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Microbio Block 1 > Strep & Enterococci > Flashcards

Strep & Enterococci Flashcards

1
Q

Necrotizing fasciitis symptoms

A

Pain out of proportion to exam, often overlying edema, cellulitis, skin discoloration, bull, gangrene
Woody feeling of SQ tissues
Crepitus or anesthesia involved skin
Late: sepsis, organ failure, death

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2
Q

Tx of nec fasc

A

Surgery - dx by easily dissected tissue planes, swollen, dull, gray fascia -> debridement
Broad AB coverage (clinda, linezolid to decrease toxins)

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3
Q

Most common cause of nec fasc

A

Pts with no risk factors = Strep. pyogenes (GAS)

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4
Q

Common diseases caused by strep/ enterococcus infections

A

S. pneumo: sinus, ear, pneumonia, menigitis
viridans: endocarditis
Group A (pyogenes): cellulitis, skin infection
Entero: UTIs

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5
Q

Lab dx of strep

A

G+ cocci in pairs or chains, facultative anaerobes (some capnophilic), blood- or serum-enriched agar, lactic acid production, cat-

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6
Q

Hemolytic patterns

A

Alpha: breakdown of hemoglobin, appears greenish
Beta: breakdown RBC, appears clear/yellow
Gamma: no hemolysis

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7
Q

Lancefield groupings

A

Serologic classification based on specific Ag in cell wall; clumping = positive

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8
Q

S. pyogenes (GAS): Lancefield group, hemolysis, bio/phys tests

A

LG: A
Hem: beta
PYR+, bacitracin sensitive

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9
Q

PYR test

A

Presence of enzyme L-pyrrolidonyl arylamidase in colony of interest turns solution of PYR broth red when PYR reagent added

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10
Q

S. agalactiae (GBS): Lancefield group, hemolysis, bio/phys tests

A

LG: B
Hem: weak beta or gamma
CAMP+, bacitracin res, hydrolyzes hippurate

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11
Q

Enterococci: Lancefield group, hemolysis, bio/phys tests

A

LG: D
Hem: gamma
Growth in bile and 6.5% NaCl, PYR+, hydrolyzes esculin

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12
Q

S. bovis: Lancefield group, hemolysis, bio/phys tests

A

LG: D
Hem: gamma
Growth in bile, hydrolyzes esculin

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13
Q

S. anginosus (a viridans): Lancefield group, hemolysis, bio/phys tests

A

LG: F, A, C, G, and none
Hem: beta
Small colonies, group A is PYR+, bacitracin res

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14
Q

Strep viridans: Lancefield group, hemolysis, bio/phys tests

A

LG: none
Hem: alpha, beta, or gamma
Optochin res, not bile soluble

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15
Q

S. pneumo: Lancefield group, hemolysis, bio/phys tests

A

LG: none
Hem: alpha
Optochin susceptible, bile soluble

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16
Q

Peptostreptococcus: Lancefield group, hemolysis, bio/phys tests

A

LG: none
Hem: gamma or alpha
Obligate anaerobe

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17
Q

Strep pyogenes infections

A

Noninvasive infxns (strep throat, pyoderma)
Invasive infections less common
Can cause rheumatic fever, PSGN

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18
Q

S. pyogenes virulence factors

A

M protein*: serotype-specific, inhibits complement = dec phago
Streptolysins O, S: hemolysins, toxic to other cells, inh by O2
Capsule, adhesins, exotoxins, C5a peptidase (dec abscess formation); DNAse, hyaluronidase, streptokinase (these 3 dec viscosity, degrade clots & CT = spread)

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19
Q

S. pyogenes prevalence, transmission, immunity

A

Asymptomatic carriage in kids and adults
Transmitted person-person via resp droplets (crowding is a problem), uncommonly food- or water-borne, not spread by fomites
Serotype-specific long-lasting immunity develops post-infxn

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20
Q

Streptococcal pharyngitis symptoms, complications

A

Resolves in 1 week
Can have scarlet fever with some strains
Rarely: contiguous or bacteremic spread (suppurative complications)
Non-suppurative complications: RF (1-5 w later), PSGN

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21
Q

Symptoms of scarlet fever

A

Blanching red rash of sandpaper texture, sparing palms and soles, red strawberry tongue

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22
Q

Rheumatic fever

A

Affects CT (heart, jj, vessels, SQ tissues), associated with certain M types
Carditis -> chronic rheumatic heart disease, polyarthritis, SQ nodules, chorea, erythema marginatum, fever, arthralgias
3% after untreated strep throat, lasts 3-6 months (but commonly recurs)

