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How are streptococcus classified?
- by serotype (cell wall carbohydrates)
- by hemolytic pattern
- by biochemical properties
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Name some basic characteristics of streptococcus bacteria (gram characterictic, shape, cultures, oxygen requirement, motility)
- Gm+
- oval shaped
- grow in pairs or chains
- facultative anaerobes
- non-motile
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Name the three (3) groups that streptococcus bacteria can be classified into
- pyogenic steptococci
- pneumococci
- viridans and nonhemolytic streptococci
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This group of streptococcus contains cell-wall antigens(group A through T) and causes purulent infections in humans
pyogenic streptococci
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This group of streptococcus contains a polysaccharide capsule and consists of only one species.
pneumococci
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This group of streptococcus is alpha-hemolytic, lacks group of carbohydrate antigens and capsular antigens, is a member of normal oral flora, and is almost never invasive.
Viridans and non-hemolytic streptococcus
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Streptococcus pyogenes (Group A strep) can cause
a variety of acute infections
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Streptococcus agalactiae (group B strep) can cause
neonatal sepsis and meningeal infection
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Streptococcus pneumoniae (pneumococci) can cause
bacterial pneumonia and purulent meningitis
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A high concentration of what sugar inhibits streptococcus growth?
Glucose
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Steptococcus colonies can be characterized by
small white colonies with large zones of Beta hemolysis
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Which group-specific and type-specific antigens are found in the cell walls of streptococcus?
- Lancefield group A antigen
- M protein: associated with virulent strains
- C-terminus: highly conserved among group A strep
- N-terminus: above surface, responsible for antigenic variability among serotypes
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Describe the significance of the hyaluronic acid capsule
encapsulated strains are more likely to be responsible for severe systemic infections
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What factors contribute to the success of a bacterial infection?
- Avoiding phagocytosis
- Adhere to Cell surface
- Invade Cells
- Produce toxins and enzymes
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What immunity and pathogenic mechanisms does streptococcus exhibit?
- To avoid phagocytosis, M proteins binds to a host serum factor H necessary for immune pathway regulation and phagocytosis. Also can form capsules
- M protein interacts with cutaneous tissues in order to adhere to cell surface
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Name four types toxins or enzymes produced by streptococcus bacteria
- streptococcal pyrogenic exotoxins (SPE)
- Streptolysin S
- Streptolysin O
- Streptokinase (A&B)
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Describe qualities of streptococcal pyrogenic exotoxins
- heat-liable toxins
- act as superantigens
- responsible for many clinical manifestations (necrotizing faciitis, strep TSS, scarlet fever)
- only produced in strains that have been lysogenized by a bacteria containing toxin gene
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Describe qualities of streptolysin S
- Oxygen stable
- non immunogenic
- cell-bound hemolysin
- causes death of phagocytic cells by stimulating release of cell contents
- Responsible for Beta hemolysis on BAP media
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Describe qualities of streptolysin O
- oxygen liable hemolysin
- antibodies readily formed against streptolysin O
- Can cause beta hemolysis under anaerobic conditions
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Describe qualities of streptokinase (A & B)
- can lyse blood clots and fibrin deposits
- facilitates rapid spread of S. pyogenes in tissues
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S. Pyogenes Suppurative Clinical Diseases
Describe characteristics of pharyngitis( strep throat)
- develops 2-4 days after exposure
- symptoms include sore throat, fever, malaise, headache
- spread through contact with secretions or large droplets
- may be followed by rheumatic fever
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S. Pyogene Suppurative Clinical Diseases
Describe the characteristics of Scarlet fever
- results from complication of streptococcal pharyngitis
- occurs when infecting strain is lysogenized by bacteriophage that mediates production of pyrogenic exotoxin
- yellowish-white coating covers the tongue, then is shed revealing red, raw surface
- after pharyngitis symptoms diffuse, rash on upper chest and extremeties appears
- rash is followed by desquamation
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S. Pyogene Suppurative Clinical Diseases:
Describe the characteristics of pyoderma (impetigo)
- affects exposed areas of the skin
- begins after contact with infected skin or fomite; introduced through a break in the skin
- pustules develop, rupture and then crust over
- can spread through skin by scratching
- primarily seen during moist, warm summer months in young children
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S. Pyogene Suppurative Clinical Diseases:
Describe the characteristics of Erysipelas
- acute skin infection
- localized pain, inflammation, lymph node enlargement and systemic symptoms
- infected skin becomes raised
- usually preceded by infections of the respiratory tract or skin with S. Pyogenes.
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S. Pyogene Suppurative Clinical Disease
Describe the characteristics of Cellulitis
- involves skin and deeper subcutaneous tissue
- distinction between infected and non-infected skin not clear
- local inflammation and systemic symptoms
- can be treated with antibiotics
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S. Pyogenes Suppurative Clinical Disease
Describe the characteristics of Necrotizing Fasciitis (flesh easting disease)
- streptococcal gangrene
- infection deep in the subcutaneous layer that spreads
- extensive destruction of muscle and fat tissue
- introduced through break in skin
- begins as cellulitis, and then bullae form and then gangrene and systemic symptoms develop
- tissue destruction is associated with obstructed blood flow
- treated with surgical removal of infected tissue
- toxicity, multi-organ failure and death may result
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S. Pyogene Suppurative Clinical Diseases
Describe the characteristics of streptococcal TSS
- soft tissue imflammation at the infection site
- pain, nonspecific symptoms: fever, chills, malaise, nausea, vomiting, and diarrhea
- progresses to shock and organ failure
- infection is bacteremic and death rate is higher (~30%) than that in staphylococcal TSS
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S. Pyogenes Suppurative Clinical Disease
Describe the characteristic Bacteremia
- rarely seen with pharyngitis, pyoderma and erysipelas
- seen mostly with TSS and necrotizing fasciitis.
