Microbiology

Biofilm Development



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Bugs, germs, bacteria, micro-organisms - we think of them as dirty and dangerous, to be avoided, controlled, exterminated. But these are living creatures. They share a lot of DNA with us. They also share our needs for food, shelter and to keep their family line going - reproduction.

A biofilm is a community of micro-organisms, attached to a wet or moist surface. Micro-organisms include

bacteria
yeasts
algae
fungi

Individual micro-organisms can only be seen under a microscope. These bugs make a sticky, slimy, gel-like substance and surround themselves with it. It's rather like frogspawn, but at a microscopic level. Some biofilms are a bit more solid. Biofilms are all around us in nature.
The complex structure of the biofilm can only be seen under high powered magnification.

Micro-organisms attach themselves to all kinds of surfaces. For example, a pebble in a pond is covered in slimy green stuff. That slime is a biofilm. The slippery layer that builds up inside a waste pipe is a biofilm.

The plaque that builds up between the gum and the tooth is a biofilm. This biofilm cannot be eliminated, but can be kept under control by proper dental hygiene. Lots of dangerous germs live in dental plaque. If they get into the bloodstream they can cause serious disease. Doctors and dentists knew this in the late 19th Century.

Biofilms start as just a few bugs forming a thin layer. They can develop into complex, three dimensional structures housing millions of individual bugs. Like miniature cities, they have towers, columns, bridges and channels for the flow of nutrients. They are built by micro-organisms themselves, working together for their own protection.

There are five stages of biofilm development:

1. Initial reversible attachment of free swimming micro-organisms to surface
2. Permanent chemical attachment, single layer, bugs begin making slime
3. Early vertical development
4. Multiple towers with channels between, maturing biofilm
5. Mature biofilm with seeding / dispersal of more free swimming micro-organisms

Most bugs want somewhere to settle down and call home. A good home will have the basic necessities of life to hand. Different bugs need different things to thrive. Some need lots of oxygen, others prefer very little. Some like it hot. A few prefer cold. Most like it warm and wet. Especially the ones that like to live with us. Humid beings are a favoured billet. But first, they have to find a way of hanging on in there. They need some way of attaching themselves to our surfaces. Some make sticky glue, and also hide in deep dark holes. When you are microscopic in size, a hair follicle counts as a deep dark hole. So does a sweat gland, the gap between your tooth and the gum, and all kinds of nooks and crannies that you will see if you put the human body under a microscope. Tonsil crypts are a classic sheltered home for bugs.

From the bug's point of view, being part of a big stable biofilm is a good place to be. It is much safer, compared with a single swimmer, alone in the hostile world. The bugs in the biofilm are like city dwellers. They live a settled, sheltered life, supported by family, friends and neighbours. But they do need to fulfill their mission, to go forth and multiply, to spread their genetic code. To do this, the biofilm will send out scouts. Single swimmers, or sometimes small clumps, go looking for new pastures to colonize. These free swimming or planktonic forms are designed to find and settle on new ground, then rapidly reproduce. Nearly all conventional microbiology relies on detecting and culturing the free-swimming or scout form of the bacterium. Showers of bacteria are released. Like fish spawn, most will not survive. Those that do find fertile ground will need to establish themselves quickly, and set up new colonies.

Because our microbiology laboratories are set up to find and deal with these rapidly replicating, colonizing bugs, and our antibiotic treatments are also directed against them, antibiotics do not work at all well on established biofilms. The bugs in the biofilm are not actively replicating, they are not forming new colonies, they take different forms altogether.

The bugs in the biofilm form a reservoir, a sheltered, sleepy home base, which can hunker down and withstand an onslaught of antibiotics. The antibiotics don't get rid of the biofilm because the bugs in the biofilm are not doing the things the antibiotics are designed to attack. Antibiotics will kill any free swimming forms, but once the antibiotic treatment has finished, more scouts can be sent out. Like guerilla warfare, terrorists with the support of an established community can go to ground and wait till the heat is off. They can then take a further opportunity at a later date.

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