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Microbiology Part 1 > Lec4 Staphylococci > Flashcards

Lec4 Staphylococci Flashcards

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1
Q

What is shape of staphylococci?

A
  • pram positive

- cocci

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2
Q

What distinguishes streptococci from staphylococci?

A
  • staphylococci are catalase positive

- staph grows in clusters, strep grows in pairs/chains

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3
Q

How can staphylococcus aureus be distinguished?

A
  • gram positive coccus
  • forms clusters [rather than chains]
  • coagulase positive
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4
Q

Is staphylococcus aureus coagulase negative or positive?

A

positive

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5
Q

What are the virulence factors of staphylococcus aureus?

A
  • growth as biofilm
  • surface factors
  • secreted proteins [exotoxins]
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6
Q

What is action of surface factors of staphylococcus aureus?

A
  • 6 surface proteins
  • facilitate binding to collagen, fibronectin, ferritin
  • they are adhesion factors
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7
Q

What is action of secreted proteins of staphylococcus aureus?

A
  • 5 cytotoxins and 12 enzymes

- facilitate hemolysis and spread of infection

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8
Q

What is the role of protein A in staphylococcus aureus?

A
  • protein A is a virulence factor present in most strains, correlated with virulence
  • bind Fc terminal of IgG –> inhibits complement and phagocytosis
  • increases ability to cause inflammatory diseases [skin infection, organ abscess, pneumonia, endocarditis
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9
Q

What is role of capsule in staphylococcus aureus?

A
  • polysaccharide capsule surrounds organism

- prevent opsonization

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10
Q

What are two staphylococal proteins that act as superantigens?

A
  • staphylococcal enterotoxin
  • TSST-1

lead to toxic shock

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11
Q

What does staphylococcal release of alpha toxin do?

A

cause septic shock

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12
Q

Are staphylocci typically pyogenic or non-pyogenic?

A

pyogenic - means they form lots of pus

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13
Q

Are coagulase positive or coagulase negative strains of staphylococci more virulent?

A

coagulase positive [s. aureus] are more virulent

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14
Q

What are 3 toxin mediated mechanisms of staph aureus [including disease and which related toxin]?

A

toxic shock syndrome [TSST-1 toxin]

scalded skin syndrome [exfoliative toxin]

rapid onset food poisoning [preformed enterotoxin]

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15
Q

What are the 4 stages of bacterial adherence and what drives each step?

A
  1. attachment: mediated by non-specific forces
  2. adhesion: driven by specific adhesion-receptor interactions
  3. aggregation: bacterial macrocolony formed imprved nutritional microenvironment and protects bacteria from host defenses
  4. dispersion
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16
Q

What are 4 potential sources for bacterial contamination of intravascular catheters?

A
  • contamination of catheter hub
  • contamination of infusate
  • transcutaneous migration
  • hematogenous seeding from different site
17
Q

What is “slime layer”

A

staph aureus and epidermis both form slime layer around foregin body

18
Q

What are the host immune responses to staph aureus infection?

A
  • primarily mechanical by epidermis [if dont have portal of entry can’t get through epidermis]
  • opsonization
  • neutrophill phagocytosis
19
Q

What are the clinical manifestations [disease] associated with staph aureus?

A
  • skin and soft tissue infection [most common]
  • vascular infection [endocarditis]
  • metastatic infection [septic arthritis]
  • osteomyelitis
  • hospital acquired infection
  • toxic shock
  • food poisoning [toxin mediated]
20
Q

What are the two non-suppurative complications of staph aureus

A
  • toxic shock [tsst-1/enterotoxin mediated]

- food poisoning [toxin mediated]

21
Q

What is the difference staph and strep vascular infection?

A
  • staph can land anywhere, does not require damaged surface or molecular mimicry
  • strep requires previous damage to cause endocarditis or works by molecular mimicry in rheumatic fever
22
Q

S aureus buttock abscess - treat?

A
  • growing vertically into bigger puss

- need to treat by drainage and antibiotics

23
Q

why are diabetics prone to infection [and s aureus in particular]?

A

high blood sugars paralyze hemotaxis–> blunt immune response

24
Q

What two things can commonly cause impetigo?

A

strep pyogenes

staph aureus

25
Q

How do you determine staphylococcoal from streptococcal cellulitis?

A
  • strep pyogenes and staph aureus both pus-formers
  • BUT –> staph produces microabscesses with visible exudation of pus. staph cellulitis can also be subtle and barely noticeable
26
Q

What is chalazion?

A
  • infected meibomian gland in eye

- due to colonizationo f conjunctiva by staph

27
Q

Why might staph endocarditis require emergency valve replacement?

A

bacterial vegetations on the valve might embolize to other parts of the body

28
Q

true or false: s. aureus can only infect previously damaged valve

A

false – staph aureus can infect any valve normal or damaged

by contrast, strep can only infect previously damaged valves

29
Q

What are roth spots?

A
  • retinal hemorrhages caused by septic microemboli from bacterial endoccarditis
30
Q

What is MRSA?

A
  • methicillin-resistant staphylococcus aureus
  • very limited therapeutic options
  • formerly almost exclusively hospital-acquired, no more common in community
31
Q

What is staphyloccocal food poinsoning?

A
  • common cause of acute food poisoning
  • asocated with unrefrigerated dairy
  • ingestion of preformed toxin causes vomitting and diarrhea
  • no invasion by organism or superantigen involved
32
Q

Treatment of staph infections?

A
  • cell wall active semisynthetic penicillins [oxacillin, nafcillin]
  • certain cephalosporins [cefazolin]
33
Q

What is treatment of MRSA and other resistant strains?

A

vancomycin

34
Q

Is staphylococcus epidermidis coagulase positive or negative?

A

negative

35
Q

What are general features of staph epidermidis?

A
  • coagulase negative
  • normal inhabitant of skin
  • rarely causes disease in normal host in absence of foreign bodies
  • associated with infections related to medical devices
  • relatively resistant to common antibiotics
36
Q

What is mech of s epidermidis as a pathogen of medical devices?

A
  • forms biofilm [slime layer] = colonizes polymer surface of intravascular catheter with thick slime multilayer containing exopolysaccharide and organisms embedded within it to keep making more exopolysaccharide
  • microcolonies resistant to antibiotics
37
Q

Two types of clinical syndromes assocated with Staph epidermidis?

A
  1. infection associated with intravascular device

2. central nervous system infection associated with foreign bodies

38
Q

What is main clinical syndrome of saphylococcus saprophyticus?

A
  • causes UTIs

- has receptor that allows it to bind mucosal receptors in GU tract and cause ascending infection

39
Q

Is staphylococcus saprophyticus resistant or sensitive to antibiotics?

A
  • highly sensitive to all antibiotics

Microbiology Part 1 (24 decks)

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