Biofilms | omvsquad

Have you ever noticed the slimy stuff that sometimes coats your teeth, or the conglomeration of gunk that sometimes clogs your drain? Well if you have, then you have seen a biofilm. A fancy definition for a biofilm is “an assemblage of surface associated microbial cells that are enclosed in an extracellular polymeric substance matrix” [3]. In simpler terms, a biofilm occurs when free floating bacterium attach to a surface and secrete a sticky substance allowing them to exponentially grow and develop into a complex three dimensional structure [1]. This “sticky” substance that helps bacterium attach to surfaces is known as the “extracellular polymeric substance,” or EPS [1]. The EPS can account for anywhere between 50-90 percent of a biofilm, and is primarily composed of polysaccharides [3]. In gram negative bacteria, such as P. aeruginosa, the polysaccharides in the EPS are mostly neutral or anionic in property [2]. This allows for cations, such as Calcium, to associate with the polymer strands of the EPS and provide a stronger binding force to a surface in a developed biofilm [3].

A major factor dictating where biofilms form is the presence of moisture – biofilms thrive in moist environments that contain both a surface to grow on and the right amount of nutrients [1]. Once the conditions are suitable for biofilm formation, biofilm development will occur. There are five stages of biofilm development. Stage 1 is known as initial attachment, or reversible attachment. It is in this stage that free floating, or planktonic, bacteria adhere to a surface [4]. Stage 2 is known as irreversible attachment, and is when cells begin to aggregate and excrete an EPS [4]. Stage 3 begins the true formation of a maturing biofilm; it is also known as Maturation I [4]. Stage 4, called Maturation II, is when three dimensional growth and further maturation of the biofilm occurs; it is during this stage that the biofilm develops protection against antibiotics [4]. And finally, Stage 5, or the dispersion stage, is when the biofilm has reached a critical mass, and releases planktonic bacteria into the surroundings so they can begin the formation of another biofilm [4].

There are a few key characteristics about biofilms that should also be mentioned. For one, a biofilm is a complex and dynamic structure composed of multiple organisms; pure species biofilms occur in labs only [2]. Another thing to note about biofilms is that their genetic expression differs from planktonic bacteria [2]. Because of this, certain genes are upregulated, or activated, and certain genes are downregulated, or deactivated [2]. The shift in gene expression can also be a reason why biofilms are more tolerant to antibiotics then their planktonic counterparts [2]. Finally, through the use of singling molecules, cells within a biofilm can coordinate behavior and “communicate” with each other [2]. Quorum sensing, as it is called, is when bacterial populations activate certain genes when they can sense, via signaling molecules, their population is big enough to safely initiate gene activity [2]. The EPS plays a role in quorum sensing because it allows for a concentration of signaling molecules to build up enough to effectively change the biofilms behavior [2].