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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
Q

Erysipelas

A

Invasive strep skin/ soft tissue infection
Lesions raised above skin with clear demarcation, bright red/ salmon color
Restricted to dermis and lymphatics

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26
Q

Cellulitis

A

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
Q

Streptococcal toxic shock syndrome

A

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
Q

Lab dx of S. pyogenes

A

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
Q

Jones criteria for RF

A

Major: migratory arthritis, carditis, valvulitis, CNS involvement, erythema marginatum, SQ nodules
Minor: arthralgia, fever, elevated APRs, prolonged PR interval

30
Q

ASO titer

A

Used to detect previous strep infection for RF and PSGN

Abs take weeks to develop, so this is not for acute infection

31
Q

Tx of S. pyogenes infections

A

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
Q

Lab dx of GBS/S. agalactiae

A

Beta-hemolysis, bacitracin resistant, +CAMP test, hydrolyzes hippurate

33
Q

S. agalactiae/GBS normal colonization sites, infections, and main virulence factor

A

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
Q

GBS in pregnancy

A

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
Q

GBS infections in adults, dx, and tx

A

Pregnant: chorioamnionitis, miscarriage, endometritis, postpartum UTI
Elderly w comorbidities: bacteremia, pneumonia, osteomyelitis, arthritis, cellulitis
Dx: culture or PCR
Tx: pen or another abx

36
Q

Viridans group of strep

A

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
Q

Viridans strep groups

A

Anginosus, mitis, mutans, salivarius, sanguinis

38
Q

Virulence of viridans strep

A

Low virulence, no exotoxins except S. anginosus group

39
Q

S. anginosus infections and virulence

A

Invasive pyogenic abscess (in 50-80% brain abscesses; dental, liver, lung)
Vir: exotoxins, hydrolytic enzymes, polysaccharide capsule

40
Q

Species in viridans strep anginosus group & shared phenotype and metabolic features

A

S. constellatus, intermedius, anginosus
Small colonies with caramel odor
Growth enhanced by anaerobes

41
Q

Clinical syndromes of viridans strep

A

Infective endocarditis (20% of cases), bacteremia, aspiration pneumonia with anaerobes

42
Q

Symptoms and tx of infective endocarditis

A

Subacute; fever, murmur, fatigue, weight loss, splenomegaly
Janeway lesions, Osler’s nodes, splinter hemorrhages, Roth’s spots
Tx: pen or ceftriaxone +/- gentamicin (sensitivities)

43
Q

Viridans strep bacteremia

A

Primarily in neutropenic fever; 25% fulminant shock, 6-12% mortality

44
Q

Lab dx S. pneumoniae

A

G+ cocci in pairs or chains, large a-hemolytic colonies, Lancefield non-typeable, optochin sensitive, bile soluble, 91 serotypes, + quellung reaction

45
Q

Quellung reaction

A

Polyvalent anticapsular Abs + bacteria, examine microscopically for increased refractiveness around bacteria = + reaction = pneumococcus

46
Q

S. pneumoniae colonization and infections

A

5-70% people colonized (nasal carriage), normal flora of oropharynx, obligate human parasite
Leading bacterial cause of meningitis, pneumonia, sinusitis, otitis media

47
Q

Pneumococcus/ S. pneumo virulence factors

A 
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
Q

How do pneumolysin, teichoic acid, peptigoglycan fragments, hydrogen peroxide, and phosphocholine help S. pneumo destroy tissue?

A 
Pneumolysin: activates classical complement
TA: alternate complement
PG frag: alternate complement
H2O2: ROS intermediates
PC: helps enter cells
49
Q

Host defenses vs. pneumococci/ S. pneumo

A

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
Q

Predisposing factors for invasive S. pneumo infection

A

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
Q

Otitis media and sinusitis

A

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
Q

Meningitis

A

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
Q

Kernig’s and Brudzinski’s signs

A

K: reluctance to allow knee extension with 90* hip flexion
B: spontaneous hip flexion with passive neck flexion

54
Q

Bacterial vs. fungal/TB vs. viral meningitis CSF parameters

A

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
Q

Sx of pneumococcal pneumonia

A

Cough, fatigue, fever, chills, sweats, SOB; tachycardia, tachypnea, crackles +/- dull to percussion, egophany, increased fremitus; infiltrate on imaging

56
Q

Dx and tx of pneumococcal pneumonia

A

Dx: resp Gram stain/culture, blood culture, Ag detection (urine or CSF)
Tx: empiric tx covers pneumococcus (ceftriaxone, azithromycin, FQs)

57
Q

Pneumococcus prevention

A

Polysaccharide vaccine: T-cell independent immunity, hyporesponsiveness for 1 year, 60-70% efficacy, ineffective in kids

58
Q

Enterococci features

A

“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
Q

Enterococcus species of clinical importance

A

E. faecalis, E. faecium

60
Q

Pathogenesis of enterococcus, virulence factors

A

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
Q

Enterococcal infections

A 
Subacute endocarditis (5-20% cases), line infections, UTIs (catheter), intra-abd and pelvic infxns
2-3rd cause of nosocomial infxns in US
62
Q

Risk factors for enterococcal infections

A

Recent hospitalization, abx use, SNF residence/stay, immunocompromised (cancer, DM), GI procedure

63
Q

Strep bovis (GDS) bacteremia tests

A

HIV ELISA and confirmatory western blot, colonoscopy (assc. w colon cancer), complement levels, Hgb electrophoresis

Microbio Block 1 (14 decks)

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