Biofilms (13)

What happens in the 5th stage of oral biofilm formation?

"Dispersal" Certain bacterial species produce enzymes that can degrade the polysaccharides (linking the bacteria together) formed by bacteria in the biofilm. This allows the bacteria to escape and go to another place where more nutrients are available. Also, if biofilm gets too thick, then the nutrients cannot get to the lower levels, so they disperse to go somewhere that nutrients are more plentiful.

What are the 4 reasons bacteria in a biofilm are more tolerant of antibiotics?

1) Nutrient depletion creates zones of altered activity (caused by a thick biofilm) - slow growth of bacteria (cell wall active antibiotics depend upon rapid growth) 2) Inner layers of biofilm cells have more time to initiate stress response --- expression of genes that protect the bacteria (stress response) 3) Outer layers of biofilm cells absorb damage -- Adsorption or inactivatoin of antibiotics by the polymeric matrix 4) "Persister" cells may be present in higher numbers

What are the 5 stages of biofilm formation?

1) Pellicle formation 2) Initial adherence 3) Aggregation 4) Maturation 5) Dispersal

What are 4 therapeutic approaches to combat oral biofilms?

1) Physical removal 2) Direct administraton of disinfectants or antimicrobial agents 3) Probiotics 4) Vaccination

What are 2 types of adhesins?

1) Pili or fimbriae - proteins produced on bacterial surface that allow them to adhere to proteins on acquired pellicle-- these are polymeric proteins 2) Afimbrial adhesins - monomeric proteins that are produced on bacterial surface and allow the bacteria to adhere to the salivary glycoproteins

Complications are associated with biofilm formation. What are the 8 things that biofilms increase the resistance of bacteria to?

1) Shear stress 2) Immune defense 3) Antibiotics 4) Disinfectants 5) Dessication 6) Nutrient depletion 7) Changes in pH 8) Oxidative stress

What is a biofilm?

A biofilm is a community of microorganisms, associated with a surface, and encased in an extracellular polymetric matrix. Bacteria are interacting with one another and adhering to one another in biofilms, and attaching to a surface

What type of adhesins are the most important for the initial binding of the bacteria to the proteins in the acquired pellicle?

Afimbrial adhesins

What does the aggregation stage of biofilm production require?

Aggregation stage of biofilm production requires production of polysaccharides. Streptococci have glucosyltransferases that convert sugars into polymers (polysaccharides/glucans). These polysaccharide polymers act as intracellular adhesins and interlink 2 bacterial cells to one another.

What is an adhesin?

An adhesin is a macromolecule that binds to specific ligands or receptors on host cells and defines the tropism of the microbe for various cells or tissues

How does direct administration of disinfectants or antimicrobial agents act as a therapeutic approach to combat biofilms?

At high enough levels of concentration of antibiotic then you can kill the bacteria in the biofilm. The problem with this is that if you give someone an antibiotic systemically then you can only give it at a certain concentration before it starts to cause side effects. If antibiotics are delivered locally then they can be very beneficial because you can deliver them at a high enough concentration to combat the oral biofilm.

How does the idea that the outer layers of biofilm cells absorb damage work?

Bacteria on the outer layers "suck" up the antibiotic so that it doesn't reach the inner layer. This prevents the antibiotic from killing the bacteria of the inner layer.

What happens during stage 3 of the biofilm formation?

Bacteria start to aggregate by interacting with one another (bacterial cells begin to divide and more bacteria are adhering to the tooth -> leads to a multilayer of bacterial organisms

How does biofilm formation help with immune evasion?

Bacterial biofilms are resistant to the immune defense. Neutrophils can penetrate the biofilm, but they can't kill any of the bacteria in the biofilm. This is because the biofilm bacteria have a slippery coat made of polysaccharides and the neutrophils just slip off of the coat.

Why are biofilms clinically important?

Because they cause an increase in resistance to just about everything. They also serve as a nidus for relapsing infection

How do biofilms help with antibiotic tolerance?

Biofilms increase antibiotic tolerance of the bacteria within the biofilm.

How is breaking up the biofilm phenotype beneficial?

Breaking up the biofilm phenotype and returning bacteria to their planktonic phenotype makes those bacteria more sensitive to antibiotics.

