Lecture 14 Flashcards
Staphylococci stain
GramPos
How does staphylococci look on a plate
Clusters of spheres
How can staphylococci live on skin?
Catalase + (for oxygen survival)
Can survive on NaCl
What are four ways to differentiate staphylococci?
Hemolysis pos vs neg
Coagulase pos vs neg (neg are mostly opportunists)
What are two coagulase- staphylococci
S. epidermidis
S. saprophyticus
What are two ways staph can cause illness?
Via growth
Via toxins
What is a more superficial manifestation of S. aureus and how does it cause illness? How does it present?
Via growth of bacteria
Classic lesion is a furuncle
Walled off my coagulase
Folliculitis and complication of acne are more specific examples of this!
What is non-bullous impetigo and what causes it?
Crusted blisters Mostly in children and teens Infection of epidermis Staph #1 cause Strep group A #2
What is the number one cause of bacteremia and wound infections?
S. aureus
Realize that this bug can also release toxins and cause toxemia
What is a manifestation of S. aureus via exotoxin release
Bullous exfoliation (SSSS)
Bullous impetigo
Toxic shock syndrome
Food poisoning
What is bullous exfoliation (SSSS) and what causes it
Intraepidermal splitting and peeling
Mostly children (daycares and neonatal wards)
Good prognosis in kids, bad in adults because of bacteremia
Caused by exotoxins from S. aureus
What is bullous impetigo and what causes it?
Fluid filled blisters in epidermis
Almost always < 2 y/o
S. aureus exotoxin is only cause
What is toxic shock syndrome and what causes it?
Abrupt onset fever, skin desquamation, hypotension, multi-system involvement, DIC
Immune response to specific toxin (TSST) from S. aureus
Also a MRSA strain
S. aureus food poisoning manifestation
Violent N/V
Occasional diarrhea
No fever (onset 4 hours, gone in 24)
It is similar to B. cereus emetic variety
S. epidermidis coagulase status
Negative
What is a common manifestation of S. epidermidis
Nosocomial infection of implanted devices, peritoneal dialysis
Biofilm formation
What is clinical manifestation of S. saprophyticus
Associated with UTI in young woman (E. coli is still number one cause)
How is S. epidermidis often spread
Fomites (sheets and clothing)
What food is staph especially associated with and why?
Ham because it can live in salty conditions (also with cream and mayo)
Why can’t staph be eradicated?
It’s a native flora
Why is staph hard to treat?
It rapidly develops resistance
MDR
MRSA (mecA on SCC cassette)
Abx resistance spread through R-plasmid
What are the antigens on staph?
GramPos so no LPS
Peptidoglycan (PAMP)
Teichoic acid
PROTEIN A (binds to Fc part of antibody-resembles B cell)
Iron binding protein (scavenge Fe from heme)
What toxins does staph have?
Coagulase-wall off infections Hyaluronidase Hemolysin (a-RBC & plat, b-sphingomyelin) Leukocidin (kills WBCs) Exfoliative toxin TSST-superantigen-induces T cells to produce IL-1, TNF Enterotoxins-food poisoning Quorum sensing-biofilms
How do you treat MRSA?
Strict isolation
Chlorhexidine washes
Vanco-for severe
SxT, clinda, linezolid for moderate
Furuncle Tx
Drainage and tetracycline
S. saprophyticus Tx
Quinolones
SxT
Augmentin
How can you be sure to optimize Tx for staph?
Do a susceptibility testing
Streptococci and enterococci stain?
GramPos
Strep and enteroc. appearance on a plate
Chains of spheres
What is capsule of strep and entero
Polysaccharide or hyaluronic acid
What are strep and entero classified by
Hemolysis (alpha, beta, or gamma-none)
Not the same as group A and B
Which type of strep and entero are native? Which is not?
Alpha-native
Beta-not
How do you determine group A-H, K-U strep infections?
Lancefield serotyping-specific amino acids and teichoic acid cell wall antigens
What are strep resistant to?
Abx, NaCl, Bile
What are the characteristics of group A strep?
Beta hemolytic
Bacitracin sensitive
What are invasive infections Strep pyogenes can cause?
