Streptococcus lecture 10 Flashcards
Infectious disease is due to…
agents/toxins, multiplication, and host responses
Three principles one can contract infectious disease…
inoculum size, host defense, toxic agents.
Bacterial classifications
Shape: cocci, curved, spiral, bacilli (rod)
Gram Stain: Positive and negative
colony morphology
spore formation
serotyping
biochemical and genetic characteristics
growth (atmosphere): obligate aerobe, microaerophile, obligate anaerobe, facultative anaerobe, capnophile
obligate aerobe
requires oxygen
microaerophile
reduced oxygen
obligate anaerobe
no oxygen
facultative anaerobe
anaerobic or aerobic
capnophile
requires increased CO2
Streptococci
Heterogeneous group of bacteria, form a significant portion of the indigenous microflora of the oropharynx
causing many diseases in humans: strep throat, meningitis, pneumonia, bacteremia, brain abscess, endocarditis, and gangrene
the genus is classified on the basis of colony morphology hemolysis, biochemical reactions, and serologic specificity
General characteristics of streptococci
gram +
cocci arranged in pairs or chains
non motile
facultative anaerobic or capnophilic
Catalase negative
nutritional requirement: complex, need blood or serum enrich media for isolation.
Streptococcal species classification
Serological: Lancefield classification: Antigenic characteristics of carbohydrate (A, B, C, D, E through S.)
Biochemical and genetic: Physiological properties
Hemolytic patterns alpha hemolytics, Beta hemolytic, and gamma hemolytic
alpha hemolytic
partial hemolysis
beta hemolytic
complete hemolysis
gamma hemolytic
no hemolysis
Group of streptococci
Group A or streptococcus pygoenes
Group B or streptococcus agalactia
Group C and G streptococci
Group D streptococci (enterococci)
Viridans streptococci
streptococcus pneumoniae
Group A or streptococcal pyogenes
Gram + with cocci in chain
facultative anaerobe
capsule (hyaluronic acid)
beta hemolytic on blood agar
M proteins (80 Types)
F protein binds to fibronectin (helps establish infection)
Capsule (GAS)
nonimmunogeneic and antiphagocytic
M proteins (GAS)
Inhibits opsonization by interfering binding of C3b and degrades C3b via factor H; binding to Fc of antibodies; immunogenic
C5a peptidase (GAS)
Antichemotactic and reduces inflammation mediated by C5a
DNase (Gas)
Aids in bacterial spread
Four immunologically distinct forms (A, B, C, D)
AntiDNAS B important marker of cutaneous group A streptococcal infections, particularly useful for those who do not failed ASO test
Depolymerizes cell free DNA in pus (reduction of viscosity); contribute to spread from local site
Streptolysin O and S (gas)
lyse blood cells and plates, stimulate release of lysosomal enzymes
O: lyses leukocytes platelets, and erythrocytes; antigenically related to oxygen labile toxins produced by other gram positive bacteria such as S. Pneumonia, clostridium tetani, bacillus cereus and listeria monocytogenes; immunogenic, indicating a recent GAS infection (ASO)
S: the s indicated serum stable. Lyses leukocytes, platelets, and erythrocytes; stimulates release of lysosomal enzymes; Beta hemolysis; nonimmunogenic
Hyaluronidase (gas)
promotes tissue destruction and bacterial spread
streptokinase (GAS)
promotes bacterial spread into tissue by breaking down blood clots
catalyzes activation of plasmin to lyse blood clots
Pyrogenic/erythrogenic exotoxins (gas)
some act as super antigens
Suppurative streptococcal disease (bacterial colonization)
pharyngitis
scarlet fever
skin infections: Impetigo (streptococcal pyoderma): purulent with crusting
cellulitis (#1 causative agent) GAS cellulitis infects wounds (burns, trauma, IV drug abuser injection site)
Erysipelas: acute infection of the skin. Mostly of the face “slapped cheek” rash
Suppurative streptococcal disease
pharyngitis: “strep throat” exudates on tonsils (children 5-15 years)
scarlet fever: complication of strep pharyngitis that occurs when the infection strain is lysogenized by a bacteriophage that produces a pyrogenic exotoxin. Within 1-2 days, red maculopapular “sand paper” rash on trunk and then spreads to extremities. Intense at skin folds white and red “strawberry tongue”. The rash disappears over 5-7 days and followed by desquamation of the superficial skin layer
Impetigo (streptococcal pyoderma): purulent with crusting
colonization is due to direct contact with an infected person or fomites. Entry of organism follwed by pathology development. Regional lymph node enlarged, but lack systemic signs.
primarily seen in young children (2-5 yr.) or poor personal hygiene
Erysipelas
localized pain, inflammation, lymph node enlargement, system sign (chills, fever and leukocytosis)
affect all age group fiery red, advancing erythema. Historically on face but now more common on the legs.
