Staphylococcus Flashcards
What are the microbiological characteristics of Staphylococcus?
- Gram (+) cocci
- aerobic or facultatively anaerobic
- often described as coagulase positive or negative
- colonies are generally creamy/white on blood agar
- organisms we know LOTS about
- grape like clusters
What is the biocontainment level of Staphylococcus?
2
What is the coagulase test?
- A biochemical test when tubes are tipped on their side, clot forms (positive reaction - this species is positive for coagulase)
What is a DNase test?
- biochemical test where a positive reaction is indicated by the zone of clearing surrounding the bacterial growth
- tests the ability of an organism to hydrolyze DNA
What is the natural host or habitat of Staphylococcus?
- these are host associated organisms
- part of the normal microbiota (skin, mucous membranes, pharynx, intestinal tract)
- different staphylococcal spp are associated w/ different animals
- environmental contamination may play a role in hospital environments (nosocomial infections)
Which is the most known about Staphylococcus?
Staphylococcus aureus
what virulence factors does Staphylococcus have?
- toxic-shock-syndrome toxin (TSST; superantigen)
- enterotoxins (responsible for food poisoning)
- exfoliatins (skin damage, result in scalded skin appearance)
- various leucocidins (ex: Panton-Valentine Leucocidin PVL; destruction of WBC)
- MSCRAMM (facilitate adherence to host tissues & structures like fibronectin, fibrinogen, elastin, & cellular lipids)
- catalase (resists hydrogen peroxide)
- hyaluronidase (degradative enzyme which facilitates spread to contiguous tissues)
What is the clinical significance of Staphylococcus aureus?
- cause of contagious mastitis in cows (udder of colonized cow is the main reservoir; adheres to & invades mammary epithelium; can form small colony variants & “L-forms”)
- disease can be (peracute - rapidly progressing clinical disease; subclinical - no clinical signs, decreased production)
- economic cost
- improved hygiene is important for control (disinfection of milking equipment; not milking affected quarter)
- culling Staphylococcus aureus carrier cows from herd
- intra-mammary antibiotics (be aware of methicillin resistance!; methicillin resistant Staphylococcus aureus (MRSA) is resistant to all B-lactam therapies (cephapirin, ceftiofur, cloxacillin)
What animal spp does Staphylococcus chromogenes affect?
cattle, sheep, goats
What is the common presentation of Staphylococcus chromogenes?
mastitis
What makes up chronic subclinical disease?
reduced production + sporadic clinical disease
What is the clinical significance of Staphylococcus aureus?
- infections of many anatomic sites (bones, tendon sheaths, & joints most common; surviving birds may have swollen joints, reluctant to stand, & may develop gangrenous dermatitis of the feet (bumblefoot))
- associated w/ green-liver osteomyelitis complex
- morbidity & mortality usually low (affects individuals rather than flocks)
- pathogenesis of poultry disease not clearly defined (likely opportunistic - infects when host defenses are breached; common colonizer)
- good management practices to reduce stress & injury are key (remove sharp objects, ensure good quality litter, control other diseases (infectious bursal disease) which may be immunosuppressive)
- vaccines are not effective
- treatment based on susceptibility test results
What is the clinical significance of Staphylococcus pseudintermedius?
- ~90% of healthy dogs are colonized w/ Staphylococcus pseudintermedius
- causes wide variety of opportunistic infections (pyoderma & otitis externa, surgical site infections, orthopedic implants, necrotizing fasciitis, nosocomial infections)
- Staphylococcus pseudintermedius otitis & pyoderma are often secondary to underlying disease (atopic dermatitis, food allergy, endocrinopathy)
- ADDRESSING PRIMARY DISEASE IS KEY TO SUCCESS!
- determine site of infection (superficial or deep pyoderma (histopathology helpful); otitis interna, media, or externa (good physical exam)
- in chronic consider consulting w/ dermatologist, these can be a challenge!
What is the clinical significance of Staphylococcus hyicus?
- exudative epidermitis (greasy pig disease)
- acute or peracute, sporadic w/in herd
- seen in suckling & newly weaned piglets, when mixing litters, animals fight, teeth are unclipped, there is rough bedding
- affected animals can have high mortality rate, up to 70%
- early antimicrobial treatment may be effective
What is the clinical significance of Staphylococcus chromogenes?
- coagulase negative
- most frequently isolated coagulase negative species from bovine mastitis
- also implicated in ovine & caprine mastitis
- in Sw, has been reported to cause a greasy pig-like syndrome
How do you collect and handle samples of Staphylococcus?
specimens to collect:
- mastitis - milk sample (clean outside of teat before collection; milk from bulk tank can also be tested, best immediately after milking)
- dermatitis/superficial infections (swabs, pus, exudates)
- urine - cystocentesis collected urine preferable to free catch
- systemic infections in chickens (yolk sacs, joints, & stab swabs of internal organs)
- staphylococci are generally pretty tough
- no special transport media is required
- do NOT freeze most samples
- milk samples MAY be frozen (milk is cryoprotective)
How does the lab identify Staphylococcus?
- Staphylococci will be easily grown using ‘standard’ culture methodologies (readily grows on blood agar; no need to request specialized testing to identify)
- major species are easily identified (MALDI-TOF or biochemically)
- consider requesting selective culture for methicillin resistance (may speed up diagnostic process)
How is Staphylococcus transmitted btwn spp?
- Staphylococcus aureus exemplifies a broad host range
- livestock associated MRSA (common in Sw & cattle; human infections are well recognized)
- another strain is common in chickens
- Eq seem to have their own population
- Ca/Fe have Staphylococcus aureus that are probably acquired from people
- transmission of Staphylococcus pseudintermedius is increasingly recognized
- standard precautions (hand washing, PPE sufficient)
What are the treatment options for Staphylococcus?
- must be guided by susceptibility testing
- resistance is emerging, & resistance profiles are unpredictable
- drugs to avoid/intrinsic resistance (intrinsic polymyxin resistance)
- locally administered therapy might be an option (Burrow’s soln for canine otitis or shampoos for pyoderma; intramammary preparations for mastitis)
- be aware of methicillin resistance (MR staphylococci are resistant to ALL B-lactam drugs)
BIG PIC: Could you use amoxicillin + clavulanic acid to treat a case of pyoderma in a dog caused by MRSP?
- clavulanic acid is a beta lactamase inhibitor, it works by preventing bacteria from destroying Amoxicillin (b-lactam): only active against Class A enzymes & not all b-lactamases can be inhibited
- MRSP: altered penicillin binding protein in methicillin resistant Staphylococcus; resistance to all b-lactams due to altered proteins in cell wall so clavulanic acid doesn’t help; usually, multidrug resistant)
BIG PIC: Staphylococci are primarily host associated (as opposed to being acquired from the environment). How might you best describe their pathogenicity (think back to lecture 3)? Beyond a culture, what other supporting evidence would you need to identify that an animal has an infection?
- normally on host, when it gets into sterile sites (ex: trauma) becomes pathogenic, or host defenses breached (secondary to an underlying disease) - opportunistic
- clinical signs/presence of secondary infection as Staphylococci are often present in hosts
