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► Med - Pathology > Staphylococci > Flashcards

Staphylococci Flashcards

1
Q

Are staphylococci catalase positive or negative?

A

Catalase POSITIVE

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2
Q

Are staphylococci motile?

A

No

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3
Q

What is the aerobic status of staphylococci?

A

Facultative anaerobes.

They undergo aerobic respiration but are capable of growing under the absence of oxygen by undergoing fermentation.

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4
Q

What is the general appearance of staphylococci described as?

A

Bunch of grapes

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5
Q

Where is staphylococci generally found?

A
  • External environment
  • Anterior nose
  • Perineum
  • Axillae
  • Vagina
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6
Q

What are factors that can predispose a person to serious staphylococci infection?

A
  • Defects in leukocyte chemotaxis
  • Defects in opsonization by antibodies secondary to congenital or acquired hypogammaglobulinemias or complement component
  • Defects in intracellular killing of bacteria following phagocytosis due to inability to activate the membrane bound oxidase system
  • Skin injuries
  • Presence of foreign bodies
  • Infection with other agents - viruses
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7
Q

What are the usual sites of staphylococci infection?

A
  • Skin
  • Nose and Throat
  • GI Tract/Urethra/Vagina
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8
Q

Pyoderma

A

Pyoderma means any skin disease that is pyogenic.

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9
Q

Furuncle

A

Furuncle (or boil) skin disease caused by infection of hair follicles, resulting in localized accumulation of pus and dead tissue.

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10
Q

Carbuncle

A

Carbuncle is an abscess larger than a boil, usually with one or more openings draining pus onto the skin.

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11
Q

What are the virulence facts of S. aureus?

A 
– Capsules
– Protein A 
– Panton-Valentine Leukocidin (PVL) 
– Coagulase
– Hemolysins
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12
Q

What is the function of capsules in virulence?

A

Prevent ingestion of organism by PMNs

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13
Q

What is the function of Protein A in virulence?

A

Binds Fc region of IgG, interfering with opsonization and ingestion of organism by PMNs

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14
Q

What is the function PVL of in virulence?

A

An enzyme that alters cation permeability of rabbit and human leukocytes resulting in white cell destruction

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15
Q

What is the function of coagulase in virulence?

A

It binds to prothrombin catalyzing conversion of fibrinogen to fibrin, which in turn acts to coat bacterial cells with fibrin, rendering them more resistant to opsonization and phagocytosis

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16
Q

What is the function of hemolysis in virulence?

A

Lyse RBCs and/or act as toxins

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17
Q

α-hemolysin

A
  • Lyses RBCs of several animals
  • Dermonecrotic on subcutaneous injection
  • Leukocyte toxicity
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18
Q

ß-hemolysin

A
  • Sphingomyelinase, varying lysis of RBCs from different animals due to differences in membrane sphingomyelin content
  • Produces “hot-cold” lysis (hemolysis enhanced at low temperature after 35 C incubation)
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19
Q

∂-hemolysin

A
  • Acts as surfactant that disrupts the cell membrane, interacts with membrane to form channels that increase in size over time resulting in leakage of cellular contents
  • Some coagulase-negative staphylococci produce enough delta toxin to cause NEC in neonates
20
Q

𝛄-hemolysin

A

Only in some S. aureus and can lyse a variety of cells

21
Q

Exfoliatins or Epidermolytic Toxins

A

Responsible for “staphylococcal scalded skin syndrome,” dissolves the mucopolysaccharide matrix of epidermis, causing separation of skin layers; rare in adults

22
Q

Enterotoxins

A

Heat stable molecules that cause staphylococcal food poison and is the most common cause of food poisoning with a quick onset and quick recovery.

23
Q

Fibrinolysins

A

Fibrinolysins - break down fibrin clots and facilitate

spread of infection to contiguous tissues

24
Q

Hyaluronidase

A

Hyaluronidase - hydrolyzes intercellular matrix of acid mucopolysaccharides in tissue acting to spread organisms to adjacent tissue

25
Q

Phospholipase C

A

Phospholipase C - described in patients with ARDS and DIC. Tissues affected by this enzyme become more susceptible to damage and destruction by bioactive complement components and products during complement activation.

