Staphylococcus Flashcards
Staphylococcus characteristics
-gram positive
-cocci (clusters of grapes)
-aerobic or facultatively anaerobic
-can be coagulase positive or negative (will appear as zone clearing on dish OR clots in tubes)
-colonies are generally creamy/white on blood agar
Staphylococcus biocontainment
level 2
Staphylococcus aureus characteristics
Blood agar:
-creamy white colonies
-hemolytic (beta-hemolysis)
CHROMagar:
-pink/purple colonies
Mannitol salt agar:
-yellow colonies
-coagulase occurs
Staphylococcus epidermidis characteristics
Blood agar:
-not hemolytic (no zone clearing)
-white colonies
Mannitol salt agar:
-does not ferment mannitol so not yellow!
-no coagulase occurs in tests
Staphylococcus pseudintermedius characteristics
Blood agar:
-beta hemolysis occurs (double zones)
-white/grey (often more than S. aureus)
Natural host or habitat
-part of normal microbiota (skin, mucous membranes, pharynx, intestinal tract)
-different species specific to different hosts (S. aureus colonize 30% people; S. pseudintermedius colonize 90% of dogs)
-environmental contamination may play role in hospital environments
Taxonomy of Staphylococcus genus
-64 species
-based on coagulase, hemolysis, hyaluronidase acetoin
What species is coagulase variable?
Staphylococcus schleiferi
>has two subspecies (schleiferi and coagulans)
need biochemical tests to differentiate
What differentiates with negative hemolysis (when coagulase positive)?
Staphylococcus hyicus
What differentiates with Hyaluronidase acetoin?
Positive: S. aureus
Negative: S intermedius group
Virulence factors of staphylococcus
-toxic shock syndrome toxin= superantigen
-enterotoxins= food poisoning
-exfoliates- skin damage (Scalded skin)
-leucocidins (ex. Panton-Valentine Leucocidin PVL; destruction of WBCs)
-MSCRAMM (facilitate adherence to host tissues and structures like fibronectin, fibrinogen, elastin, cellular lipids)
-Catalase (resists hydrogen peroxide)
-Hyaluronidase (degradation enzyme which facilitates spread to contiguous tissues)
Clinical significance of S aureus
- cattle, sheep, goats, pigs, horses- Mastitis
- Poultry- bumblefoot
- dogs and cats- opportunistic and skin infections
Clinical significance of S. pseudintermedius
- Dogs and cats- opportunistic and skin infections
Clinical significance of S schleiferi
Dogs- opportunistic and skin infections
Clinical significance of S hyicus
Pigs- exudative epidermitis (greasy pig)
Clinical significance of S chromogenes
Cattle, sheep, goats- Mastitis
Mastitis in cows
-udder of colonized cow is main reservoir
-Adheres to and invades mammary epithelium, and can form small colony variants and L-forms (metabolically inactive mutant strains that are difficult to treat)
Staphylococcus aureus mastitis disease categories
- Peracute- rapidly progressive clinical disease
2.Subclinical- no clinical signs, decreased production
Staphylococcus aureus as mastitis- role in economics
-chronic subclinical disease can lead to reduced production and sporadic clinical disease
How to go about a herd with S. aureus/mastitis?
-improved hygiene (disinfection of equipment; not milking affected quarter)
-cull carrier cows
-intra-mammary antibiotics (be careful of MRSA…avoid beta-lactams
Staphylococcus aureus/bumblefoot in poultry
-infections of many sites (bones, tendon sheaths, joints)
-associated with green-liver osteomyelitis complex
-morbidity and mortality usually low (affects individuals not flocks)
How to go about bumblefoot cases?
-likely opportunistic, common colonzer; not contagious
-good management practices (remove sharp objects, ensure good litter quality, control other diseases)
-vaccines not effective
-treatment based on susceptibility test results
Staphylococcus pseudintermedius in dogs
-90% healthy dogs are colonized
-causes wide array of infections:
>pyoderma and otitis externa- often secondary to disease (atopica dermatitis, allergy, endocrinopathy)
>surgical site infections
>orthopedic implants
>necrotizing fasciitis
>nosocomial infections
Staphylococcus hyicus in pigs
-Exudative epidermitis (greasy pig disease)- dark brown crusty lesions
-acute or peracute, sporadic within herd
-seen in suckling and newly weaned piglets when:
>mixing litters
>animals fight
>teeth unclipped
>rough bedding
-affected animals can have high mortality rate (up to 70%)
-early antimicrobial treatment may be effective
Staphylococcus chromogenes in cattle, sheep, goats, pigs
-coagulase negative
-mastitis in cattle, sheep, goats
-greasy pig syndrome in pigs
Collecting specimens for mastitis
-clean outside of teat before collection, or use milk from bulk tank immediately after milking
Collecting specimens for dermatitis/superficial infections
-use swabs to collect pus or exudates
Collecting specimens of urine
cystocentesis collected urine preferable to free catch
collecting specimens for systemic infections in chickens
-test yolk sacs, joints, and stab swabs of internal organs
Staphylococcus transport
-tough genus;no special transport needed
-do not freeze most samples; can freeze milk since it is cryoprotective
Lab ID of staphylococcus
-easily grown using standard culture (blood agar)
-easily identifies major species by MALDI-TOF or biochemicals
-Need to request selective culture for Methicillin resistance
Zoonotic/interspecies transmission
- Staphylococcus aureus has broad host range
-Livestock associated MRSA common in pigs and cattle and found in humans
- strain common in chickens (ST5)
-horses have own population
-dogs and cats have S aureus that they probably got form people - Rise of staphylococcus pseudintermedius in people, likely got from dogs
Treatment options for staphylococcus
-must be guided by susceptibility testing
-resistance is emerging and unpredictable
-Be aware of intrinsic polymyxin resistance and methicillin resistance
-can use locally administered therapy (Burrows solution for canine otitis or shampoos for pyoderma; intramammary prep for mastitis)
Nosocomial
acquired from hospital
Superantigen
antigen which is capable of stimulating a much larger number of T-cells than an ordinary antigen, resulting in an exaggerated response
Peracute vs acute vs subacute vs chronic
Peracute- Fastest
Acute- sudden onset, sharp rise
Subacute- between acute and chronic
Chronic- continuing, constant, long term
Subclinical
-not clinically apparent (doesn’t appear sick)
-may be disease with mild, less obvious effects… BUT NOT asymptomatic
