staphylococci

Staphylococci are Gram-positive cocci about 0.5 – 1.0 ?m in diameter. They grow in clusters, pairs and occasionally in short chains. The clusters arise because staphylococci divide in two planes, catalase positive, oxidase negative, non-motile, non-spore forming. Traditionally they were divided into two groups on the basis of their ability to clot blood plasma (the coagulase reaction). The coagulase-positive staphylococci constitute the most pathogenic species S. aureus. The coagulase-negative staphylococci (CNS) are now known to comprise over 30, other species such as S. epidermidis and S. saprophyticus. The CNS are common commensals of skin, although some species can cause infections.Phenotypic characteristics of Staphylococcus aureus:-

Gram-positive, cluster-forming coccus, non-motile, non-spore forming facultative anaerobe, fermentation of glucose produces mainly lactic acid, ferments mannitol (distinguishes from S. epidermidis), catalase positive, coagulase positiv, golden yellow colony on agar, normal flora of humans found on nasal passages, skin and mucous membranes pathogen of humans, causes a wide range of suppurative infections, as well as food poisoning and toxic shock syndrome.
Pathogenesis of S. aureus:-
S. aureus infections can spread through contact with pus from an infected wound, skin-to-skin contact with an infected person by producing hyaluronidase that destroys tissues, and contact with objects such as towels, sheets, clothing, or athletic equipment used by an infected person. Deeply penetrating S. aureus infections can be severe. Prosthetic joints put a person at particular risk of septic arthritis, and staphylococcal endocarditis (infection of the heart valves) and pneumonia.