Biofilms

 

You may not be familiar with the term “biofilm,” but you have certainly encountered biofilm on a regular basis. The plaque that forms on your teeth and causes tooth decay is one type of bacterial biofilm. The “gunk” that clogs your drains is also biofilm. If you have ever walked in a stream or river, you have probably slipped on biofilm-coated rocks.

They’re found in natural environments such as hot springs, rivers and streams, lakes, subterranean stromatolites, and tide pools, to man-made and industrial environments such as water and drainage pipes, sanitation systems, house-hold sinks, toilets, and showers, and even in the water tanks of nuclear power plants. Biofilms avidly colonize many household surfaces, including toilets, sinks, countertops, and cutting boards in the kitchen and bath. Poor disinfection practices and ineffective cleaning products may increase the incidence of illnesses associated with pathogenic organisms in the household environment.

Biofilms form when bacteria adhere to surfaces in moist environments by excreting a slimy, glue-like substance. Sites for biofilm formation include all kinds of surfaces: natural materials above and below ground, metals, plastics, medical implant materials—even plant and body tissue. Wherever you find a combination of moisture, nutrients and a surface, you are likely to find biofilm.

Biofilm communities can be formed by a single bacterial species, but biofilms almost always consist of rich mixtures of many species of bacteria, as well as fungi, algae, yeasts, protozoa, other microorganisms, that cohabitate and engage in “quorum sensing”, and evolutionarily old form of bacterial communication. Biofilms are used to both protect the bacteria from the hosts’ immune system, while also serving as a nutritional reservoir in times of harsh environmental conditions.  It’s a very evolutionarily old and efficient way to ensure that many bacteria of a certain species survive, thrive and replicate.

Biofilms, also referred to as “bacterial slime”, are generally composed of extracellular DNA, proteins, polysaccharides, microbes, minerals and heavy metals.  Biofilms are said to be anchored at certain places by positively charged ions including: calcium, magnesium, mercury, lead, etc.

They are held together by sugary molecular strands, collectively termed “extracellular polymeric substances” or “EPS.” The cells produce EPS and are held together by these strands, allowing them to develop complex three-dimensional, resilient, attached communities. Biofilms can be as thin as a few cell layers or many inches thick, depending on environmental conditions.

Biofilms grow virtually everywhere, in almost any environment where there is a combination of moisture, nutrients, and a surface. Biofilms grow in rain forests and in deserts, as “desert varnish.” They have been found at the bottom of the ocean as early colonizers of new deep-sea vents and living on glaciers in the Antarctic. Bacteria that live in these very hot or very cold environments are called extremophiles. Yellowstone National Park in the United States is home to an amazing array of colorful communities of extremophiles. In fact, the entire globe—both above and below ground—is “seeded” with the bacteria that form biofilms, and bacterial communities flourish, disperse or become dormant depending on changing environmental conditions.

Ninety percent of the cells in a human body are not human; the body is heavily colonized by microbes that have found it a great place to live. We have communities of microbes living on all mucous surfaces and in our digestive tract, as well as on and in layers of our skin. For the most part we all get along; in fact, we depend on some of our gut microbes to help with digestion. Sometimes, however, the microbial load causes problems of infection. When the normal balance of microbial populations is upset or when our immune system is overwhelmed, we can have a real battle with microbial opportunists.

In the 1990s, as the biofilm concept was being introduced to the medical community, doctors began to make the connection between chronic, low-grade infections and the biofilm mode of growth. Internal cases of chronic infection have shown that many troublesome diseases have entrenched microbial populations at their core. The NIH estimates that 80% of all human infections have biofilm involvement.

The most common cause of children’s recurrent earache (Otitis Media) is an example of a typical biofilm-based infection.  Other diseases in which biofilms play a role include bacterial endocarditis (infection of the inner surface of the heart and its valves), cystic fibrosis (a chronic disorder resulting in increased susceptibility to serious lung infection), and Legionnaire’s disease (an acute respiratory infection resulting from the aspiration of clumps of Legionnella biofilms detached from air and water heating/cooling and distribution systems).  Chronic sinusitis patients undergoing surgery also presented with Biofilms most of the time.

Biofilms may also be responsible for a wide variety of nosocomial (hospital-acquired) infections. Sources of biofilm-related infections can include the surfaces of catheters, medical implants, wound dressings, or other types of medical devices, such as joint prostheses, heart valves, intrauterine devices and catheters.  More recently it has been noted that bacterial biofilms may impair cutaneous wound healing and reduce topical antibacterial efficiency in healing or treating infected skin wounds.

Research of recent years has revealed that bacterial communities exhibit properties, behaviors and survival strategies that far exceed their capabilities as individual bacteria. For instance, microbial biofilms are naturally tolerant of antibiotic doses up to 1,000 times greater than doses that kill planktonic bacteria.  Sub-therapeutic levels of β-lactam antibiotics induce biofilm formation in Staphylococcus aureus. This sub-therapeutic level of antibiotic may result from the use of antibiotics as growth promoters in agriculture, or during the normal course of antibiotic therapy. The most prevalent fungal biofilm-forming pathogen is Candida albicans, which can cause both superficial and systemic infections.