Compendium January/February 2009 : Page 25

existed, these cell-to-cell signals reached a sufficient concen- tration for activation of genes involved in biofilm differen- tiation. Yung-Hua et al10 showed that the induction of genetic competence was mediated by quorum sensing and that transformation frequencies were 10 to 600 times higher in biofilms than in planktonic cells. Biofilms are difficult to deal with through conventional recovery methods (swab, etc), and growth mediums are not sufficient to grow biofilms.11 According to these same authors, a 90% error occurred in bacterial determination when compared with fluorescent in situ hybridization screening. Not only are biofilms hard to culture, but it also is difficult to ascertain the individual bacteria as 50% to 90% of biofilms are comprised of extracellular polymeric substance (EPS).12 Most EPS structure is composed of polysaccharides, which provide both hydrophilic and hy- drophobic properties because of the structure of their hydro- gen bonding.13 The EPS formation varies spatially and structurally by different organisms and increases with the age of the biofilm.14 The hydrated nature of the EPS con- tributes to the antimicrobial resistance by impeding the mass transport of antibiotics through the biofilm, most prob- ably by direct bonding properties.15 Colonies containing motile cells can alter their structure through intermixing Duane Keller, DMD J. William Costerton, PhD and migration of cells from one microcolony to another.16 Nonmicrobial EPS surface components (erythrocytes, fib- rin, platelets) also modify the biofilm and may protect the biofilm from polymorphonuclear leukocytes (PMN) and host defenses.17 Exopolysaccharide intercellular adhesions (PIAs) reside in fibrous strands on the bacterial cell surface of some bacteria, and these PIAs inhibit phagocytosis and death by human PMN.18 Organisms within biofilms can share and readily acquire resistance through transfer of re- sistance plasmids or genetic materials19 (Figure 2). IMMUNE SYSTEM RESPONSE The host immune system is able to protect against most planktonic bacteria invasions through one of three mecha- nisms: (1) phagocytosis of invading microorganisms by Figure 1 The biofilm life cycle in three steps: attachment, growth of colonies, and detachment in clumps. (Adapted from Peters LB. Desinfectie van het wortelkanallstelsel bij de endodontishche behandeling. Ned Tijdschr Tandheelkd. 2005;112:461- 512(p468). Used with permission from Montana State University Center for Biofilm Engineering.) Compendium 25

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