Necrotizing faciitis (suppurative streptoccoccal disease)
“flesh eating” rapidly spreading gangrene of skin and fascia
stars with trivial skin infection but is rapidly fatal (due to multi-organ failure)
Nonsuppurative streptococcal disease-AGN (GAS)
no group A streptoccus present (autoimmune)
AGN (acute glomerular nephritis)
acute inflammation of the renal glomeruli with edema, hypertension, hematuria and proteinura
post pharyngitis or post skin infection (after infection resolves)
symptoms: facial edema, blood in urine (smoky urine)
AGN: acute inflammation of renal glomeruli (GAS)
occurs most commonly in children
nephritogenic strain
damage due to immune complex deposition on the glomerular basement membrane.
Acute rheumatic fever (GAS)
pancarditis (endo, peri, and myocarditis)
no group A streptococcus present
post pharyngitis only
due to cross reactivty of anti M protein antibody with human cardiac tissue
symptoms: migratory arthritis, subcutaneous nodules, carditis and erythema marginatum
may proceed to rheumatic fever
Source of transmission: GAS
normal flora of skin and oropharynx
cause infection upon penetration of tissue
transmission: person to person
Diagnosis: GAS
microscopy
antigen detection: throat swabs
antibody detection: ASO test in rheumatic fever
culture: blood agar or specialized selective agar
TX: very sensitive to penicillin. Oxacillin or vancomycin (in mixed culture) Sensitive to bacitracin
Group B streptococcus (GBS) S agalactiae
Gram positive
cocci in pair
capsule
CAMP test positive
Beta hemolytic (1-2% non hemolytic)
threat to infants infected perinatally
also responsible for post partum endometritis (especially following C section)
Source and transmission: GBS
normal flora of GI tract and vagina
vertical transmission: either at birth or via ascension in utero
Virulence factors: GBS
capsule: resist phagocytosis
Sialic acid: capsular component, inhibit alternate pathway of complement
Group B streptococcal diseases
early onset neonatal disease begins with 7 days of birth
acquired in utero or at delivery. Most common in premature infants. High mortality rate. Symptoms: Bacteremia, pneumonia, meningitis.
Late onset neonatal disease begins 1 week to 3 months after birth.
Acquired postpartum. Low mortality rate (<20%) Symptoms: bacteremia, meningitis
Postpartum sepsis (GBS)
usually acquired via wound inflected during parturition
SX: post partum endometriosis
fever, chills
wound infection
possible UTI
CAMP test GBS
CAMP factor produced by GBS that enhances beta hemolysis of S. Aureus
TX of GBS
penicillin G alone or in combination with an aminoglycosides
passive immunization in serious caes
Streptococcus pneumoniae
gram positive
cocci in pair or short chain
capsule= Most important
CAMP test negative
bile solubility- positive
Alpha hemolytic (aerobically)
beta hemolytic (anaerobically)
genome diversity: 20% of DNA sequences different, still the same species
Catalase: negative: grow best in 5% CO2. Requires a source of catalase (blood) to grown on agar. Chronic granulomatous disease resistance to SP
Virulence factors of streptococcus pneumoniae
capsules: resist phagocytosis; >90 serotypes identified, the major protective antigen
robust biofilm formation
IgA proteases cleaves IgA into FAB and Fc fragments
adhesins: mediates attachment of S. Pneumonia to epithelial cell lysis
pneumolysis: destroys the ciliated epithelial cell
Streptococcus pneumoniae infections
lobar pneumonia (#1 causative organism in adults and in sickel cell disease)
meningitis (1# causative agent in adult meningitis)
Sinusitis (#1 causative organism)
Otitis media (1# causative organism)
Diagnosis: Streptococcus Pneumoniae
Microscopic examination: Gram stain
Quellung reaction: Polyvalent anticapsular antibodies are mixed with the bacteria: increase in refractive mass around the bacteria
bile sensitive
optochin sensitive
TX and prevetion of streptoccus pneumoniae
penicillin
vancomycin combined with ceftriaxone in penicillin allergy
two vaccines 13 and 23 valent polysaccharide vaccine
