6 – Staphylococcus Flashcards
Microbiological characteristics
- 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
Staphylococcus aureus
- Hemolytic (beta-hemolysis, 2 zones)
- FERMENTS mannitol=yellow colonies
Staphylococcus aureus: clinical significance (contagious mastitis in cows)
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
Staphylococcus aureus: clinical significance (infections in chickens)
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
Staphylococcus epidermidis
- NOT hemolytic
- Does NOT ferment mannitol=not yellow
Staphylococcus pseudointermedius
- More white/grey on blood agar than S. aureus
- Double zone beta-hemolysis on blood agar
Staphylococcus pseudointermedius: clinical significance
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
Staphylococcus hyicus: clinical significance
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
Staphylococcus chromogenes
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
Coagulase test
- Positive test=when tubes tipped on side can see clot formation
DNase test
- Positive reaction=zone of clearing surround bacterial growth (‘halo’)
Natural host associated organisms
- 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)
Taxonomy
- 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
Virulence factors (most known about S. aureus)
- Toxic-shock syndrome toxin (TSST)
- Enterotoxins
- Exfoliatins
- Various leucocidins (ex. Panton-Valentine Leucocidin PVL
- MSCRAMM
- Catalase
- Hyaluronidase
- Toxic-shock syndrome toxin (TSST)
o Super antigen (can stimulate a much larger number of T-cells than ordinary antigen)
- Enterotoxins
o Responsible for food poisoning
- Exfoliatins
o Skin damage: results in scalded appearance
- Various leucocidins (ex. Panton-Valentine Leucocidin PVL)
o Destruction of WBCs
- MSCRAMM
o Facilitate adherence to host tissues and structures
Ex. fibronectin, fibrinogen, elastin, cellular lipids
- Catalase
o Resists hydrogen peroxide
- Hyaluronidase
o Degradative enzyme which facilitates spread to contiguous tissues
Specimens to collect
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
Handling
o No special transport media required
o Do NOT freeze most samples
o Milk MAY be frozen (cryptoprotective)
Lab ID
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)
Zoonotic/interspecies transmission
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
Treatment options
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
Peracute
o Very fast
Acute
o Sudden onset, sharp rise
Subacute
o Between acute and chronic
Chronic
o Continuing, constant, long term
Subclinical
o Not clinically apparent
o May be disease with mild, less obvious effects
