Staphylococci

Question 1

Describe staphylococci

Answer 1

Staphyle = greek for bunch of grapes

Gram +, coccus shaped anaerobe

Question 2

Name coagulase positibe and negative staphylococci

Answer 2

positive: S. aureus (latin for gold)
negative: S. epidermidis, S. saprophyticus (many others)

Question 3

is S. aureus virulent?

Answer 3

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

Question 4

Where does S. aureus colonize and how does it spread?

Answer 4

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)

Question 5

How does S. aureus get into the host?

Answer 5

surface proteins bind host proteins using adhesins

adhesins are important in endocarditis

Question 6

How many nosocomial infections does S. aureus cause?

Answer 6

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

Question 7

Is S. aureus an extra or intracellular pathogen?

Answer 7

extracellular pathogen

Question 8

S. aureus is a pyogenic infection, what does this mean?

Answer 8

pus-producing infection

Question 9

What is the “Hallmark” of S. aureus infection?

Answer 9

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

Question 10

Do abscesses from S. aureus heal on their own?

Answer 10

No they typically do not, they require drainage and maybe antibiotics

Question 11

What kind of infections can S. aureus cause?

Answer 11

enourmous range:

stye, boils, carbuncles, sinusitis, furuncles, hematogenous spread, endocarditis, pnemonia, emesis impetigo, diarrhea, toxic shock syndome, scalded skin syndrom, osteomyelitis, uti cystitis

Question 12

What are S. aureus’ regulated virulence factors?

Answer 12

produces many virulence factors

surface virulence factors expressed during exponential growth (colonization purposes)

secreted virulence factors (exotoxins) expressed during stationary phase (invasion adn spread)

Question 13

How do S. aureus’ virulence factors let it evade phagocytosis?

Answer 13

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

Question 14

How do S. aureus’ virulence factors let it evade leukocytes?

Answer 14

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

Question 15

What diseases due the virulence factors of S. aureus cause?

Answer 15

• skin lesions
• deep abscesses
• systemic infections

Question 16

What skin lesions do S. Aureus cause?

Answer 16

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

Question 17

What are deep abscesses caused by S. aureus?

Answer 17

• 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

Question 18

What are examples of S. aureus systemic infections, how hard are they to treat?

Answer 18

• bacteremia/epticemia, pneumonia, osteomyelitis, endocarditis
• very dangers, difficult to treat

Question 19

What is the systemic infcetion which affects bone marrow caused by S. aureus? describe it

Answer 19

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

Question 20

How can one get osteomyelitis?

Answer 20

• hematogenous spread (blood stream) or local infection (cellulitis)
• fractures
• joint replacement

Question 21

What is the systemic infection caused by S. aureus which affects heart valves?

Answer 21

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

Question 22

What class is an S. areus localized infection with systemic effects?

Answer 22

Toxin-mediated disease

• eg. toxic shock syndrome, staphylococcal scalded skin syndrome, food poisoning

Question 23

What causes toxic shock syndrome?

Answer 23

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)

Question 24

What are the symptoms of toxic shock syndrome?

Answer 24

Fever

red rash

hypotension leading to shock

desquamation

mortality <10%

Question 25

What are superantigens?

Answer 25

• 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

Question 26

What is staphylococcal scaled skin syndrome?

Answer 26

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

Question 27

What does staphylococcal food-borne illness?

Answer 27

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

Question 28

What are superbugs and what is an example?

Answer 28

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

Question 29

What is Methicillin resistant S. aureus associated with?

Answer 29

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

Question 30

What is Community acquired MRSA treated with? How virulent is it?

Answer 30

CA-MRSA strains lack exposure to health care setting

hypervirulent

still susceptible to a # of other antibiotics

Question 31

How does one Control MRSA?

Answer 31

• 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

Question 32

What does S. epidermidis colonize and how dangerous is it?

Answer 32

• colonizees the skin
• coagulase negative
• not as dangerous as S. aureus

Question 33

What are some defenses of S. epidermidis?

Answer 33

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)