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Microbiology > Streptococcus and Enterococcus > Flashcards

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
Q

S. pyogenes (Group A) ID tests

A

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

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26
Q

Other S. pyogenes tests

A

commercial particle agglutination tests, immunoassays, nucleic acid probes (PCR and DNA probes)

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27
Q

Virulence factors of S. agalactiae (Group B) strep

A

capsule, sialic acid for inhibiting complement, hemolysin, CAMP factor, DNases, hyaluronidase, protease

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28
Q

Transmission of S. agalactiae (Group B) strep

A
  • normal GU flora, sometimes respiratory

- vertical transmission at birth or in utero, nosocomial (meningitis), in unpasteurized bovine milk

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29
Q

Invasive disease in newborns

A
  • 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)
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30
Q

Endometritis and endocarditis

A
  • caused by Group B strep

- to mothers after childbirth or abortion

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31
Q

S. agalactiae (Group B) infections

A
  • immunodeficiency in elderly people

- treated with ampicillin

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32
Q

Detecting Group B strep before vertical transmission

A
  • vaginal and rectal material between 35-37 of pregnancy
  • inoculate to select broth and culture on SBA
  • can use nucleic acid tests
33
Q

Identification of Group B strep

A

facultative, extracellular, gram-positive, grayish-white colonies on SBA, non-motile

34
Q

Group B strep tests

A
  • 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
Q

Group B hemolysis

A
  • Beta hemolytic

- colony is larger than Group A, but zone is smaller

36
Q

CAMP

A

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
Q

Positive CAMP test

A

enhanced hemolysis will appear as an arrowhead shaped zone of beta clearing

38
Q

CAMP test

A

only group B strep are positive

39
Q

Rapid CAMP test

A

use beta-lysin on strep colony

40
Q

Hippurate hydrolysis

A
  • tests for the presence of hippuricase (which hydrolyzes hippurate to produce glycine)
  • glycine turns it purple and differentiates Group B from other streptococcus
41
Q

S. dysgalactiae

A

Group C, beta hemolytic, sometimes type group A

42
Q

Group C and G Strep

A
  • S. dysgalactiae, S. anginosus, S. milleri (alpha hemolytic)
  • less than 1% of all bacteremias
43
Q

Virulence factors of S. pneumoniae

A

capsule, IgA protease, pneumolysin O, neuraminidase, hyaluronidase

44
Q

IgA protease

A

prevents opsonization by IgA at mucous membrane

45
Q

Pneumolysin O

A

cytolytic for cells, causes the alpha hemolysis, elicits strong cellular response

46
Q

Neuraminidase

A

degrades surface structure of host cell

47
Q

Transmission of S. pneumoniae

A
  • normal flora of upper respiratory tract

- respiratory secretions and aerosols, when pulmonary-mucosillary action fails, meningitis from sinusitis

48
Q

Clinical infections of S. pneumoniae

A

lobar pneumoniae, otitis media, sinusitis, meningitis, peritonitis, endocarditis

49
Q

lobar pneumoniae

A
  • number 1 etiological agent of pneumonia
  • inflammatory response that impairs lung function
  • caused by viral infection, smoking, bacteremia
50
Q

otitis media

A

often with bacteremia, number 1 etiological agent after viral infection

51
Q

S. pneumoniae

A

number 1 etiological cause of adult meningitis

52
Q

Identification of S. pneumo

A

falcultative, extra cellular, autolytic, gram-positive, mucoid colonies on SBA

53
Q

Tests for S. pneumo

A
  • non-motile, catalase neg., no Lancefield group, CAMP negative, bile esculin negative, no growth in 6.5% salt
  • optochin sensitive, bile solubility positive
54
Q

Optochin

A
  • lyses pneumococci , other alpha strep are resistant

- disk test

55
Q

Bile solubility test

A

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
Q

Treatment for strep pneumo

A

Penicillin - erythromycin or chloramphenicol if resistant; vaccine

57
Q

Viridans strep

A
  • normal flora or GU tract, GI tract
  • alpha hemolysis, fastidious
  • anginosus, mitis, mutans, salivarius, bovis
58
Q

Viridans infections

A
  • opportunistic, penicillin susceptible

- subacute bacterial endocarditis, tooth decay, meningitis, abscesses, osteomyelitis

59
Q

Group D strep

A
  • S. equinus
  • endocarditis, UTIs, wound infections
  • susceptible to penicillin, while enterococcus is resistant
  • no virulence factors, opportunistic
60
Q

Identification of Group D strep

A
  • facultative, gram-positive cocci, non-motile

- grayish-white colonies and alpha or no hemolysis on SBA

61
Q

Tests for Group D strep

A
  • catalase negative, alpha or non hemolytic, CAMP negative, bile esculin positive, PYR negative, no growth in 6.5% NaCl
62
Q

Bike esculin test

A

Organisms ability to grow in bile and hydrolyze glycoside esculin; gram-positives are negative except for Group D strep and enterococcus

63
Q

Salt test (6.5% NaCl)

A

Used to differentiate Group D (no growth) from enterococcus (growth)

64
Q

Enterococcus virulence factors

A

Antibiotic resistance, adherence to heart valves and renal epithelium

65
Q

Transmission of enterococcus

A
  • E. feacium and E. faecalis are normal GI flora

- UTI from fecal floral contamination, person-to-person, nosocomial, bacteremia

66
Q

Infections of enterococcus

A

UTIs, bacteremia, endocarditis

67
Q

Identification of enterococcus

A

Facultative, small grayish-white colonies and non hemolytic on SBA, non-motile, gram-positive cocci

68
Q

Tests for enterococcus

A

Catalase negative, usually non hemolytic, Group D, CAMP negative, bile esculin positive, PYR negative, growth in 6.5% NaCl

69
Q

Enterococcus resistance

A
  • acquired resistance to beta lactam, amino glycosides, glycoproteins
  • VRE = vancomycin resistant
70
Q

Beta hemolytic strep

A

Groups A, B, C, F, G, D, enterococcus

71
Q

Alphas hemolytic strep

A

Enterococcus, Group D, S. pneumo, Viridans

72
Q

Non hemolytic strep

A

Group D, enterococcus

73
Q

Abiotrophia and Granulicatella

A
  • strep-like, grow as satellite colonies, nutritionally variant
  • bacteremia, endocarditis, otitis media
  • difficult to treat with antibiotics
74
Q

Aerococcus

A

“Strep-like”, opportunistic, bacteremia, endocarditis and UTIs

75
Q

Gamella

A

De-stain easily, may be in pairs, tetrads, clusters

76
Q

Lactococcus

A

“Strep-like”, UTIs and endocarditis

77
Q

Leuconostoc

A

Irregular coccoid morphology, bacteremia, UTIs, meningitis, vanco resistant

78
Q

Pediococcus

A
  • tetrads, pairs and clusters
  • meningitis, bacteremia, abscesses
  • vanco resistant

Microbiology (26 decks)

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