Infections On Surfaces Flashcards
What counts as a surface ?
Interface between a solid and either a liquid or a gas
Look at the patient park of the mechanisms of infection model
Need to look at surface of the patient - Skin - hair, nails and epithelium
- internal Mucosal surfaces - GI, respiratory, genitourinary and conjunctival
Skin microorganisms
Viruses - papilloma, herpes simplex
Bacteria - Gram positive (staph aureus or corynebacterium)
- Gram negative (enterobacteriaceae)
Fungi - yeasts and dermatophytes
Parasites - mites
Mucosal flora
Eye - Coagulase negative staphylococci, diphtheroids, saprophytic Neisseria species, viridans group streptococci
Nares - Staph aureus
Nasopharynx - Neisseria meningitidis, Streptococcus pneumoniae, Haemophilus influenzae,
Mouth - Viridans Streptococci, Neisseria, Veillonella, Lactobacillus, Actinomyces, Bacteroides, Capnocytophaga, Eikenella, Prevotella, fusobacteria, clostridia, propionibacteria, Candida, Geotrichum species
Stomach - Helicobacter, streptococci, staphylococci, lactobacilli,
Intestine - Bacteroides, Bifidobacterium, Eubacterium, Lactobacillus, coliforms, aerobic and anaerobic streptococci, Clostridium, yeasts
Urethra - Enterobacteriaceae, lactobacilli, diphtheroids, alpha and non-haemolytic streptococci, enterococci,
Vagina - Lactobacilli (this reduces the pH of the vagina by producing lactic acid - so if you give a women antibiotics then, you may reduce these numbers therefore increasing pH therefore allowing thrush to grow) , diphtheroids, micrococci, coagulase-negative staphylococci, Enterococcus faecalis, microaerophilic and anaerobic streptococci, mycoplasmas, ureaplasmas, yeasts
How do people get infections
Microbiota, otherwise known as commensals
Examples of natural surface infections and prosthetic surface infections
External - Cellulitis Pharyngitis Conjunctivitis Gastroenteritis Urinary tract infection Pneumonia
Internal - Endovascular - Endocarditis - Vasculitis Septic arthritis Osteomyelitis Empyema
Prosthetic surface infections - Intravascular lines Peritoneal dialysis catheters Prosthetic joints Cardiac valves Pacing wires Endovascular grafts Ventriculo-peritoneal shunts
Prosthetic infections
Prosthetic valve endocarditis - infection of the heart valves:
Native valve endocarditis and prosthetic valve endocarditis >1 year post-operation -
viridans, Streptococci, Enterococcus faecalis, Staph aureus, HACEK group Candida (usually very rare - but common in intravenous drug users)
Prosthetic valve endocarditis <1 year post-operation - coagulase negative staphylococci - bacteria from patients skin that got there during the operation - have grown over the last 12 months - if this does grow can be hard to treat as many of these bacteria are multi resistant against antibiotics
Prosthetic joint infections
Causative organisms -
coagulate negative staphylococci
Staph aureus
Cardiac pacing wire endocarditis
Causative organisms -
Coagulase negative staphylococci
Staphylococcus aureus
Processes in the pathogenesis of infections at surfaces
The pathogen adheres to host cells or prosthetic surface
Then forms a Biofilm around itself for protection
Invasion and multiplication then follow
Host response - 2 types
Pyogenic (neutrophils -> pus)
Granulomatous (fibroblasts, lymphocytes, macrophages -> nodular inflammatory lesions)
Adherence
Pili or fimbriae on bacteria cell wall which can bind to host cell membrane
Can produce a biofilm - EC material - can produce nucleic acids that will be secreted in the surrounding environment - essentially a slime layer to cover the bacteria
Bacteria work together (communicating) - protects the bacteria from hosts defences - stops neutrophils from phagocytosis - stops chemicals attacking the bacteria
Slime moves down the surfaces - so can spread infection along surfaces
Biofilm formation
1) starvation can induce bacteria to shrink and adopt a spore-like state known as ultramicrobacteria, which wait in water, soil, rock or tissue until conditions are suitable for active growth
2) active bacteria can attach to almost any surface. Changes in gene expression transform ‘swimmers’ to ‘stickers’ within minutes
3) attached bacteria multiply and encase the colonies with a slimy matrix
4) nutrients can diffuse into this matrix
5) The close proximity of cells in the matrix facilitates the exchange of molecular signals (Quorum sensing) that regulate behaviour
6) Chemical gradients create micro-environments for different microbial species or levels of activity
7) Although antimicrobial damage outer cell layers the biofilm community is resistant
8) propelled by shear forces, aggregated cells can become detached, or roll or ripple along a surface in sheets and remain in their protected biofilm state
Bacteria communicated via quorum sensing - essentially I’m here are you there?
Controls/importance in the production of
Sporulation (spores)
Biofilm formation
Vir
Management, treatment and prevention of surface infections
Management - Diagnosis - aim to identify infecting organisms and its antimicrobial susceptibilities
Use blood cultures or do prosthetic material sonication and culture
Challenges - can get adherent organisms on prosthetics, can have small colony variants, in a low metabolic state which may not be seen on diagnoses/ blood cultures
Treatment - Aim -
sterilise tissue
reduce bioburden
Antibacterials
Remove prosthetic material
Surgery - to
