6 – Staphylococcus

Question 1

Microbiological characteristics

Answer 1

• Gram-positive cocci
  o Grape like clustering
• Aerobic or facultatively anaerobic
• Often described as coagulase positive or negative
• Colonies: creamy/white on blood agar
• Biocontainment level 2

Question 2

Staphylococcus aureus

Answer 2

• Hemolytic (beta-hemolysis, 2 zones)
• FERMENTS mannitol=yellow colonies

Question 3

Staphylococcus aureus: clinical significance (contagious mastitis in cows)

Answer 3

 Udder of colonized cow is main reservoir
 Adheres and invades mammary epithelium
 Can form small colony variants and ‘L-forms’ (inactive=hard to grow and treat)
 Disease
* Peracute: rapidly progressive clinical disease
* Subclinical: no clinical signs, decreased production
 Economic cost
* Reduced production
* Sporadic clinical disease
 Improve hygiene for control
* Disinfect equipment
* Not milking affected quarter
 Cull S. aureus carrier cows
 Intramammary antibiotics
* Be aware of methicillin resistance
* MR S. aureus=resistant to all beta-lactam therapies

Question 4

Staphylococcus aureus: clinical significance (infections in chickens)

Answer 4

 Bones, tendon sheaths, joints
* Bumble foot
 Associated with green-liver osteomyelitis complex
 Morbidity and mortality usually low (individuals not flocks)
 Pathogenesis not clearly defined
* Likely opportunistic
 Good management to reduce stress and injury
* Remove sharp objects, ensuring good quality
 Vaccines NOT effective
 Treatment based on SUSCEPTIBILITY TEST results

Question 5

Staphylococcus epidermidis

Answer 5

• NOT hemolytic
• Does NOT ferment mannitol=not yellow

Question 6

Staphylococcus pseudointermedius

Answer 6

• More white/grey on blood agar than S. aureus
• Double zone beta-hemolysis on blood agar

Question 7

Staphylococcus pseudointermedius: clinical significance

Answer 7

o Wide variety of opportunistic infections
 Pyoderma and otitis externa
* Often secondary to underly disease
 Surgical site implants
 Necrotizing fasciitis
 Nosocomial infections
o *addressing primary disease is key to success
 Determine site of infection

Question 8

Staphylococcus hyicus: clinical significance

Answer 8

o Exudative epidermitis (greasy pig disease)
 Acute or peractue (sporadic within herd)
 Seen in suckling and newly weaned piglets when
* Mixing liters
* Animals fight
* Teeth are unclipped
* Rough bedding
 High mortality rate, up to 70%
 Early antimicrobial treatment may be effective

Question 9

Staphylococcus chromogenes

Answer 9

o Coagulase negative
o Clinical significance
o Most frequently isolated coagulase negative species from bovine mastitis
o Implicated in ovine and caprine (goats) mastitis
o Pigs: cause a greasy pig-like syndrome

Question 10

Coagulase test

Answer 10

• Positive test=when tubes tipped on side can see clot formation

Question 11

DNase test

Answer 11

• Positive reaction=zone of clearing surround bacterial growth (‘halo’)

Question 12

Natural host associated organisms

Answer 12

• Part of normal microbiota
• Different species are associated with different animals
  o 30% people: Staphylococcus aureus
  o 90% dogs: Staphylococcus pseudintermedius
• *environmental contamination may play a role in hospital environments (NOSOCOMIAL INFECTIONS)

Question 13

Taxonomy

Answer 13

• 64 SPECIES
  o 1. Coagulase negative or positive
   Negative= label CoNS
   S. schleiferi are coagulase variable
  o 2. Hemolysis negative or positive
   Negative=S. hyicus
  o 3. Hyaluronidase Acetoin negative or positive
   Positive=S. aureus
   Negative=
• S. intermedius group
  o Hard to differentiated biochemically
  o S. pseudintermedius

Question 14

Virulence factors (most known about S. aureus)

Answer 14

• Toxic-shock syndrome toxin (TSST)
• Enterotoxins
• Exfoliatins
• Various leucocidins (ex. Panton-Valentine Leucocidin PVL
• MSCRAMM
• Catalase
• Hyaluronidase

Question 15

• Toxic-shock syndrome toxin (TSST)

Answer 15

o Super antigen (can stimulate a much larger number of T-cells than ordinary antigen)

Question 16

• Enterotoxins

Answer 16

o Responsible for food poisoning

Question 17

• Exfoliatins

Answer 17

o Skin damage: results in scalded appearance

Question 18

• Various leucocidins (ex. Panton-Valentine Leucocidin PVL)

Answer 18

o Destruction of WBCs

Question 19

• MSCRAMM

Answer 19

o Facilitate adherence to host tissues and structures
 Ex. fibronectin, fibrinogen, elastin, cellular lipids

Question 20

• Catalase

Answer 20

o Resists hydrogen peroxide

Question 21

• Hyaluronidase

Answer 21

o Degradative enzyme which facilitates spread to contiguous tissues

Question 22

Specimens to collect

Answer 22

o Mastitis – milk sample
o Clean outside of teat before collection (but don’t disinfect)
o Dermatitis/superficial infections – swabs, pus, exudates
o Urine – cystocentesis collected urine preferable to free catch
o System infection in chickens – yolk sacs, joints, stab swabs of internal organs

Question 23

Handling

Answer 23

o No special transport media required
o Do NOT freeze most samples
o Milk MAY be frozen (cryptoprotective)

Question 24

Lab ID

Answer 24

o Easily grown using ‘standard’ culture
o Readily grows on blood agar
o Major species are easily ID (MALDI-TOF or biochemical)
o Could test for methicillin resistance (may speed up diagnostic process)

Question 25

Zoonotic/interspecies transmission

Answer 25

o S. aureus = wide host range
o Livestock associated MRSA
o Common in pigs and cattle
o Human infections well recognized
o Horse have own population
o Dogs/cats with S. aureus probably got it from people
o S. pseudintermedius transmission increasingly recognized
o Human infections is 700x lower

Question 26

Treatment options

Answer 26

o Must be guided by SUSCEPTIBILITY training
o Resistance is emerging
o *avoid polymyxin (intrinsic resistance)
o Locally administered therapy may be an option
o Burrow’s solution for canine otitis
o *be aware of methicillin resistance

Question 27

Peracute

Answer 27

o Very fast

Question 28

Acute

Answer 28

o Sudden onset, sharp rise

Question 29

Subacute

Answer 29

o Between acute and chronic

Question 30

Chronic

Answer 30

o Continuing, constant, long term

Question 31

Subclinical

Answer 31

o Not clinically apparent
o May be disease with mild, less obvious effects