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23
Q

PSGN

A

Post-streptococcal glomerulonephritis
After strep throat or pyoderma
Edema, HTN, proteinuria, hematuria
90% recover completely, recurrence uncommon

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24
Q

Streptococcal pyoderma/impetigo

A

Discrete purulent skin lesions with thick crusts
Peak: age 2-5 in warmer climates/months
*Can also be caused by S. aureus, so tx is abx to cover both

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25
Erysipelas
Invasive strep skin/ soft tissue infection Lesions raised above skin with clear demarcation, bright red/ salmon color Restricted to dermis and lymphatics
26
Cellulitis
Invasive strep skin/ soft tissue infection Spreading inflammation of skin and SQ tissues Most commonly caused by strep in absence of pus or penetrating trauma
27
Streptococcal toxic shock syndrome
Any GAS infxn a/w shock and organ failure, usually serotypes M1, M3 Primarily exotoxin-mediated Phases: 1) flu-like prodrome, confusion, pain; 2) tachycardia, tachypnea, fever, inc pain; 3) shock, organ failure Tx: source control, fluids, abx (PCN + clinda), ICU care, +/- dialysis and IVIG
28
Lab dx of S. pyogenes
Strep throat: rapid Ag detection test; throat culture* Invasive infxn: blood/tissue culture; clinical for pyoderma, erysipelas, cellulitis RF: Jones criteria, evidence of previous GAS infxn PSGN: clinical picture + evidence of previous GAS infxn
29
Jones criteria for RF
Major: migratory arthritis, carditis, valvulitis, CNS involvement, erythema marginatum, SQ nodules Minor: arthralgia, fever, elevated APRs, prolonged PR interval
30
ASO titer
Used to detect previous strep infection for RF and PSGN | Abs take weeks to develop, so this is not for acute infection
31
Tx of S. pyogenes infections
Strep throat: pen or another abx Invasive infxn: longer course abx RF: ASA, steroids, pen prophylaxis for 5-10 y to prevent recurrence PSGN: pen (as for strep throat)
32
Lab dx of GBS/S. agalactiae
Beta-hemolysis, bacitracin resistant, +CAMP test, hydrolyzes hippurate
33
S. agalactiae/GBS normal colonization sites, infections, and main virulence factor
Colonizes GI, oropharynx, vagina (20% women) Source of sepsis for babies and elderly w comorbidities (DM, liver disease), meningitis Main: polysaccharide capsule to interfere w phagocytosis
34
GBS in pregnancy
50% neonates colonized if mother not treated Pregnant women screened at 35-37 weeks and given intrapartum pen prophylaxis if positive Infants: 1-7d bacteremia, sepsis, pneumonia, meningitis; 1-13w bacteremia, meningitis, focal infxn (osteomyelitis, cellulitis)
35
GBS infections in adults, dx, and tx
Pregnant: chorioamnionitis, miscarriage, endometritis, postpartum UTI Elderly w comorbidities: bacteremia, pneumonia, osteomyelitis, arthritis, cellulitis Dx: culture or PCR Tx: pen or another abx
36
Viridans group of strep
Genetically related, mostly a-hemolytic but any hemolysis and Lancefield group possible; treat different strains diff for testing and clinical purposes Normal flora of oropharynx, GI, upper resp, female GU
37
Viridans strep groups
Anginosus, mitis, mutans, salivarius, sanguinis
38
Virulence of viridans strep
Low virulence, no exotoxins except S. anginosus group
39
S. anginosus infections and virulence
Invasive pyogenic abscess (in 50-80% brain abscesses; dental, liver, lung) Vir: exotoxins, hydrolytic enzymes, polysaccharide capsule
40
Species in viridans strep anginosus group & shared phenotype and metabolic features
S. constellatus, intermedius, anginosus Small colonies with caramel odor Growth enhanced by anaerobes
41
Clinical syndromes of viridans strep
Infective endocarditis (20% of cases), bacteremia, aspiration pneumonia with anaerobes
42
Symptoms and tx of infective endocarditis
Subacute; fever, murmur, fatigue, weight loss, splenomegaly Janeway lesions, Osler's nodes, splinter hemorrhages, Roth's spots Tx: pen or ceftriaxone +/- gentamicin (sensitivities)
43
Viridans strep bacteremia
Primarily in neutropenic fever; 25% fulminant shock, 6-12% mortality
44
Lab dx S. pneumoniae
