Streptococcus and Enterococcus Flashcards Preview

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Flashcards in Streptococcus and Enterococcus Deck (78):
1

Gram-positive cocci, catalase negative

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

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

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

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- 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

Streptococcaceae

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Hemolysin patterns

determines if bacteria produce extracellular enzymes that lyse RBCs in agar

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complete clearing of the erythrocytes around a bacterial colony

beta hemolysis

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partial clearing of the erythrocytes around a bacterial colony

alpha hemolysis

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gamma hemolysis

no hemolysis or clearing around a bacterial colony

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Lancefield classification

classification of strep bacteria based on carbohydrate antigens

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Strep group that exhibits Beta hemolysis

Group A streptococcus

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Strep that exhibit alpha hemolysis

Strep pneumoniae

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Strep that exhibit gamma or no hemolysis

Group D strep and enterococcus

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Virulence factors of S. pyogenes (Group A)

- Protein F, Protein M
- DNase, hyaluronidase, streptokinase, Streptolysin O, Streptolysin S
- erythrogenic toxins, capsule

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mediates epithelial cell attachment

Protein F

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- in the cell wall, blocks opsonization
- helps avoid phagocytosis, essential for virulence

Protein M

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- causes beta hemolysis
- inactivated by oxidation (elicits ASO production)

Streptolysin O

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- causes beta hemolysis
- not inactivated by oxidation, leucocidin activity

Streptolysin S

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Erythrogenic toxins produced by S. pyogenes

- 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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Transmission of S. pyogenes

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

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Clinical infections associated with S. pyogenes

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

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Complications with Strep. pyogenes (Group A)

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

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

Streptococcal toxic shock syndrome

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- 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

Post-streptococcal acute rheumatic fever

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- 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

Post-streptococcal acute glomerular nephritis

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Identification of S. pyogenes (Group 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

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

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Other S. pyogenes tests

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

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Virulence factors of S. agalactiae (Group B) strep

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

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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

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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)

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Endometritis and endocarditis

- caused by Group B strep
- to mothers after childbirth or abortion

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S. agalactiae (Group B) infections

- immunodeficiency in elderly people
- treated with ampicillin

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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

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Identification of Group B strep

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

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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

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Group B hemolysis

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

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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

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Positive CAMP test

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

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CAMP test

only group B strep are positive

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Rapid CAMP test

use beta-lysin on strep colony

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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

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S. dysgalactiae

Group C, beta hemolytic, sometimes type group A

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Group C and G Strep

- S. dysgalactiae, S. anginosus, S. milleri (alpha hemolytic)
- less than 1% of all bacteremias

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Virulence factors of S. pneumoniae

capsule, IgA protease, pneumolysin O, neuraminidase, hyaluronidase

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IgA protease

prevents opsonization by IgA at mucous membrane

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Pneumolysin O

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

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Neuraminidase

degrades surface structure of host cell

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Transmission of S. pneumoniae

- normal flora of upper respiratory tract
- respiratory secretions and aerosols, when pulmonary-mucosillary action fails, meningitis from sinusitis

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Clinical infections of S. pneumoniae

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

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lobar pneumoniae

- number 1 etiological agent of pneumonia
- inflammatory response that impairs lung function
- caused by viral infection, smoking, bacteremia

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otitis media

often with bacteremia, number 1 etiological agent after viral infection

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S. pneumoniae

number 1 etiological cause of adult meningitis

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Identification of S. pneumo

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

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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

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Optochin

- lyses pneumococci , other alpha strep are resistant
- disk test

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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

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Treatment for strep pneumo

Penicillin - erythromycin or chloramphenicol if resistant; vaccine

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Viridans strep

- normal flora or GU tract, GI tract
- alpha hemolysis, fastidious
- anginosus, mitis, mutans, salivarius, bovis

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Viridans infections

- opportunistic, penicillin susceptible
- subacute bacterial endocarditis, tooth decay, meningitis, abscesses, osteomyelitis

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Group D strep

- S. equinus
- endocarditis, UTIs, wound infections
- susceptible to penicillin, while enterococcus is resistant
- no virulence factors, opportunistic

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Identification of Group D strep

- facultative, gram-positive cocci, non-motile
- grayish-white colonies and alpha or no hemolysis on SBA

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Tests for Group D strep

- catalase negative, alpha or non hemolytic, CAMP negative, bile esculin positive, PYR negative, no growth in 6.5% NaCl

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Bike esculin test

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

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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

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Transmission of enterococcus

- E. feacium and E. faecalis are normal GI flora
- UTI from fecal floral contamination, person-to-person, nosocomial, bacteremia

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Infections of enterococcus

UTIs, bacteremia, endocarditis

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Identification of enterococcus

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

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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

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Beta hemolytic strep

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

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Alphas hemolytic strep

Enterococcus, Group D, S. pneumo, Viridans

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Non hemolytic strep

Group D, enterococcus

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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

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Lactococcus

"Strep-like", UTIs and endocarditis

77

Leuconostoc

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

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Pediococcus

- tetrads, pairs and clusters
- meningitis, bacteremia, abscesses
- vanco resistant