- Staphylococcus aureus is a Gram-positive, spherical bacterium that typically appears in clusters resembling grapes when viewed under a microscope. It is a facultative anaerobe, meaning it can grow in both the presence and absence of oxygen. S. aureus is commonly found on the skin and mucous membranes of healthy individuals, especially in the nasal passages. While it often exists harmlessly as part of the normal flora, it can become an opportunistic pathogen under certain conditions, leading to a wide variety of infections.
- This bacterium is distinguished by several important laboratory characteristics. It is catalase-positive, which helps differentiate it from Streptococcus species, and coagulase-positive, setting it apart from other Staphylococcus species. On blood agar, S. aureus typically displays beta-hemolysis, indicating its ability to completely lyse red blood cells. Its colonies often have a golden-yellow pigment, which is the origin of the species name “aureus” (Latin for “golden”).
- Staphylococcus aureus is responsible for a broad range of infections. These include superficial skin infections like boils, impetigo, and cellulitis, as well as more serious conditions such as pneumonia, osteomyelitis (bone infection), septic arthritis, and endocarditis (infection of the heart valves). It can also cause life-threatening bloodstream infections (sepsis). Moreover, S. aureus is capable of producing several toxins that can lead to distinct clinical syndromes such as toxic shock syndrome, staphylococcal scalded skin syndrome, and food poisoning caused by enterotoxins.
- The bacterium owes its virulence to a variety of factors. Protein A helps it evade the immune system by binding to antibodies in a way that prevents them from functioning properly. It produces enzymes like coagulase, which helps form protective clots around the bacteria, and several toxins that damage host tissues and immune cells. These features make S. aureus a formidable pathogen, especially in hospital environments.
- Antibiotic resistance is a significant concern with S. aureus. Methicillin-resistant Staphylococcus aureus (MRSA) is resistant to many commonly used antibiotics, making infections difficult to treat. MRSA is prevalent both in healthcare settings (HA-MRSA) and in the community (CA-MRSA). Treatment of MRSA infections often requires the use of stronger antibiotics such as vancomycin, linezolid, or daptomycin. Preventing the spread of S. aureus, especially resistant strains, involves proper hygiene, wound care, and infection control measures in clinical settings.