G+ cocci in pairs or chains, large a-hemolytic colonies, Lancefield non-typeable, optochin sensitive, bile soluble, 91 serotypes, + quellung reaction
45
Quellung reaction
Polyvalent anticapsular Abs + bacteria, examine microscopically for increased refractiveness around bacteria = + reaction = pneumococcus
46
S. pneumoniae colonization and infections
5-70% people colonized (nasal carriage), normal flora of oropharynx, obligate human parasite Leading bacterial cause of meningitis, pneumonia, sinusitis, otitis media
47
Pneumococcus/ S. pneumo virulence factors
``` Surface adhesins (attach) IgA protease and pneumolysin (evade removal by cilia) Pneumolysin, teichoic acid, peptidoglycan fragments, hydrogen peroxide, phosphocholine (tissue destruction) Polysacch capsule (prevent phago), pneumolysin (suppress killing by phago) ```
48
How do pneumolysin, teichoic acid, peptigoglycan fragments, hydrogen peroxide, and phosphocholine help S. pneumo destroy tissue?
``` Pneumolysin: activates classical complement TA: alternate complement PG frag: alternate complement H2O2: ROS intermediates PC: helps enter cells ```
49
Host defenses vs. pneumococci/ S. pneumo
Mucous and ciliated epithelial cells in lungs move them up and out of resp tract Spleen clears bact from blood Anticapsular Ab opsonizes for phagocytosis
50
Predisposing factors for invasive S. pneumo infection
65 yoa Native America, AA, Australian aboriginal: 2-10x higher risk Asplenia/dysfunctional (100x in SCD), DM (6x), COPD (7x), CHF (10x), alcoholics (11x) Immunodef: HIV/AIDS (47x), solid cancer (33x), hematologic malignancy (56x)
51
Otitis media and sinusitis
Leading cause: S. pneumo (30-40%), followed by H. flu Prior resp infection contributes to congestion of sinuses/ ear canal -> obstruction OM: young children, #1 reason abx in kids Sin: all ages
52
Meningitis
Leading cause: pneumococcus (70% of adult, >6 mo) Direct extension from ear, sinuses, or bacteremia Sx: fever, nuchal rigidity, AMS, HA, seizures, focal neuro defects, N/V, photophobia, Kernig's and Brudzinski's signs Tx: vanco, ceftriaxone
53
Kernig's and Brudzinski's signs
K: reluctance to allow knee extension with 90* hip flexion B: spontaneous hip flexion with passive neck flexion
54
Bacterial vs. fungal/TB vs. viral meningitis CSF parameters
B: >1000 WBC, mostly neutros, low glucose, high protein, elevated opening pressure F/TB: 10-500 WBC, mostly lymphs, low glucose, slightly high protein, elevated opening pressure V: 10-500 WBC, mostly lymphs, nrl glucose, nrl-elevated protein, normal opening pressure
55
Sx of pneumococcal pneumonia
Cough, fatigue, fever, chills, sweats, SOB; tachycardia, tachypnea, crackles +/- dull to percussion, egophany, increased fremitus; infiltrate on imaging
56
Dx and tx of pneumococcal pneumonia
Dx: resp Gram stain/culture, blood culture, Ag detection (urine or CSF) Tx: empiric tx covers pneumococcus (ceftriaxone, azithromycin, FQs)
57
Pneumococcus prevention
Polysaccharide vaccine: T-cell independent immunity, hyporesponsiveness for 1 year, 60-70% efficacy, ineffective in kids
58
Enterococci features
"Intestine berry"; GPC in pairs and short chains; usually y-hemolytic, can be a or b; can grow in high conc NaCl or bile salt; facultative anaerobes; optochin resistant; PYR+
59
Enterococcus species of clinical importance
E. faecalis, E. faecium
60
Pathogenesis of enterococcus, virulence factors
No potent toxins or well-defined virulence factors Surface adhesins, cytolysin (hemolytic), gelatinase and serine protease Inherently resistant to many abx, can acquire resistance easily Tx of choice: ampicillin +/- gentamicin (if sensitive)
61
Enterococcal infections
``` Subacute endocarditis (5-20% cases), line infections, UTIs (catheter), intra-abd and pelvic infxns 2-3rd cause of nosocomial infxns in US ```
62
Risk factors for enterococcal infections
Recent hospitalization, abx use, SNF residence/stay, immunocompromised (cancer, DM), GI procedure
63
Strep bovis (GDS) bacteremia tests
HIV ELISA and confirmatory western blot, colonoscopy (assc. w colon cancer), complement levels, Hgb electrophoresis

Microbio Block 1 (14 decks)

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