Mannitol Salt Agar (MSA)- Composition, Principle, Preparation, Results, Uses


Staphylococcus aureus is a gram-positive, spherical bacterium that belongs to the family Staphylococcaceae. It is one of the most common causes of skin and soft tissue infections, such as boils, abscesses, impetigo, and cellulitis. It can also cause more serious infections, such as pneumonia, endocarditis, osteomyelitis, septicemia, and toxic shock syndrome. Some strains of S. aureus produce toxins that can cause food poisoning, scalded skin syndrome, and enterotoxin-mediated diarrhea.

S. aureus is a facultative anaerobe that can grow in the presence or absence of oxygen. It is catalase-positive and coagulase-positive, meaning that it can produce enzymes that break down hydrogen peroxide and clot plasma, respectively. These characteristics help to distinguish S. aureus from other staphylococci and other gram-positive cocci.

S. aureus is widely distributed in nature and can be found on the skin and mucous membranes of humans and animals. It can also survive on inanimate objects, such as clothing, bedding, furniture, and medical equipment. S. aureus can be transmitted by direct contact with infected or colonized individuals or by indirect contact with contaminated objects or surfaces.

S. aureus has a remarkable ability to adapt to different environments and resist various antimicrobial agents. It can acquire resistance genes through horizontal gene transfer or mutation. Some strains of S. aureus are resistant to multiple antibiotics, such as methicillin-resistant S. aureus (MRSA) and vancomycin-resistant S. aureus (VRSA). These strains pose a serious threat to public health and require special infection control measures.

S. aureus can be identified by various laboratory methods, such as culture, microscopy, biochemical tests, serological tests, and molecular techniques. One of the commonly used media for the isolation and differentiation of S. aureus is Mannitol Salt Agar (MSA), which will be discussed in detail in the following sections.