- Mortality ~40%
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S. Pyogenes Nonsuppurative clinical disease
Describe the characteristics of Rheumatic Fever
- complication of pharyngitis
- inflammatory disease involving heart, joints, blood vessel and subcutaneous tissues
- causes vigorous antibody response
- high fever, swollen joints, damage to heart valves
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S. Pyogenes Nonsuppurative clinical disease
Describe the characteristics of acute glomerulonephitis
- kidney infection
- children usually show full recovery
- adults progress to loss of kidney function and death
- can follow with respiratory or cutaneous strep infection
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How can streptococcus pyogenes be diagnosed on a microscopic level?
- gram stains of the affected tissue
- is not apart of normal flora
- is apart of normal respiratory flora
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How can antigens of streptococcus pyogenes be identified?
- antibodies react with group-specific carbohydrate in cell wall
- sensitivity to antigens is low
- negative results must be confirmed by throat culture
- nut used for cutaneous and non-suppurative disease
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How can cultures be used in the identification of streptococcus pyogenes?
- tonsil culture
- from impetigo, sample comes from purulent material under crusted top of lesion
- tissue and blood cultures can be used for necrotizing fasciitis
- antibiotics can be added to suppress normal flora, but s. pyogenes growth takes longer under these conditions
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Name the only species of streptococcus that carries the B antigen
streptococcus agalactiae
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Which streptococcus causes childbed fever, septicemia, pneumonia, and meningitis in new borns?
streptococcus agalactiae
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Characterize streptococcus agalactiea colonies
- colonies are large with narrow zone of Beta Hemolysis
- some strains are non-hemolytic
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Describe the pathogenesis and immunity characteristics of streptococcus agalactiea
- Makes use of polysaccharide capsule that interferes with phagocytosis until patient develops protective, type-specific antibodies.
- Some types have sialic acid on capsular polysaccharide, which inhibits activation of the immune system pathway necessary for phagocytosis.
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Where does S. agalactiea colonize?
In the GI tract and genitourinary tract. There is some vaginal carriage
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What is the risk for of S. agalactiea colonization in pregnant women?
- 60% of infants born to colonized mothers become colonized and the risk of premature birth increases
- Pregnant women are at a greater risk of disease than men and non pregnant women
- Commonly manifests as UTI and wound infections in pregnant women
- Manifests as skin and soft-tissue infections, bacteremia, UTI and pneumonia in men and nonpregnant women.
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S. agalactiea: early-onset neonatal disease
- acquired in utero or at birth and develops in the first week of life
- manifests as bacteremia, pneumonia and meningitis
- mortality is less than 5%
- those who survive meningitis have neurological conditions (blindness, deafness, mental retardation)
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S. agalactiea: late-onset neonatal disease
- acquired from an exogenous sources (mother or another infant); develops after 1wk-3months of age
- manifests as bacteremia with meningitis
- Mortality is ~3% but neurologic complications are common
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Who do S. agalactaie infections typically affect men and non-pregnant women?
- generally occurs in older patients with underlying conditions
- manifests as bacteremia, pneumonia, bone and joint infections, skin and soft tissue infections
- higher risk of mortality
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How can one distinguish a sample of Strep agalactiea in a laboratory diagnosis?
- Group B strep cultures readily grow in enriched media and large colonies generally appear after 24 hours.
- S. Agalactiea is catalase negative and cAMP positive (CAMP factor enlarges zone of beta hemolysis forms by Staph Aureus.
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How can strep agalactiea be treated?
- witth penicillin (intravenous for pregnant women)
- requires 10x more penicillin than strep pyogenes
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Is a heterogenous group of alpha hemolytic and non hemolytic strep. (can have beta hemolytic strains though)
Viridans streptococci
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Species of streptococci that generally colonize in the respiratory, GI tract and genitourinary tract and that lack specific antigens, toxins and virulence that other groups have
Viridans streptococci
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Viridians streptococci growth on media can be described as ________ _______
nutritionally fastidious
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Describe physiological and structural features of strep pneumoniae
- encapsulated
- colonies undergo autolysis with aging (causes a dimple in the center of the colony)
- can be beta-hemolytic if grown anaerobically and alpha hemolytic if grown aerobically.
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If grown aerobically on a BAP, strep pneumoniae is ___-hemolytic due to the production of ____ that degrades hemoglobin.
alpha; pneumolysin
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this species of strep colonizes in the respiratory tract, then spreads to the lungs, sinuses and middle ear. Can be transported in blood to distal sites (brain)
strep pneumoniae
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this species of strep produces secretory IgG (sIgA) protease and pneumolysin to counteract envelopment
strep pneumoniae
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Describe characteristics of enterococcus
- Gm+ cocci
- grows aerobically and anaerobically
- had complex nutritional needs.
- forms large colonies that can either be non-hemolytic or alpha-hemolytic
- can grow in the presence of high concentrations of NaCl and bile salts
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name clinical diseases associated with enterococcus
- Nosicomal infections (usually involving urinary tract, peritoneum and heart tissue)
- can result in endocarditis
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Laboratory diagnosis of enterococcus
- grows on nonselective media (BAP and chocolate agar)
- is resistant to optochin
- does not dissolve when exposed to salts (s. pneumoniae does)
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