Lecture 4: Gram positive bacteria -Streptococci Flashcards
1) Classify Streptococci 2) Analyze different groups of Streptococcal species 3) Evaluate different diseases caused by Streptococcal species based on local invasion and exotoxin release 4) Evaluate the different diseases caused by Streptococcal species based on delayed antibody mediated
Identification of Streptococci
- Gram (+) or Gram (-)?
- Strip or cluster?
- Catalase (+) or (-)?
- Gram (+)
- Line up like a strip
- Catalase negative
Streptococcal Classification
Classified based on a combination of tests:
-Hemolysis
Alpha- partial hemolysis
Beta- complete hemolysis
Gamma- no hemolysis
-Antigenic composition (C Carbohydrate)
Lancefield antigens (A through S)
-Biochemical rxns
-Growth characteristics
-Genetic studiesThere are ___ species of Streptococci, only ___ of them are significant human pathogens.
30; 5
Streptococcus pyogenes
(Group ___ ___ hemolytic Streptococci)
-Antigenic components of cell wall
- Lancefield group A antigen
- Beta hemolytic
- Antigenic components of Streptococcal cell wall
(1) C carbohydrate -Lacefield group A
(2) M protein -major virulence factor. inhibits activation of complement and protects the organism from phagocytosis.- B Cells produce antibodies against the M protein
Streptococcus pyogenes
(GAS)
-Enzymes that contribute to pathogenicity
1) Streptolysin O: O stands for oxygen labile
- destroys RBC and WBC
- is antigenic as GAS infection causes antistreptolysin (ASO) to develop
2) Streptolysin S: S stands for oxygen stable
- principle factor for Beta-hemolysis but not antigenic
3) Pyrogenic exotoxin -aka erythrogenic toxin
- causes scarlet fever
- superantigens, cause streptococcal TSS
4) Streptokinase -activates plasminogen to lyse fibrin clots
Streptococcus pyogenes
(GAS)
-Diseases
->Local Invasion/Exotoxin Release
Streptococcal Pharyngitis
-classic strep throat w/red swollen tonsils and pharynx
-throad culture test and RADT (rapid antigen detection test)
Scarlet Fever
-certain GAS sps. produce pyrogenic toxin that produces fever and scarlet red rash
-rash begins on trunk and neck and spreads to extremeties sparin the face
Streptococcal Toxic Shock Syndrome
-like Staph. aureus, GAS can cause toxic shock syndrome
Streptococcus pyogenes
(GAS)
-Diseases
->Local Invasion/Exotoxin Release
->Skin InfectionsSkin Infections
- Folliculitis: infection of hair follicles
- Pyoderma: a pustule on the extremity or face that creaks down after 4-6 days to form a thick crust
- Erysipelas: infection of the dermis, rarely caused by Staphylococcus areus
- Necrotizing Faciitis (flesh eating streptococcus): skin color changes from red to purple to blue and large blisters (bullae) form. Later the skin dies and muscle becomes infected (myositis)
- > also cuased by Staphylococcus, Clostridium sps., gram (-) enterics
Streptococcus pyogenes
(GAS)
-Diseases
->Local Invasion/Exotoxin Release
->TreatmentTREATMENT: high dose penicillin and clindamycin that inhibits bacterial ribosome and shuts down protein synthesis of pyrogenic toxin and M protein
Streptococcus pyogenes
(GAS)
-Diseases
->Delayed Antibody-Mediated Disease
Rheumatic Fever
-Fever, myocarditis, migratory arthritis, rash, etc
-Immune responses against M protein can cross react with heart tissue (molecular mimicry)
-can cause permanent damage to heart valves
TX: prophylactic penicillin therapy req’d for much of patients life
Acute Post-Streptococcal Glomerulonephritis
-antibody mediated inflammatory disease of glomeruli of kidney
-occurs ~1 wk after pharynx or skin infections by nephritogenic strains of beta hemolytic GAS
-Ab-Ag complexex in circulation deposit in kidneys, result in damage due to complement and PMN
-generally does not cause long term kidney damage
Streptococcus agalactiae
(Group \_\_ Streptococci)
-who affected?
-causes what?
-treatment?-Lancefield group B
-Beta hemolytic
-25% of women carry the pathogen and a baby can aquire during delivery
-causes neonatal meningitis, pneumonia, and sepsis
TX: antibiotics against E. coli, Listeria monocytogenes, and Group B Strep. as most neonatal meningitis is caused by these 3
-can infect pregnant women causing bacteremia and sepsis. secondary infection of fetus results in stillbirth or spontaneous abortion in 30% of cases
Viridans Group Streptococci
- includes: - represents \_\_\_% from \_\_\_\_\_\_ - color - \_\_\_\_ hemolytic
- includes: S. mitus, S salivarius, S. mutans, S. anginosus groups
- represents more than 30% of culturable bacteria from dental plaque, gingival crevices, tongue, and saliva
- “Verde” -green, most of viridans streptococci are Alpha hemolytic
Viridans Group Streptococci
-3 main types of infections
1) Dental infections
-some, esp. S.mutans, can bind to teeth and ferment sugar that produces acid and dental carries
2) Endocarditis
-microbes entering the bloodstream implant on the endocardinal surface of the heart, most commonly on a previously damaged heart valve (old rheumatic fever, congenital heart defect, or mitral valve prolapse)
-results in subacute bacterial endocarditis (SBE)
(*S.aureus causes acute endocarditis and group D strep. can cause SBE)
3) Abscesses
-Anginosus sps. group comprising S.intermedius, S. constellatus, and S. anginosus
-often found in abscesses in the brain or abdominal organs
-if S.intermedius group bacteria grows in the blood, then it is suspected that there is an abscess hiding in an organ (CAT scan)
Group D Streptococci
-2 Subgroups
Enterococci
-Enterococcus faecalis & E. faecium
-alpha or gamma hemolytic
-commonly the infecting agents in UTI infections, biliary tract infections, bacteremia, & SBE
-2nd to 3rd most common cause of hospital acquired (nosocomial) infections
-resistant to ampicillin plus aminoglycoside and now are resistant to vancomycin (VRE)
Non-enterococci
-Streptococcus bovis & S. equinus
-grows in 40% bile (but not in 6.5% NaCl
-lives in GI tract and causes similar diseases
-unique association between S. bovis infection and colon cancer
-50% of people with S. bovis bacteremia have a colonic malignancy
Streptococcus pneumoniae
- aka? - Lancefield antigen? - cause of? - appearance - virulence factors
- NO Lancefield antigen
- major cause of bacterial pneumonia and meningitis in adults and otitis media in children
- appear as lancet shaped gram (+) cocci arranged in pairs (diplococci)
- major virulence factor is the polysaccharide capsule. capsule is antigenic
- > Capsule: 91 distinct antigenic types, impedes phagocytosis
- > Pneumolysin: cytotoxin
- > Hydorgen peroxide: hemolysin
- > IgA1 Protease: cleaves IgA1
- > Neuraminidase: cleaves terminal sialic acid exposing glycoconjugates for adhesion
- Adhesins- Teichoic acids, CbpA
Identification of Streptococcus pnuemoniae
-3 ways
(1) Quelung reaction -bacterial smear mixed with antiserum and methylene blue. Capsule swells up providing rapid ID
(2) Optochin sensitivity - S.pneumoniae and S.viridans are alpha-hemolytic, growth of S.pneumoniae is inhibited when placed in a dish with optochin disc, whereas S.viridans is resistant
(3) Lysis by bile acids
