Streptococci Flashcards
Streptococci occur in
Gpos cocci occuring in chains
All Streptococci are
- Catalase negative
- Gpos cocci occuring in chains
- check for hemolysis pattern
Types of Streptococci
6 listed
- Streptococcus pyogenes (Group A)
- Streptococcus agalactiae (Group B)
- Streptococcus pneumonae
- Streptococcus viridans
- Enterococcus (Group D)
- Streptococcus bovis
Group A strep
Streptococcus pyogenes
Group B strep
Streptococcus agalactiae
Group D strep
Enterococcus
Features of Streptococcus pyogenes
- Group A strep
- Pyrrolidonyl arylamidase (PYR) positive
- Substrate (L-napthylamide-beta-napthylamide) hydrolyzed by bacterial enzyme to beta-naphthylamide
- can be detected by color change with detection reagent
- M protein virulence factor
- inhibits phagocytosis
Strep pyogenes illnesses
- infections
- Pharyngitis (strep throat)
- skin: Cellulitis, impetigo
- Toxin-mediated disease
- Scarlet fever
- Necrotizing fasciitis
- Toxic Shock Syndrome
- Immune-disease
- Rheumatic fever
- Post-strep glomerulonephritis
Strep pharyngitis
- 15-30% of pharyngitis is due to S. pyogenes
- most cases are viral
- important to identify and treat S. pyogenes
- prevent transmission
- limit symptoms and severity
- prevent Rheumatic fever
- Dx
- Throat culture
- Rapid antigen test (useful if positive)
- Tx
- Penicillin
- Amoxicillin
- Cephalosporins
Strep pyogenes skin infections
- cellulitis and impetigo
- can also be caused by Staph aureus so antibiotics need to cover both
Strep pyogenes Scarlet fever
- Rash following pharyngitis
- Skin reaction to ***erythrogenic toxin***
- gene for toxin transferred by lysogenic bacteriophage (not found in bacterial genome)
- symptoms
- fever
- sore throat
- diffuse red rash
- strawberry tongue (can also get from Kawasaki Disease)
- also many small papules (“sandpaper” skin) (palms and soles usually spared)
- starts on the head/neck -> expands to cover the trunk
- Eventually skin desquamates (palms and soles usually spared)
Differentiating Scarlet fever from Kawasaki disease
Look for a sore throat to determine Scarlet Fever
Infectious rashes that involve the palms and soles
- Syphilis
- RMSF
- Coxsackie virus
Necrotizing fasciitis
- Caused by Strep pyogenes strains that produce streptococcal pyrogenic exotoxin
- Infection of deep tissues
- muscle fascia/subcutaneous fat
- Streptococcal pyrogenic exotoxin released
- fulminant and deadly
- infection spreads along the muscular fascia and requires surgical debridement
Necrotizing fasciitis toxin
Strep pyogenes that produce streptococcal pyrogenic exotoxin
Type 1 Necrotizing fasciitis
- polymicrobial (Bacteroides, Clostridium, etc. anaerobes)
- occurs in diabetics, immunocompromised, post-surgery
Type 2 Necrotizing fasciitis
- Group A strep
- sometimes Staph
- Occurs in otherwise heallthy people after skin injury
Classic case of Type 2 Necrotizing fasciitis
- minor skin trauma
- redness/warmth (can be confused with cellulitis)
- pain out of proportion to exam
- fever
- hypotension
Rheumatic fever
- A type II autoimmune reaction
- Follows Group A strep pharyngitis infection
- Streptococcus -> anti-strep antibodies cross react with tissue-antigens
- Dx: Jones criteria
Rheumatic fever pathology
- Aschoff bodies (form of granuloma) ***Pathognomonic for rheumatic carditis***
- Anitschkow’s cells
- Elevated ASO titers (Anti-streptolysin O antibodies)
Jones Criteria
- Major
- carditis
- polyarthritis
- chorea
- Erythema marginatum
- subcutaenous nodules
- Minor
- fever
- arthralgia
- prior RF
- elevated WBC, ESR, CRP
- prolong PR interval
