LESSN 2a: Staphylococcus species Flashcards
General description
- Gram-positive cocci (approx. 1µm diameter)
resembling grapes
-Grow on non-enriched media
-facultative anaerobes, oxidase-negative, and
catalase-positive
-non-motile and and non spore forming - causing pyogenic infections
-some are coagulase positive which correlates with pathogenecity - comparatively stable in environment
usual habitat of staphylococcus :
commensals on skin and mucous membrane
Colonial characteristics:
: colonies are usually white, opaque and up to 4 mm in diameter.
Colonies
produce double haemolysis
of S. aureus and S. pseudintermedius
The colonies of bovine and human strains of S. aureus are
golden yellow
Colonies of some coagulase-negative staphylococci are also
pigmented
Haemolysis in sheep or ox blood agar: Four staphylococcal haemolysins s are
recognized
Alpha, beta, gamma and delta
Staphylococcal cell wall proteins, which bind to
facilitate bacterial attachment to tissues
fibronectin and fibrinogen,
Pyogenic characteristics causes
suppurative lesions
Structural features including including
-capsular polysaccharide
-teichoic acids and
protein A interfere with opsonization and subsequent phagocytosis
Exoenzymes such as kinases and hyaluronidase promote tissue invasion, and
exotoxins including haemolysins and leukocidin lyse host cell membranes
Pathogenic effects can range from relatively minor local infections to lifethreatening septicaemia
(dx)
Sample source: lesions (skin scrapings, swab samples);
exudates; mastitic milk sample
Demonstration of bacteria:
Gram-staining, or culture on blood agar, selective blood agar, MacConkey agar