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100 Cards in this Set
- Front
- Back
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What type of organism are Streptococcus?
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G+, catalase-negative bacteria that assemble in chains.
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What is a simple way to distinguish between Staphylococcus and Streptococcus?
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Streptoccus is a catalase-negative organism
Staphylococcus is a catalase-positive organism |
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What are the oxygen requirements for Streptococcus?
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Microaerophilic organism
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What does microaerophilic mean?
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Streptococcus can grow in teh presence of air, but prefers low oxygen tension
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What lab conditoins are used to grow Streptococcus?
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Usually grown aerobically, in candle jars or 5% CO2 incubators.
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What are three ways in which Streptococcus can be classified?
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1) Hemolytic properties
2) Metabolic and growth properties 3) Serologic groups (lancefield) |
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What are the three types of hemolytic reactions?
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Alpha
Beta Gamma |
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What is alpha hemolysis?
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Alpha hemolytic streptococcus causes partial red blood cell lysis, resulting in a green ring around their colonies when cultured on blood agar.
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What are two alpha hemolytic streptococci?
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Strep pneumoniae
Strep viridans |
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How can you distinguish between the two alpha hemolytic streptococci?
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S. pneumoniae has a capsule (+ Quellung rxn) and shows sensitivity to Optochin.
S. viridans has no capsule and is Optochin resistant. |
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What is gamma hemolysis?
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Gamma hemolytic streptococcus causes NO RBC lysis, resulting in no color change when cultured on blood agar.
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What are two gamma hemolytic streptococci?
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Enterococcus (E. faecalis)
Peptostreptococcus Some Enterococcus can also demonstrate alpha- or beta-hemolytic properties |
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How can you distinguish between the two?
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Enterococcus, can be grown in bile and 6.5% NaCl.
Peptostreptococcus is obligate anaerobic organism. |
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What is the Lancefield grouping system?
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Serologic classification system that primarily categorizes Beta hemolytic Streptococcus.
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What is the basis of the lancefield system?
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C-carbohydrate polysaccharides tha are found in cell walls of most Streptococcus and are clasified in Groups A through U.
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Which groups are of major medical importance?
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Group A Streptococcus (GAS) corresponding to S. pyogenes
Group B Streptococcus (GBS) corresponding to S. agalactiae |
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Which four streptococci are not classified under the Lancefield system?
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1) S. pneumonia
2) Viridans streptococcus 3) S. mutans 4) Enterococcus |
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What is S. pneumoniae?
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Encapsulated
Alpha-hemolytic Optochin-sensitive streptococci |
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What are two major virulence factors of S. pneumoniae?
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Capsule
Pneumolysin |
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What is the Quellung reaction?
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When the bacterial capsule appears to swell-when mixed with type-specific antisera.
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What type of Quellung reaction do S. pneumoniae display?
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Positive
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What other organisms also give a positive Quellung reaction?
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Neisseria meningitides
Haemophilus influenzae Klebsiella |
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Who is at risk of S. pneumoniae infection?
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1) Individuals who have had their spleens removed or who have a decrease in splenic function (secondary to sickle cell anemia)
2) Individuals with decreased respiratory function or after anesthesia (infants, elderly, alcoholic) Splenic function is critical in clearing encapsulated bacteria such as S. pneumonia. |
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How many different serotypes of S. pneumoniae exist?
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85 different serotypes.
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What are the serotypes of S. pneumoniae based on?
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The capsule.
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What is the function of the capsule that surrounds S. pneumoniae?
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Confers antiphagocytic properties.
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What is pneumolysin?
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An important virulence factor that lyses phagocytes and is released when S. pneumoniae lyses itself.
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How does pneumolysin work on phagocytes?
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1) S. pneumoniae is engulfed by phagocytic cells
2) S. pneumoniae releases autolysins to lyse itself. 3) Pneumolysin, which ws intrabacterial, is now present inside the phagocyte and degrades the cell from the inside out. "I'm going down, but I'm taking you with me!" |
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What clinical syndromes are associated with S. pneumoniae?
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1) Pneumonia (most common cause)
2) Otitis media (most common cause) 3) Sinusitis 4) Meningitis 5) Sepsis |
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What commonly predisposes an individual to get pneumonia?
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Previous viral infection and being immunocompromised.
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What key laboratory tests are useful when identifying S. pneumoniae?
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1) Sputum or blood culture on blood agar.
2) Optochin sensitivity |
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What is a characteristic finding in a patient with S. pneumoniae?
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Rusty colored sputum.
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Which antibiotics are useful against S. pneumoniae strains?
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Penicillin G of a cephalosporin, although resistance is spreading rapidly.
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What treatment is indicated for resistant forms of S. pneumoniae?
