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Streptococcus and Enterococcus Flashcards

1
Q

Gram-positive cocci, catalase negative

A
  • streptococcus, enterococcus, and some other non-pathogenic species
  • part of normal flora
  • not usually associated with infection, except in ICPs
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2
Q

Catalase negative gram-positive cocci cause infection by gaining access to sites that are normally sterile

A

S. pyogenes, groups C & G, S. agalactiae, S. pneumoniae, Viridans strep., E. faecium, E. faecalis

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3
Q
  • gram-positive, catalase negative cocci
  • form chains in liquid medium
  • facultative anaerobes, non-motile, susceptible to penicillin and vancomycin, some are fastidious
  • ID based on hemolysis and Lancefield classification
A

Streptococcaceae

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4
Q

Hemolysin patterns

A

determines if bacteria produce extracellular enzymes that lyse RBCs in agar

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5
Q

complete clearing of the erythrocytes around a bacterial colony

A

beta hemolysis

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6
Q

partial clearing of the erythrocytes around a bacterial colony

A

alpha hemolysis

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7
Q

gamma hemolysis

A

no hemolysis or clearing around a bacterial colony

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8
Q

Lancefield classification

A

classification of strep bacteria based on carbohydrate antigens

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9
Q

Strep group that exhibits Beta hemolysis

A

Group A streptococcus

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10
Q

Strep that exhibit alpha hemolysis

A

Strep pneumoniae

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11
Q

Strep that exhibit gamma or no hemolysis

A

Group D strep and enterococcus

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12
Q

Virulence factors of S. pyogenes (Group A)

A
  • Protein F, Protein M
  • DNase, hyaluronidase, streptokinase, Streptolysin O, Streptolysin S
  • erythrogenic toxins, capsule
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13
Q

mediates epithelial cell attachment

A

Protein F

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14
Q
  • in the cell wall, blocks opsonization

- helps avoid phagocytosis, essential for virulence

A

Protein M

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15
Q
  • causes beta hemolysis

- inactivated by oxidation (elicits ASO production)

A

Streptolysin O

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16
Q
  • causes beta hemolysis

- not inactivated by oxidation, leucocidin activity

A

Streptolysin S

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17
Q

Erythrogenic toxins produced by S. pyogenes

A
  • produces erythematous reaction (coded in viral DNA and integrated in bacteria by lysogeny)
  • causes rash of Scarlet fever and multisystem disease
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18
Q

Transmission of S. pyogenes

A
  • normal skin and oropharynx flora
  • causes infection when tissues are penetrated
  • aerosol spread of infection (person-to-person)
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19
Q

Clinical infections associated with S. pyogenes

A

skin infections, impetigo, erysipelas (red rash on face), cellulitis, puerperal fever, necrotizing fasciatus, pharyngitis, pharyngitis with scarlet fever

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20
Q

Complications with Strep. pyogenes (Group A)

A

Streptococcal toxic shock syndrome, Post-streptococcal acute Rheumatic fever, Post-streptococcal acute glomerular nephritis

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21
Q

multisystem involvement presenting with rash, diarrhea, renal and respiratory problems

A

Streptococcal toxic shock syndrome

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22
Q
  • cross-reaction with heart antigens after strep pharyngitis resolves; no group A strep present
  • symptoms: migratory arthritis, subcutaneous nodules, carditis and erythema marginatum
  • can lead to rheumatic heart disease
A

Post-streptococcal acute rheumatic fever

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23
Q
  • occurs after strep pharyngitis or skin infection; no group A strep present
  • deposits of strep antigen-antibody complex deposit in the kidneys and damage glomeruli
  • symptoms: facial edema, blood and protein in urine
A

Post-streptococcal acute glomerular nephritis

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24
Q

Identification of S. pyogenes (Group A)