26
Q

What are the characteristics of super antigens?

A
  • Pyrogenicity
  • Superantigenicity
  • Enhance lethal effects of minute amounts of endotoxin
27
Q

What do super antigens all induce?

A

Polyclonal T-cell proliferation

28
Q

What are examples of super antigens?

A
  • Toxic shock syndrome toxin-1 (TSST-1) of S. aureus
  • Streptococcal pyrogenic exotoxins (SPE)
  • Streptococcal superantigens
29
Q

What is the use of coagulase in the lab?

A

Quick determination of S. aureus - it will cause coagulation as coagulase is traditionally associated with S. aureus

30
Q

What are the tests for coagulase?

A
  • Tube Coagulase

- Latex Agglutinization (fast)

31
Q

What is the most clinical significant coagulase negative staphylococci?

A

Staphylococcus epidermidis

32
Q

What are Staphylococcus epidermidis infections related to?

A

Indwelling devices like catheters, etc. Removal of the foreign body is necessary for cure of infection.

33
Q

What is Staphylococcus saprophyticus the main cause of?

A

Acute UTI in young women and cystitis

34
Q

How is Staphylococcus saprophyticus identified?

A

Identification based on negative coagulase and resistance to novobiocin

35
Q

What does Staphylococcus lugdunensis generally colonize?

A

Human inguinal area

36
Q

What diseases does Staphylococcus lugdunensis cause?

A

WIDE range of diseases just like S. aureus

37
Q

How is Staphylococcus lugdunensis identified?

A

Only species that is both PYR and Ornithine positive

38
Q

An organism identified as gram-positive cocci in clusters is isolated from the urine of a 21 year female with symptoms of acute cystitis. The laboratory reports that the organism is coagulase- negative, furozolidone susceptible and novobiocin resistant. What is the most likely identification of this bacterium?

A Staphylococcus aureus
B Staphylococcus epidermidis 
C Staphylococcus lugdunensis 
D Staphylococcus pyogenes
E Staphylococcus saprophyticus
A

E Staphylococcus saprophyticus

39
Q

What are six settings that area associated with MRSA outbreaks?

A

– Sports participants: football, wrestlers, fencers - MPSM
– Correctional facilities: prisons, jails
– Military recruits
– Daycare and other institutional centers
– Newborn nurseries and other healthcare settings
– Men who have sex with men - MSM

40
Q

Why did the rate of MRSA increase so much?

A

MRSA moved from a hospital only infection to a community infection that led to a doubling of the rate.

41
Q

What makes S. aureus methicillin resistant?

A

They acquire the mec A gene

42
Q

What is the function of the mecA gene?

A

Encodes for altered “penicillin-binding protein 2a” which has decreased binding affinity for ß-lactam antibiotics and allows peptidoglycan synthesis even in the presence of B-lactam antibiotics

43
Q

Where is mecA found?

A

mecA is carried on a mobile genetic element called “staphylococcal cassette chromosome mec” (SCCmec)

44
Q

What are five severe disease syndromes in which MRSA should be considered in the differential diagnosis?

A 
– Sepsis syndrome
– Osteomyelitis
– Necrotizing pneumonia
– Septic arthritis
– Necrotizing fasciitis
45
Q

What is the most effective measure to control the spread of MRSA?

A

MRSA testing of all patients entering ICUs and contact precautions for all patients testing positive, produced:

-A 75% decrease in MRSA bacteremia in ICUs
-And a 67% drop hospital wide

46
Q

What is the most effective lab technique for MRSA detection?

A

Real Time PCR as it allows for results VERY quickly

47
Q

What is the most important reservoir of methicillin resistant Staphylococcus aureus (MRSA) in hospitals?

A Colonized or infected patients
B Colonized or infected medical staff
C Clothing worn by patient care personnel
D Child visitors who attend day care centers
E Medical equipment

A

A Colonized or infected patients

► Med - Pathology (203 decks)

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