Flashcards in Infection - Infections On Surfaces Deck (18)
Define a 'surface'
An interface between a solid and either a liquid or a gas
What are the sites of potential surface infections on a patient?
- skin (epithelium, hair, nails)
- mucosal surfaces (conjunctival, gastrointestinal, respiratory, genitourinary)
What are the viruses found on skin?
Papilloma, herpes simplex
What are the gram positive bacteria found on skin?
Staph aureus, coagulase negative staphylococci, corynebacterium
What are the gram negative skin microorganisms?
What fungi can be found on the skin?
Yeasts and dermatophytes
What parasites can be found on the skin?
What are commensals?
Microorganisms carried on the skin and mucosal surfaces which are normally harmless/beneficial, but can be harmful if transferred to other sites
How can a patient get an infection from bacteria which is already in their body?
- invasion by the pathogen
- migration to somewhere it shouldn't be
- inoculation, eg. infection of a prosthetic joint
- haematogenous (spread through bloodstream)
What is the difference between the causation of prosthetic valve endocarditis less than 1 year post-operation and over one year post-operation?
Less than one year post operation it is most likely to be caused by viridans streptococci, enterococcus faecalis, staph aureus, HACEK group and candidia. Over 1 year post-op, its more likely to be coagulase negative staphylococci
What are the most common causative organisms of prosthetic joint infections and cardiac pacing wire endocarditis?
Coagulase negative staphylococci and staphylococcus aureus
What are the processes in the pathogenesis of infections at surfaces?
- adherence to host cells or prosthetic surfaces
- biofilm formation
- invasion and multiplication
- host response (may be pyogenic or granulomatous)
What is a biofilm?
An assemblage of microbial cells which is irreversibly associated with a surface and enclosed in a matrix of primarily polysaccharide material
What is quorum sensing?
This is a way that bacteria are able to signal each other through three principles - signalling molecules ('autoinducers'), cell surface/cytoplasmic receptors, and gene expression
What does quorum sensing control?
Sporulation, biofilm formation and virulence factor secretion
What are the challenges of treating biofilms?
Poor antibacterial penetration into the biofilm, low metabolic activity of biofilm microorganisms, dangers/difficulties of surgery
How can infections on a natural surface be prevented?
Maintain surface integrity, prevent bacterial surface colonisation, remove colonising bacteria