Staphylococcus infections

Introduction

Staphylococcus is an opportunistic pathogen that can cause infections through broken skin or when introduced into the body via a catheter or other device. Most Staph infections are skin and surface infections that vary in their presentation depending on the depth and extent of infection. These include impetigo, folliculitis, carbuncles, furuncles and wound infections. Systemic infections (bacteremia, endocarditis, and pneumonia) as well as toxic shock syndrome and food poisoning also occur. Staphylococcus infections cause tissue and cell damage through production of certain virulence factors (e.g. hylaronidase) and exotoxins such as TSST-1.

Staphylococcus aureus

1. Cause: Staphylococcus aureus
2. Microscopy: Gram-positive clusters
3. Diagnosis: Selective media such as Mannitol Salt Agar; coagulase; DNAse

Staphylococcal Scalded Skin Syndrome

• Symptoms: Redness and inflammation around the mouth, spreading to entire skin surface. Any pressure causes skin to blister and come loose. Entire epithelium can come loose and is replaced after 7-10 days
• Complications: Secondary infections in denuded skin
• Pathogenesis: Exotoxins (ETA, ETB) break desmosomes between cells in epidermis
• Treatment: Supportive/prevent infection

Toxic Shock Syndrome

• Symptoms: fever, hypotension, diffuse reddening rash, skin exfoliation
• Complications: Multiple organ system damage, shock leading to death
• Pathogenesis: Local production of TSS-1, particularly in environment of hyperabsorbent tampons. TSS-1 stimulates cytokine release, inflammation, endothelial fluid leakage
• Treatment: Antibiotics to prevent recurrence

Cutaneous infections:

The production of virulence factors such as lipase and hyaluronidase increases the spread and severity of the infection, especially important in furuncles and carbuncles

• Impetigo: Superficial infection on face and limbs. Small pus-filled vecicle on a  red area; eventually crusts over
• Folliculitis: Pus-filled infection of hair follicle
• Furuncles (boils): Extended folliculitis; large painful nodules with dead tissue; may need to be drained
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• Carbuncles: Multiple furuncles joined; surface drainage, deeper infection, bacteremia leading to fever and chills
• Wound infections: Pus, pain, edema, redness

Systemic Staphylococcus infections

• Endocarditis: 50% mortality
• Pneumonia: abscesses
• Osteomyleitis/arthritis: may start with skin infection

Coagulase-negative Staphylococcus

1. Endocarditis, esp. of artificial valves
2. catheter & shunt infections
3. Prosthetic joints
4. Urinary tract infections