23a: streptococci - jonathan Flashcards
What is the gram status, O2 status, and Catalase status of Streptococci?
Gram + found in chains
Faculative anaerobe and aerotolerant
Catalase negative
What are the groups of streptococci and what is the basis of distinguishing them?
A, B, C, D, and nontypable
Carbohydrate antigens
A and B are distinguished from other groups based on their patterns of hemolysis
On growth mediums containing intact RBCs, explain the difference between…
Gamma hemolysis
Alpha hemolysis
Beta hemolysis
1) no hemolysis
2) a cloudy green zone (RBCs are intact but the heme is green)
3) a clear zone with lysed RBCs
Note: depending on the depth of hemolysis in the petri dish, the clear zone may not look completely clear
Describe the Lancefield classification of streptococci.
Carbos extracted from the bacteria are subjected to precipitation tests with antisera. This places the beta-hemolytic groups into A through O.
Note: group D is not beta-hemolytic
How are Group A streptococci further subdivided?
Analysis of their M proteins divides Group A into 90 types
There is a schema of Streptococcus pyogenes on page S-2
There is a diagram for classification of Streptococcus pyogenes on page S-2.
What are the three tiers of tests for Streptococcus classification?
1) Alpha, Beta, Gamma
2) of the Betas, Test for C carbohydrates A through O
3) of the A carbohydrates, Test for M proteins 1 through 90
Epidemiology of Streptococcus…
On what tissues are they found?
What is the mode of transmission?
Skin, oropharynx, and nose (nose-type is most infectious)
Respiratory droplets
General pathogenesis of Streptococcus…
What are the lysogenic compounds?
What are the antiphagocytic compounds?
What are the proteases?
1) Streptolysins O and S, Streptokinase, DNAase
2) Hyaluronic acid capsule and M proteins
3) SpeA, SpeB, SpeC
What kind of hemolysis do Streptolysin O and Streptolysis S cause (alpha, beta, or gamma)?
Beta
What are the differences between Streptolysin O and Streptolysin S in terms of oxygen stability and antigenicity.
O: oxygen labile and antigenic to antibody ASO
S: oxygen stable and not antigenic
Are acapsular streptococci pathogenic?
No
What are M proteins in streptococci?
M-proteins extend from the bacterial membrane through the capsule and into the extracellular membrane
They aid in adhesion and antiphagocytosis
They are antigenic and are a possible target for the immune system
What are SpeA, SpeB, and SpeC?
What are the two illnesses that they cause?
Protease pyrogenic exotoxins
SCARLET FEVER (origin oropharyngeal streptococci)
STREPTOCOCCAL TOXIC SHOCK SYNDROME
What are invasive syndromes associated with streptococcus (6)?
1) puerperal fever
2) Acute pharyngitis and tonsilitis
3) Impetigo
4) Erysipelas
5) Necrotizing fascitis
6) a bunch of other illnesses covered next year
What is Puerperal Fever?
Infection of the uterus after childbirth
Once was fatal, now is uncommon in developed countries
What is Acute Pharyngitis and Tonsilitis?
Why must this be Dx and Tx (ie, what is the progression of the disease if untreated)?
Strepthroat
Dx and Tx with penicillin
All strep strains must be treated because some strep strains can progress to RHEUMATIC FEVER
What is impetigo?
Minor superficial skin infection of streptococcus
What is Erysipelas?
Severe cellulitis of the dermis and underlying tissues by streptococcus
What is necrotizing fascitis?
“Flesh-eating bacteria disease”
Invasive S. pyogenes
Rapid infection
Surgery may be required
What are two important sequelae of S. pyogenes infections?
Rheumatic fever
Acute glomerulonephritis
Explain the pathogenesis of Rheumatic Fever.
On what tissue was the initial infection?
How long after initial infection?
What protein is involved?
What tissues are involved?
Throat only. 2-3 weeks after strep infection M-PROTEINS activate antigens that attack SKIN, JOINTS, AND HEART Skin and joint problems subside. Heart problems may be ongoing
Why is treatment of ALL streptococcus infection important?
We haven’t nailed down which M-protein varieties produce Rheumatic fever, therefore we should treat all streptococcus infections with penicillin
Explain the pathogenesis of Acute Glomerulonephritis.
On what tissue was the initial infection?
