Lecture 6.1 - Infections on surfaces

Surfaces

• Interface between a solid and either a liquid or gas
• Natural body surfaces: skin, GI tract, urinary tract
• Artificial surfaces: intravenous lines, central venous line catheters, NG tubes, prosthetic devices, and implants

Microorganisms on Skin

• Viruses: papilloma, herpes simplex
• Bacteria:
  • Gram positive: Staphylococcus aureus, coagulase negative staphylococci, Corynebacterium
  • Gram negative: Enterobacteriaceae
• Fungi: yeasts, dermatophytes
• Parasites: mites

Mucosal Microflora

• No specific information provided

Natural Infection Sites

• External surfaces:
  • Pharyngitis (sore throat)
  • Conjunctivitis (infection of conjunctiva)
  • Gastroenteritis (inflammation of the gastrointestinal tract)
  • Urinary tract infection (infection in any part of the urinary system)
  • Pneumonia (infection of one or both lungs)
• Internal surfaces:
  • Endocarditis (infection of the endocardium)
  • Septic arthritis (joint infection)
  • Osteomyelitis (infection of the bone)
  • Empyema (pus in the pleural cavity)

Cystic Fibrosis

• Mucus build-up in lungs and digestive system
• Persistent lung infections:
  • Pseudomonas aeruginosa
  • Mycobacterium abscessus
  • Aspergillus species

Adhesins

• Proteins that help bacteria bind to host surfaces (e.g., skin, mucous membranes, deeper tissues)
• Examples: fimbriae (pili) in E. coli, non-fimbriae proteins, and polysaccharide adhesins
• Teichoic acids in gram-positive bacteria serve as adhesins for staphylococcus and streptococcus species

Prosthetic Surface Infections

• Examples:
  • Intravascular lines
  • Central venous catheters
  • Peritoneal dialysis catheters
  • Prosthetic joints
  • Breast prostheses
  • Cardiac valves
  • Pacing wires
  • Endovascular grafts
  • Ventriculoperitoneal shunts

Prosthetic Joint Infections

• Result in morbidity and are costly
• Require antibiotic therapy for weeks/months
• Longer stay in hospital
• Incidence of infection:
  • Hip replacement: approximately 0.43% for primary and 1.58% for revision
  • Knee replacement: approximately 0.54% for primary and 2.1% for revision

Microorganisms Causing Infections of Joint Replacements

• Early post-operative infections (<1 month):
  • S. aureus
  • Gram-negative organisms (E. coli, Proteus, Klebsiella)
  • Enterobacteraceae
  • Enterococci (E. faecalis)
• Late post-operative infections (2-12 months):
  • Coagulase negative staphylococci (mainly S. epidermidis)
  • S. aureus
  • Other species (e.g., S. haemolyticus, S. simulans, S. warneri)

Endocarditis (Prosthetic and Non-Prosthetic Valve)

• Coagulase negative staphylococci (including S. epidermidis)
• S. aureus
• Viridans streptococci
• Enterococcus faecalis
• HACEK group (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella)
• Candida

Cardiac Pacing Wire Endocarditis

• No specific information provided

Processes in the Pathogenesis of Infection at Surfaces

• Adherence to host cells or prosthetic surface
• Biofilm formation
• Invasion and multiplication
• Host response

Biofilms

• Stages of biofilm formation:
  • Attachment
  • Maturation
  • Dispersion

Quorum Sensing

• Controls:
  • Sporulation
  • Biofilm formation
  • Virulence factor secretion
• Three principles:
  • Signalling molecules (autoinducers)
  • Cell surface or cytoplasmic receptors
  • Gene expression -> co-operative behaviours and more AI production

Symptoms of Infection

• Fever
• Inflammation at the site of insertion
• Purulence or erythema
• Pain
• Malaise

Investigations

• Full blood count (FBC)
• C-reactive proteins
• ESR
• Blood culture (gram stain, antibiotic sensitivity)
• Samples (fluid, biopsy) - bacterial growth; PCR
• Scans

Management

• Diagnosis:

  • Aim is to identify infecting organism and its antimicrobial susceptibilities
  • Challenges: adherent organisms, low metabolic state/small colony variants
  • Blood cultures
  • Tissue/prosthetic material sonication and culture

• Treatment:

  • Aim is to sterilize tissue
  • No specific information provided