Human erysipelas-dermis and SQ fat infection Puerperal fever-Sterp inf. of uterus after delivery Surgical sepsis Scarlet fever Streptococcal toxic shock-like syndrome Necrotizing fasciitis Pneumonia Bacteremia
Scarlet fever (S. pyogens) symtoms
Strep bacteremia Diffuse upper body rash Fever Strawberry tongue Usually starts as pharyngitis
How does S. pyogens cause toxic shock-like fever?
TSLT which is a superantigen toxin like TSST
Does does S. pyogens cause necrotizing fasciitis
Deep cellulitis that spreads through SQ and fascia
What types of local infections can S. pyogens cause?
Pharyngitis (can spread to OM, sinuses, meninges)
Impetigo
Post-infection sequellae (immune mimicry)
What are symptoms of S. pygogens strep throat
Fever
Ant. cervical lymphadenopathy
Tonsil exudate
NO COUGH
What are symptoms of S. pyogens impetigo
Crust, purulent drainage especially on face
Always non-bullous type
What are post-infection problems from S. pyogens?
Acute glomerulernephritis (blood and protein in urine, may become chronic) Acute rheumatic fever (heart valve damage)
What is the way strep throat is most often spread?
Nasal droplets
How is s. pyogens impetigo most often spread?
Contact, fomites
When is rheumatic fever like to present?
1-4 weeks after disseminated strep infection
Not likely from first infection
What is strep pyogens pathogenesis
M-proteins (some cause secretion of heart-reactive antibodies)
Hyaluronic acid capsule (evasion)
C5a peptidase (antiphagocytic)
Strepodornase (DNAase)
Hyaluronidase
Exotoxin A,B,C-pyrogenic,associated with scarlet fever
Hemolysins
Strep pyogens control?
Keep from spreading (pasteurize milk)
All Group A suscepticle to PenG
Treat ARF/AGN with anti-inflammatories
What are characteristics of strep agalactiae
Beta hemolytic
CAMP+
Bacitracin resistant
How are strep agalactiae organized?
Polysaccharide capsule (5 types)
What diseases are caused by s. agalactiae? Who do they affect?
Infants, immunocompromised, elderly Neonatal sepsis and pneumonia (1-7 days post partum) Neonatal meningitis 1 week old RDS, bacteremia, soft tissue infections in eldery
How is s. agalactiae transferred?
From infected mothers during delivery
s. agalactiae treatment?
Screen from Group B strep before delivery
If positive cephtriaxone or amp + streptomycin
What are the two types of Group D streps?
Enterococci and S. bovis
Group D strep characteristics
Non hemolytic
Grow in NaCl and bile
How does group D strep infections usually get transferred?
Nosocomial
Mostly from hands of hospital workers
Also from colon lesions
Group D strep diseases
Bacteremia
Endocarditis
UTI (especially from caths)
How do you treat Group D strep?
Very resistant
High doses of PCN and aminoglycosides
Vanc for enterococcus but becoming resistant
Viridans streptococci characteristics
alpha hemolytic
Optochin resistant
Ox bile resistant
Viridans strep infection
Most commonly sub-acute bacterial endocarditis especially after tooth extraction
How does viridan strep cause endocarditis?
Is a normal URT flora, gets into blood after dental work
Viridan strep treatment
High does of PCN or Vanc
Prophylactic Abx before dental work in some PTs
Surgical management usually better for endocarditis
Strep pneumonia characteristics
alpha hemolytic
Optochin sensitive
ox bile sensitive
Diplococci with large polysaccharide capsule
What is clinical manifestation of S. pneumonia
Sudden onset lobar pneumonia with fever
Sharp pain
May spread to OM (#2) or meninges (#1 for adults)
Most common cause of CAP
S. pneumonia
Remember this is a native URT flora
How does s. pneumonia survive phagocytes?
Living in mucous protects them
Who is more at risk for S. pneumonia infection?
Alcohol or drug users because of aspiration risk
People with general debility
S. pneumonia control
23-valent for adults
13 valent for kids
3rd gen cephalosporins, macrolides, quinolones
