Bacteria Biofilm

Dr. Yousef Elshrek

• As humans, our environment consistently exposes us to a variety of dangers. Tornadoes, lightning, flooding and hurricanes can all hamper our survival.

• Not to mention the fact that most of us can encounter swerving cars or ill-intentioned people at any given moment.

• Thousands of years ago, humans realized that they could better survive a dangerous world if they formed into communities, particularly communities consisting of people with different talents.

• They realized that a community is far more likely to survive through division of labor– one person makes food, another gathers resources, still another protects the community against invaders.

• Working together in this manner requires communication and cooperation.

• Inhabitants of a community live in close proximity and create various forms of shelter in order to protect themselves from external threats.

• We build houses that protect our families and larger buildings that protect the entire community.

• Grouping together inside places of shelter is a logical way to enhance survival.

• With the above in mind, it should come as no surprise that the pathogens we harbor are seldom found as single entities.

• Although the pathogens that cause acute infection are generally free-floating bacteria – also referred to as planktonic bacteria – those chronic bacterial forms that stick around for decades long ago evolved ways to join together into communities.

• Why? Because by doing so, they are better able to combat the cells of our immune system bent upon destroying them.

• It turns out that a vast number of the pathogens we harbor are grouped into communities called biofilms “a structured community of bacterial cells enclosed in a self-produced polymeric matrix and adherent to an inert or living surface.”

• That means bacteria can join together on essentially any surface and start to form a protective matrix around their group.

• The matrix is made of polymers – substances composed of molecules with repeating structural units that are connected by chemical bonds.

• Biofilms form when bacteria adhere to surfaces in aqueous or dry ( e.g. in milk powder) environments and begin to excrete a slimy, glue-like substance that can anchor them to all kinds of material – such as metals, plastics, soil particles, medical implant materials and, most significantly, low moiture food, human or animal tissue.

• The first bacterial colonists to adhere to a surface initially do so by inducing weak, reversible bonds called van der Waals forces.

• If the colonists are not immediately separated from the surface, they can anchor themselves more permanently using cell adhesion molecules, proteins on their surfaces that bind other cells in a process called cell adhesion.

• These bacterial pioneers facilitate the arrival of other pathogens by providing more diverse adhesion sites.

• They also begin to build the matrix that holds the biofilm together.

• If there are species that are unable to attach to a surface on their own, they are often able to anchor themselves to the matrix or directly to earlier colonists.

• During colonization, things start to get interesting.

• Multiple studies have shown that during the time a biofilm is being created, the pathogens inside it can communicate with each other thanks to a phenomenon called quorum sensing (fig. 1).

• Although the mechanisms behind quorum sensing are not fully understood, the phenomenon allows a single-celled bacterium to perceive how many other bacteria are in close proximity.

• If a bacterium can sense that it is surrounded by a dense population of other pathogens, it is more inclined to join them and contribute to the formation of a biofilm.

• Bacteria that engage in quorum sensing communicate their presence by emitting chemical messages that their fellow infectious agents are able to recognize.

• When the messages grow strong enough, the bacteria respond en masse, behaving as a group.

• Quorum sensing can occur within a single bacterial species as well as between diverse species, and can regulate a host of different processes, essentially serving as a simple communication network.

• A variety of different molecules can be used as signals.

• Biofilms cause sanitary and industrial nuisances.

• Besides the positive ecological roles assumed by sessile microbial communities, biofilms that form in industrial and medical settings, in particular on indwelling medical devices, are difficult to eradicate and are therefore associated with both health and economic issues.

• During the last decade, their negative impact on human activities has stimulated research aimed at providing clues to fight detrimental biofilms

• A study just published in the International Journal of

Food Microbiology examined the survival rates of free-

floating cells of salmonella enterica Tennessee versus

those in biofilm form when stored in dry milk powder

for up to 30 days.

• In such a dry environment, pathogens cease to

reproduce, but adhere to surfaces and produce a biofilm

that protects them from a harsh environment when

placed in such a dry environment. Experts disagree over

whether pathogens prompted to produce biofilms in this

way are more or less likely to survive passage into the

human intestine and thus more likely to cause illness.

• "Biofilms are becoming an increasing problem within the food industry due to their ability to adhere to surfaces and withstand current sanitation practices," the paper states.

• Low moisture foods • At various points during the study, the

Salmonella was tested in a simulated gastrointestinal system. It survived this long-term storage in large numbers but the biofilm Salmonella proved more resilient than the free-floating cells.

• The researchers from US institute Virginia Tech also

said the bacteria's stress response to the dry

conditions made it more likely to cause disease. And

they added that biofilms allowed the Salmonella to

survive the harsh, acidic environment of the gut,

increasing its chances of reaching the intestines.

• Outbreaks of Salmonella associated with dried foods

such as nuts, cereals, spices, spices, powdered milk

and pet foods have been associated with more than

900 illnesses in the past five years, the scientists

claimed. These foods were previously thought to be

safe, because their dry nature would protect them

from microbial growth.