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Infectious Agents > Staphylococcus > Flashcards

Staphylococcus Flashcards

1
Q

Staphylococcus is the only pathogenic member of the family _____

A

Micrococcus

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2
Q

Staphylococcus

A

Gram-pos, clustered cocci

  • natural host: any warm blood animals
  • normal flora of skin, nares, genitalia
  • opportunistic pathogens
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3
Q

Coagulase test

A
  • coagulase positive staph are more virulent
  • react with prothrombin in the serum in presence of coagulase reacting factor (CRF) = staphylothrombin
  • staphylothrombin converts fibrinogen to fibrin = clotted serum
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4
Q

______ serum is commonly used for a coagulase test

A

Rabbit

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5
Q

Catalase positive

A

Biochemical test that differentiates staph from strep!!!

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6
Q

Confirm coagulase positive with a _______

A

Tube test

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7
Q

What are the 5 species of coagulase positive staphylococci?

A
  • S. aureus
  • S. intermedius
  • S. pseudointermedius
  • S. delphini
  • S. schleiferi subspecies coagulans
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8
Q

S. aureus

A

Natural hosts are humans (nasal), primates

  • ectotypes have adapted to other animals (cattle)
  • infections in all mammals and birds
  • highly resistant to many antibiotics
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9
Q

S. intermedius

A

Residents of skin and hair coat of carnivores, esp. in dogs

  • isolated from cats, rarely horses, rodents, and birds
  • phenotypically similar to S. pseudointermedius and S. delphini
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10
Q

S. pseudointermedius

A

Most common residents of skin and hair coat of dogs

- often identified as S. intermedius

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11
Q

S. delphini

A

Residents of dolphins

- nearest relative is S. intermedius

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12
Q

S. schleiferi coagulans

A

Natural host are humans and animals

- causes external otitis in dogs

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13
Q

Coagulase variable specie

A

S. hyicus

  • 50/50 chance it will be coagulase positive
  • commonly isolated from dog, cat, pig, cattle, poultry
  • causes exudative epidermitis in pig, mastitis in cattle
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14
Q

Coagulase negative staphylococcus

A
  • limited to humans and/or primates, uncommon in other animals (S. epidermidis, saprophyticus, auricularis, saccharolyticus, carnosus, caseolyticus)
  • isolated from all mammals (S. xylosus, simulans, sciuri)
  • artiodactlya (S. lentus)
  • poultry (S. gallinarum)
  • goat (S. caprae)
  • cattle (S. chromogenes)
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15
Q

Diagnosis

A

Gram stain, catalase test, coagulase tube test, mannitol salt agar (MSA) fermentation

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16
Q

Complete hemolysis

A

Alpha, delta, gamma hemolysin

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17
Q

Incomplete hemolysis

A

Beta

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18
Q

What are the coagulase positive species?

A
  • S. aureus
  • S. intermedius
  • S. hyicus (variable)
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19
Q

What are the slide coagulase positive species?

A

Only S. aureus

20
Q

What are the MSA growth positive species?

A

All staph species

- S. aureus, intermedius, hyicus, epidermidis

21
Q

What are the MSA fermentation positive species?

A

Only S. aureus

- key test in differentiation

22
Q

Peptidoglycan

A

Consists of N-acetyl-glucosamine (NAG) and N-acetyl-muramic acid (NAM)

  • crosslinked by covalent bonds between pentapeptides and pentaglycine bridge
  • confers osmotic resistance and shape
23
Q

Teichoic acid

A

Polymer of glycerol phosphate

- involves in mucosal membrane attachment

24
Q

Capsular polysaccharide

A

Inhibit chemotaxis and phagocytosis

  • 4 serotypes (1, 2, 5, 8)
  • used in vaccine approach: CP5, CP8, exotoxin A
25
Q

What are the 4 membrane proteins?

