Plaque as a Biofilm

Previously, bacteria have been studied as they grew in colonies on culture plates in the laboratory. More sophisticated microscopy, such as confocal scanning laser, has permitted examination of the biofilms in their natural states.⁵

Microorganisms in biofilm behave differently than bacteria in a culture medium (see Table 1).

Table 1. Basic Biofilm Properties²¹

Cooperating community of various types of microorganisms
Microorganisms are arranged in microcolonies
Microcolonies are surrounded by protective matrix
Within the microcolonies are differing environments
Microorganisms have primitive communication system
Microorganisms in biofilm are resistant to antibiotics, antimicrobials, and host response

Seen through a microscope, bacteria in a biofilm are not distributed evenly. They are grouped in microcolonies surrounded by an enveloping intermicrobial matrix (Figure 8).

The matrix is penetrated by fluid channels that conduct the flow of nutrients, waste products, enzymes, metabolites, and oxygen. These microcolonies have micro environments with differing pH's, nutrient availability, and oxygen concentrations (Figure 9). The bacteria in a biofilm communicate with each other by sending out chemical signals (Figure 10). These chemical signals trigger the bacteria to produce potentially harmful proteins and enzymes.⁵

Our previous attempts to predict and control periodontal diseases have been based on the performance of bacteria cultured under laboratory conditions.^1,5 Increased understanding of biofilms have demonstrated there are great differences between bacterial behavior in laboratory culture and in their natural ecosystems. For example, bacteria in biofilm produce compounds in biofilm that they do not produce when in culture. Also, the matrix surrounding the microcolonies serves as a protective barrier. This helps explain why systemic and locally delivered antimicrobials have not always proven successful, even when they were targeted at specific microorganisms. It also helps explain why mechanical plaque control and personal oral hygiene have continued to be an integral part of periodontal therapy.¹⁸ Biofilms can be removed by mechanical means. However, they immediately begin to reform, so the search continues for ways to combat biofilms.