How long after initial infection?
What proteins from what subgroup of streptococci?
What are symptoms?
What is mechanism?
throat or skin. Skin is more common. 1 week after infection select M-proteins of Group A beta-hemolytic streptococci hematuria and edema deposition of immune complexes
Explain the differences between
Glomerulonephritis and Rheumatic Fever…
Major symptoms?
Glomerulonephritis: edema, hypertension, hematuria
Rheumatic fever: carditis, polyarthritis, subcutaneous nodules, skin lesions (erythema marginatum)
Explain the differences between Glomerulonephritis and Rheumatic Fever... Major symptoms? M-protein serotypes? Site of infection? Pathogenic mechanism?
1) G: edema, hypertension, hematuria. R: carditis, polyarthritis, subcutaneous nodules, skin lesions (erythema marginatum)
2) G: only a few types of M-protein. R: selected types of M-proteins but infection varies markedly by type
3) G: throat or skin, SKIN is more common. R: ONLY THROAT
4) G: deposition of immune complexes. R: antigenic mimicry between S. pyogenes and host tissue (heart, skin, and joints)
Are Streptococcus pyogenes found at site of damage in Glomerulonephritis or Rheumatic Fever?
Nope. Infection is immunologically mediated either with immune complexes or cross reactivity of antigen vs host mimicry
What are Dx techniques do LABORATORIES use for Streptococcus?
1) G + chains
2) beta-hemolysis on blood agar
3) Sensitivity to Bacitracin indicates group A
4) Titer of >160 or a four-fold increase of Streptolysin O (ASO titer)
What Dx techniques do physicians use?
A bead test that demonstrates linkage by strep chains
pharyngeal swab is used
In Dx for Streptococcus, sensitivity to Bacitracin indicates what group?
Group A
What is Tx for Streptococcus?
PENICILLIN
Resistance has never been a problem
What are the qualities of Group B strepococci... Gram stain and growth phenotype? Hemolysin type? Bacitracin status? Hippurate status? What is the most important species?
G+ cocci in chains
Beta hemolysin, but less hemolysis than Group A
Bacitracin resistant
Hydrolizes hippurate
Streptococcus agalactiae is the most important species
Epidemiology of Group B streptococci…
What tissue does this group commonly inhabit?
What major infection does Group B cause?
Vaginal and colonic flora
1/3 of all NEONATAL INFECTIONS: septicemia, meningitis, pneumonia, and death
Group B streptococci…
What two patterns of infection occur?
What is mode of transmission for each?
Which has more severe health risks?
Early onset within 1 week caused by vertical transmission from mother to newborn is more severe
Later onset is caused by infant-to-infant spread with a less fulminant course and lower mortality
Fulminant = quickly
What is prevention of early onset/vertical transmission infection of Group B streptococci neonatal infection?
Culture pregnant women’s VJ and treat intrapartum parenteral penicillin or ampicillin
Intrapartum = during childbirth Parenteral = infusion via route other than mouth
Bacteriology of Group D Streptococci (Enterococci)... What are the most important species? What are the hemolysis pattern? Growth in Salt status? Natural tissue habitat? Antibiotic resistance? Last resort antibiotic?
Enterococcus faecalis and Enterococcus faecium
Hemolysis varies from strain to strain
Can grow in high salt
Common in GI tract
Resistant to many antibiotics.
Vancomycin is last resort, but resistance is a problem
What are common infections by enterococcus Group D strep?
UTI
Wound infections
Sepsis, especially in older patients
Quick note: Strep Group C and D cause beta-hemolysis and are bacitracin resistant. They cause various infections.
.
Viridans Streptococci…
What type of hemolysis?
What are the most common species?
What tissues do they normally inhabit?
Alpha hemolysis
Streptococcus mutans and Streptococcus sanguis
mouth, nose, and pharynx
What major illness is caused by Viridans Streptococci?
INFECTIVE ENDOCARDITIS
What is the pathogenesis and course of infection of infective endocarditis from Viridans Streptococci?
Alpha-hemolytic streptococci can infect through the mouth via oral trauma (including chewing)
Causes transient bacteremia
Bacteria can then bind to pre-existing lesion on heart valve
Vegetation on valve
Then has subacute course with intermittent bacteremia.
Possibly fatal
