L30 - Schreckenberger - Streptococcus and Enterococcus Flashcards
Compare and Contrast Staph vs Strep - Catalase?
Staph - catalase positive (bubble in presence of H2O2)
Strep - catalase negative
Compare and Contrast Staph vs Strep - colony structure?
Staph - cocci in clusters
Strep - cocci in pairs/chains
Compare and Contrast Staph vs Strep - medium for growth?
Staph - grows in minimal media
Strep - requires complex media
Compare and Contrast Staph vs Strep - optimal temperature?
For both staph and strep, they grow best between 35-37 Celsius
Compare and Contrast Staph vs Strep - environmental conditions?
Staph = aerobic environment preferred
Strep = anaerobic or CO2 atmosphere preferred
Compare and Contrast Staph vs Strep - color/appearance on agar?
Staph = off color/whitish
Strep = opaque
Streptococcus belongs to what family and has what 3 subsets?
Family = Streptococcaceae
3 groups = Pyogenic, pneumococci , viridans
What are 3 ways to classify strep?
- serologic properties - lancefield groups (letters of alphabet)
- hemolytic properties - beta/gamma/alpha
- biochem properties
How does hemolytic classification of streptococci work?
Looks at amount hemolysis in blood agar
Beta = complete hemolysis Alpha = incomplete hemolysis Gamma = no hemolysis
What are the 6 important species for strep?
- Streptococcus pyogenes (Group A)
- Streptococcus agalactiae (Group B)
- Other Beta hemolytic streptococci
- Viridans group streptococci
- Nutritionally Deficient streptococci
- Streptococcus pneumoniae
What are the clinical manifestations that can appear with Strep pyogenes infections?
- Acute Pharyngitis (strep throat)
- Impetigo
- Erysipelas
- Necrotizing Fasciitis
- Toxic-Shock like Syndrome
- Pueperal Sepsis
“7.” Scarlet Fever (is a complication of strep throat)
Describe Acute pharyngitis caused by s pyogenes
strep throat
transmitted by respiratory droplets
self limiting = will go away without antibiotics (but can result in sequelae)
Reoccurs b/c strep has different m proteins and antibiotics have an antibody to a specific m protein
Define Impetigo
localized skin disease that has a pustule with yellow crust that appears on face/extremities
associated with trauma/insect bites
seen in kids 2-5 yrs old
Define erysipelas
Spreading erythema (superficial reddening) that’s well demarcated
get fever and lymphadenopathy
lesions on face/legs often accompany strep throat
What is scarlet fever?
Complication of strep throat caused by eryrthrogenic toxin
typically spares the face
What are the clinical manifestations of scarlet fever?
Sore throat
Fever
Bright red tongue with a “strawberry” appearance
*Note: rash begins to fade 3-4 days after onset and desquamation begins
What is necrotizing fasciitis?
Strep infection in deep subcutaneous tissues at the fascia level (spreads along fascial planes)
There’s extensive destruction of muscle/fat
Mortality > 50%
Erysipelas and Impetigo affect what layer (skin, subcutaneous, or muscle)?
skin
What is the key clinical clue for necrotizing fasciitis?
Pain for necrotizing fasciitis is disproportionate to how it looks
What is toxic shock-like syndrome?
Multisystem organ failure (heart, respiratory tract, kidney)
SPE toxins are similar to Staph aureus TSST-1
Cultures are usually positive for group A strep (unlike staph toxic shock)
What is peuerperal sepsis?
After delivery/abortion
Organisms invade upper genital tract and cause a variety of symptoms
What are the 2 post-streptococcal sequelae (can occur if you don’t treat strep throat)?
Rheumatic Fever and Acute Glomerulonephritis
Describe Rheumatic Fever
Non-suppurative inflammatory disease that occurs 1-5 weeks after strep throat
Reoccurs in adulthood
Has characteristic cardiac lesions (Aschoff bodies) and valvular damage
Symptoms = Fever, carditis, subcutaneous nodules, chorea, polyarthritis
Describe Acute glomerulonephritis
Edema, hypertension, hematuria, proteinuria
Occurs after skin / respiratory infection
Certain M types are “nephritogenic”
Antigen-antibody-complement complexes are deposited in glomeruli (seen on kidney biopsy)
What are 4 forms of virulence associated with Strep pyogenes?
- Ability of the bacteria to adhere to the surface of the host cells
- Invade into the epithelial cells
- Avoid opsonization and phagocytosis
- Produce a variety of toxins and enzymes
What are 4 key virulence factors associated with Strep pyogenes?
Streptococcal pyrogenic exotoxins
M protein
Streptolysins and Streptokinase
What are Streptococcal pyrogenic exotoxins (SPE)?
