Infections on Surfaces Flashcards
What is a surface?
Interface between a liquid solid or gas
What 5 things does a bacteria have to do in order to cause an infection
Exposure Adherence Invasion Multiplication Dissemination
What might cause a blood culture to have a false positive?
Microorganisms that are on the skin
Name two viruses that can cause skin infections
Herpes simplex
Papilloma - warts
How does cdiff cause a problem?
Invasion causes replacement of multiforal culture in bowel and becomes almost singularly occupying
What has helicobacter pylori got to do with cancer?
Predisposes to increased gastric reflux, barretts oesophagus and risk of cancer
Which 4 ways can people get infected?
Invasion - e.g. from a person - strep throat
Migration - e.g. from normal commensal E coli from bowel to urinary tract
Inoculation - e.g. put there - prosthetic joint
Haematogenous - e.g. via blood - strep viridian’s endocarditis
What are natural surface infections divided into? Give examples
Internal - endocarditis, osteomyelitis, septic arthritis
External - cellulitis, pharyngitis, UTI, pneumonia
Where might you see a prosthetic surface infection?
Cardiac valves Intravascular lines Cardiac pacing wires Prosthetic joints Ventriculo-peritoneal shunts
What is a Ventriculo-peritoneal shunts
Device that relieves pressure in brain
What is the likely cause of endocarditis >1 year after valve replacement or with native valve?
Strep viridians
Staph aureus
Candida
What is the likely cause of endocarditis <1 year post op prosthetic valve?
Staph epidermis
coagulase negative staph
What is the most common cause of prosthetic joint infections?
Staph epidermis
Staph aureus
Which is a common coagulase positive staph compared to a common coagulase negative staph
Positive - Aureus
Negative - Epidermis
Difference between Empyema and Abscess?
Empyema is pus in an existing natural cavity e.g. pleura
Abscess is pus in a new cavity
What kind of host responses might you have to infections e.g. on prosthetic surface (2)?
Pus
Granulomas (fibroblasts, lymphocytes, macrophages) leading to nodular inflammatory lesions
What structures on bacteria help them adhere to host cell?
Pili
Fimbrae
Why are biofilms resistant to antibiotics?
Low metabolic activity
Antibiotics most effective on metabolising organisms
How do biofilms form? How do they communicate? What does a biofilm do?
Bacterial cells aggregate and adhere - secrete slime ECM matrix. Adhere to surface (first reversibly then irreversibly). Grow by multiplying and recruitment
Resist phagocytosis and antibiotics
Communication by quorum sensing
How is biofilm behaviour controlled?
Quorum sensing
What does quorum sensing control?
Sporulation
Biofilm formation
Virulence factor secretion
What is a spore?
Structure produced by bacteria in environment change e.g. starvation. Helps with survival of bacteria as can withstand heat etc and is dormant - contains bacterial DNA
What are the three principles of quorum sensing?
Signalling molecules - autoinducers that coordinate gene expression
Cell surface cytoplasmic receptors
Gene expression –> cooperative behaviours and more AI production
How do you manage a patient with a bacterial infection that has a biofilm? What are the problems with each of these?
Antibacterials - biofilms resistant
Resect infected tissue
Remove prosthetics - dangers of surgery
