Examination of a patient with pustular skin lesions allowed to isolate a causative agent that forms in the blood agar roundish yellow middle-sized colonies surrounded by haemolysis zone. Smears from the colonies contain irregularshaped clusters of gram-positive cocci. The culture is oxidase- and catalasepositive, ferments mannitol and synthesizes plasmocoagulase. What causative agent was isolated?

Answer options

1. Streptococcus agalactiae
2. Staphylococcus saprophyticus
3. Staphylococcus aureus
4. Staphylococcus epidermidis
5. Streptococcus pyogenes

Explanation

Staphylococcus aureus is a gram-positive, round-shaped bacterium. It is often positive for catalase and nitrate reduction and is a facultative anaerobe that can grow without the need for oxygen. S. aureus produces various enzymes such as coagulase (bound and free coagulases) which clots plasma and coats the bacterial cell, probably to prevent phagocytosis. S. aureus appears as staphylococci (grape-like clusters) when viewed through a microscope, and has large, round, golden-yellow colonies, often with hemolysis, when grown on blood agar plates.