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Respiratory Pathogens I- Streptococcus pyogenes, Streptococcus agalactiae
Respiratory Pathogens I- Streptococcus pyogenes, Streptococcus agalactiae Professor: Dr. Barrett TSOM- Term 4, Unified Exam 1
Terms in this set (94)
What is 'upper respiratory disease'?
Any infectious disease at the level of the vocal cords or above
what conditions are included in 'upper respiratory diseases'?
pharyngitis and nasopharyngitis
dental and oral diseases
infections of the eyes
what is 'lower respiratory disease'?
any infectious disease at the level of the vocal cords or lower
what conditions are included in 'lower respiratory diseases'?
what are the major bacterial agents of upper respiratory disease?
Haemophilus influenza type B and non typable strains
what are the major viral agents of upper respiratory disease?
Respiratory Syncitial Virus
Influenza and Parainfluenza viruses
Coxsackie and Enteroviruses
what are the less frequent bacterial agents that cause upper respiratory disease?
which bacterial agents cause walking pneumonia?
what are the dimorphic fungi that cause upper respiratory infections?
what types of fungal pathogens cause upper respiratory disease?
what type of bacterium is streptococcus pyogenes?
gram positive cocci in chains, pairs, and singles
what are the features of the growth media required by S. pyogenes?
needs enriched media
colonies in one day on BAP (blood agar plates)
nutrient medium with 5% sheep blood
does S. pyogenes lyse RBC?
is beta hemolytic
what atmospheric conditions are favorable for culture of S. pyogenes?
CO2 atmosphere aids growth, modern gas flow incubators
is S. pyogenes aerobic or anaerobic?
is S. pyogenes catalase positive or negative?
what Genus of respiratory pathogen is catalase positive?
what happens when a bacterium is catalase positive?
bacteria added to H2O2, oxygen evolved in a positive test
beta hemolysis around small colonies is typical of whch species of bacteria?
Group A streptococci
what is the catalase activity of Streptococci?
What group does s. pyogenes belong to, based on its cell wall carbohydrate?
what is the most important virulence factor of Streptococci?
M protein is the key antigen to provoke immunity and is also considered the most important virulence factor
What are the most common M types of Streptococci?
M1 and M3
how are M types identified?
by presence of emm gene with a gene probe rather than serologic tests
what are the features of the amino acid sequence of M protein of Streptococci?
1. amino terminus amino acid sequence varies and is the site of anitgenicity.
2. carboxyterminus sequence is common to all M types
what happens if the aminoterminus amino acid sequence of the M protein is varied?
immunity to new type is needed
what are the features of alpha hemolysis on 5% blood agar plates?
green or brown around colony,
defines viridans streptococci
no lysis of RBC
change in Hb color
what are the features of beta hemolysis on 5% blood agar?
lysis of RBC's
clear area around colony as Hb diffuses away
what are the features of gamma hemolysis on 5% blood agar?
what type of hemolysis on 5% blood agar is typical of group A and B streptococci?
are alpha and gamma hemolytic streptococci typeable by the Lancefield method?
not, but they can be medically important
what type of hemolysis is associated with group A streptococci?
What is the habitat for streptococci?
some but not all with Ab to the M protein
plus acutely ill and convalescent persons
what is the mode of transmission of streptococci?
- pharyngitis- aerosols
- skin/soft tissue infection- aerosol and contact
when is streptococcus most transmitted?
winter-spring, especially with crowding, droplet nuclei in dry environment, dry mucosal tissues
what are the three forms of streptococcal infection?
what is the common local streptococcal infection?
what is a common toxic streptococcal infection?
streptococcal toxic shock syndrome
what are the pathogenic features of streptococcal pharyngitis?
- 2-4 day incubation
- rapid onset
- para-tonsillar exudate
-millions of cases per year
what is more common, viral or streptococcal pharyngitis?
what are the pathogenic features of scarlet fever?