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Vancomycin, erythromycin, or clindamycin.
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What vaccine are available for S. pneumoniae?
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1) Pneumovax: a polyvalent capsular polysaccharide vaccine that immunizes against 23 serotypes.
2) Prevnar: a heptavalent conjugate vaccine which is made up of 7 pneumococcal antigens conjugated to a nontoxic diptheria toxin. |
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Whic vaccine is used in infants?
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The heptavalent conjugate vaccine in children <2yrs.
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What are Viridans streptococcus?
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Unencapsulated,
Optochin resistent Alpha-hemolytic streptococcus |
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Where are Viridans streptococcus normally found?
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Oral flora
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What is the predominant species of viridans streptococcus?
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Streptococcus mutans
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What are two clinical concerns regarding s. mutans?
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1) Subacute bacterial endocarditis
2) Dental carries |
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What would be the appropriate proplylactic management considering the two clinical concerns of S. mutans are subacute bacterial endocarditis and dental caries?
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Certain vulnerable patients; those with artificial heart valves or valve abnormalities, may be treated with penicillin before undergoing dental procedures.
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What is S. pyogenes?
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1) Encapsulated, bacitracin sensitive, Beta hemolytic streptococcus (aka Group A Streptococcus - GAS)
2) Remember that the two most clinically relevant groups of Beta hemolytic Streptococcus are lancefield groups A and B 3) S. pyogenes is the most virulent member of the group A Beta-hemolytic streptococcus. |
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What is the structure of S. pyogenes?
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Gram-positive
nonmotile cocci that can appear as long chains, pairs, clusters, or individual cocci. |
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What are the two postinfectious immunological sequelae that are associated with S. pyogenes?
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1) Acute rheumatic fever
2) Acute glomerulonephritis |
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What is the most common means of S. pyogenes transmission?
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Aerosolized respiratory droplets.
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What is another means of transmission of S. pyogenes that is not so common?
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Direct spread can occur, by invading intact skin.
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What is unique about teh capsule of group A S. pyogenes
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Composed of hyaluronic acid
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What is the sidnificance of the capsule of S. pyogenes?
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The body does not recognize it as foreign because hyaluronic acid mimics the outer layer of human connective tissue.
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What are nine virulence factors associated with S. pyogenes?
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1) M. proteins and teichoic acids
2) C-carbohydrate 3) Protein F 4) Streptococcal pyogenic exotoxins (SPEs) 5) Streptolysin O and S 6) Streptokinase 7) Streptodornases 8) C5a Peptidase 9) Hyaluronidase |
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Which four virulence factors are components of the cell wall?
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1) M. proteins
2) Teichoic acid 3) C-carbohydrate 4) Protein F. |
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What confers antiphagocytic properties of S. pyogenes?
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1) Fibrillar M proteins with highly variable N-terminus regions
2) Adherence to some epithelial cells |
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What is the significance of the high variability?
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Variability gives the bacteria new "camoflage", limiting the host's use of antibodies that would opsonize the bacteria.
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What is the function of protein F?
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Attachment of S. pyogenes to host tissues; e.g. to pharyngeal epithelium
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What is SPE A?
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A superantigenic exotoxin corresponding to classic erythrotoxin.
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How is SPE A expressed?
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Carried by baceriophages that lysogenize S. pyogenes
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What is the pathogenesis of SPE A?
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Superantigen-mediated response that increases T-cell antigen presenting cell mitogenicity and cytokine expression (IL-1, IL-2, interferon-gamma, and TNF).
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What are two clinical manifestations associated with SPE A?
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1) Rash of scarlet fever
2) Toxic shock-like syndrome |
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What is SPE B?
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A superantigenic exotoxin corresponding to cysteine protease.
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How is SPE B expressed?
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Chromosomally encoded cysteine protease that is variably expressed
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What is a clinical manifestation of elevated levels of SPE B?
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Necrotizing faciitis.
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What is streptolysin O?
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An antigenic oxygen-labile hemolysin that can lyse mammalian cells, releasing enzymes that damage tissue.
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What are antibodies against streptolysin O useful for?
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Documentating recent group A streptococcus infection.
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What is streptolysin S?
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An oxygen stable, but nonimmunogenic hemolysin that lyses leukocytes, platelets, and red cells
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How is streptolysin S useful for diagnosis?
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Responsible for the clear ring observed around Beta-hemolytic streptococci colonies on blood agar.
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What is streptokinase?
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Catalyses the conversion of plasminogen to plasmin resulting in hylsis of clots adn facilitating rapid spread of group A Streptococcus.
Streptokinase is not, in the biochemical sense, a kinase. |
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What are streptodornases?
