Team:SHPH-Shanghai/Description
What is biofilm ?
The detrimental effect of biofilm
Possible sources of biofilm
What is biofilm?
Biofilm refers to an organized microorganism population, such as bacteria and fungi, that is attached to the surface of living or inanimate object. It is usually surrounded by extracellular macromolecules (also called extracellular matrix) which include lipoproteins, polysaccharides, fibrin, peptidoglycan lipids, and other substances.
When the planktonic organisms first come into contact with a proper surface, they will adhere to the surface of the object due to weak van der Waals forces and hydrophobic effects. At this stage, named as attachment stage, the formation of biofilm has not been initiated yet. Since the single attached cell is only encased by a small amount of extracellular polymer, it is likely to re-enter the floating stage, which means the adhesion is still very weak. Various kinds of environmental factors determine the initial surface condition for cell attachment, such as the flow rate of the surrounding medium, pH, temperature, antifungal or antibacterial factors and extracellular polymeric substances.
An electron micrope picture of biofilm from Wikipedia
When the formation process enters the growth stage, gene expression will be regulated. Those associated with the formation of the biofilm are activated so that a large amount of extracellular polymer-bound will be secreted, which leads to irreversible adhesion. After a period of time, the biofilm will become mature and form a highly organized structure with channels used for transporting nutrients. 2 At last, the extracellular matrix will be degraded by certain enzymes and a part of the cells will be release, becoming floating ones. These can recolonize on another surface and form new biofilms. Studies have shown that the formation of Candida albicans biofilm, one of the most common fungal biofilm, can be divided into three independent phases: early (0 ~ 11 h), medium (12 ~ 30 h) and mature (31 ~ 72 h), which indicates the limited time needed for biofilms to mature.
The detrimental effect of biofilm
Biofilm is ubiquitous in nature and is very likely to thrive in the humid environment including the surface of rocks or pebbles, potable water pipelines, sewage treatment plants, clinical indwelling catheter, and even inside a human body. Although biofilms can indeed repair contaminated water bodies and become indicators for metal content in water, they still directly threaten human being’s heath in various ways, such as corroding the mental surface of ships and contaminating interventional medical devices as well as drinking water pipes. The presence of biofilm may introduce pathogenic bacteria and fungi into the human body and cause overproduction of microorganisms which can cause serious infection and inflammation. What’s more, the structure of biofilms makes the process of disinfection ineffective. The firm extracellular matrix prevents the microorganisms inside the biofilm from being washed away or being in contact with disinfectors. So biofilms accumulation inside drinking water pipes and dwelling catheters have been interested in researchers for a long time[1].
[1] A. Camper, M. Burr, B. Ellis, P. Butterfield, and C. Abernathy Center for Biofilm Engineering, Montana State University, Bozeman, MT, USA
Possible sources of biofilm
Biofilms usually exit in the nook of the machines or the turning angle of pipes, which makes it hard to be cleaned. The common method applied to eliminate biofilm is chemical removal by using disinfectors and antibiotic or antifungal drugs. Take Candida albicans as an example again: compared with the free cells, the sensitivity of the Candida albicans biofilm to the antifungal drugs is much less than that of the suspension cells. What’s more the degree of resistance of various fungi is related to the process of biofilm formation. The more mature the biofilm, the stronger the resistance of the fungus. However, due to the special micro-environment, they can’t work as effectively as they do to a planktonic cell. Abuse of antibiotic or antifungal drugs or applying them with high concentration will induce strong antibiotic and antifungal resistance and further contaminates the water supply.
Thus, an environmentally friendly and effective way of biofilm degradation is indispensable for many industries. Biological methods of degrading biofilm have the advantages of harmless, sustainable, and effective over traditional chemical methods.