the mechanism of β-lactams?
They block the active site of the penicillin binding protein, so the bacterial cell wall cannot form
What are the two main paths to β-lactam resistance?
β-lactamases and modifications of the PBPs
What are the two types of resistance development?
Inducible resistance and plasmid transfer
What is the most common adverse effect of β-lactam drugs?
GI adverse effects
How is bacterial pharyngitis distinguished from viral?
Viral pharyngitis also has coryza, conjunctivitis, and a cough
What are the two major diagnostic tests for strep?
Bacterial culture of pharyngeal swab (24-48 hours); strep rapid antigen detection test (10 min; follow-up culture if negative)
Name the five Centor criteria (and the one extra).
Fever >38°C, tender anterior cervical LNs, tonsillar swelling, lack of a cough, age 3-14; -1 for age 45; test with RADT for 2+
What is the treatment for GAS pharyngitis?
Penicillin (or azithromycin/clindamycin if allergic)
