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36 Cards in this Set

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Streptococci Classification
1. Alpha = partial hemolysis
2. Beta = complete hemolysis
- subgroup A is most virulent in humans
- subgroup B is normal flora in females
3. Gamma = no hemolysis
Why are Strep colonies so small?
They get their energy by fermentation; they don't use oxygen as their end product. So, since the plate is exposed to oxygen it prevents huge growth, meaning that colonies are going to remain small. Best is to use sheep blood agar.
Beta-hemolytic group A
Most common strep strain that causes disease in humans. It is further subdivided into 55 different strains. It is also called strep pyogenes, but name is not correct, since most pyogenes do not cause pus.
Beta-hemolytic group B
Strep Agalactiae - normal flora in the female genitalia (ie, vagina). Under certain circumstances this can cause disease, especially neonatal meningitis.
Beta-hemolytic group D
Enterococci - normal flora of GI tract.One of the most troublesome causing diseases of this strain is UTI Unfortunately, most of these are very resistant today. Why? Because if they are in GI so they come into contact with any antibiotic we put into our body. They are not hemolytic.
Why might a dentist give a patient preventative antibiotics?
Strep viridans is normal flora of upper respiratory tract. During dental procedures, sometimes this bacteria gets in the blood. If someone has heart problems, or prosthetic devices in heart, they need preventative antibiotics to be safe.
Dental Caries and Strep
Strep Mutans causes dental caries (cavities). It can synthesize polymers of dextran and levan. Dextran is the polymer of glucose and levan is the polymer of fructose. When we put sugar in our mouth, strep mutans can synthesize these polymers. Then lactic acid is produced, leading to enamel destruction.
Beta-hemolytic group A strep have enzymes that contribute to their pathogenicity:
Streptolysin O: O stands for oxygen labile as it is inactivated by oxygen. This enzyme breaks down rbcs and wbcs. Enzyme is also antigenic, thus antibodies develop against the O. So, you could check for ASO titers.
Streptolysin S: S stands for oxygen Stabile. Also responsible for hemolysis, but is not antigenic.
Enterococcus
Fecalis and Fecium
Normal flora of bowels. Can cause UTIs, biliary tract infections, bacteremia, and subacute bacterial endocarditis. Frequently cause nosocomial infections, such as prosthetic valve endocarditis (like viridans).
C carbohydrate
The C carbohydrate was used by Rebecca Lancefield to divide streptococci into groups. For example, strep pyogenes has the Lancefield Group A type of C carbohydrate.
M protein
This is a major virulence factor for the group A streptococcus. It inhibits the activation of complement and protects the organism from phagocytosis. However, it is also the weakest point in the organism's defense, because plasma (B ) cells generate antibodies against the M protein. These antibodies bind to the M protein (opsonization), aiding in the destruction of the organism by macrophages and neutrophils.
Streptokinase
Produced by beta-hemolytic strep. Is a fibrinolytic substance that activates plasminogen via cleavage to produce plasma. Is a cheap and effective clot-dissolving medication.
Streptodornase
Bacterial DNAase. Cleaves phosphodiester linkages.
Hyaluronidase
Degrades hyaluronic acid. This gives bacteria increased mobility and also provides antigenic disguise so phagocytes don't recognize them.
Erythrogenic Toxin
Erythro = rash
So, it is a rash-producing toxin. From beta-hemolytic group A strep, this toxin causes scarlet fever.
Hemolysins
Streptolysins: S and O
-antigenic
Streptococcus Pyogenes (Group A)
suppurative infections
-pharyngitis
-scarlet fever
-erysipelas: localized skin infection with pain, inflammation, lymph node enlargement and systemic symptoms
-cellulitis: infxn of the skin that involves the subcutaneous tissues
-necrotizing fasciitis: deep infxn of skin that involves destruction of muscle and fat layers
-strep TSS: multi-organ systemic infxn resembling staph TSS; however, most patients bacteremic and with fasciitis.
Streptococcus Pyogenes (Group A)
Nonsuppurative Infections (2)
-Rheumatic fever: characterized by inflammatory changes of the heart, joints, blood vessels, and subcutaneous tissues
-Acute glomerulonephritis: actue inflammation of the renal glomeruli w/ edema, hypertension, hematuria, and proteinuria
Streptococcus Agalactiae (Group B) Infections
-Early-onset neonatal disease: w/in 7 days of birth, infected newborns develop signs and symptoms of pneumonia, meningitis, and sepsis
-Late-onset neonatal disease: more than a week after birth, neonates develop signs and symptoms of bacteremia w/ meningitis
-Infxns in pregnant women: most often present as UTI; bacteremia and disseminated complications may occur
-Infxns in other adult patients: most common include bacteremia, pneumonia, bone and joint infxns, and skin and soft-tissue infxns
Viridans Streptococci Infections
(3 main types)
1. dental infections - esp s. mutans
2. endocarditis -
3. abscesses - s. anginosus
Streptococcus Pneumoniae Infxns (3)
1. Pneumonia
2. Meningitis
3. Bacteremia
Strep strains are sensitive to Penicillin, yet sometimes it doesn't work. Why?
Normal flora streps in the pharynx acquire plasmids that allow them to express beta-lactamase and degrade penicillin. If strep is working in conjunction w/ another bacteria that has beta-lactamase, it will confer resistance to the strep.
60% of Pneumonia cases are caused by:
Strep Pneumonia (pneumococci)
Major virulence factor of pneumococcus?
Polysaccharide capsule, which protects from phagocytosis.
Is the strep pneumonia polysaccharide capsule antigenic?
Yes. So, antibodies specific for the capsule can neutralize the bacteria. The only problem is that there are 84 different capsule serotypes, so surviving an infxn only provides immunity to 1 out of 83 possible capsule types.
Streptococcus pneumonia is the most common cause of _____ in children and the most common cause of _____in adults.
otitis media in children
bacterial meningitis in adults
80% of lobar pneumonia is caused by which type?
type 14
Which strain of pneumococcus is the most virulent?
type 3
Different strains of pneumococcus are differentiated by...
Capsular polysaccharide coat, which stimulates production of serotype-specific protective antibodies.
40-70% of healthy people have pneumococci in upper respiratory tract. How does body prevent them from invading?
-reflex of epiglottis prevents swallowing of contaminated mucus
-mucus
-hairs on epithelium
-coughing
-regional lymphatics
-local macrophages
Predisposing factors for getting pneumonia from pneumococci.
-loss of natural resistance
-viral contamination
-alcoholism and malnutrition prevent coughing and phagocytosis
-pulmonary congestion
Lab diagnosis of pneumococcus - saliva or sputum?
Need sputum. High possibility that saliva will harbor pneumococci.
Pneumococci and gram-staining.
Will see gram-positive diplococci. This is an indication, but not enough for definitive diagnosis.
Quellung Reaction
Pneumococci on slide smear are mixed with small amount of anti-serum (serum w/ antibodies to the capsular antigens) and methylene blue. The capsule will appear to swell. This technique allows for rapid identification.
Most common diseases caused by pneumococci. (5)
-lobar pneumonia
-bacteremia
-meningitis
-sinusitis
-otitis media
Pneumococcal vaccines.
-Vaccine: composed of capsular antigens. The vaccine for adults has 23 different capsular antigens. Called pneumovax. Low efficacy in children.
-Newer heptavalent conjugated vaccine (contains 7 antigens) is effective in children at preventing otitis media and pneumonia