Medical Characteristics of Staphylococci Species

Scalded Skin Syndrome

Primarily affecting newborns (typically between 3–7 days of age), Scalded Skin Syndrome is caused by exfoliative toxin. This toxin destroys the attachments between keratinocytes specifically in the stratum granulosum. Because the damage is intraepidermal, the skin sloughs off but heals completely without scarring.

A hallmark clinical finding is Nikolsky's sign, where the skin slips off with only a gentle rub.

Infectious and Pyogenic Diseases

Beyond toxins, S. aureus is a major cause of various localized and systemic infections.

• Skin Infections: It can cause impetigo (honey-colored, crusted lesions) and bullous impetigo, a variant featuring large fluid-filled sacs (bullae) caused by exfoliative toxin. It also causes cellulitis, an infection of the deep dermis and subcutaneous fat.
• Abscesses: S. aureus is a common cause of skin abscesses, including furuncles (boils/hair follicle infections) and carbuncles (clusters of furuncles). The mainstay of treatment for these walled-off pockets of pus is incision and drainage.
• Endocarditis: S. aureus is a classic cause of acute endocarditis, characterized by a rapid onset of symptoms, bacteremia, and sepsis. This is much more aggressive than the subacute endocarditis typically caused by Streptococcus viridans.
• Osteomyelitis: This bacterium is a common cause of bone infections. In children, it often presents via hematogenous spread to long bones (e.g., femur), whereas in adults, it may affect the vertebrae.

Antibiotic Resistance: Beta-lactamase and MRSA

A major challenge in treating Staphylococci is their inherent resistance to many antibiotics. Most strains produce beta-lactamase, an enzyme that inactivates penicillin. While antistaphylococcal penicillins (like Nafcillin) and certain cephalosporins can be used, the rise of Methicillin-Resistant Staphylococcus aureus (MRSA) has complicated treatment.

MRSA is resistant to all $\beta$-lactam antibiotics due to the production of altered penicillin-binding proteins (PBPs). MRSA can be found in both hospital and community settings and often requires treatment with Vancomycin, Daptomycin, or Linezolid.

Coagulase-Negative Staphylococci

Other species in this genus are often "coagulase-negative" and present different clinical challenges.

Staphylococcus epidermidis

As a normal inhabitant of the skin, S. epidermidis is frequently a contaminant in blood cultures. However, it is highly significant in patients with prosthetic materials (such as catheters, pacemakers, or prosthetic heart valves). The bacteria produce a biofilm—a protective surface layer—that allows them to adhere to these devices and resist host defenses.

Staphylococcus saprophyticus

This species is a notable cause of Urinary Tract Infections (UTIs), particularly in young, sexually active women (sometimes referred to as "honeymooner's cystitis"). While E. coli is the most common cause of UTIs, S. saprophyticus is a significant secondary cause.

Exam Tip: When differentiating between staphylococcal species, always look for the presence or absence of coagulase. S. aureus is (+) and highly virulent, while S. epidermidis and S. saprophyticus are (-) and often associated with specific niches like medical devices or the urinary tract.