Staphylococci Flashcards
Describe staphylococci
Staphyle = greek for bunch of grapes
Gram +, coccus shaped anaerobe
Name coagulase positibe and negative staphylococci
positive: S. aureus (latin for gold)
negative: S. epidermidis, S. saprophyticus (many others)
is S. aureus virulent?
No, it is an efficient colonizer of humans that doesn’t usually cuase problems
Carriers of S. aureus are asymptomatic, but at greater risk for infection, prognosis is also generally better
Where does S. aureus colonize and how does it spread?
Colonizes skin and mucous membranes, nose (30% of people are colonized)
spreads by direct or indirect contact (person to person)
fomites (objects capable of transmitting disease like towels, bandaids razors)
How does S. aureus get into the host?
surface proteins bind host proteins using adhesins
adhesins are important in endocarditis
How many nosocomial infections does S. aureus cause?
leading cause of hospital-aquired (nosocomial) infections
In the US: >10 million skin and soft tissue infections/year,
94,000 invasive infections
19,000 deaths
Is S. aureus an extra or intracellular pathogen?
extracellular pathogen
S. aureus is a pyogenic infection, what does this mean?
pus-producing infection
What is the “Hallmark” of S. aureus infection?
abscess
- heat, redness, swelling and pain
- a collection of dead neutrophils (pus) due to infection
- abscesses can occur in any organ but are most frequent on the skin
- can cause major complications if the organisms spread from the abscess
Do abscesses from S. aureus heal on their own?
No they typically do not, they require drainage and maybe antibiotics
What kind of infections can S. aureus cause?
enourmous range:
stye, boils, carbuncles, sinusitis, furuncles, hematogenous spread, endocarditis, pnemonia, emesis impetigo, diarrhea, toxic shock syndome, scalded skin syndrom, osteomyelitis, uti cystitis
What are S. aureus’ regulated virulence factors?
produces many virulence factors
surface virulence factors expressed during exponential growth (colonization purposes)
secreted virulence factors (exotoxins) expressed during stationary phase (invasion adn spread)
How do S. aureus’ virulence factors let it evade phagocytosis?
S. aureus is resistant to phagocytosis
- protein A is a surface protein
- binds to the Fc protion of IgG
- antibodies are bound in the incorrect orientatino to be recognized by neutrophil Fc-receptors
How do S. aureus’ virulence factors let it evade leukocytes?
Toxins kill leukocytes
- S. aureus can make a # of cytolytic toxins that kill white blood cells
- often called “hemolysins” they can lyse red blood cells
- alpha toxin and leukocidins
- actual targets are likely white blood cells
- helps protect S. aureus in abscesses and for spreading
What diseases due the virulence factors of S. aureus cause?
- skin lesions
- deep abscesses
- systemic infections
What skin lesions do S. Aureus cause?
Impetigo - superficial skin infection usually in young children
- the non-bullous form has pimple-like lesions with pus (also caused by S. pyogenes)
- bullous form has painless fluid filled blisters
Stye - infection of the eye sebaceous gland
- will drain on its own
- warm compress, do not lance
Furuncle (boil) - infectino of hair follicle
- warm compress to drain
Carbuncles - infection of several hair follicles
- coalescing furuncles
What are deep abscesses caused by S. aureus?
- not superficial but still localized (has focus of infection
- e.g. cellulitis, liver, lung, kidney, tooth, etc
- wound or surgical infections
- symptoms may not be obvious and may be more “consititutional” (whole body, like fever abd chills)
- deep abscesses can become systemic
What are examples of S. aureus systemic infections, how hard are they to treat?
- bacteremia/epticemia, pneumonia, osteomyelitis, endocarditis
- very dangers, difficult to treat
What is the systemic infcetion which affects bone marrow caused by S. aureus? describe it
Osteomyelitis
- Caused by other types, but S. aureus is the most common
- can be very difficult to treat and may require open surgery, i.v. antibiotics
How can one get osteomyelitis?
- hematogenous spread (blood stream) or local infection (cellulitis)
- fractures
- joint replacement
What is the systemic infection caused by S. aureus which affects heart valves?
Infective endocarditis
- typically occurs on damaged or prosthetic heart valves and with i.v. drug users
- lesion is called the vegetation
- bacteria can grow to large #s and seed causing strokes and pulmonary embolisms
- fever, heart murmurs splinter hemorrhages
- ~25% are due to S. aureus but are more aggressive
What class is an S. areus localized infection with systemic effects?
Toxin-mediated disease
- eg. toxic shock syndrome, staphylococcal scalded skin syndrome, food poisoning
What causes toxic shock syndrome?
superantigens
non-menstrual form
- can occur from any S.aureus infection
- also caused by Strepococcus pyogenes during invasive infections
Menstrual form
- due to S. aureus vaginal colonization and is associated with high absorbancy tampons (due to toxic shock syndrom toxin-1)
What are the symptoms of toxic shock syndrome?
Fever
red rash
hypotension leading to shock
desquamation
mortality <10%
What are superantigens?
- secreted toxins
- function to over activate large #s of T cells and cause systemic inflammatory responses
- produces a cytokine storm
- eventually results in vascuolar leakage leading to shock and organ failure
- toxic shock syndrome toxin-1 is responsible for the menstrual form
- staphylococcal enterotxoins are also superantigens
What is staphylococcal scaled skin syndrome?
Caused by exfoliative toxin
- these are proteases that destroy host proteins that hold cells together in the superficial layers of the skin
- primaryily affects neonates (newborns)
- causes skin peeling
- heals in 1-2 weeks
What does staphylococcal food-borne illness?
Staphylococcal enterotoxins cause staph food poisoning
- proteins also function as superantigens
- the toxin is preformed in food - does not require the ingestion of vialbe staphylococci
- 1 nanogram is sufficient to induce projectile vomiting
- mechanism remains uncharacterized
What are superbugs and what is an example?
Example: Methicillin resistant S. aureus
- Superbugs are resistant to multiple antibiotics
- early penecillin resistance due to S. aureus beta-lactamases
- methicillin is a modified penicillin that is insensitive to beta-lactamases
- methicillin resistance encoded by the “mec” region - encodes a “penicillin binding protein” called PBP2a
- normal PBP is bound by beta-lactam antibiotics but these antibiotics can’t bind PBP2a
What is Methicillin resistant S. aureus associated with?
Typically hospital associated or health care-associated
- HA-MRSA
- patients generally have co-morbitidy
Index cases for “community acquired” MRSA
- CA-MRSA
- 1997-1999 North Dakota and Minnesota
- 4 pediatric deaths from pneumonia
What is Community acquired MRSA treated with? How virulent is it?
CA-MRSA strains lack exposure to health care setting
hypervirulent
still susceptible to a # of other antibiotics
How does one Control MRSA?
- Wash hands
- screen and isolate patients in hospitals (single rooms)
- proper cleaning using disinfectants
- proper use of antibiotics
- vancomycin only as a last resort
- new antibiotics need to be developed
What does S. epidermidis colonize and how dangerous is it?
- colonizees the skin
- coagulase negative
- not as dangerous as S. aureus
What are some defenses of S. epidermidis?
Produces a capsule (surface polysaccharide)
S. epidermidis is known for forming biofilms
- Complex structured communities of bacteria
- not free living (planktonic)
- resistant to antibiotics and hard to remove
- major problem for implanted devices (indwelling catheters and medical prostheses)
