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43 Cards in this Set

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  • Back
What are the major diseases caused by Streptococci
Bacteremia (all types)
Pneumonia (Streptococcus pneumoniae)
Otitis media (S. pneumoniae)
Meningitis (Streptococcus pneumoniae, group B streptococci)
Cellulitis (group A, less commonly group B)
Necrotizing fasciitis and myositis (group A)
Impetigo (group A)
Pharyngitis (Group A)
Scarlet fever (group A)
Toxic shock-like syndrome (group A)
rheumatic fever (group A)
Acute glomerulonephritis (group A)
Wound infections (group A streptococci, enterococci, anaerobic streptococci)
Endocarditis (Enterococcus species, Viridans streptococci)
UTIs (Enterococcus species)
What are some characteristics of all streptococci
Gram positive, spherical, grow in pairs or chains, non motile, catalase negative
What is the most common cause of community-acquired pneumonia in the United States (500,000/year)
Streptococcus pneumoniae
What is one of the most common causes of acute suppurative otitis media in the US (7,000,000/year)
Streptococcus pneumoniae. The bacteria also causes bacteremia and bacterial meningitis
What is the morphology of Streptococcus pneumoniae
Alpha hemolytic (but not true lysis)
Gram positive, lancet-shaped diplococci
Catalase negative
Grow best with 5-10% blood on media
Autolytic enzymes cause lysis of colony in bile salts (bile solubility) and susceptibility to optochin
What are the three main virulence factors in Streptococcus pneumoniae
Capsular polysaccharides; Adhesins; Pneumolysin
What are the characteristics of capsular polysaccharides in Streptococcus pneumoniae
Antigenic, ~90 serotypes
Antiphagocytic (main virulence factor). Prevents deposition of C3b
What are the adhesins in Streptococcus pneumoniae
Pneumococcal surface protein A (PspA) and choline-binding proteins. Thought to facilitate binding of pneumococci to pharyngeal cells
How does Pneumolysin in Streptococcus pneumoniae work
This is a membrane active, pore-forming toxin. The toxin may also destroy ciliated epithelial cells and block the phagocytic burst
What are the predisposing factors to acquiring pneumonia from Streptococcus pneumoniae
Viral infection of upper respiratory tract, particularly influenza
Compromised pulmonary function, alcoholism, general anesthesia
Basic immunity is impaired
Serotype present (type 3 responsible for most disease)
Where does an infection of Streptococcus pneumoniae usually come from
Most are caused by endogenous infection
What is the pathogenesis of pneumococcal pneumoniae
Organism colonizes pharynx and gains access to the lungs
Moves to alveoli and is phagocytized by macrophages
Multiplies in edematous fluid
Exudate spills into bronchioles and adjoining alveoli
Inflammatory response, air is displaced
What are the clinical manifestations of pneumococcal pneumonia
Sudden onset of chills, fever, pleuritic pain, rusty sputum
Positive blood cultures in 30%
What are some possible complications in pneumococcal pneumonia
Direct-lung abscess
Via blood-Empyema, pericarditis, meningitis, intrapleural abscess, septic arthritis
What is the morbidity and mortality of Streptococcus pneumoniae
Causes pneumonia, otitis media, invasive diseases including meningitis. Death occurs in 14% with invasive disease. Factors that affect severity include age, bacteremia, and serotype
What are some upper respiratory tract infections caused by Streptococcus pneumoniae
Otitis media, Mastoiditis, Sinusitis
What are some extrapulmonary infections caused by Streptococcus pneumoniae
Meningitis- most common cause in US
Septic arthritis
How is Streptococcus pneumoniae identified on blood agar
Colonies are mucoid, alpha hemolytic, bile soluble. The bacteria are also sensitive to optochin
What are the different types of specimens that can be used to identify Streptococcus pneumoniae
Blood, CSF, sputum, transtracheal aspirate. Concentrated urine can be used for detection of C polysaccharide (teichoic acid plus tightly adherent fragments of peptidoglycan), which is present in all pneumococci. This is not recommended for patients with pneumonia
What can be used for rapid, presumptive identification of Streptococcus pneumoniae
Gram stain appearance in CSF or sputum or detection of soluble capsule by latex agglutination. Can also use CIE (serum or CSF) or ELISA
How is Streptococcus pneumoniae treated in:
Otitis media
There has been an increase of pen G resistance and cephalosporins, due to altered PBPs.