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Bacterial DNAse made by S. pyogenes that degrade viscous DNA in tissue, further facilitating spread of infection.
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What is the role of C5a peptidase?
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Inactivates C5a that is interfering with complement-mediated recruitment of white blood cells.
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What is hyaluronidase?
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Hydrolyzes hyaluronic acid in the ground substance of conective tissue, further aiding spread of infection.
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What are eight clinical syndromes caused by S. pyogenes?
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1) Cellulitis
2) Acute pharyngitis/epiglotitis 3) Impetigo 4) Erysipelas 5) Puerperal sepsis 6) Necrotizing fascitis 7) Acute rheumatic fever 8) Acute glomerulonephritis |
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What is cellulitis?
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Rapidly spreading inflammation of the skin adn subcutaneous tissue.
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What is pharyngitis?
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Redness and edema of the throat and tonsils frequently covered with yellow-white exudates.
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What is the treatment for acute pharyngitis?
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Penicillin G or a macrolide if the patient is allergic to penicillin.
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What is impetigo?
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Common superficial infection usually on the face of children with small vessels turning into pustules and eventually spread into a thick yellowish crust.
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What is the treatment for impetigo?
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Topical mupirocin or systemic first-generation cephalosporin.
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What is erysipelas?
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An advancing erythematous cellulitis with a defined border, usually on the face or lower limbs
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What is peurperal sepsis?
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A postpartum infection of the uterine endometrium that presents as a purulent vaginal discharge with systemi signs of infection
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What is necrotizing fasciitis?
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A rapidly spreading systemic infection caused by S. pyogenes, which is also known as "flesh-eating bacteria".
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What is acute rheumatic fever?
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An autoimmune disease appearing 3 weeks after streptococcal pharyngitis leading to fever, rash, arthritis and pancarditis.
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What is the pathogenesis of acute rheumatic fever?
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A cross-reaction between streptococcal antigens and host tissues associated with specific M proteins.
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What is acute glomerulonephritis?
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A postinfectious sequelae appearing 10 days after streptococcal pharyngitis or 3 weeks after cutaneous S. pyogenes infection.
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What is the pathogenesis of acute glomerulonephritis?
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Believed to be caused by antigen-antibody complexes being deposited in the basement membrane of the glomerulus.
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What is S. agalactiae?
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Unencapsulated, bacitracin resistant, Beta-hemolytic streptococci, also known as Group B strep (GBS).
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Where is S. agalactiae found?
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Vagina
Urethra GI tract |
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How is S. agalactiae spread?
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Sexually transmitted
During childbirth (parturition) |
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What are the clinical yndromes caused by S. agalactiae?
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1) Neonatal sepsis and meningitis (leading cause)
2) Endometritis 3) Pneumonia 4) Lower-extremity infections in diabetes. |
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Which antibiotics are useful against S. agalactiae?
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Penicillin and ampicillin
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What measures should be taken to prevent S. agalactiae transmission from a mother to her child during prolonged labor?
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A prophylactic course of penicillin or ampicillin should be administered during prolonged labor, fever, or prior eveidence of GBS colonization/amnionitis.
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What are enterococci?
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Gamma-Hemolytic group D streptococcus.
Some Enterococcus can also demonstrate alpha- or beta-hemolytic properties. |
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What are the two clinically important species of enterococci?
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E. faecalis
E. faecium |
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Why is Enterococcus a prominent caue of nosocomial infection?
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Resistance to multiple antibiotics.
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Where is Enterococcus found?
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Normal part of the fecal flora.
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How is Enterococcus identified in the laboratory?
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1) Group D Lancefield grouping
2) Can survive in bile salts adn 6.5% NaCl 3) Yields a positive pyrrolidonyl arylamidase (PYR) test. |
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What property do Enterococcus and Strepbococcus bovis share?
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Group D Lancefield classification.
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How is S. bovis differentiated from Enterococcus?
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Enterococcus yields a positive PYR test
S. bovis does NOT yield a positive PYR test. |
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What are two clinical manifestations of Enterococcus?
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1) Urinary tract infection
2) Subacute endocarditis |
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As enterococcus infections easily treated?
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NO
They are often resistant and survive on infected surfaces for a long time. |
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What is Peptostreptococcus?
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Gamma-hemolytic anaerobic streptococci that are relatively avirulent.
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Why is peptostreptococcus not part of the Lancefield system?
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It lacks the C-carbohydrate cell wall antigen and thus is not part of the lancefield system.
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What distinguishes peptostreptococci from other streptococci?
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Peptostreptococci, unlike other streptococci, are obligate anaerobes.
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What clinical manifestations are associated with Peptostreptococcus?
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Infections in soft tissues
Pneumonia Genitourinary infections. |
