Streptococcus Flashcards
Strep and Staph, which one clusters, which one is in chains?
Strep in chains
Staph in clusters
What does pyogenic mean?
Pus
Streptococcus pyogenes
Pharyngitis and skin/soft tissue infections
viridans (means green) streptococci
common cause of infective endocarditis
streptococcus pneumoniae
pneumonia, upper respiratory infections, meningitis
enterococcus faecalis and enterococcus faecium
nosocomial infections
Streptococcus gram stain and culture?
Gram positive cocci (spherical)
Arranged in chains or pairs (divides in one plane)
streptococcus pneumoniae gram stain and culture
diplococci but can be in chains
lancet-shaped
catalase test to distinguish what?
Strep is catalase negative
Staph is catalase positive
What do you look at to distinguish between strep types?
Hemolysis patterns
Beta strep/hemolysis
Clear zone from complete lysis of RBCs because of production of hemolysins (streptolysin O and streptolysin S)
alpha strep/hemolysis
Green zone due to incomplete lysis of RBCs
Gamma strep/hemolysis
No hemolysis
Strep pyogenes hemolysis pattern?
Beta
Strep pneumoniae hemolysis?
alpha
How to distinguish between strep pneumoniae and viridans strep?
Strep pneumoniae is bile soluble and inhibited by optochin
viridans strep hemolysis?
alpha, green!
Besides hemolysis patterns, what is another way to classify strep?
Lancefield classification A-V
Based on antigenic differences in C carbohydrate of cell wall
Group A strep is sensitive to bacitracin, whats an example?
strep pyogenes
Group B is resistant to bacitracin and hydrolyzes hippurate. Ex?
Strep agalactiae
Group D strep hyrolyzes esculin in the presence of bile producing a black pigment. Examples?
Enterococcus grows in high salt
streptococcus bovis does not grow in high salt
What is the most important virulence factor for strep pyogenes? What does it do? Is there an antibody for it?
M protein
inhibits opsonization: blocks phagocytosis
Yes but its only strain specific
Does strep pyogenes have a capsule? Can antibodies be made against it?
Yes, it is an anti-phagocytic capsule
Antibodies can’t be made against it because the capsule is made of hyaluronic acid which is a normal component of the human body
2 enzymes made by group A strep (strep pyogenes)
streptokinase - activates plasminogen to form plasmin, which dissolves fibrin in clots streptolysin O (anti-streptolysin O antibody can be used to diagnose recent group A strep infections which can be important for diagnosing rheumatic fever)
What is strep pyogenes erythrogenic toxin? What is it produced by?
causes the rash of scarlet fever
functions as superantigen (polyclonal stimulation of subset of T cells to produce cytokines)
produced only by strains that carry a lysogenic phage
There are toxins involved with specific clinical presentations. strep pyrogenic exotoxin A (superantigen) ?
strep toxic shock syndrome
There are some toxins involved with specific clinical presentations. Strep pyrogenic exotoxin B?
necrotizing fasciitis
Strep pyogenes is normal flora… where?
skin
Strep pyogenes can cause 3 types of disease:
- pyogenic - inflamm produced locally at site where organisms are present (pharyngitis, cellulitis)
- toxigenic - exotoxin production can cause systemic symptoms at sites where organism is not present (scarlet fever, strep toxic shock syndrome)
- immunologic - inflamm at sites where there are no organisms (rheumatic fever, acute glomerulonephritis)
strep pyogenes is the most common bacterial cause of
sore throat, strep throat
throat swab of someone with strep pyogenes doesn’t distinguish between normal flora and infection, why?
Some people are carriers but doesn’t mean they are sick
erysipelas?
strep pyogenes infection involving the skin
cellulitis?
strep pyogenes infection involving the skin and superficial fascia
necrotizing fasciitis?
strep pyogenes infection affecting the fascia
scarlet fever is caused by what and looks like what?
strep pyogenes toxin mediated disease (erythrogenic toxin)
diffuse sand paper rash and sunburn look
how do you distinguish strep and staph toxic shock?
strep toxic shock usually has obvious site of soft tissue infection and positive blood cultures
What are two presentations of inflammation (at different sites than the original microorganisms) created by a post-strep pyogenes infection?
