Difference between revisions of "Staphylococcus spp."

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<big><center>[[Infectious agents and parasites|'''BACK TO INFECTIOUS AGENTS AND PARASITES''']]</center></big>
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#REDIRECT[[:Category:Staphylococcus species]]
<big><center>[[Bacteria|'''BACK TO BACTERIA''']]</center></big>
 
 
 
===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
 
*Alpha-haemolysin prouces a narrow zone of complete haemolysis, whereas beta-haemolysin produces a wide zone of incomplete haemolysis
 
*Haemolysins act as toxins
 
*''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
 
*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
 
 
 
 
 
===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 ([[Bacterial skin infections#Greasy pig disease|Pathology]])===
 
 
 
*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
 
*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'')
 
 
 
 
 
===[[Muscles - inflammatory#Botryomycosis|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 [[Bacterial skin infections#Deep pyoderma|deep pyoderma]], otitis externa, mastitis, endometritis, cystitis, osteomyelitis, wound infections, [[Joints - inflammatory#In Dogs|dyscospondylitis]]
 
*''S. aureus'' may cause [[Intestines - disease due to pathogens#Staphylococcus|gastroenteritis]]
 
 
 
 
 
===Other infections===
 
 
 
**[[Bacterial skin infections#Impetigo|Impetigo]] in cattle and pigs
 
** [[General Pathology - Oedema#Permeability type|Permeability types of pulmonary oedema]]
 
**Haemorrhagic disease by [[General Pathology - Haemostasis#Secondary Thrombocytopenic Disease|secondary thrombocytopenic disease]]
 
**May infect [[Joints - inflammatory#In Sheep|joints of sheep]]; [[Joints - inflammatory#In Pigs|arthritis in pigs]]
 

Latest revision as of 22:55, 14 May 2010