Staphylococcal diseases

Staphylococci are gram-positive, spherical-shaped bacteria that form clusters and are commonly found on the skin and mucous membranes. Clinically, the most important species include Staphylococcus aureus and Staphylococcus epidermidis, which are categorized according to their coagulase activity. S. aureus is coagulase positive and expresses several virulence factors which support evasion of the host immune response. S. epidermidis is coagulase negative and is usually less virulent, although it can evade the host immune system by forming and subsequently hiding in a biofilm. S. aureus is commonly responsible for many localized infections (e.g., folliculitis, cervical lymphadenopathy) and also severe organ infections in the setting of bacteremia (e.g., endocarditis, osteomyelitis). As a toxin producer, S. aureus can cause food poisoning (see Staphylococcal food poisoning) and, in severe cases, life-threatening diseases such as staphylococcal scalded skin syndrome (SSSS) or toxic shock syndrome (TSS). Methicillin-resistant S. aureus (MRSA), in particular, poses a major threat to both immunocompromised and multimorbid patients and is a considerable challenge to hospital hygiene. S. epidermidis is mostly responsible for foreign body infections caused by, for example, contaminated peripheral lines or prosthetic joints. The treatment of choice is anti-staphylococcal penicillins (e.g., oxacillin, flucloxacillin) or first and second-generation cephalosporins.

Staphylococci are immotile, gram-positive bacteria that have a round shape and are found in clusters.

• Approx. 30% of the general human population are long-term carriers of S. aureus. ^[1]
  • Three patterns of carriage have been observed: 20% are permanent carriers, 60% are intermittent carriers, 20% are noncarriers
  • MRSA carrier rates and invasive infections have increased during the last decades.

Epidemiological data refers to the US, unless otherwise specified.

• Coagulase-positive; : Staphylococcus aureus
• Coagulase-negative; : Staphylococcus epidermidis

Staphylococcus aureus

For more information, see methicillin-resistant Staphylococcus aureus and “Gram-positive cocci” section in the bacteria overview.

• Enzymes
  • Catalase
  • Coagulase
  • Hemolysins
  • Hyaluronidase
  • Lipase
  • Penicillinase
• Toxins
  • Superantigens: can activate large numbers of T cells, resulting in the massive release of cytokines ^[2]
    • Toxic shock syndrome toxin 1 (TSST-1)
    • Enterotoxin B (heat stable)
  • Exfoliative toxin (causes epidermolysis in SSSS)
  • Leukocidin (causes necrosis of the skin and mucous membranes)
• Proteins
  • Clumping factor A: binds to fibrinogen → platelet activation, aggregation, and blood clumping
  • Protein A: inhibits phagocytosis and complement fixation by binding to the Fc region of IgG
  • Modified penicillin-binding protein (PBP) in MRSA
  • Microbial surface components recognizing adhesive matrix molecules (MSCRAMMs): facilitate the adherence of S. aureus to the extracellular matrix of host tissue ^[3]
• Capsular polysaccharides: promote colonization and persistence in host tissues

Staphylococcus epidermidis

• S. epidermidis produces a biofilm that consists of proteins and extracellular polysaccharides.
  • Protects S. epidermidis from host defense mechanisms and antibiotics
  • Facilitates colonization of surfaces of prosthetic material and IV catheters → device-associated infections

Staphylococcus aureus

• Anti-staphylococcal penicillins: oxacillin, flucloxacillin
• First and second generation cephalosporins
• In case of penicillin allergy: clindamycin
• MRSA: drugs of last resort such as vancomycin and linezolid

Coagulase-negative staphylococcus (particularly S. epidermidis)

• Methicillin-sensitive: oxacillin, nafcillin, or cefazolin
• Methicillin-resistant: vancomycin or daptomycin
• Second-line treatment (if susceptible): levofloxacin and rifampicin

Skin

• Impetigo
• Folliculitis, boils and carbuncle
• Abscess
• Empyema
• Wound infections
• Pyomyositis
  • A bacterial infection affecting skeletal muscle that is most commonly caused by Staphylococcus aureus and Streptococcus pyogenes
  • Symptoms typically include fever, pain, and swelling of the affected area (usually the lower extremities)
• Postpartum mastitis

Ear, nose, and throat

• Otitis media
• Sinusitis
• Parotitis
• Mastoiditis

Lymphatic system

• Lymphadenopathy

Systemic infections

• Endocarditis
• Osteomyelitis
• Pneumonia
• Meningitis
• Sepsis

Staphylococci are the most common causative pathogen of infective endocarditis!

Foreign body infections

• Infections associated with catheters and shunts
  • > 50%: staphylococcus, particularly S. epidermidis
  • 25%: gram-negative bacteria (e.g., Pseudomonas aeruginosa)
• Prosthetic joint infection
• Treatment: treatment with antibiotics and foreign body removal

Toxin-mediated diseases

• Staphylococcal food poisoning (heat stable enterotoxins)
• Staphylococcal scalded skin syndrome (SSSS)
• Toxic shock syndrome (TSS)