staphylococci

Staphylococci are a genus of Gram-positive, nonmotile cocci that occur in irregular grape-like clusters. They are facultative anaerobes and generally non-spore-forming. They are part of the normal flora of the skin and mucous membranes and can cause opportunistic infections when barriers are breached.

The most clinically significant species are Staphylococcus aureus, which is coagulase-positive and often pathogenic, and coagulase-negative species such as S. epidermidis and S. saprophyticus. S. aureus can produce toxins and enzymes that contribute to tissue damage, while S. epidermidis readily forms biofilms on medical devices.

Identification: Gram-positive cocci in clusters; catalase-positive helps distinguish from streptococci; S. aureus is coagulase-positive and often ferments mannitol on mannitol salt agar. S. saprophyticus is novobiocin-resistant; S. epidermidis is usually novobiocin-sensitive.

Clinical relevance: S. aureus causes skin and soft tissue infections, pneumonia, bone and joint infections, bacteremia, toxic shock syndrome, and food poisoning. S. epidermidis is a frequent cause of device-related infections due to biofilm formation. S. saprophyticus is a common cause of uncomplicated urinary tract infections in young women.

Antibiotic resistance: Methicillin-resistant S. aureus (MRSA) strains harbor the mecA gene and are resistant to beta-lactam antibiotics; treatment may involve vancomycin, linezolid, or daptomycin depending on susceptibility. VRSA and VISA have been reported, though rare. Non-susceptible strains exist among other species as well.

Prevention and control: good hand hygiene, proper wound care, and sterile technique in healthcare settings; decolonization strategies with mupirocin and chlorhexidine in certain carriers; careful management of indwelling devices to prevent biofilm formation.