A
  • protein A
  • clumping factor A and B
  • staphylokinase
  • MSCRAMMs
26
Q

Protein A

A

Small basic protein which reacts with Fc of IgG

  • fixes complement
  • antiphagocytic: promotes evasion of or interference with host immune system
27
Q

Clumping factor A and B

A

Cause of biofilm formation

  • binds to fibrinogen
  • induces adherence to host epithelial cell and platelet aggregation
28
Q

Staphylokinase (SAK)

A

Activates plasminogen to plasmin –> plasmin digests fibrin clot
- serine protease activity: degrades C3b (complement factor) and IgG

29
Q

MSCRAMMs

A

Microbial surface components recognizing matrix molecules

  • induce adherence and invasion (internalization) to host epithelial cell
  • fibronectin binding protein and alpha5beta1 integrin
  • autolysin (Atl) and heat shock protein (Hsc70)
  • clumping factor B and cytokeratins
  • protein A and tumor necrosis factor alpha receptor
30
Q

Hemolysins (hemotoxins)

A

Clear or complete hemolysis
- alpha: leukocidal, cytocidal, vasoconstriction, necrosis (skin and udder)
- delta: phospholipase, leukocidal, necrosis
- gamma or epsilon: weal hemolysis
Incomplete hemolysis
- beta (sphingomyelinase): enzymatic damage to RBC membrane in vitro, results in discolorization but not lysis

31
Q

Leukocidins

A
  • cytotoxic: leukocytes (granulocyte, monocyte, macrophage)
  • common in community acquired S. aureus
  • causes necrotizing pneumonia
32
Q

Exfoliative toxins

A

Cause blistering skin disease: scalded skin syndrome

- cleave desmoglein-1

33
Q

All staphylococcal enterotoxins are _____

A

Superantigen

  • directly binds to TCR and MHC 2
  • massive T cell activation
  • massive cytokine production leading to toxic shock
34
Q

What staphylococcal enterotoxins cause food poisoning?

A

A, B, C, D, E, G, and I

- emesis, diarrhea, fever, abdominal cramping

35
Q

Urease and phosphatase

A

In cystitis: hydrolyze urea –> increasing ammonia –> increase urine pH —> crystallization of struvite and apatite = calculi formation

36
Q

Most staph infections are ____ in origin

A

Endogenous

  • naturally colonized 30-40% population
  • non invasive colonization and adhesion to surface are common
  • may act as opportunistic or secondary invaders
37
Q

Quorum sensing

A

Regulating virulence factors by signaling molecules, autoinducing peptide: produced by agr locus

  • low AIP density: expression of adhesion molecules such as MSCRAMMs
  • high AIP density: expression of toxins and enzymes
38
Q

Staph usually does not cause _____

A

Any unique diseases or conditions

  • pyogenic host response most common
  • abscesses and septicemias in many species
39
Q

Canine staph infection

A

Common infections with S. intermedius followed by S. aureus
- pyodermas: superficial, deep, juvenile (usually secondary), hypersensitivity/allergic dermatitis, demodicosis, flea bites

40
Q

Dairy cattle and sheep staph infection

A

Leading cause of contagious mastitis

41
Q

Pig staph infection

A

S. hyicus

- exudative seborrheic dermatitis/greasy pig disease

42
Q

Botryomycosis

A

S. aureus

- granules with chronic granulomatous lesions of udder in mare, cow, sow, and spermatic cord of horses

43
Q

Tick pyemia

A

Type of septicemia that leads to widespread abscesses of lamb

44
Q

Purulent synovitis and bumblefoot of birds

A

S. aureus
- osteitis and tenosynovitis (proliferation of synovial membrane producing solid tumor-like mass) are common extensions of bumble foot

45
Q

No single virulence factor has been identified that can be used to make a _______

A

Vaccine

46
Q

Commercial products are commonly used to

A

Prevent bovine mastitis

47
Q

Treatments

A

Antimicrobials: use results of antibiotic sensitivity test, bactericidal drugs are best

  • penicillin G if sensitive
  • keflex or cefadroxil
  • clavamox
  • ciprofloxacin

Infectious Agents (44 decks)

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