- associated with pharyngitis
- temperate bacteriophage carries gene for streptococcal pyogenic Spe exotoxin
- bacteria not in skin
- red skin
- raw strawberry tongue
what are the white spots seen in strep throat?
white flecks in the para-tonsillar are actually colonies of streptococci
what do strep bacteria do in scarlet fever?
Streptococcus pyogenes Group A located in the nasopharynx secretes its erythrogenic toxin which is distributed through the blood to express its activity on the skin.
are bacteria present in the skin in scarlet fever?
what are the pathogenic features of necrotizing fasciitis
- streptococcal gangrene due to 'flesh eating streptococci'
- subcutaneous spread along fascial planes
- severe toxicity
- may progress to septic shock
- 20% fatal
what are the pathogenic features of streptococcal toxic shock syndrome?
- prominent in immunocompromised but also in normal health
- due to streptococcal pyrogenic exotoxin (Spe) present in 10% of isolates
- rapid demise
- 50% fatal due to septic shock and multi-organ failure
What are the purulent local skin diseases caused by S. pyogenes?
what happens in impetigo?
- skin break allows bacterial entry
- vesicular lesion becomes pustular with brown, drying crust
- usually facial
- in children
- poor hygeine
- in summer
what happens in erysipelas caused by S. pyogenes?
more inflammatory skin response with local pain and local node enlargement
what happens in cellulitis caused by S. pyogenes?
subcutaneous tissue invaded, any anatomic site, significant pain, marked inflammation and spread
what are the features of the lesions of erysipelas?
the lesions of erysipelas are red and warm to the touch
- considerable inflammation is present and spreads from the initial infected site
what are the features of cellulitis?
- fever and chills may be present
- more inflammatory state
what are the 2 major types of post-infectious streptococcal disease?
when does post streptococcal rheumatic fever take place?
2 -3 weeks after pharyngitis but not after skin infections, children 5-15 years of age
what are the complications associated with rheumatic fever?
1. myocarditis due to autoimmune cross reaction of certain M proteins with cardiac myosin
2. peri-carditis, endo-carditis, arthralgia, subdermal nodules
what is post-infectious streptococcal glomerulonephritis?
inflammation of the renal tubules due to immune complex deposits of antibody and streptococcal antigen with complement
what causes post-infectious streptococcal glomerulonephritis?
any prior form of Group A disease
- M types 1,2,3,4 most common
What are the virulence factors of S. pyogenes?
1. hyaluronic acid capsule
2. M protein
3. C5a peptidase
5. Streptococcal pyogenic exotoxins (Spe)
7. Streptokinase A and B
8. DNA-ases (A to D), B most important
how does the hyaluronic acid capsule of S pyogenes act as a virulence factor?
hyaluronic acid capsule avoids phagocytes
- humans have hyaluronic acid so no protective antibody
how does M protein of S pyogenes act as a CRITICAL virulence factor?
M protein binds factor H of complement, decays C3b, blocks opsonization and phagocytosis
how does the C5a peptidase of S pyogenes act as a virulence factor?
what are the adhesins that act as virulence factors of S pyogenes and what do they do?
- aid cell binding
how do Spe act as a virulence factors of S. pyogenes?
-4 in number, are superantigens
- bind T cells and macrophages
--> TNFα, IL1, other interleukins are released
--> may lead to septic shock
what are the major streptolysins that act as virulence factors of S. pyogenes?
are streptolysins of S. pyogenes hemolytic?
no hemolysis in vivo but considered as toxins
what does streptolysin S do?
- not antigenic
- stable to oxygen and heat
- beta hemolysis on bood agar plates
what does streptolysin O do?
- oxygen labile
- no hemolysis in aerobic growth
which streptolysin can be detected by an important serologic test?
how do streptokinase A and B act as virulence factors for S. pyogenes?
convert plasminogen to plasmin that digests fibrin clots--> bacteria and toxins free to spread
what do antibodies to DNA-ase B tell about S. pyogenes?
indicate prior infection
What is involved in using microbial culture for laboratory diagnosis of S. pyogenes?