A
  • falcultative, extracellular, gram-positive, may chain
  • grow on SBA and CA, not on MacConkey
  • small, white colonies; beta hemolysis
  • non-motile, hyaluronic acid capsule
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25
S. pyogenes (Group A) ID tests
catalase negative, beta hemolytic, PYR positive, CAMP negative, Bile esculin negative, Group A, Bacitracin susceptible, SXT resistant, no growth in 6.5% NaCl, latex agglutination
26
Other S. pyogenes tests
commercial particle agglutination tests, immunoassays, nucleic acid probes (PCR and DNA probes)
27
Virulence factors of S. agalactiae (Group B) strep
capsule, sialic acid for inhibiting complement, hemolysin, CAMP factor, DNases, hyaluronidase, protease
28
Transmission of S. agalactiae (Group B) strep
- normal GU flora, sometimes respiratory | - vertical transmission at birth or in utero, nosocomial (meningitis), in unpasteurized bovine milk
29
Invasive disease in newborns
- caused by Group B strep (agalactiae) - early onset usually caused by vertical transmission (< 7 days after birth), results in premature birth, pneumonia, meningitis, and bacteremia - late onset causes meningitis (1-12 weeks old)
30
Endometritis and endocarditis
- caused by Group B strep | - to mothers after childbirth or abortion
31
S. agalactiae (Group B) infections
- immunodeficiency in elderly people | - treated with ampicillin
32
Detecting Group B strep before vertical transmission
- vaginal and rectal material between 35-37 of pregnancy - inoculate to select broth and culture on SBA - can use nucleic acid tests
33
Identification of Group B strep
facultative, extracellular, gram-positive, grayish-white colonies on SBA, non-motile
34
Group B strep tests
- catalase negative, beta hemolytic, typing kit Group B, Bacitracin (A) resistant, PYR negative, SXT resistant, no growth in 6.5% NaCl, CAMP positive, hippurate-hydrolysis positive
35
Group B hemolysis
- Beta hemolytic | - colony is larger than Group A, but zone is smaller
36
CAMP
determines if organism produces diffusible extracellular CAMP factor protein, which acts synergistically with beta-lysin strain of S. aureus which enhances lysis in SBA when organisms are streaked perpendicular
37
Positive CAMP test
enhanced hemolysis will appear as an arrowhead shaped zone of beta clearing
38
CAMP test
only group B strep are positive
39
Rapid CAMP test
use beta-lysin on strep colony
40
Hippurate hydrolysis
- tests for the presence of hippuricase (which hydrolyzes hippurate to produce glycine) - glycine turns it purple and differentiates Group B from other streptococcus
41
S. dysgalactiae
Group C, beta hemolytic, sometimes type group A
42
Group C and G Strep
- S. dysgalactiae, S. anginosus, S. milleri (alpha hemolytic) - less than 1% of all bacteremias
43
Virulence factors of S. pneumoniae
capsule, IgA protease, pneumolysin O, neuraminidase, hyaluronidase
44
IgA protease
prevents opsonization by IgA at mucous membrane
45
Pneumolysin O
cytolytic for cells, causes the alpha hemolysis, elicits strong cellular response
46
Neuraminidase
degrades surface structure of host cell
47
Transmission of S. pneumoniae
- normal flora of upper respiratory tract | - respiratory secretions and aerosols, when pulmonary-mucosillary action fails, meningitis from sinusitis
48
Clinical infections of S. pneumoniae
lobar pneumoniae, otitis media, sinusitis, meningitis, peritonitis, endocarditis
49
lobar pneumoniae
- number 1 etiological agent of pneumonia - inflammatory response that impairs lung function - caused by viral infection, smoking, bacteremia
50
otitis media
often with bacteremia, number 1 etiological agent after viral infection
51
S. pneumoniae
number 1 etiological cause of adult meningitis
52
Identification of S. pneumo
falcultative, extra cellular, autolytic, gram-positive, mucoid colonies on SBA
53
Tests for S. pneumo
- non-motile, catalase neg., no Lancefield group, CAMP negative, bile esculin negative, no growth in 6.5% salt - optochin sensitive, bile solubility positive
54
Optochin
- lyses pneumococci , other alpha strep are resistant | - disk test
55
Bile solubility test
Determines if organism is lysed by bile salt; determines the amount of autolytic enzyme; S. pneumo is positive, other alpha hemolytic strep are negative
56
Treatment for strep pneumo
Penicillin - erythromycin or chloramphenicol if resistant; vaccine
57
Viridans strep
- normal flora or GU tract, GI tract - alpha hemolysis, fastidious - anginosus, mitis, mutans, salivarius, bovis
58
Viridans infections
- opportunistic, penicillin susceptible | - subacute bacterial endocarditis, tooth decay, meningitis, abscesses, osteomyelitis
59
Group D strep
- S. equinus - endocarditis, UTIs, wound infections - susceptible to penicillin, while enterococcus is resistant - no virulence factors, opportunistic
60
Identification of Group D strep
- facultative, gram-positive cocci, non-motile | - grayish-white colonies and alpha or no hemolysis on SBA
61
Tests for Group D strep
- catalase negative, alpha or non hemolytic, CAMP negative, bile esculin positive, PYR negative, no growth in 6.5% NaCl
62
Bike esculin test
Organisms ability to grow in bile and hydrolyze glycoside esculin; gram-positives are negative except for Group D strep and enterococcus
63
Salt test (6.5% NaCl)
Used to differentiate Group D (no growth) from enterococcus (growth)
64
Enterococcus virulence factors
Antibiotic resistance, adherence to heart valves and renal epithelium
65
Transmission of enterococcus
- E. feacium and E. faecalis are normal GI flora | - UTI from fecal floral contamination, person-to-person, nosocomial, bacteremia
66
Infections of enterococcus
UTIs, bacteremia, endocarditis
67
Identification of enterococcus
Facultative, small grayish-white colonies and non hemolytic on SBA, non-motile, gram-positive cocci
68
Tests for enterococcus
Catalase negative, usually non hemolytic, Group D, CAMP negative, bile esculin positive, PYR negative, growth in 6.5% NaCl
69
Enterococcus resistance
- acquired resistance to beta lactam, amino glycosides, glycoproteins - VRE = vancomycin resistant
70
Beta hemolytic strep
Groups A, B, C, F, G, D, enterococcus
71
Alphas hemolytic strep
Enterococcus, Group D, S. pneumo, Viridans
72
Non hemolytic strep
Group D, enterococcus
73
Abiotrophia and Granulicatella
- strep-like, grow as satellite colonies, nutritionally variant - bacteremia, endocarditis, otitis media - difficult to treat with antibiotics
74
Aerococcus
"Strep-like", opportunistic, bacteremia, endocarditis and UTIs
75
Gamella
De-stain easily, may be in pairs, tetrads, clusters
76
Lactococcus
"Strep-like", UTIs and endocarditis
77
Leuconostoc
Irregular coccoid morphology, bacteremia, UTIs, meningitis, vanco resistant
78
Pediococcus
- tetrads, pairs and clusters - meningitis, bacteremia, abscesses - vanco resistant

Microbiology (26 decks)

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