Infections on surfaces

Question 1

Surfaces that may provide areas for infection on/in a patient include what?

Answer 1

Skin surfaces (epithelium, hair, nails)
Mucosal surfaces
Prosthetic surfaces

Question 2

What are some examples of infections of the skin by viruses?

Answer 2

Papilloma (warts)

HSV

Question 3

What are some examples of bacterial infections of the skin?

Give examples of gram positive and gram negative bacteria

Answer 3

Gram positive: staph. aureus, coagulase negative staph.

Gram negative: enterobacteriaceae (e.g. Salmonella, E.Coli)

Question 4

Give some areas that are prone to mucosal surface infections and some examples for these sites

Answer 4

Eye
Nose: Staph. aureus
Nasopharynx: Neisseria Menigitidis, Streptococcus Pneumoniae, Haemophillus Influenza
Mouth: Viridans Strep., Neisseria, Candida, Lactobacillus
Stomach: H. Pylori, Streptococci, Staphylococci, Lactobacillus
Intestine: Lactobacillus, Clostridium, Yeasts
Urethra: Lactobacilli, alpha and non-haemolytic strep
Vagina: Lactobacilli, yeasts, coagulase negative strep

Question 5

Give some examples of prosthetic surfaces that may provide an ideal habitat for colonisation by microorganisms

Answer 5

IV lines 
Peritoneal dialysis catheters 
Prosthetic joints 
Cardiac valves 
Pacing wires

Question 6

What causative organism do these surfaces tend to have in common: prosthetic valve endocarditis (<1 year after replacement), prosthetic joint infections and cardiac pacing wires?

Answer 6

Coagulase negative Staph.

Question 7

Native valve endocarditis and prosthetic valve endocarditis are at risk of infection by which organisms?

Answer 7

Staph. Aureus
Viridans Streptococci
HACEK group
Candida

Question 8

What are the processes involved in the pathogenesis of infection at surfaces?

Answer 8

Adherence to host cells or prosthetic surface
Biofilm formation
Invasion and multiplication
Host response

Question 9

Through what intermediates might we get infections?

Answer 9

Direct from source
Via the environment 
Direct from animals 
Via intermediary 
Commensals!

Question 10

What are commensals and why might they be harmful?

Answer 10

Microorganisms that inhabit the skin/mucosal surfaces of the body and usually provide benefit to these sites
When they move to a site where they do not usually belong, they can become harmful

Question 11

How might commensals be transferred to sites where they do not usually grow?

Answer 11

Invasion
Migration
Inoculation
Haematogenous

Question 12

Name some infections that may arise at external natural surfaces?

Answer 12

Cellulitis 
Pharyngitis 
Conjunctivitis 
Gastroenteritis 
UTI 
Pneumonia

Question 13

Name some infections that may occur at internal natural surfaces?

Answer 13

Endovascular- endocarditis, vasculitis
Septic arthritis
Osteomyelitis
Empyema

Question 14

What facilitates the ability of organisms to adhere to surfaces?

Answer 14

Pili or fimbrae

Question 15

What is involved in biofilm formation and why is this so beneficial to organisms that are trying to colonise a surface?

Answer 15

Once attached the microorganisms secrete proteins that contribute to biofilm matrix formation and attracting other species
They are safe from antimicrobials within the biofilm and allows microorganisms to regulate their behaviour/phenotype based on their environment

Question 16

What is quorum sensing and what does it control?

Answer 16

A system of signalling and response correlating to population density
Controls sporulation, biofilm formation and virulence factor secretion

Question 17

What three principles govern quorum sensing?

Answer 17

Signalling molecules (autoinducers, AIs)
Cell surface/cytoplasmic receptors
Gene expression- to modify behaviour and AI production

Question 18

Invasion and multiplication involves what?

Answer 18

Virulence factors (endotoxins and exotoxins)

Question 19

Damage to cellular host can occur in which two ways?

Answer 19

Directly by the organism

As a consequence of host immune response

Question 20

What three stages are involved in the management of infection on surfaces?

Answer 20

Diagnosis - identify the causative organism and antimicrobial susceptibility
Treatment - specific and supportive
Prevention - remove colonising bacteria, prevent contamination

Question 21

What challenges may be present when trying to diagnose infections on surfaces?

Answer 21

Identifying adherent organisms

Identifying low metabolic rate/small colony variants

Question 22

What is the aim of treatment of infected surfaces?

Answer 22

Sterilise the tissue

Reduce bioburden

Question 23

Describe the two stage approach involved in resecting infected materially surgically

Answer 23

1. Take out the old device and pack with antibiotic polymer

2. Weeks later, new prosthetic device put in