1. throat swab
2. Gram stain
3. inoculate BAP and observe for hemolysis
4. confirmatory gram stain on colony
5. bacitracin disk test
6. catalase test
7. pyrrolidonyl arylamidase test
what are the specs for bacitracin disk test for S. pyogenes?
can be done with original specimen of Streptococci suspected, or on transfer plate--> inhibition of growth near the disk
what happens in a catalase test for S. pyogenes?
add bacteria to hydrogen peroxide and observe for failure of oxygen evolution
what is the difference between a bacitracin disk test done on group C vs group A Streptococci?
no growth around bacitracin disk in Group A streptococci plate
what happens in the PYR test for S. pyogenes?
pyrrolidonyl β naphthylamide on impregnated paper is hydrolyed by streptococci, product is detected with a developing reagent that produces color
what are the serologic tests done in laboratory diagnostics of S. pyogenes?
1. ASTO [anti-streptolysin O test]
2. Anti-DNAase B test
what happens in the ASTO test for S. pyogenes?
commercial source of streptolysin O is added to tubes that contain RBC's, dilutions of patient serum added and observed for inhibition of hemolysis after incubation
how is the Anti-DNAaseB test for S. pyogenes done?
Western Blot test
what is the other non-culture, non serologic laboratory diagnostic test for S. pyogenes?
DNA probe for GAS DNA
what is Group A streptococcal antigen detection test for?
pharyngitis only, not other tissue infections
what happens in Group A streptococcal antigen detection test?
1. throat swab in digest fluid (lyses bacteria), add buffer to neutralize solution
2. antigen solution added to teflon matrix with embedded anti-Group A antibody
3. Diffusion contact of Ag with Ab results in precipitation and color development
4. control with extraneous system
how is a rapid group A Strep test interpreted?
the red line indicates a positive test for the Group A Ag.
the blue line indicates the control system is working satisfactorily
what is immunity to S. pyogenes based on?
antibody to M protein-
M protein can can change by strand invasion or mutation, subsequent pharyngitis again
is there a vaccine for S. pyogenes?
risk of post-streptococcal disease if vaccine contains M Ag
how is S. pyogenes prevented/controlled?
1. avoid intimate contact with ill or those recently recovered
2. Beta lactams (penicillins) still effective and used for treatment and long term prophylaxis of rheumatic fever
what is streptococcus agalactiae?
- Group B streptococcus
- often beta hemolytic and encapsulated
where does the name for S. agalactiae come from?
causes mastitis in cows (no milk)
where is S. agalactiae seen?
1. normal intestinal flora of males and females
2. frequent inhabitant of the female reproductive system-- 10-30% pregnant women
3. Newborns- 60% colonized from positive mothers
what is the virulence factor of S. agalactiae?
the capsular polysaccharide
what is the common pathogenesis of S. agalactiae?
1. puerperal fever of the delivered mother, endometritis, local vaginal abscess, UTI
2. early onset infant. <7 days old, pneumonia, maternal-child vertical transmission
3. late onset infant. 1-3mo old--> infant meningitis, variable source
what is involved in the laboratory diagnosis of S. agalactiae?
1. sputum or CSF to BAP, Gram stain, CSF sediment
2. Beta hemolysis usual, some strains negative
3. negative catalase test
4. positive CAMP test
5. DNA probe available
6. Hippuricase test
What happens in CAMP test?
cross streak of staphylococcus with a Group B streptococcus causes an enhancement of the hemolysis at the juncture
what does Hippuricase test for S. agalactiae look for??
an enzyme that splits Hippuric acid into glycine and benzoate identified by a color developing reagent (ninhydrin) for glycine
what is involved in the prevention and control of S. agalactiae?
1. Screen pregnant women at 35th to 37th week, most sensitive time for positive vaginal result
2. Chemoprophylaxis and treatment with penicillin or other antibiotic if allergic to beta lactams
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