Streptococcus and Enterococcus
How can we treat and prevent S. pneumoniae infections?
-Amoxacillin for non-invasive infections (need to use alternative for invasive inf.)
What are the virulence factors of Streptococcus pyogenes?
-Capsule inhibits phagocytosis -M protein- cell wall component that inhibits phagocytosis in the absence of specific antibody (>80 antigenic types it can make) -Enzymes and Toxins
What is the epidemiology of Strep. pyogenes, how is it transmitted and what Lancefield group is it in?
-Epidemiology- normal flora in throat in 5-20% of healthy people (less common in skin) -Transmitted person to person, respiratory droplet, and direct contact -Group A
Streptococcus pyogenes can create enzymes and toxins as a virulence factor. What are the toxins?
-Erythrogenic toxin- causes rash and scarlet fever -Exotoxin A- "super antigen" of streptococcal toxic shock syndrome -Exotoxin B- protease of necrotizing fasciitis
What are the different groups of Lancefield grouping and what species of bacteria belong to them?
-Group A- Streptococcus pyogenes -Group B- Streptococcus agalactiae -Group D- Enterococcus faecalis and Enterococcus Faecium
What are the alpha-hemolytic streptococci?
-S. pneumoniae -viridans group strep (no Lancefield antigens): S. sanguinis, S. mutans, S. sobrinus
Streptococcus pyogenes can create enzymes and toxins as a virulence factor. What are the enzymes?
-Streptokinase- degrades fibrin clots by activating host plasminogen (inactive) to plasmin (active) -Hyaluronidase- degrades hyaluronic acid which is the ground substance that holds tissues together -Streptolysin O and S/hemolysins- anti-streptolysin-O antibody
What are the three most frequent nosocomial infections? And what are the top 3 bacteria that cause them?
-UTI and would infections/intestinal abscesses (endocarditis and meningitis can also be added, but not as common) -Staphylococci, E. coli, enterococci
Enterococci are resistant to many antimicrobials, what is the recommended treatment for uncomplicated UTIs and for invasive infections?
-Uncomplicated UTIs- nitrofurantoin -Invasive infections- ampicillin (or vancomycin) w/ aminoglycoside (gentamycin)
How is a physiological identification done on bacteria?
-alpha-hemolytic organisms are much more susceptible to optochin than others (sensitivity is indicative of S. pneumoniae) -beta-hemolitic organisms are susceptable to bacitracin (S. pyogenese most effected)
What are the symptoms of pneumoniae?
-difficulty breathing -fatigue -cough ("rusty" or bloody sputum) -violent shaking chill -high fever (102-106 degrees F)
What type of bacteria is in Lancefield Group D? and how many species are there? Where is it normally found?
-nonhemolytic enterococci -about 17 species -normal microbiota of intestinal tract
What are some common illnesses cause by S. pneumoniae?
-pneumonia -otitis media -sinusitis
What are the virulence factors for S. pneumoniae?
-polysaccharide capsule (>90 serological types of capsular polysaccharide)
What are the invasive pneumococcal diseases (IPD)?
-septicemia (10-20% cases) -meningitis- very common cause in adults (40% fatality rate) -endocarditis (not very frequent)
What fraction of isolates from invasive pneumococcal diseases are fully resistant to one or more clinically relative antimicrobials? And what are good choices to treat these diseases?
1/3 -quinolones or vancomycin are good choices
How many different types of S. pyogenes in Group A?
>80 that have unique M proteins on their cell wall or fimbria
How many different types of S. pneumoniae are there?
>90 that have antigenically unique capsular polysaccharides
What is the identification scheme of alpha-hemolytic streptococci?
Do an optochin disc sensitivity test and if it is sensitive, then it is S, pheumoniae, and if it is resistant then it can be S. sanguinis, S. mutans or others
What are the main species of enterococci that cause 90% of clinical enterococcal infections?
Enterococcus faecalis Enterococcus faecium
What species of enterococcus is emerging as antibiotic resistant?
Enterococcus faecium- vancomycin resistant
How would you classify streptococcus & Enterococcus?
Gram-positive cocci (spherical to ovoid) often arranged in chains and/or pairs, facultative and catalase negative
What is used to serologically identify bacteria?
Lancefield grouping- presence of antigenically unique "C" carbohydrates in cell wall
What is the RST or the RADT and what do they detect?
Rapid Strep Test and the Rapid Antigen Detection Test that can be done quickly in clinic -they detect Group A antigens in 10-15 min (65-100% sensitivity, guidelines suggest to follow up negative tests with culture)
What is the most common cause of community-acquired pneumonia?
S. pneumoniae
What are the two beta-hemolytic streptococcus species we need to know and what Lancefield groups are they in?
S. pyogenes- group A S. agalactiae- group B
What are the bacteria in viridans group streptococci? How many species are there and are they hemolytic?
S. sanguinis S. mutans S. sobrinus ->12 species -yes, alpha hemolytic
What is the epidemiology of viridans group streptococci and what is a good antibiotic to use for an infection?
S. sanguinis, mutans, and sobrinus are normal microbiota of the oral cavity colonizing the teeth and oral mucosal tissue. *all usually sensitive to penicillins
What are some common clinical diseases caused by viridans group streptococci?
S. sanguinis, mutans, sobrinus -dental caries (mutans & sobrinus) -bacterial endocarditis (very common by sanguinis and mutans)
What percent of nosocomial enterococcal infections are caused by VRE?
about 30%
Which type of hemolysis is considered complete, partial, and nonhemolytic? alpha, beta, and game
alpha is partial beta is complete gamma is nonhemolytic
Where in humans is S. pneumoniae usually found?
as the normal flora colonized in the oropharynx. (children>adults)
Define hemolysis.
death of red blood cells
Who are susceptible to an S. pneumoniae infection?
immunocompromised, alcoholism, chronic cardiac/respiratiory disease *healthy individuals are usually resistant