Flashcards in Micro - Pharyngitis, otitis, epiglottitis, sinusitis Deck (54)
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What are the most common causes of pharyngitis?
Young children and adults most commonly viral
Older children usually strep pyogenes (group a), viruses, mycoplasma pneumoniae
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What is the microbiology of corynebacterium diphtheriae?
Aerobic, non motile, non spore forming, non encapsulated, gram positive rod with clubbed ends
Grows on loeffler's medium or medium with potassium tellurite
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How is corynebacterium diphtheriae transmitted?
From patient or asymptomatic carrier through nasopharyngeal secretions or skin lesions
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What is a pseudo membrane produced by corynebacterium diphtheriae?
Induced by diphtheria toxin and is dirty grey colored leathery membrane covering tonsils and may extend to larynx
Should NOT be removed because of risks
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What is bull neck?
Extensive pseudo membrane from corynebacterium diphtheriae involvement of pharynx associated with cervical adenopathy and severe neck swelling
Accompanying upper airway obstruction
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What is the virulence factor of corynebacterium diphtheriae?
Potent exotoxin
Can act locally to produce pseudo membrane or systemically to affect heart or peripheral nerves (effects depend on how much toxin absorbed)
Phage encoded AB toxin - tox gene is necessary and sufficient or disease
B interacts with receptor and A ADP ribosylates EF2 which blocks protein synthesis - one A sufficient to inactivate all EF2 in cell
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How can one be immunized against diphtheria?
Antitoxin can treat along with antibiotics
DTaP vaccine - toxoid for diphtheria toxin and tetanus toxin with acellular pertussis components
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How can strep be distinguished from other gram positive bacteria?
They do not have catalase - cant break down hydrogen peroxide and have negative reaction
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What are the three different kinds of hemolysis by strep?
Alpha - colony surrounded by partial zone of clearing with green coloring, incomplete hemolysis (s. pneumoniae, viridans strep comprising normal oral flora)
Beta - surrounded by clear zone, complete hemolysis (s pyogenes)
Gamma or non - no hemolysis (enterococcus)
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What are the lancefield groups?
Further classify beta hemolytic strep based on group specific carbohydrates
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How can group a beta hemolytic strep (GABHS) be differentiated from other beta hemolytic strep?
Sensitive to bacitracin
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How can GABHS (s. pyogenes) be further classified?
By m protein - cell attachment molecule
Virulence factor that correlates with certain diseases
Antibodies to m protein are protective - humoral immunity is type specific against certain strains only
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What are the major virulence factors of s. pyogenes?
Adherence factors - m protein, ECM binding proteins (fibronectin), capsule
Invasion and spread
Toxicity - super antigens, exotoxins
Immune evasion - Ig binding protein, m protein, capsule, c5a peptidase
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How is s. pyogenes transmitted?
Air - respiratory droplet
Food - prepared by person with open lesion
Hands
Rare transmission from fomites - bedding, clothing, etc
Most common is direct contact with saliva or nasal discharge from infected person
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How does host immunity to GABHS work?
Antibodies against m protein, streptolysin o, or DNAase
Primarily opsonophagocytosis by neutrophils or PMNs
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How is GABHS diagnosed?
Culture - aerobic growth, takes 1-2 days
Serology - anti streptolysin o or anti DNAase, minimum few days
Antigen detection - rapid detection of group a antigen directly from swab, minutes
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Which types of strep infections cause which delayed sequelae?
Throat infection can cause either rheumatic fever or glomerulonephritis
Skin inf only causes glomerulonephritis
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What are the suppurative vs. the toxin mediated diseases caused by strep?
Suppurative - pharynx, skin or soft tissue infection, other sites
Toxin mediated - scarlet fever, streptococcal TSS
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What is the epidemiology of tonsillopharyngitis?
Children 5-15 yrs
Asymptomatic carriage can happen
Incubation 2-4 days
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What are some key clinical features of strep?
Tonsil liar exudate
Soft palate petechiae
Can be distinguished from viruses by virus also having conjunctivitis, hoarseness, runny nose
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How is strep treated?
Make sure treat only bacterial, not viral
IV penicillin if severe
I'm benzathine penicillin, one shot
Oral penicillin or amoxil for ten days
Oral macrolide or cephalosporin if allergy to penicillin
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What are the general features of scarlet fever?
From organism that secretes SPE - encoded by lysogenic prophages = superantigens
mostly with pharyngitis but can happen with skin inf
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What are the clinical feature of scarlet fever?
High fever and headaches
Sandpaper rash on upper trunk then spreads - palms, sole, and face spared and mouth has circumoral pallor, maculopular and blanches to touch
Pastia's lines - red lines in fold of skin around elbows, underarms, stomach and neck
Strawberry tongue progressing to raspberry tongue
May have desquamation of hands and feet
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What are the three feature delayed sequelae have in common?
Evidence of preceding GABHS inf
Incubation of 7-21 days (1-5 weeks following inf)
No GABHS in damaged tissues
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What is the pathogenesis of acute rheumatic fever (ARF)?
5-15 yr olds
Toxins - streptolysin o, SPE, and others cause direc injury
Cross reactive antibodies
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What are the jones criteria for diagnosing ARF?
Major - carditis, polyarthritis, chorea, erythema marginatum on trunk or proximal extremities, subcutaneous nodules
Minor - clinical or lab evidence
2 major or 1 major and 2 minor with evidence of preceding GABHS inf
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How can ARF be prevented?
Penicillin treatment of strep pharyngitis within 9 days
At least 10 days of therapy
For recurrent attacks - daily oral penicillin or monthly IM penicillin, prophylaxis at least 5-10 yrs or longer
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What is the epidemiology and general clinical features of APSGN?
All ages, usually children
Repeat attacks rare
Clinical - dark urine, headache, back pain, edema, hypertension
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What is the theory of pathogenesis of APSGN?
Immune complexes of strep antigen and host antibody within glomerulus
Or
Anti strep antibodies directly cause injury
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