Wakgari Oljira Fayisa and Nugusa Fikadu Tuli
Staphylococcus aureus are Gram-positive, catalase positive cocci belonging to genus Staphylococcus in the family Staphylococcaceae, order Bacillales. They are approximately 0.5-1.5 μm in diameter, non-motile, non-spore-forming, facultative anaerobes that usually form in clusters. Staphylococcus aureus are uniquely resistant to adverse conditions such as high salt content and osmotic stress. Staphylococcus aureus are ubiquitous and are a part of the normal skin flora of animals and humans. This organism does not normally cause infections on healthy skin however, if it is allowed to enter the bloodstream or internal tissues, these bacteria causes a variety of potentially serious infections. In humans, Staphylococcus aureus causes various suppurative diseases, food poisoning, pneumonia and toxic shock syndrome. In animals, Staphylococcus aureus is considered one of the significant etiological agents of intra mammary infections in dairy ruminants causing both clinical and subclinical mastitis and resulting in substantial economic losses. Staphylococcus aureus produces many virulence factors, such as hemolysins, leukocidins, enterotoxins, exfoliative toxin. There is an evidence of bidirectional transmission of Staphylococcus aureus in humans and animals. Antibiotic resistance of Staphylococcus aureus is based on a wide variety of resistance genes. The most important is methicillin resistance mediated mainly by the mecA gene, which encodes for a penicillin-binding protein. MRSA strains have developed resistance to all beta-lactam antibiotics due to the overuse of these antibiotics. The increasing resistance to these antibiotics poses a great threat to the treatment of infections.