The protective dome of a biofilm shields bacteria from antibiotics.
When bacteria flock together and form a community, this is called a biofilm. Found all over the planet — from desert rocks to the surfaces of buildings — biofilms are an integral part of nature.
Biofilms are tricky beasts because they have a tendency to become resistant to all manner of efforts employed to eradicate them. This spells bad news for anyone with conditions such as cystic fibrosis, periodontitis, or chronic wounds as medical implants and catheters are hotspots for biofilm formation.
But why are biofilms so persistent, and what are doctors and scientists doing to outsmart these clever microbial communities?
What are biofilms?
"Biofilms are one of the most widely distributed and successful modes of life on Earth," says Prof. Hans-Curt Flemming — director of the Institute for Interface Biotechnology at the University of Duisburg-Essen in Germany — in a 2016 article published in Nature Reviews Microbiology.
Biofilms can be made up of populations of the same bacteria or of communities, which, in turn, are made up of many different species, all living together under a protective dome.
This dome is composed of a so-called matrix of extracellular polymeric substances (EPS), which contains a mixture of sugars, proteins, fats, and DNA molecules.
In much the same way as human communities, biofilms have highly specialized areas: some of them are responsible for nutrient recycling, while others produce new EPS components or send messages from one area of the biofilm to another.
Living together in such close proximity allows bacteria to share resources more successfully than when they are in their free-living state. Crucially, it allows them to avoid conventional methods of eradication.
Interestingly, antibiotics can actually enter a biofilm in many instances, but the EPS actively shields its inhabitants from such compounds, promoting antibiotic resistance.
Biofilm residence also affords the bacteria with antibiotic-resistant genes the ability to easily share these among their neighbors using a process called horizontal gene transfer. Although this also happens in free-living bacterial communities, it is significantly more efficient in biofilms.
The result of this is that antibiotic resistance spreads like wildfire. So, when faced with biofilm infections, what can doctors do?
The battle against biofilms
Biofilms are a serious threat to health, which is why doctors utilize aggressive treatments in the fight against them. Such treatments include surgically removing the area that is infected with a biofilm or using high-velocity water sprays to physically disrupt the biofilm, often in combination with antibiotics.
However, Prof. Hyun Koo — director of research at the Levy Centre for Oral Health in the School of Dental Medicine at the University of Pennsylvania in Philadelphia — explains in a recent review article that "killing [the bacteria] does not necessarily eradicate the biofilm."
If the EPS matrix remains intact, other opportunistic microbes can lie in wait and take up residence.
Researchers hope to disrupt biofilms by using many different approaches, including targeting the formation of the EPS or using enzymes to degrade this complex mesh, disrupting cell-to-cell communication, and inhibiting nutrient sources.
Many believe that the path to treatment lies in prevention. Advances in technology have allowed researchers to develop new materials actively designed to stop bacteria from attaching and forming biofilms in the first place.
The ultimate aim is that these will stop bacteria from sticking to the surface of medical implants and catheters, by coating surfaces with antibiotics or by including certain topographic surface features that are naturally hostile to bacteria.
One of these is called the Sharklet micropattern and is inspired by shark skin, which is naturally resistant to bacteria colonization. Made of groves arranged in a microscopic diamond pattern, researchers have shown that bacteria do not stick to this pattern as well as they do to smooth surfaces.
While there are no guaranteed treatments to rid us of biofilms just yet, researchers are increasingly getting to grips with the complex biology that underpins these microbial communities. In the meantime, the hunt for effective ways to eradicate this threat to our health continues.