Biofilms – living in slime

Biofilm of Streptococcus mutans stained using DNA-binding DAPI fluorescent stain

Bacteria are diverse – also with respect to their life form. On the one hand, they are capable of swimming around in an aquatic environment, e.g. a pool, a sink, blood, or some other body fluid. When swimming in such a way, they are loners and, depending on their individual virulence, cause more or less serious acute infections. On the other hand, they also build large communities that stick to surfaces. They settle down, send out molecules, which tell other bacteria that a new bacterial colony was just founded, and coat themselves in a slimy matrix. They are in lively contact with each other via a chemical broadcasting system known as quorum sensing. In this state, they cause chronic infections that may lead to acute infectious episodes whenever individual bacteria are released from the biofilm community.

Covered by a thick slimy coating made of biopolymers, the bacteria shield themselves from the immune system and antibiotics. In Germany alone, some 100,000 infections annually are related to biofilms – with clinically relevant pathogens including pseudomonads, staphylococci, and streptococci. Scientists at the Helmholtz Centre for Infection Research are studying biofilms from several different angles. Their aim is to understand the principles underlying the biofilm communities and manipulate them. They are also searching for strategies to dissolve the biofilms – so that they can be attacked by the immune system and antibiotics.

Understanding biofilms

Petri dishes are used to cultivate microorganisms and cells in the lab.

Biofilms are complex communities, which house many different types of bacteria and even fungi. However, not every biofilm is also pathogenic. The behaviour of the biofilms depends on many different factors and is controlled by chemical signalling. Every day, we effectively get rid of the biofilms when we brush our teeth or wipe the sink, and then, soon afterwards, they re-organize. One thing that cannot be prevented is the presence of biofilms on medical implants: whether stents, pacemakers, or dental implants – the biofilm always grows on them. But perhaps we might find a surface coating for these medical devices so that the biofilms are no longer harmful to the patient? Or might we be able to disrupt the bacterial communications and thus disturb their communities? What is the influence of the patient on the biofilm? Should these communities even be considered useful disease markers? Our scientists are convinced that yes, they are.

Fighting biofilms

A bacterial cluster forming a biofilm against a blue background.

If pathogenic biofilms form in a seriously ill patient, the bacteria, which could cause a severe infection, have to be killed. One approach taken by HZI scientists as part of an interdisciplinary consortium is to dissolve the biofilm. The researchers are looking for natural substances that interfere with the bacterial communication system and signal the community to disintegrate. Then, the immune system and antibiotics can intervene and kill the bacteria. One important consideration is that many of the clinically relevant pathogens have developed multi-resistance, caused through overuse of antibiotics during disinfection treatment of biofilms in medical everyday life. Trying to identify a suitable antibiotic for the patient often takes days, during which the already weakened patient is at the bacteria’s mercy. Therefore, our scientists are developing methods that work significantly faster than traditional microbiological techniques: They identify exactly those bacterial genes, which encode antibiotic resistance.

(Dr Jo Schilling)

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