Bacteria, biofilms, and antibiotics

[SusanSD]

I read in today's Washington Post newspaper about the social lives of bacteria and thought I'd share some excerpts. You can read about the “Social lives of bacteria…” by David Brown, online after free registration with washingtonpost.com

From a study published last week in the online Public Library of Science journal PLoS One:

An international team of biologists reported that when some species of marine bacteria form immobile “biofilms” — thereby becoming sitting ducks — they begin to produce chemicals that are specifically toxic to the predators that show up to eat them.

“We found that biofilms are resistant whenever an attacker comes their way. The question is, how do they do it?” said Carsten Matz, a microbiologist at the Helmholtz Center for Infection Research in Germany who led the research team.

Biofilms consist of large collections of bacteria stuck together in a slimy “matrix” that the organisms themselves produce and secrete into the environment. They allow microbes to stay in a place that has lots of nutrients and thereby maximize their growth and cell division.

The existence of biofilms has been known for a long time. But what has become clear in recent years is that a bacterium in a biofilm behaves quite differently from the very same bacterium in the free-floating (or planktonic) state. The difference is in the organism's metabolism — the making and breaking down of chemical compounds — activities that require energy and are done only if there is a payoff.

A major insight was that biofilm-based metabolism is triggered by an event called “quorum sensing.” Somehow, bacteria are able to detect the presence of other bacteria (usually of the same species) right around them. When the density gets high enough, the organisms switch into biofilm mode, producing and excreting the slime that then cements them together.

Quorum sensing depends on some sort of signaling among bacteria — although because the organisms have no nervous systems, the signaling is clearly unintentional in the conventional sense.

For some biofilm-producing species, waste products appear to be the signal. When many bacteria are near one another, those substances rise to a concentration at which they are detectable by the individual organisms. They then trigger the metabolic changes. In other cases, though, there seem to be hormonelike compounds that exist for signaling purposes alone.

How quorum sensing works, and how it evolved, are big topics in biology that are only now being explored in earnest.

What the new study shows is that once it kicks in, quorum sensing stimulates the bacteria in biofilms to do more than make slime. They also make weapons.

Matz and his colleagues, several working at the Center for Marine Biofouling and Bio-Innovation at the University of New South Wales in Australia, studied 30 widely differing types of marine bacteria that were all readily eaten by protozoan predators when they were in their free-floating state. In their biofilm state, however, 22 were resistant to a surface-grazing flagellate, a single-celled organism called Rhynchomonas nasuta, and 17 caused the predator's numbers to decline drastically.

Further study revealed the bacteria were making a purple compound called violacein that was lethal to the predator. While they also made it when they were free-floating, production went way up in the biofilm state, triggered somehow by quorum sensing.

Numerous other bacterial species also made violacein, and other protozoa were susceptible to it. In one case, an amoeba dissolved within an hour of eating a single violacein-producing bacterium. This suggests, as other studies have, too, that something akin to altruism may have originated in single-cell organisms.

“Even though individual cells are ingested and do not survive to reproduce, the remaining [bacterial] population may benefit from reduced grazing pressure,” the scientists wrote.

Biofilms are far more than curious biological communities; they have huge practical consequences, as well.

Bacteria in biofilms are often resistant to antibiotics that kill them easily when the organisms are free-floating. (By one estimate, 80 percent of chronic bacterial infections involve biofilms.) Finding ways to block their formation — or to soften them up so that predators like white blood cells of the immune system can move in more easily — is a major area of research.

 

Food for thought, eh, Maz? I wonder if AP degrades these biofilms so that the bacteria have less energy, fewer weapons to cause damage to tissues and joints.

– Susan

[Michele]

Hi Susan,

Really interesting find!! Thanks for sharing!

It is so exciting to see research on bacteria, biofilms, and antibiotics finally getting international attention in the scientific community!

Michele

[Maz]

Hi Susan,

Thanks for sharing this interesting information. I'd done a bit of research on bio-films just for my own edification a few months back. It's a complicated subject and I didn't get too far….just gleaning a gist of what they were. Does seem, however, that there is lots of talk in microbiology circles about their existence (Lyme Disease is no exception). The new movie, “under Our Skin,” though I haven't yet had an opportunity to see it, is said to have some coverage on the bio-film phenomenon. Seems that many different types of pathogen have this ability to group together (safety in numbers) when conditions in the environment become hostile. Seems that bio-films are found everywhere in nature…anywhere where there is a damp or liquid environment – one sees bio-films on stagnant ponds, for instance…bio-films have even been reported in ear infections.

When I first read of bio-films, I was struck by how “plant-like” this pleomorphic-protective-community state seemed to be. It was also recently discovered by botonists that plants of the same species, closely planted together, were able to communicate environmental threats to one another through bio-chemical signals passed via their root systems, as the roots of other plants took up water from the soil. So if a caterpillar or two starts attacking the leaves of one plant, this causes a chemical release, via its root system, to notify other plants in the vicinity to produce less foliage, thus ensuring vital nutrients were stored in the stem and roots. Sort of an altruistic way for the plant being attacked to warn others.

Nature is amazing….and, as we've all experienced, first hand, can be cruel, too. 

Here are a couple of studies you might interesting:

Biofilms Protect Mycoplasma pulmonis Cells from Lytic Effects of Complement and Gramicidin

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1951995

Biofilm formation by mycoplasma species and its role in environmental persistence and survival

Laura McAuliffe1, Richard J. Ellis2, Katie Miles1, Roger D. Ayling1 and Robin A. J. Nicholas1

http://mic.sgmjournals.org/cgi/content/abstract/152/4/913

Like you, I also wonder how AP, though it might initiate bio-film formation, might act…in the long term….to impede bio-films…there are a few other threads on this topic with some interesting insights from other posters…if interested, just type in bio-films in the search box.

Thanks, Susan, for sharing this interesting article!

Peace, Maz

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