Biofilms

Question 1

biofilms are important defence mechanisms bacteria have developed to

Answer 1

survive in hostile environment

Question 2

what is a biofilm?

Answer 2

bacteria cluster together and embed themselves into a slimy extracellular matrix made of extracellular polymeric substance (EPS).

Question 3

‘extracellular polymeric substance’

Answer 3

is made up of carbohydrate polysaccharides and proteins possibly with DNA, lipids and other substances in the mix.

Question 4

Biofilms can form on a range of surfaces ranging from

Answer 4

living to non-living and are key in allowing bacteria to embed on prostheses.

Question 5

There are 4 key principles required in this process for biofilm formation:

Answer 5

• Quorum sensing- quorum sensing is the modulation of gene expression in response to changes in cell population density (i.e. are there enough bacteria to carry out a process). These processes include; biofilm formation, sporulation and virulence factor release.
• Release of a signal- known as an autoinducer when a quorum (critical number of bacteria required) has been reached
• A receptor for the signal- on the bacteria to carry out the process
• A switching mechanism- to alter gene expression to carry out the process

Question 6

There are 5 steps used to produce a biofilm:

Answer 6

1. Bacteria adopt a spore-like state (also known as planktonic phase) under starvation or limited nutrients availability. In this state, they are found as individual freely moving cells.
2. Once they encounter an environment suitable for growth, the bacteria change their gene expression from a ‘swimming’ state to a ‘sticking’ state in which they can attach to their chosen surface.
3. Upon attachment, the bacteria start to multiply, forming colonies and adhering to each other by producing a slimy matrix of EPS.
4. This matrix allows for diffusion of nutrients between bacteria. It also allows for the transmission of molecular signals between cells. This molecular signal (an autoinducer) allows the behaviour of the entire biofilm to be regulated. This includes signalling bacteria to switch to a slower metabolism and to stop dividing which is beneficial in resisting anti microbials and preserving resources. Different microenvironments can evolve within the matrix with varying chemical gradients, which allow for different microbial species to co-exist or different activities to take place.
5. Under certain circumstances, either voluntary (self-programmed due to stress) or non-voluntary (shear external forces breaking up the matrix), bacteria can detach from their matrix. They can be released from their colony in a planktonic state (sporulation) or detach as whole chunks of biofilm that then go on to invade other surfaces.

Question 7

autoinducers

Answer 7

allows the behaviour of the entire biofilm to be regulated. This includes signalling bacteria to switch to a slower metabolism and to stop dividing which is beneficial in resisting anti microbials and preserving resources. .

Question 8

the matrix allows

Answer 8

Different microenvironments to evolve within the matrix with varying chemical gradients, which allow for different microbial species to co-exist or different activities to take place

Question 9

clinical significance

Answer 9

• Biofilms are a major cause for concern in hospitals where they are responsible for a considerable share of healthcare acquired infections.
• The cause of a biofilm based infection is usually iatrogenic.

Question 10

common biofilm based infections

Answer 10

indwelling devices, mechanical ventilators, intravascular lines, urinary catheters, prosthetic heart valves or orthopaedic implants. The issue is further compounded by the fact that many of these instruments eg ventilators, are used in critically unwell patients who are already more susceptible to infection.

Question 11

organisms responsible for infection are usually

Answer 11

commensal bacteria living on :

• the surface of the skin
• upper resp tract
• low GI tract
• Urogenital tract

When moved from their usual niche to a different part of the body or given opportunity to do so by a medical device they may become pathogenic.

Question 12

common pathogens which cause biofilm infecgtions

Answer 12

Staphylococcus epidermidis and Staphylococcus aureus.

Question 13

virulence factors of biofilms

Answer 13

autoinducers can induce expression of virulence factors such as beta lactamases and exotoxins–> amke bacterial colonies more resilient to immune attack and antibiotics

Question 15

efficacy of antimicrobials to treat biofilms is limited because:

Answer 15

• Most antimicrobials lack the ability to penetrate biofilms
• Biofilms on prosthetic joints have a poor blood supply making it difficult to achieve a high concentration of antimicrobial.
• After the switching process has occurred the bacteria have a slower metabolism and do not divide as rapidly reducing antimicrobial effectiveness.

Question 16

prevention opf biofilm formation

Answer 16

sterilisation of indwelling devices e.g. any prostethic material

Question 17

Patients that have been infected should have a sample taken so

Answer 17

the microorganism can be identified and tested for its antimicrobial susceptibilities to prescribe the most effective agent.