Biofilm phenotypes

In recent years, it has become obvious that the biofilm mode of growth is associated with a specific expression of genes and altered growth rates. To take into consideration the adoption of characteristic biofilm phenotypes by planktonic bacteria, a modern definition of a biofilm has been given by Donlan and Costerton (2002), who described a biofilm as a microbially derived sessile community characterized by cells that are irreversibly attached to a substratum or interface or to each other, are embedded in a matrix of EPS that they have produced, and exhibit an altered phenotype with respect to growth rate and gene transcription . 

Patterson, J.L., Girerd, P.H., Karjane, N.W., and Jefferson, K.K. (2007) Effect of biofilm phenotype on resistance of Gardnerella vaginalis to hydrogen peroxide and lactic acid. Am J Obstet Gynecol 197, 170 el71-177. 

Drug resistance in the defined sense, however, is not always the reason for treatment failures. The formation of biofilms may be as well regarded as a resistance mechanism. Cells within such a film withstand the antibiotic treatment. Some antibiotics (e.g. the aminoglycoside tobramycin) penetrate only slowly into the film. A further explanation is the existence of cells living in a non-growing, protected phenotypic state. 

Bacterial resistance to biocides (Table 13.2) is usually considered as being of two types (a) intrinsic (innate, natural), a natural property of an organism, or (b) acquired, either by chromosomal mutation or by the acquisition of plasmids or transposons. Intrinsic resistance to biocides is usually demonstrated by Gram-negative bacteria, mycobacteria and bacterial spores whereas acquired resistance can result by mutation or, more frequently, by the acquisition of genetic elements, e.g. plasmid- (or transposon-) mediated resistance to mercury compounds. Intrinsic resistance may also be exemplified by physiological (phenotypic) adaptation, a classical example of which is biofilm production. 

Biofilm production Phenotypic adaptation Plasmid transfer may occur within biofilms... 

In order to understand current approaches for prevention and control of biofilms, we must first consider the reasons for the failure of conventional antimicrobial protocols. There are thought to be three main reasons as to why biofilm bacteria out-survive their planktonic counterparts during antimicrobial treatments (reviewed by McBain et a/.16).These are i) poor penetration of antimicrobial compounds due to the presence and turn-over of exopolymer slime (glycocalyx) ii) the imposition of extreme nutrient limitation within the depths of the biofilm community and the co-incident expression of metabolically-dormant, recalcitrant phenotypes and (iii) the expression of attachment-specific phenotypes that are radically different and intrinsically less susceptible than unattached ones. 

Although reaction-diffusion limitation and the presence of nutritionally restricted phenotypes are obviously important determinants of biofilm drug resistance, neither, either separately or in combination, provides a complete explanation of the phenomena. Cells on the periphery of the biofilm, subject to nutrient fluxes similar to planktonic organisms would succumb to antibacterial concentrations that are effective against the planktonic cells. Cell-death at the periphery would lead to increased nutrient availability for deeper-lying cells. These would, in turn, grow faster and adopt a more susceptible... 

A biofilm is a community of microorganisms that settles on a surface and is covered by an exopol)mier matrix. Cells in biofilms are slow-growing, and exhibif clear phenotypic differences from free-living planktonic cells. Biofilm sfmcfure is bofh complex and dynamic, and... 

A A/ca/l-mu(ant of S. epidermidis, synthesizing only fully /V-acetylated polymer, and hence displaying a biofilm-negative phenotype, had decreased resistance against phagocytosis, increased susceptibility to antimicrobial peptides LL-37 and human (3-defensin 3 as well as attenuated virulence in a mouse catheter infection model [117]. 

Existence of a triofilm phenotype in the sense that biofilm-assodated microbes differ from their planktonic counterparts genetic-wise. However, reportedly, this mechanism has been doubted by a number of researchers, mainly due to the small number of different genes. - ... 

It is now recognized that bacteria regulate high-density phenotypes, such as biofilm formation, and phenotypes that are important for a number of pathogenic... 

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