Lecture Notes on Staphylococcus and Related Infections

Staphylococcus Overview

  • Family: MICROCOCCACEAE, Genus: Staphylococcus

  • Gram-positive cocci, nonmotile, non-spore-forming, catalase-positive

General Properties

  • Morphology: observed individually, in pairs, and in irregular clusters.

  • Coagulase positive: bound and extracellular coagulase mechanisms.

  • Resistant to high temperatures (~50°C), high salt, and drying.

  • Colonies are golden/yellow and often β-hemolytic on blood agar.

Virulence Factors

  • Adhesins: Protein A, fibronectin-binding proteins, and clumping factors.

  • Enzymes: Coagulase, lipase, hyaluronidase, staphylokinase, nuclease.

  • Toxins: α-toxin, β-toxin, PVL, enterotoxins, exfoliative toxins, and TSST-1.

Tissue Invasion

  • α-toxin induces pore formation, breaching epithelial cell junctions.

Clinical Manifestations

  • Infections: skin and soft tissue (impetigo, folliculitis, furuncles, carbuncles), pneumonia, osteomyelitis, septic arthritis, food poisoning, and toxic shock syndrome.

Diagnostic Criteria

  • Skin and Soft Tissue: clinical appearance, culture.

  • Osteomyelitis: blood culture, bone aspirate, bone scan, MRI.

  • Septic Arthritis: joint fluid examination, Gram stain, culture.

  • Endocarditis: large-volume blood cultures, echocardiography.

Treatment

  • MSSA: Penicillinase-resistant penicillins (nafcillin, oxacillin), cephalosporins, clindamycin.

  • MRSA: Vancomycin, daptomycin, linezolid, and others.

Prevention

  • Maintain cleanliness and hand hygiene.

  • Use mupirocin for nasal colonization reduction in high-risk settings.

Coagulase-negative Staphylococci

  • Species include S. epidermidis, S. saprophyticus; associated with opportunistic infections and biofilms on medical devices.

Lab Diagnosis

  • Techniques: microscopy, culture, biochemical reactions (catalase, coagulase), automated systems (ID32Staph, bioMerieux), MALDI TOF spectroscopy.