Infections on surfaces Flashcards
What is a surface?
Interface between solid and either liquid or gas
Viruses present on skin
Papilloma
Herpes simplex
Gram positive bacteria on skin
Staph Aureus
Coagulase negative staphylococci
Corynebacterium (accidental contamination usually)
Gram negatice bacteria on skin
Enterobacteriaceae
usually below waist as contamination from GI tract
Fungi present on skin
Yeasts (single celled eg Candida)
Dermatophytes (multicell eg ringworm)
Parasites
usually around hair follicles
Mites
Bacteria wiped out by antibiotics causing…
Lactobacilli wiped out of vagina
Candida albicans overgrows
= yeast infection
Clostridum difficile overgrowth in gut
= inflammation and perforation of gut
What is microbiota?
Commensals
harmless usually, helpful to make vitamins and prevent colonisation of pathogens
When is microbiota harmful?
When transferred to other sites
How do people get infections?
Invasion (strep pyrogens = pharyngitis)
Migration (E coli = UTI)
Innoculation (CN staphloccocus = prosthetic joint infection)
Haematogenous (Strep viridans = infective endocarditis)
External natural surface infections
Cellulitis Pharyngitis Conjunctivitis Gastroenteritis UTI Pneumonia
Internal surface infections
Endocarditis Vasculitis Septic arthritis Osteomyelitis Empyema (pleural sac infection)
Prosthetic surface infections
IV lines Catheters Prosthetic joints Cardiac valves Pacing wires Endovascular grafts Ventriculo-peritoneal shunts
What are <1 year after prosthetic valve endocarditis cases caused by?
Coagulase negative staphylococcus
What are >1 year prosthetic valve endocarditis caused by?
same as Native valve endocarditis:
Viridans Streptococci Enterococci Staph aureus Candida
Causes of prosthetic joint infections
Coagulase negative staphlococcus
Staphylococcus aureus
Cardiac pacing wire endocarditis causes
Coagulase negative staphylococcus
Staphyloccocus Aureus
Pathogenesis of infection at surfaces
Adherence to host cell
Biofilm formed
Invasion/multiply
Host response
Types of host response to infections at surface
pyogenic = neutrophils and pus Granulomatous = fibroblasts, lymphocytes, nodular legions
How do pathogens adhere to cells?
Pilli
What are biofilms?
Microbial communities encased in extracellular matrix
What do biofilms do?
Protect the bacteria by oreventing phagocytosis, antibodies and complement recognition/binding of receptors
What is quorum sensing?
Communication between bacteria via chemicals
What does quorum sensing control?
sporulation
biofilm formation
virulance factor secretion
3 components of quorum sensing
Autoinducers (AI) are signalling molecules
Cytoplasmic/cell surface receptors
Gene expression (cooperate behaviours and produce more AI)
Virulance factors exotoxins
Cytolytic AB toxins Superantigens Enzymes BIOFILM production
Investigations of infections on surface
Tissue/prosthetic valve sonication (shake to remove) and culture
Blood culture
Treatment of infections on surface
Antibacterials
Remove prosthetic material
Surgery (resect infected material)
Challenges of treatment on infections at surface
Poor antibacterial penetration into biofilm
Low metabolic activity of biofilm microorganisms
Dangers/difficulties of surgery
Prevention of infections at natural surface
Maintain surface integrity
Prevent bacterial colonisation
Remove colonising bacteria
Prevention of infections on prosthetic surface
Prevent contamination (aseptic)
Inhibit surface colonisation
Remove colonising bacteria
Stages of forming biofilm
Surface attachment (reversible/irriversible)
Microcolonies (cell proliferation and aggregation)
Macrocolonies (mushroom and tower like, cell detachment)