How is physical removal of the biofilm a therapeutic approach to combat oral biofilms?

Brushing your teeth breaks up the biofilm and returns it to its planktonic phenotype. In the planktonic phenotype, the bacteria become more susceptible to antibiotics and fluoride.

How is antibiotic tolerance determined?

By the phenotype state

Why is fusobacterium nucleatum important in the oral biofilm?

Fusobacterium nucleatum acts as a bridge to connect the middle and late colonizers. Fusobacterium produce adhesins that allow them to adhere to ALL oral bacteria which can lead to a huge species diversity of bacteria that adhere to the biofilm. This includes really bad bacteria which can start causing problems (inflammation and decay) that result in a lot of damage.

How does the idea that the inner layers of biofilm cells have more time to initiate stress response work?

It takes time for the antibiotic to get through the biofilm, so the inner layer of the biofilm gets hit with the low concentration of antibiotic first and allows those bacteria enough time to express genes code for protection from antibiotics.

Why is metabolism important in the oral biofilm?

Metabolic pathways are incorporated into the biofilm. Early colonizers take simple sugars and turn them into lactic acid. Middle colonizers cannot use simple sugars but can use the lactic acid from early colonizers.

Why is periodontal disease considered a relapsing disease?

Periodontal disease is a bacterial infection. Periodontal infection should respond to the antibiotic treatment, but it relapses because of the biofilms. Antibiotic treatment fails long term because the bacteria in biofilms are more tolerant to antibiotics

Why can't you sterilze a culture with an antibiotic?

Persister cells are present in any population (biofilm, or planktonic). They enter a quiescent state (aren't dividing or producing proteins) so they can tolerate high concentrations of different classes of antibiotics (ex: cell wall active, protein synthesis inhibitors, DNA synthesis inhibitors). Even if you kill 99% of bacteria in the biofilm, the persister cells that represent the other 1% will eventually become active again and reproduce to re-establish the biofilm. Therefore, antibiotics cannot sterilize a culture of bacteria.

What happens during stage 1 of biofilm formation?

Salivary glycoproteins begin to adhere to the tooth surface within a few minutes after brushing. This forms an acquired pellicle.

At what point would you need to use scaling and root planing to physically remove the biofilm?

Scaling and root planing are 2 very aggressive methods for removing the biofilm and smoothing out the tooth surface if a biofilm has gotten established on the teeth. (People don't brush often, etc.)

What happens during stage 2 of the biofilm formation?

The indigenious bacteria (streptococci and actinomyces) begin to recognize the glycosylated proteins in the acquired pellicle and adhere to them. These bacteria produce certain adhesins that allow them to bind to the proteins in the saliva.

What are periochips and arrestin examples of?

These are examples of how direct administration of disinfectants can act as a therapeutic approach to combat biofilms. Periochip is embedded between the tooth and the gum line. It slowly releases antibiotic directly at higher concentrations and over longer periods of time. Arrestin are small beads that are placed into the gum line of infected tooth. These take 2 weeks for antibiotics to be fully released.

What is the idea behind probiotics (ex: Streptococcus salivarius or a safe strain of S. mutans)?

These aren't in practice yet. Basically the idea is that we can take a safe/good strain of S. mutans and introduce it into the oral cavity. The good strain would kill of the bad strain of S. mutans

How does nutrient depletion that creates zones of altered activity help with antibiotic tolerance?

These bacteria are growing very slowly, so the cell wall activated antibiotics, that rely on bacteria to rapidly divide changing their cell walls while doing so, do NOT work on the biofilm. Bacteria in a biofilm are not changing their cell walls because they are slowly growing.

Why are dental biofilms extremely complex?

They have a complex community: multi species and multi-kingdom. (can be exposed to bacterial species along with fungi) They also develop in stages

What happens during stage 4 of biofilm formation?

This is considered maturation. Species diversity increases. A lot of middle and late colonizing bacteria don't produce adhesins that allow them to stick to the acquired pellicle. Instead, they produce adhesins that allow them to adhere to other bacteria. (Middle colonizers adhere to early colonizers and later colonizers adhere to fusobacterium nucleatum)

What is the idea behind vaccinations (ex: P. gingivalis vaccine)?

Vaccines against oral pathogen that causes problems like periodontal disease would be introduced and potentially combat those pathogens.