Staphylococci

Question 1

What is staphylococci?

Answer 1

• “Staphyle” – Greek for Bunch of Grapes
• Gram-positive, coccus shaped
• All staphylococci are haloduric

Question 2

Staphylococci species

Answer 2

Coagulase Positive Staphylococci
- Staphylococcus aureus
- "aureus" = Latin for gold
- Staphylococcus pseudintermedius
- Staphylococcus lugdenensis
Coagulase Negative Staphylococci
- Staphylococcus epidermidis
- Staphylococcus saprophyticus
- many other coagulase negative species

Question 3

What is staphylococcus epidermidis?

Answer 3

• coagulase negative
  not as dangerous as S. aureus
• a great skin colonizer
• resistant to several antibiotics
• produces a capsule (surface polysaccharide)
• S. epidermidis is known for forming biofilms
• major problem for implanted devices
• indwelling catheters and medical prostheses

Question 4

What is Staphylococcus pseudintermedius?

Answer 4

• Coagulase positive
• Common colonizer of dogs
• Causative agent of canine pyoderma
• Resistant to several antibiotics
• Transmission to humans can occur but is very rare

Question 5

What is Staphylococcus aureus?

Answer 5

• coagulase positive
• an efficient colonizer of humans that doesn’t usually cause problems
• 30% of human population is persistently colonized with a further 20-30% of the population is transiently colonized
• carriers of S. aureus are healthy, asymptomatic people
• colonization leads to greater risk of infection, but prognosis is also generally better

Question 6

Colonization of Staphylococcus aureus

Answer 6

• skin and mucous membranes, nose
• spread person-person by direct or indirect contact
• fomites (inanimate objects capable of transmitting an infectious disease) e.g. towels, razors, bandages
• S. aureus surface proteins bind host proteins using adhesins (e.g. fibronectin, collagen and elastin binding proteins)
• a leading cause of hospital-acquired (nosocomial infections)

Question 7

Local infections of S. aureus

Answer 7

• sinusitis
• boils
• soft tissue infections

Question 8

Systemic infections of S. aureus

Answer 8

• pneumonia
• infective endocarditis
• sepsis
• osteomyelitis

Question 9

Toxin mediated infections of S. aureus

Answer 9

• menstrual toxic shock syndrome

Question 10

More details about S. aureus

Answer 10

• generally an extracellular pathogen
• a “pyogenic” or pus-producing infection
• the “Hallmark” of S. aureus infection is the 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
• abscesses don’t typically heal on their own – require drainage and maybe antibiotics

Question 11

Skin lesions

Answer 11

• impetigo
• stye
• furuncle
• carbuncles

Question 12

What is impetigo?

Answer 12

• superficial skin infection usually in young children
• the non-bullous form has
  pimple-like lesions with pus
  (also caused by Streptococcus pyogenes)
• the bullous form has painless, fluid filled blisters
• Ecthyma – pus filled sore that turns into a deep ulcer

Question 13

What is stye?

Answer 13

• infection of the eye sebaceous glands
• often will drain on its own, warm compress
• do not lance

Question 14

What is furuncle?

Answer 14

• infection of hair follicle

- warm compress to drain

Question 15

What is carbuncles?

Answer 15

• infection of several hair follicles

- coalescing furuncles

Question 16

What are deep abscesses?

Answer 16

• not superficial but still localized – has a “focus” of infection
• e.g. cellulitis, liver, lung, kidney, tooth etc
• wound or surgical infections
• symptoms may not be obvious and may be more “constitutional” (whole body) e.g. fever, chills, malaise etc
• deep abscesses can become systemic

Question 17

What are systemic infections?

Answer 17

• often no single “focus” of infection
• e.g. bacteremia/septicemia, pneumonia, osteomyelitis, endocarditis
• very dangerous, often difficult to treat

Question 18

What is osteomyelitis

Answer 18

• infection of bone or bone marrow
• S. aureus is the most common cause
• can come from:
• hematogenous spread or local infections
• fractures
• joint replacement
• diagnosed with X-ray/CT/MRI and biopsy
• can be very difficult to treat and may require open surgery and prolonged i.v. antibiotics

Question 19

What is infective endocarditis?

Answer 19

• Infective Endocarditis infection of the heart valves
• typically occurs on damaged or prosthetic heart valves and with i.v. drug users
• the lesion is called the “vegetation”
• bacteria can grow to large numbers and “seed” causing strokes and pulmonary embolisms
• fatigue, fever, heart murmurs, splinter hemorrhages

Question 20

What are toxin-mediated diseases?

Answer 20

• infection often localized, but effects are systemic

- e.g. food poisoning, toxic shock syndrome, staphylococcal scalded skin syndrome

Question 21

What is staphylococcal food-borne illness

Answer 21

• Staphylococcal enterotoxins cause “Staph” food poisoning - proteins also function as superantigens
  the toxin is preformed in food - does not require the ingestion of viable staphylococci
• Symptoms include the sudden onset nausea, vomiting, and stomach cramps. Most people also have diarrhea.
• 1 µg sufficient to induce “projectile” vomiting
  mechanism remains poorly characterized

Question 22

What is the toxic shock syndrome?

Answer 22

• characterized by acute onset of fever, hypotension, rash, multi-organ dysfunction, (desquamation)
• caused by both Staphylococcus aureus and Streptococcus pyogenes
• staphylococcal TSS has menstrual and non-menstrual forms (<5% mortality)

Question 23

What are superantigens?

Answer 23

• superantigens are secreted toxins
• function to over activate large numbers of T cells and cause a systemic inflammatory response
• produces a “cytokine storm”
• eventually results in vascular leakage leading to shock and organ failure
• toxic shock syndrome toxin-1 is responsible for the menstrual form
• staphylococcal enterotoxins are also superantigens

Question 24

What is staphylococcal scalded skin syndrome?

Answer 24

• caused by exfoliateive toxin
• exfoliative toxins are proteases that destroy host proteins that hold cells together in the superficial layers of the skin
• primarily affects neonates
• cause skin peeling
• heals in about 1 to 2 weeks

Question 25

Virulence factors of S. aureus

Answer 25

- expression of the virulence factors is regulated - surface virulence factors expressed during exponential growth - secreted virulence factors (exotoxins) expressed during stationary phase

Question 26

What is S. protein A (SpA)?

Answer 26

- S. aureus surface protein - binds the Fc portion of IgG - antibodies are bound in the incorrect orientation to be recognized by phagocyte Fc-receptor

Question 27

Toxins that kill leukocytes

Answer 27

- S. aureus can make a number of cytolytic toxins that kill white blood cells - often called “hemolysins” because they can lyse red blood cells - actual targets are mostly white blood cells - work by forming holes in membranes which results in the lysis of the cell - e.g. a-toxin and leukocidins - helps to protect S. aureus in abscesses and for spreading

Question 28

What is livestock associated (LA-MRSA)

Answer 28

Many livestock species are now regularly colonized by S. aureus due to the frequency of contact with humans Many domestic livestock suffer diseases due to S. aureus infection Antibiotics have been frequently used as growth factors in livestock farming The combination of these factors has resulted in the emergence of strains of MRSA that have acquired antibiotic resistance in animals but have subsequently transmitted back into humans These strains of S. aureus are termed Livestock associated (LA)-MRSA