- acute glomerulonephritis - immune complex deposition
- acute rheumatic fever - autoimmune disease caused by cross-reaction of strep M protein antibodies with human antigens in heart, brain, joints
acute glomerulonephritis occurs after what? Preventative treatment?
Occurs after skin/soft tissue infection or pharyngitis
No preventative treatment
smoky or rust colored urine
Acute rheumatic fever occurs after what? What can it cause? Preventative treatment?
Pharyngitis, not skin/soft tissue infections
Can cause mitral and aortic valve damage
Yes, antibiotics within 9 days of onset of pharyngitis
All group A strep are sensitive to what antibiotic?
penicillin G
What is the most important virulence factor for strep pneumoniae?
polysaccharide capsule
it is anti-phagocytic like all capsules
how many different capsular types of strep pneumoniae?
> 90
What do the antibodies against strep pneumoniae do?
opsonize them
What is the Quellung reaction?
anti-capsular antibody causes the capsule to swell
What percent of adults and children have strep pneumoniae as normal flora in their oropharynx?
5-10% adults
20-40% children
What two things can strep pneumoniae also cause?
bacteremia and meningitis
How often do people with strep pneumoniae also get bacteremia?
10-20% of cases
What does the sputum of a person with strep pneumoniae look like?
purulent - bloody
What do people who have had a splenectomy, hyposplenism, and sickle cell disease have in common?
At risk for invasive pneumococcal disease
What is a rapid test for strep pneumoniae
Latex agglutination test of CSF
When would you use a strep pneumoniae urinary test, what is it looking for?
When you suspect bacteremia
C polysaccharide from cell wall
Its not as sensitive for mild infections
How many strains of strep pneumoniae are not fully penicillin susceptible? Why?
5%
Altered penicillin binding protein with decreased binding affinity for penicillin (not inhibited by beta lactamase inhibitor)
What are the two vaccines available for strep pneumoniae?
- polysaccharide vaccine for adults and older children (23 valent)
- conjugate vaccine for young children (13 valent, conjugated to a carrier protein diphtheria toxoid which stimulates a helper T cell response)
Group D streptococcus that grows in high salt
enterococcus
Enterococcus is normal flora where?
colon
2 main enterococcus pathogens?
E. faecalis - more common, usually not vancomycin resistant
E. faecium - more likely to be resistant to vancomycin
vancomycin resistant enterococcus cause what?
nosocomial infections
how does enterococcus become resistant to vancomycin?
altered cell well oligopeptide with low affinity for vancomycin so there would be decreased inhibition of peptidoglycan synthesis
vancomycin resistant enterococcus is acquired in the hospital. Where does it hang out?
In colons of patients and is transferred to other patients by healthcare workers
are vancomycin resistant enterococcus infections usually E. faecium or E. faecalis?
E. faecium
Most positive VRE cultures represent what?
Colonization
Treatment: penicillin sensitive, penicillin resistant, vancomycin resistant?
penicillin-sensitive: penicillin + aminoglycoside (gentamicin) for synergy
penicillin-resistant: vancomycin
VRE: linezolid or daptom
what is a group D streptococcus that doesn’t grow in high salt?
streptococcus bovis
there is an association with strep bovis bacteremia and endocarditis with what?
colon carcinoma
What is a common cause of infective endocarditis?
viridans streptococcus (endocarditis presents several weeks after a dental procedure)
What is strep agalactiae? what group?
Group B
Colonizes genital tract of some women
Causes neonatal meningitis and sepsis and postpartum endometritis
Prevention/treatment of strep agalactiae?
Screen with vaginal/rectal cultures at 35-37 weeks of pregnancy
Rapid antigen test
If test is positive, treat with penicillin G at delivery
