L12: Infections on a surface Flashcards
What is a surface?
Interface between a solid and a liquid/gas
What surfaces are there on a patient for microorganisms to colonise?
Skin --> Epithelium --> Hairs --> Nails Mucosal surface --> Conjunctiva --> Gastrointestinal tract --> Respiratory tract --> Genitourinary tract
What microorganisms can be found on the skin?
Viruses –> Papilloma (warts) and Herpes simplex (coldsaw)
Bacteria
–> Gram positive–> Staph Aureus (coagulase positive–> enzyme for invading tissues) coagulase negative streptococci, corynebacterium
–> Gram negative–> Enterobacteriaceae
Fungi–> Yeast (single celled), dermatophytes (multicellular)–> Athletes foot, ringworm
Parasites–> mites
What does the human microbiota show?
Range of bacteria
Varies from place to place
Varies in concentration from place to place
Where can infections come from?
Self –> transferred from normal environment on patient to new abnormal environment–>
Transmitted from animal
Environment–> contaminated water, food, air, surfaces
Source–> patient or via intermediate
What is one of the most common ways of patients getting infected?
Self transferred
Microbiota in one area entering a new area
Define microbiota?
Micro-organisms on the surface of the skin or mucosa
Normally harmless and beneficial
Wrong area–> harmful
How can infections be transferred from one area to another?
Invasion
Migration
Innoculation–> during operation etc… bacteria introduced into the body
Haematogenous–> in the blood
What are some example of naturally occurring external surface infections?
Cellulitis Pharyngitis Conjuctivitis Gastroenteritis--> inflammation of large bowel--> diarrhoea mechanism for expelling organism but also helps distribute it Urinary tract infection Pneumonia
What are some examples of naturally occurring internal surface infections?
Endovascular–> endocarditis, vasculitis
Septic arthritis–> infection of joint
Osteomyelitis–> infection of bone
Empyema–> infection of pulmonary space (between external surface of wall and internal chest wall)
What are examples of prosthetic surface infections?
Intravascular lines Peritoneal dialysis catheters Prosthetic joints Cardiac valves Pacing wires Endovascular grafts Ventriculo-peritoneal shunts
What is prosthetic valve endocarditis?
Infection of the heart valves
Native–> valves your born with which are damage
–> Normally caused by bacteria in mouth –> Staph aureus
Prosthetic valves–>replaced
–> Normally causes by skin bacteria–> coagulase negative staphylococci
What are the organisms normally found in prosthetic joint infections? How is risk reduced? How is it treated?
Coagulase negative streptococci
Staphylococcus aureus
Preventative–> sterile area (filtered and high pressure room), Surgeons wear ‘space’ suits
Antibiotics aren’t very good–> poor blood supply so concentration of antibiotic to reach joint low
Removal of prosthetic–> treat with antibiotics–> redo several months later–> 2 stage replacement
1 Stage replacement possible but risk of infection to new prosthetic
What are the causative organisms in cardiac pacing endocarditis?
Coagulase negative staphylococci–> pts own skin
Staphylococcus aureus
What is the process of development of infection at the cell surface?
Adherence to host cell/ prosthetic surface
Biofilm formation
Invasion and multiplication of tissues
Host reponse
–> Pyogenic–> pus formation by neutrophils
–> Granulomatous–> fibroblasts, lymphocytes, macrophages–> nodular inflammatory surfaces
What allows bacteria to stick to the surface? What happens when they bind?
Bacterial cell specialised structures–> pili or fimbriae (specialised proteins)
Bind to surface receptor on host cell membrane
Change from vegetative form to activated form
Start to produce biofilm
What is a biofilm?
Production of 'slime' layer by multiple bacteria communicating together Excrete ECM (polysaccharides, nucleic acids etc)
Why do bacteria produce a biofilm?
Protect bacteria from host defences
Suffocates neutrophils–> prevent antibodies and complement from attacking the bacteria
How is a biofilm produced?
- Starvation–> bacteria shrink form spores until conditions right for growth
- Active bacteria adhere to surface
- Attached bacteria multiply and encase the colonies within a slimey matrix
- Nutrients diffuse into matrix
- Molecular signs that regulate behaviour transferred between cells in matrix
- Chemical gradients create microenvironments for different species and different activites
- Antimicrobial damage outer cell layer but biofilm community resistant
- Aggregates can become detached and move to a new surface but remain in biofilm
How do bacteria communicate?
Quorum sensing
Enough bacteria–> communicate–> control biofilm formation, sporulation, and virulence factor secretion
How does quorum sensing work?
Bacteria produce signalling molecules–> autoinducers (AI)
Cell surface receptors/ cytoplasmic receptor on other cells detect signalling molecule
Gene expression is altered –> co-operative behaviours and more AI production
How do microorganism causes disease?
Exposure- adherence- invasion- multiplication and dissemination
Production of virulence factors–> exotoxins (cytolytic, AB toxins, superantigens, enzymes) and endotoxins–> host cell damage (direct, consequent to host immune response)
How are surface infections diagnosed? What are the challenges?
Identify infecting organism and its antimicrobial susceptibilites
Blood culture
Tissue/ prosthetic material sonication (apply sound to remove infection) and culture
Challenges–> adherent organisms (difficult to get bacteria off)
–> Low metabolic state/ small colony variants–> more difficult to grow
How are surface infections treated?
Aim–> sterilise tissue, reduce bioburden
Antibacterials
Remove prosthetic
Surgery–> resect infected material
What are the challenges with treatment?
Poor antibacterial penetration into biofilm
Low metabolic activity of biofilm
Danger/difficulties of surgery
How can surface infections be prevented?
Natural surfaces–> Maintain surface integrity, prevent bacterial surface colonisation, remove colonising bacteria
Prosthetic surfaces–> prevent contamination, inhibit surface colonisation and remove colonising bacteria