Otitis media: amoxicillin
Sinusitis: amoxicillin or quinolone
Pneumonia: third generation cephalosporins
Meningitis: vancomycin plus Beta-lactam antibiotics
How is immunity to Streptococcus pneumoniae acquired
It is serotype specific. Recovery correlates with development of opsonizing antibody to polysaccharide capsule
What are the two vaccines available for Streptococcus pneumoniae
Prevenar-heptavalent pneumococcal conjugate vaccine (23 months or younger)
Polysaccharide only vaccine. All 23 serotypes, primarily protects against bacteremia
What streptococci, other than pneumococci, are frequently associated with human disease
Groups A, B (sometimes C, F and G) and Enterococcus (old group D)
What is the most important Streptococcus group A species
Streptococcus pyogenes
What is the background of Streptococcus pyogenes
Responsible for majority of all streptococcal diseases
Transient flora in upper respiratory tract of 15-20% of school-age children
In a conventional culture, how is Streptococcus pyogenes identified
Gram positive cocci
Beta-hemolytic pinpoint; convex colonies on blood agar; colonies may be mucoid
Catalase negative
PYR test positive
Bactitracin sensitive
What are the two main laboratory identifications for Streptococcus pyogenes
Direct antigen test (ELISA) or conventional culture
What is the cellular structure of Streptococcus pyogenes
Lipoteichoic acid- adherence to fibronectin
M protein- major virulence factor, antiphagocytic, 90 different types
F protein- mediates binding to fibronectin
Hyaluronic acid capsule- same as host surface
Group specific Lancefield CHO antigen
What are the extracellular Streptococcus pyogenes products
Streptococcal pyrogenic toxins- similar to Staphlococcal pyrogenic toxins. Super antigens, involved in scarlet fever and toxic shock-like syndrome
Streptolysin- O2 labile, antigenic, hemolytic, toxic to wide variety of cells
Streptokinase plus streptodornase- enzymatic debridgement
C5a peptidase degrades C5a that attracts PMNs
What Acute suppurative infections does Streptococcus pyogenes cause
Impetigo- climate and hygiene affect incidence
Wound infections
Necrotizing fasciitis and myositis- probably due to group A streptococci that make both pyrogenic exotoxin A and a cysteine protease
Streptococcal toxic shock syndrome. Clinically like Staphylococcal toxic shock syndrome except patients are bacteremic
What are two non-suppurative sequelae of Streptococcus pyogenes
Rheumatic fever and acute glomerulonephritis
How is Streptococcus pyogenes treated
Penicillin G. If in shock, add clindamycin. If coinfected with S. aureus, use penicillinase-resistant antibiotic
What is the only Group B streptococci species
Streptococcus agalactiae
What is the background of Streptococcus agalactiae (Group B)
First isolated from bovine mastitis
Most common cause of neonatal meningitis
Normal flora in the gut and transient flora in the vagina of pregnant women
How are Streptococci agalactiae identified
Gram positive cocci, catalase negative
Beta hemolytic and bacitracin insensitive
CAMP test positive CAMP factor
Detection of group B specific cell wall antigen
What are the characteristics of neonatal infections with Streptococci agalactiae
Early or Delayed onset. Vertical transmission. Can see meningitis, sepsis, 20% mortality
What Streptococcus agalactiae infections are seen in adults
Pregnant- bacteremia
Non pregnant- bacteremia, meningitis, cellulitis
How is Streptococcus agalactiae treated
Penicillin G plus aminoglycoside
How are Streptococcus agalactiae infections prevented
Working on a vaccine
Penicillin G during labor to women at risk
What are the characteristics of Enterococci (group D) and Streptococcus bovis (group D or Viridans)
Normal flora on skin and GI tract
Gram positive cocci, catalase negative
Alpha, beta, or gamma hemolytic
Bacitracin insensitive, hydrolyze bile-esculin
Enterococci grow in 6.5% NaCl
Cause infections in the urinary tract, bacteremia (most common type of streptococcal bacteremia in adults), and wound infections
How are enterococci treated
Penicillin G + aminoglycoside
What are the characteristics of Viridans streptococci
Were called alpha hemolytic streptococci
Normal flora of the mouth, URT. Not typable by CHO antigen, usually don't cause disease
Gram positive cocci, catalase negative, alpha hemolytic, optochin insensitive
Can cause Endocarditis after dental work, or dental cares. Treat with penicillin G