Biofilms are an ingenious evolutionary creation, but one that gives us humans a lot of trouble in fighting bacteria.
Originally, there was no real need for bacteria to clump together in most situations, due to their free-floating water environment. But land surfaces (and debris in the waters) enabled them to form extracellular matrixes in conjunction with each other in order to raise the survivability of the entire group.
First properly studied after the development of the electron microscope, they were found to be more widespread on surfaces than previously thought. The material secreted by the bacteria to surround them on a surface was also found to largely be made of polysaccharides, long chains of carbohydrates.
It was also found that the bacteria living in such an environment that form a biofilm are distinctly different from their counterparts elsewhere, such as those in the ocean, even if they are the same species. They are also incredibly difficult to remove from the surface they are attached to and are resistant to most forms of chemicals that would otherwise kill them. Antibiotics become largely useless in a fight against biofilms.
Eating Away Biofilms
Researchers at the University of Wisconsin decided to look into an amoeba known to prey upon bacteria, including those commonly found to form biofilms. Dictyostelium is a bacterivore amoeba that is found in most soil environments around the world. While still known as a part of the slime mold group, the genus has remained a part of the Protista group and is directly not a part of fungi, unlike other slime molds.
For their study into the effectiveness of the amoeba against bacteria, they decided to try its hands against four well known and dangerous biofilm creating bacteria.
The Target Bacteria
Pseudomonas aeruginosa is an opportunistic pathogen that has, in recent years, developed multi-drug resistance and has been responsible for a large number of deaths in hospital settings. Those that have become immunocompromised due to severe burn tissue or lung diseases have been found to be most susceptible to this bacterium.
Pseudomonas syringae is a plant based pathogen that has a highly effective injection system that can overcome plant resistance. The many different pathovars of this bacteria prey on a wide variety of plants and especially agricultural crops like beans and wheat. It has also become a fairly common model organism for plant bacterial pathogen research.
Klebsiella oxytoca is a complicated dual-focused bacteria. In plants, it helps in the process of nitrogen fixation and can allow plants to grow better even under certain stressful conditions like high salinity. However, if inside a human, it appears to contribute to the effects of conditions like colitis and sepsis and is able to resist efforts to use antibiotics against it. So, while helpful in agriculture, it is dangerous in certain other settings.
Lastly, they used Erwinia amylovora, which causes the more commonly named plant disease of fire blight. This is a dreadful disease of fruit trees, especially of apples and pears, and can be spread by insects, birds, and even just the wind. It is a full on quarantine disease, where any infected trees and even those in the immediate area are to be cut down immediately. Several countries even today have strict laws against importation of fruit from countries infected with the bacteria.
In their experiment, they took several different strains of the amoeba species and put them up against biofilms of each type of the above-noted bacteria. All of the amoeba strains were capable of feeding on the biofilms, but how successful they were appeared to depend on the strain used and which bacteria the strain was used on. Several of the tests resulted in the complete destruction of the biofilm by the amoeba.
The study looked into several capabilities of the amoeba beyond just its feeding on biofilms. They also looked at the effectiveness of its spore germination on a biofilm substrate and the later stages of its multicellular development. Specifically the process of fructification, where it formed a fruiting body for reproduction.
For Now, Agriculture
The experiment concluded by showcasing the success of the amoeba against biofilms, but also acknowledging that more research is needed to determine which strains work best against which bacteria, in order to most effectively utilize them. They will likely prove quite useful in the fight against plant pathogenic bacteria and the biofilms formed in the cases of diseases like fire blight.
Human usage is probably a bit farther off though, as actually treating any interior bodily biofilm with the amoeba would be complicated to pull off. But, at minimum, this advancement in the understanding of Dictyostelium may prove to be necessary for future agriculture and medical treatments.
Photo CCs: Dictyostelium discoideum 43 from Wikimedia Commons