Week 7 - Infections on Surfaces + Allergy Flashcards
What is microbiota?
- The microorganisms that typically inhabit a body organ
- Micro-organisms carried on skin and mucosal surfaces
- Normally harmless or even beneficial
- Transfer to other sites can be harmful
What is the normal microbiota found on the skin?
- Viruses:
— Papilloma
— Herpes simplex - Bacteria
— Gram positive
• Staph aureus
• Coagulase negative streptococci
• Corynebacterium
— Gram negative
• Enterobacteriaceae - Fungi
— Yeasts
— Dermatophytes - Parasites
— Mites
How can people get surface infections?
- Invasion
- – E.g. step pyogenes pharyngitis
- Migration
- – E.g. Escherichia coli urinary tract infection
- Innoculation
- – E.g. coagulase negative staphylococcus prosthetic joint infection
- Haematogenous
- – E.g. viridans strep endocarditis
What are some examples of external natural surface infections?
- Cellulitis
- Pharyngitis
- Conjunctivitis
- Gastroenteritis
- Urinary tract infection
- Pneumonia
What are some examples of internal natural surface infections?
- Endovascular
- – Endocarditis
- – Vasculitis
- Septic arthritis
- Osteomyelitis
- Empyema
What are some examples of prosthetic surface infections?
- Intravascular lines
- Peritoneal dialysis catheters
- Prosthetic joints
— Causative organisms:
• Coagulase negative staphylococci
• Staphylococcus aureus - Cardiac valves
— E.g. prosthetic valve endocarditis
• Coagulase negative staphylococci
• Viridans streptococci
• Enterococcus faecalis
• Staph aureus
• HACEK group
• Candida - Pacing wires
— Endocarditis, causative organisms:
• Coagulase negative staphylococci
• Staph aureus - Endovascular grafts
- Ventriculo-peritoneal shunts
Describe the pathogenesis of infections at a surface
- Adherence to host cells or prosthetic surface
- Biofilm formation
- Invasion and multiplication
- Host response
- – Pyogenic
- – Granulamatous
How can you identify surface infections?
- Aim is to identify infecting organism and its antimicrobial susceptibilities
- Challenges:
- – Adherent organism
- – Low metabolic state/small colony variants
- Blood cultures
- Tissue/prosthetic material sonication and culture
How do you treat surface infections?
- Aim:
- – Sterilise tissue
- – Reduce bioburden
- Antibacterials
- Remove prosthetic material
- Surgery – resect infected material
- Challenges:
- – Poor antibacterial penetration into biofilm
- – Low metabolic activity of biofilm microorganism
- – Dangers/difficulties of surgery
How can you prevent surface infections?
- Natural surface
- – Maintain surface integrity
- – Prevent bacterial surface colonisation
- – Remove colonising bacteria
- Prosthetic surfaces
- – Prevent contamination
- – Inhibit surface colonisation
- – Remove colonising bacteria
What are the different types of hypersensitivity reactions?
- Type I or immediate (
What is hypersensitivity?
The non-specific immune response that are either inappropriate or excessive and that result in harm to the host
What are the common features of hypersensitivity reactions?
- Sensitisation phase
- – First encounter with the antigen
- Effector phase
- – Clinical pathology upon re-exposure to the same antigen
Describe the pathophysiology behind a hypersensitivity reaction
- People are born with the TH2 phenotype
- – TH2 phenotype leads to allergic reactions
- Upon appropriate and sufficient immune system exposure, the phenotype can change to TH1, which does not produce allergic reactions
What are some common allergens?
- House dust mite, cockroaches
- Animals, especially domestic pets such as cats and dogs
- Tree and grass pollens
- Insect venom such as that contained in wasp and bee stings
- Medicines
- – E.g. penicillin
- Chemicals
- – E.g. latex
- Foods
- – E.g. peanuts, nuts, milk
