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Bacteriology > Staphylococci > Flashcards

Staphylococci Flashcards

1
Q

What is staphylococci?

A
  • “Staphyle” – Greek for Bunch of Grapes
  • Gram-positive, coccus shaped
  • All staphylococci are haloduric
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2
Q

Staphylococci species

A 
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
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3
Q

What is staphylococcus epidermidis?

A
  • 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
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4
Q

What is Staphylococcus pseudintermedius?

A
  • Coagulase positive
  • Common colonizer of dogs
  • Causative agent of canine pyoderma
  • Resistant to several antibiotics
  • Transmission to humans can occur but is very rare
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5
Q

What is Staphylococcus aureus?

A
  • 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
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6
Q

Colonization of Staphylococcus aureus

A
  • 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)
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7
Q

Local infections of S. aureus

A
  • sinusitis
  • boils
  • soft tissue infections
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8
Q

Systemic infections of S. aureus

A
  • pneumonia
  • infective endocarditis
  • sepsis
  • osteomyelitis
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9
Q

Toxin mediated infections of S. aureus

A
  • menstrual toxic shock syndrome
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10
Q

More details about S. aureus

A
  • 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
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11
Q

Skin lesions

A
  • impetigo
  • stye
  • furuncle
  • carbuncles
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12
Q

What is impetigo?

A
  • 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
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13
Q

What is stye?

A
  • infection of the eye sebaceous glands
  • often will drain on its own, warm compress
  • do not lance
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14
Q

What is furuncle?

A
  • infection of hair follicle

- warm compress to drain

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15
Q

What is carbuncles?

A
  • infection of several hair follicles

- coalescing furuncles

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16
Q

What are deep abscesses?

A
  • 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
17
Q

What are systemic infections?

A
  • often no single “focus” of infection
  • e.g. bacteremia/septicemia, pneumonia, osteomyelitis, endocarditis
  • very dangerous, often difficult to treat
18
Q

What is osteomyelitis

A
  • 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
19
Q

What is infective endocarditis?

A
  • 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
20
Q

What are toxin-mediated diseases?

A
  • infection often localized, but effects are systemic

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

21
Q

What is staphylococcal food-borne illness

A
  • 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
22
Q

What is the toxic shock syndrome?

A
  • 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)
23
Q

What are superantigens?

A
  • 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
24
Q

What is staphylococcal scalded skin syndrome?

A
  • 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
25
Q

Virulence factors of S. aureus

A
  • expression of the virulence factors is regulated
  • surface virulence factors expressed during exponential growth
  • secreted virulence factors (exotoxins) expressed during stationary phase
26
Q

What is S. protein A (SpA)?

A
  • S. aureus surface protein
  • binds the Fc portion of IgG
  • antibodies are bound in the incorrect orientation to be recognized by phagocyte Fc-receptor
27
Q

Toxins that kill leukocytes

A
  • 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
28
Q

What is livestock associated (LA-MRSA)

A

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

Bacteriology (8 decks)

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