Must have evidence of strep infection and 2 major or 1 major & 2 minor to diagnose Rheumatic fever
Clues to diagnosing Rheumatic fever
Sore throat or URI followed by joint pain, new murmur
Tx of Rheumatic fever
Penicillin (often indefinitely for prevention of recurrent infection)
Cardiac involvement of Rheumatic fever
Acute RF -> severe valve disease, heart failure
Later -> mitral stenosis (rarely aortic or tricuspid valves)
Post-streptococcal GN
- Nephritic syndrome 2-3 weeks after GAS infection
- Nephritogenic strains of strep
- bacteria with particular M protein subtypes cause nephritis
- specific subtypes are associated with RF and others with post-streptococcal GN (so pts get on or the other but not both)
- bacteria with particular M protein subtypes cause nephritis
Strep agalactiae features
- Group B strep
- Beta-hemolytic (like GAS)
- Makes CAMP factor
- Staph aureus makes beta-hemolysin
- CAMP factor enhances lysis by beta-hemolysis
- hydrolyzes hippurate
- alters the color of hippurate test
- Colonizes the vagina
- causes infections in newborns
- babies infected in utero or during birth
- Pneumonia, meningitis, sepsis
- Pregnant women screened at 35-37 weeks
- GBS+ pregnant women recieve prophylaxis
- 4 hours pre-delivery
- Penicillin, ampicillin or cefazolin
Beta-hemolytic strep
- GAS (Strep pyogenes)
- GBS (Strep agalactiae)
Rapid Strep agalactiae test
Hippurate test
Step pneumonia features
- “Lancet-shaped” gram (+) cocci
- Makes IgA protease
- Key virulence factor: polysaccharide capsule
- prevents phagocytosis
- basis of vaccine from capsular material
- Asplenic patients at risk for sepsis
- splenectomy
- Sickle cell anemia
Step pneumonia illnesses
- Lobar pneumonia
- Meningitis
- Ottitis media
- Sinusitis
Strep viridans features
- group of similar bacteria
- No strep Lancefield grouping
- Normal mouth flora
Strep viridans illnesses
- Dental caries (Strep mutans)
- Subacute endocarditis (Strep sanguis)
Subacute endocarditis
- caused by Strep sanguis
- slow-onset of symptoms
- less sick pts
- often affects abnormal vales
- Dextran -> fibrin
- Requires endothelial damage
- Mitral valve prolapse
- PEARL= Recent Dental Procedure
Dextran?
Strep viridans
Types of enterococcus
- E. faecalis
- E. faecium
Features of Enterococcus
- normal colonic bacteria
- Group D Strep (Lancefield Group D)
- Resistant to penicillin
- Vancomycin resistant Enterococcus (VRE)
- dangerous hospital acquired infection
Enterococcus illnesses
- UTIs
- Endocarditis (rare)
- VRE (Vancomycin Resistant Enterococcus)
- dangerous hospital acquired infection
Antibiotics for Enterococcus
- relatively resistant to cell wall agents (penicillin, ampcillin, vancomycin)
- Impermeable to aminoglycosides
- For bacteremia us synergystic therapy
- Vancomycin/Gentamycin
- Ampicillin/Gentamycin
- For VRE use
- Linezolid
- Daptomycin
- Micro lab sensitivities are very important for therapy
Enterococcus UTIs
- Often hospital acquired (associated with catheters)
- Removal of catheter alone may cure infection
- Urinalysis: negative for nitrites
UTIs negative for nitrites
only 2 bacteria do this
- Staph saprophyticus
- Enterococcus
Enterococcus Endocarditis
- Rare cause of endocarditis
- usually caused by GU tract manipulation
- TURP procedure for enlarged prostate
- Cystoscopy
- Vancomycin/Gentamycin often used for empiric therapy before culture data is available
Strep bovis features
normal colonic bacteria
Strep bovis illnesses
- Rare cause of bacteremia/endocarditis
- endocarditis or bacteremia infection is strongly associated with colon cancer (breakdown of the colon wall is how bovis got into the blood stream)
