Difference between revisions of "Staphylococcus spp."
Jump to navigation
Jump to search
m |
m |
||
Line 1: | Line 1: | ||
− | + | {{toplink | |
− | + | |backcolour = | |
− | + | |linkpage =Bacteria | |
+ | |linktext =BACTERIA | ||
+ | |pagetype=Bugs | ||
+ | }} | ||
+ | <br> | ||
===Overview=== | ===Overview=== | ||
Revision as of 16:08, 22 September 2008
|
Overview
- Commensals on skin and mucous membranes of animals and man
- Enodgenous or exogenous infections
- Opportunistic pyogenic infections associated with trauma, immusuppression, other infections
- Coagulase-positive S. aureus and S. intermedius as well as S. hyicus are important pathogens of animals
- Fairly stable in environment
- Strains selective for particular species
- Cause mastitis, tick pyaemia, exudative epidermitis, botryomycosis and pyoderma
Characteristics
- Clusters of Gram-positive cocci
- At least 30 species
- Facultative anaerobes
- Catalase positive, oxidase negative, non-motile
- Virulent strains are coagulase positive
- Grow on non-enriched media
- White or golden colonies
- S. aureus and S. intermedius produce double haemolysis; they produce alpha-haemolysin and beta-haemolysin
- S. hyicus is non-haemolytic
- Coagulase-negative strains vary in ability to cause haemolysis
- Slide test to detect bound coagulase (clumping factor) on surface of bacteria; bacteria clump within 1-2 minutes
- Tube test detects free coagulase, secreted by bactera; positive result indicated by clot formation in tube following 24-hour incubation; free coagulase converts prothrombin to thrombin which converts fibrinogen to fibrin
- Biochemical tests to differentiate S. aureus and S. intermedius
- PCR to differentiate species
Pathogenesis and pathogenicity
- Cause suppurative lesions
- Trauma or immunosuppression predispose to infection
- Capsular polysaccharide, teichoic acids and potein A prevent opsonisation and therefore phagocytosis
- Cell wall proteins bind fibronectin and fibrinogen, allowing bacteria to attched to damaged tissues
- Coagulase, DNase and protein A production mark pathogenicity
- Haemolysins made by S. aureus and S. intermedius act as toxins
- Alpha-haemolysin prouces a narrow zone of complete haemolysis; this toxin causes necrosis and targets mast cells and plasma cells, whose contents cause damage
- Beta-haemolysin produces a wide zone of incomplete haemolysis; damages membranes and causes leakage, contributing to necrosis
- Also gamma and delta toxins
- Toxic shock syndrome toxin acts as a superantigen, which causes T cell proliferation and production of cytokines, leading to cardiovascular shock, with microthrombus formation in capillaries
- Enterotoxins produced by some strains of S. aureus cause food poisoning in humans
- Proteases, hyaluronidases and lipases facilitate survival of bacteria and spread and tissue destruction
Diagnosis
- Clusters of bacteria in Gram-stained smears of pus
- Culture on selective blood agar and MacConkey agar
- No growth on MacConkey
- Colony characteristics, haemolysis, catalase and coagulase production
- Phage typing for epidemiological studies
Bovine mastitis
- S. aureus is a common cause of mastitisin cattle worldwide
- Most infections subclinical
- Systemic infection can occur with peracute and gangrenous forms
- In gangrenous mastitis, the quarter may become necrotic and slough off; alpha toxin causes necrosis of smooth muscle in blood vessel walls, reducing blood flow to the affected quarter, and causes release of lysomal enzymes from leukocytes
Tick pyaemia
- Infection of lambs with S. aureus in hill-grazing areas of the UK
- Lambs carry S. aureus on their skin and nasal mucosa; infection via skin trauma including tick bites
- Ixodes ricinus tick acts as a vector for Ehrlichia phagocytophila, which causes immunosuppression in lambs, predisposing to staphylococcal infection
- Acute septicaemia and death or localised abscess formation in many organs
- Arthritis, posterior paresis and ill-thrift
- Microscopic identification of bacteria in pus and isolation of S. aureus
- Prophylactic antibiotics e.g. tetracyclines initiated at 1 week of age may prevent infection
- Tick control important
Exudative epidermitis (Greasy pig disease)
- Worldwide disease of pigs under 3 months of age caused by S. hyicus
- Highly contagious and persists in the environment for long periods
- S. hyicus produces exfoliative toxin that causes separation of cells in stratum spinosum resulting in rapid intraepidermal spread of organisms
- Similar to “scalded skin syndrome” in human neonates, due to skin infection by exfoliative toxin-producing Staphylococcus aureus
- Excessive sebacious secretion and exudation on surface of skin
- Pigs are anorexic, febrile, depressed and have a greasy, non-pruritic dermatitis
- SKin thickened, wrinkled and scaley
- Acute death in piglets under 3 weeks due to dehydration and septicaemia
- 20-100% morbidity; up to 90% mortality
- Organism enters skin via abrasions e.g. bite wounds
- Carried in vaginal mucosa and skin of sows
- Predisposed by lack of milk, weaning and other infections
- Piglets from non-immune sows are predisposed
- Passive transfer of antibodies from immune sows and development of immunity with age protect against disease
- Isolation from skin lesions
- Early systemic antibiotics amd topical antiseptics/antibiotics useful
- Disinfection after outbreak
- Wash sows before farrowing
- Differential diagnosis:
- Mange (Sarcoptes scabiei var. suis)
- Swine parakeratosis (zinc and essential fatty acid deficiency)
- Porcine juvenile pustular psoriasiform dermatitis (collarettes or rings typically on the ventrum of young pigs)
- Dermatosis vegetans (associated with a giant cell pneumonia)
- Dermatophytosis (most commonly Microsporum nanum)
Botryomycosis
- Chronic, suppurative granulomatous condition
- S. aureus
- Occurs following castration of horses due to infection of stump of spermatic cors
- Occurs in mammary tissues of sows
- Mass of fibrous tissue containing pus and sinus tracts
Infections in dogs and cats
- S. intermedius causes deep pyoderma, otitis externa, mastitis, endometritis, cystitis, osteomyelitis, wound infections, dyscospondylitis
- S. aureus may cause gastroenteritis
Other infections caused by S. aureus
- Impetigo in cattle and pigs
- Permeability types of pulmonary oedema
- Haemorrhagic disease by secondary thrombocytopenic disease
- May infect joints of sheep; arthritis in pigs
- Dermatitis in sheep and goats
- Arthritis and septicaemia in turkeys
- Bumblefoot and omphalitis in chickens
Coagulase-negative staphylococci
- Usually harmless commensals or secondary invaders
- May adhere to indwelling catheters leading to urinary tract infections
- Often display multiple antibiotic resistance