3 distinct heat labile toxins (A, B, C)
Are “superantigens” that stimulate cytokine response leading to shock and organ failure
Strep toxic shock-like syndrome
Responsible for the rash in scarlet fever “erythrogenic exotoxin”
How do Streptolysins and Streptokinase enhance pathogenesis of S pyogenes?
allow spread of bacteria in tissues
How does M protein play a role in the virulence of S pyogenes?
binds epidermal cells and allows bacteria to survive (anti-phagocytic)
Degrades complement C3b
*Note: strains without M protein are AVIRULENT
How do you treat strep pyogenes?
Penicillin /ampicillin/amoxacillin
Drug of choice
No resistance worldwide
Cephalosporins
Erythromycin (if there’s penicillin allergy)
Streptococcus Agalactiae belongs to what group?
GBS…Group B Strep
What are the 2 forms of GBS infections that affect neonates? Describe each
Early Onset neonatal disease = 1st week of life –> Bacteremia, pneumonia, or meningitis
Late onset neonatal disease = 1 week-3 months old –> Bacteremia with meningitis
How does neonate GBS infection occur?
Maternal colonization of vagina or rectum exposes baby at delivery
Lack of protective maternal antibody
Sialic acid on polysaccharide capsule inhibits C’ allowing organisms to multiply
Thus…vaginal/rectal swabs are collected between 35-37 weeks gestation
How is GBS treated?
Penicillin / ampicillin = drug of choice
Add gentamicin to enhance killing
For culture positive pregnant women during labor – penicillin / ampicillin to prevent neonatal disease (KNOW)
Clindamycin if penicillin allergy
What are the limitations of Rapid Group A Detection kits (KNOW)
Good specificity but sensitivity is only 70%
If it’s positive you can be sure they have group a strep = good specificity
If it’s negative, it can still be there…false negative
So if you have a negative rapid antigen test you always do a backup culture
Isolation of S. bovis from blood is associated with ______
carcinoma of colon
The Strep Milleri group includes which 3 species of strep?
S. anginosus
S. constellatus
S. intermedius
*Note: these pyogenic bacteria are identified by characteristic caramel (butterscotch) odor when cultured on agar plates
The nutritionally deficient streptococci include? Have what vitamin deficiency?
Abiotrophia
Granulicatella
*Vitamin B6 deficient
A 7-year-old child presents with a fever, pain in his ankles, knees and wrist, and a new heart murmur. His mother said that he complained of a “sore throat” last month, but the symptoms resolved without taking him to the pediatrician. A rapid screening test for strep throat is negative. His most likely diagnosis is:
Rheumatic Fever
Are strep pneumoniae gram + or -? what about catalase?
Gram positive
Catalase negative
If you suspect strep pneumoniae, what tests do you run?
Always do both a sputum and blood culture
How do you identify strep pneumoniae in the lab?
Gram stain
Agar plates
Optochin test
Bile solubility
How do you identify strep pneumoniae from a gram stain?
Gram positive and lancet shaped diplococci (sometimes seen alone or in chains)
In csf = menigitis
In sputum = pneumonia
How do you identify strep pneumoniae from an agar plate?
can be runny mucoid colony or have flat dime shaped morphology with indented centers
What are the breakpoints for treating strep pneumoniae with penicillin?
If you give penicillin for meningitis, it won’t cross BBB well so a low MIC is needed (.06 or less) for it to be susceptible
If non-meningeal target – MIC can be as high as 2 (sepsis or pneumonia)
What are alternatives to penicillin for strep pneumoniae?
If allergic…uses macrolides or fluoroquinolones
What are the 2 major species of enterococci causing infection in humans?
E. Faecalis
E. Faecium
*enterococcus was formally group d streptococci
They are inherently resistant to many commonly used antibiotics
Are enterococci gram + or -?
Gram positive
What is PYR?
used in testing for enterococci, which are PYR positive (get a red color)
What infections are seen with enterococci?
Urinary tract
Mixed bacterial wound infections and decubiti
Sepsis, endocarditis, meningitis (rare)
Second most common nosocomial pathogen
Where is enterococci found and how is it spread?
Originates in flora of bowel
Transferred between patients
Acquired thru consumption of contaminated food/water
What is VRE?
Vancomycin Resistant Enterococci
What are the 3 VRE phenotypes?
A - plasmid mediated, highly resistant
B - chromosomal, high or low resistance
C - intrinsic intermediate level in E. gallinarum and casseliflavus (casseliflavus = yellow colonies)
*Treat via linezolid
How are enterococcal infections treated? (know!)
Intrinsically resistant to all cephalosporins, trimethoprim-sulfa, aminoglycosides
Faecalis is susceptible to penicillin/amp
Faecium is resistant to penicillin/amp
An organism is isolated from the blood of a 65 year-old male patient with a diagnosis of probable bacterial endocarditis. The organism displays streptococcus-like morphology on gram stain and is catalase-negative. On blood agar the colonies appear gamma hemolytic and are PYR positive. Patient was being treated with vancomycin plus an aminoglycoside with no response. This isolate is likely to be ____ species
Enterococcus
