Staphylococci

Year 1 - Semester 2

Features of staphylococci that allow it to be identified

catalase-positive, oxidase-negative, grow in NaCl concentrations as high as 15%

main coagulase-positive staphylococci

S aureus, S pseudintermedius, S hyicus

main coagulase-negative staphylococci

S scuiri, S equorum, S epidermidis

What are the 2 main groups of staphylococci?

coagulase-positive and coagulase-negative

Where in animals are commensal staphylococci populations most commonly found?

mucosal surfaces, muco-cutaneous junctions, ear canal

What is the most common coagulase-positive staphylococcus?

S. pseudintermedius

pyoderma

a superficial or deep bacterial/fungal skin disease which causes papules, pustules, crusts and folliculitis due to an alteration to the skin surface micro-environment caused by trauma, allergic reaction and breed associations

What does S. pseudintermedius cause in infected patients?

abscess formation, endocarditis, wound infections, mastitis, chronic and recurrent pyoderma, otitis externa

How is pyoderma treated?

antimicrobials, underlying disease must be treated if recurring

How does pyoderma contribute to AMR?

often recurring disease which causes patients to undergo multiple courses of antimicrobials which increases the chance of the development of resistance

Which disease is associated with S. hyicus?

greasy pig disease

Which disease is associated with S. gallinarum/ S. aureus?

bumblefoot

Diseases caused by S. aureus

mastitis, endometritis, osteomyelitis, endocarditis, pneumonia, septicaemia, toxinoses causes food poisoning, scalded-skin syndrome and toxic shock syndrome

What mediates stick-adhesion of staphylococci?

microbial surface components recognising adhesive matrix molecules (MSCRAMMS), surface proteins, collagen, other adhesins

How does clumping factor help staphylococci to survive?

bacteria attaches to blood clots and traumatised tissue which protects against oxidisation and phagocytosis

What does protein A do in S. aureus?

it binds to the wrong end of specific antibodies which allows immune evasion

How do capsular polysaccharides help S. aureus to survive?

prevent phagocytosis, allow biofilm formation to protect against AMs, allow bacteria to spread more easily between tissues and between animals through milk in mastitis

How does chemotaxis inhibitory protein help S. aureus to survive?

it attracts neutrophils and then binds to receptors to stop them from being attracted to the area of infection

Which gene encodes the resistance of MRSA?

mecA

How does MRSA resist AM treatment?

carries multiple resistance genes so resistant to many different antimicrobials, alternative penicillin-binding protein 2a provides an alternative target for b-lactam drugs to bind to, preventing damage to the bacteria

What is the most common strain of MRSA in small companion animals?

EMRSA-15

What is the most common strain of MRSA in horses?

equine associated unique strains and ST398

Where is MRSP most often acquired?

in hospital

features of MRSP

more multi-drug resistant than MRSA, can be carried for up to 11 months after first infection, more common in animals with skin infections, not very common

Which drugs is MRSA resistant to?

all beta-lactam antimicrobials and fluoroquinolones

Which factors put dogs and cats at higher risk of being infected with MRSA?

surgery, non-healing wounds, multiple courses of broad-spectrum antibiotics, owner has recent healthcare contact

Which group of staphylococci is seen as more virulent?

coagulase-positive

Which factors put horses at higher risk of infection with MRSA?

surgery, extended in-patient hospitalisation, broad spectrum antibiotics

general features of staphylococci

gram-positive, occur in microscopic clusters resembling grapes, broad temperature range

Which strain of staphylococcus causes the majority of pyoderma cases?

S. pseudintermedius

How does S. aureus evade phagocytosis?

secretion of chemotaxis inhibitory protein S. aureus (CHIPS) and staphylococcus complement inhibitor (SCIN), fibrinogen-binding protein, staphylokinase

function of chemotaxis inhibitory protein S. aureus

to block a specific receptor on monocytes and neutrophils which prevents them from moving toward and killing s. aureus

function of staphylokinase

converts plasminogen to plasmin which breaks down fibrin clots which enables S. aureus to invade deeper tissues, neutralises antimicrobial peptides and antibodies

function of fibrinogen-binding protein

to bind to fibrinogen which forms a protective coat around the bacteria to prevent phagocytosis

2 main types of toxins produced by staphylococci

pyrogenic toxin superantigens and cytolytic toxins

pyrogenic toxin superantigens produced by staphylococci

toxic shock syndrome toxin-1, enterotoxins, exfoliative toxins

cytolytic toxins produced by staphylococci

alpha, beta, leukocidins