Infections on Surfaces

Question 1

What is a surface?

Answer 1

Interface between a solid and either liquid or gas

Question 2

List some body surfaces.

Answer 2

Skin- Epithelium, Hair, Nails

Mucousae- Conjunctiva, GI, resp and GU epitheliums.

Question 3

What micro-organisms are quite normal on the skin?

Answer 3

Viruses - papilloma and herpes simplex (neither are normal but they are common and not that bad)

Bacteria-
Gram +Ve= Staph aureus, coagulase negative staph
Gram -Ve= enterobacteriaceae

Fungi- yeasts and dermatophytes

Parsites - mites

Question 4

List some commensals of the nasopharynx

Answer 4

Neisserria meningitidis, Streptococcus pneumoniae, Haemophillus influenzae.

Question 5

How does a pathogen get to where they infect?

Answer 5

Invasion - breaches physical barrier
Migration- moves to a different site
Innoculation- gets in by a needle of surgery
Haematogenous- through the blood stream like viridians Strep endocarditis.

Question 6

List some external surface infections.

Answer 6

Celluilitis 
Pharyngitis 
Conjunctivitis 
Gastroenteritis 
UTI
Pneumonia

Question 7

List some internal surface infections.

Answer 7

Endovascular- endocarditis or vasculitis
Septic arthritis
Osteomyelitis
Empyema

Question 8

List prosthetic surface infections

Answer 8

Pacing wires 
Endovascular grafts
Ventriculo-peritoneal shunts 
Cardiac valves 
Prosthetic joints 
Intravascular lines
Peritoneal dialysis catheters

Question 9

What determines which pathogen infect surfaces?

Answer 9

Prosthetic or natural surface
Time since prosthesis.

Important in endocarditis of valves. (prosthetic greater than a year think coagulase negative staph)

Question 10

What microbe is suspected in prosthetic joint infections?

Answer 10

Staph aureus of coagulase negative Staph.

Question 11

Infected pacing wires are likely to carry which microbe?

Answer 11

Staph aureus or coagulase negative Staph

Question 12

Outline the pathogenesis of surface infections.

Answer 12

Adherence to surface or host cells.
Biofilm forms
Invades and multiplies
Host responds - fever and granulomatous response

Question 13

How do microbes adhere?

Answer 13

Pili help adherence in cell to cell contact

Question 14

What is a biofilm?

Answer 14

A slime secreted by bacteria on a surface. Slime contains polysaccharides, proteins and nucleic acids with pores for nutrient diffusion. The biofilm offers antimicrobial resistance.

Question 15

What is Quorum sensing?

Answer 15

Signalling molecules, receptors and the resulting gene expression will control sporlation, biofilm formation and Virulence factor regulation.

Question 16

How to manage surface infections?

Answer 16

Identify the micro-organism and its susceptibility by blood cultures.
The challenge is adherent organisms in low metabolic states leave minimal targets for antimicrobials.
Sterilise tissue and reduce bio-burden with antibacterials but ultimately prosthetic material may need removal and resection of surrounding tissue.

Question 17

How do we prevent surface infections?

Answer 17

Natural surfaces- good integrity, remove bacterial colonisation, prevent colonisation.
Prosthetics- prevent contamination, inhibit colonisation and remove any colonies.