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Abstract

Biofilms--matrix-enclosed microbial accretions that adhere to biological or non-biological surfaces--represent a significant and incompletely understood mode of growth for bacteria. Biofilm formation appears early in the fossil record (approximately 3.25 billion years ago) and is common throughout a diverse range of organisms in both the Archaea and Bacteria lineages, including the 'living fossils' in the most deeply dividing branches of the phylogenetic tree. It is evident that biofilm formation is an ancient and integral component of the prokaryotic life cycle, and is a key factor for survival in diverse environments. Recent advances show that biofilms are structurally complex, dynamic systems with attributes of both primordial multicellular organisms and multifaceted ecosystems. Biofilm formation represents a protected mode of growth that allows cells to survive in hostile environments and also disperse to colonize new niches. The implications of these survival and propagative mechanisms in the context of both the natural environment and infectious diseases are discussed in this review.

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Quorum-sensing signals indicate that cystic fibrosis lungs are infected with bacterial biofilms.

P. K. Singh, A. L. Schaefer, M R Parsek … (2000)

The bacterium Pseudomonas aeruginosa permanently colonizes cystic fibrosis lungs despite aggressive antibiotic treatment. This suggests that P. aeruginosa might exist as biofilms--structured communities of bacteria encased in a self-produced polymeric matrix--in the cystic fibrosis lung. Consistent with this hypothesis, microscopy of cystic fibrosis sputum shows that P. aeruginosa are in biofilm-like structures. P. aeruginosa uses extracellular quorum-sensing signals (extracellular chemical signals that cue cell-density-dependent gene expression) to coordinate biofilm formation. Here we found that cystic fibrosis sputum produces the two principal P. aeruginosa quorum-sensing signals; however, the relative abundance of these signals was opposite to that of the standard P. aeruginosa strain PAO1 in laboratory broth culture. When P. aeruginosa sputum isolates were grown in broth, some showed quorum-sensing signal ratios like those of the laboratory strain. When we grew these isolates and PAO1 in a laboratory biofilm model, the signal ratios were like those in cystic fibrosis sputum. Our data support the hypothesis that P. aeruginosa are in a biofilm in cystic fibrosis sputum. Moreover, quorum-sensing signal profiling of specific P. aeruginosa strains may serve as a biomarker in screens to identify agents that interfere with biofilm development.

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Biofilms and planktonic cells of Pseudomonas aeruginosa have similar resistance to killing by antimicrobials.

A L Spoering, K Lewis (2001)

Biofilms are considered to be highly resistant to antimicrobial agents. Strictly speaking, this is not the case-biofilms do not grow in the presence of antimicrobials any better than do planktonic cells. Biofilms are indeed highly resistant to killing by bactericidal antimicrobials, compared to logarithmic-phase planktonic cells, and therefore exhibit tolerance. It is assumed that biofilms are also significantly more tolerant than stationary-phase planktonic cells. A detailed comparative examination of tolerance of biofilms versus stationary- and logarithmic-phase planktonic cells with four different antimicrobial agents was performed in this study. Carbenicillin appeared to be completely ineffective against both stationary-phase cells and biofilms. Killing by this beta-lactam antibiotic depends on rapid growth, and this result confirms the notion of slow-growing biofilms resembling the stationary state. Ofloxacin is a fluoroquinolone antibiotic that kills nongrowing cells, and biofilms and stationary-phase cells were comparably tolerant to this antibiotic. The majority of cells in both populations were eradicated at low levels of ofloxacin, leaving a fraction of essentially invulnerable persisters. The bulk of the population in both biofilm and stationary-phase cultures was tolerant to tobramycin. At very high tobramycin concentrations, a fraction of persister cells became apparent in stationary-phase culture. Stationary-phase cells were more tolerant to the biocide peracetic acid than were biofilms. In general, stationary-phase cells were somewhat more tolerant than biofilms in all of the cases examined. We concluded that, at least for Pseudomonas aeruginosa, one of the model organisms for biofilm studies, the notion that biofilms have greater resistance than do planktonic cells is unwarranted. We further suggest that tolerance to antibiotics in stationary-phase or biofilm cultures is largely dependent on the presence of persister cells.

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Pseudomonas biofilm formation and antibiotic resistance are linked to phenotypic variation.

Eliana Drenkard, Frederick M Ausubel (2002)

Colonization of the lungs of cystic fibrosis (CF) patients by the opportunistic bacterial pathogen Pseudomonas aeruginosa is the principal cause of mortality in CF populations. Pseudomonas aeruginosa infections generally persist despite the use of long-term antibiotic therapy. This has been explained by postulating that P. aeruginosa forms an antibiotic-resistant biofilm consisting of bacterial communities embedded in an exopolysaccharide matrix. Alternatively, it has been proposed that resistant P. aeruginosa variants may be selected in the CF respiratory tract by antimicrobial therapy itself. Here we report that both explanations are correct, and are interrelated. We found that antibiotic-resistant phenotypic variants of P. aeruginosa with enhanced ability to form biofilms arise at high frequency both in vitro and in the lungs of CF patients. We also identified a regulatory protein (PvrR) that controls the conversion between antibiotic-resistant and antibiotic-susceptible forms. Compounds that affect PvrR function could have an important role in the treatment of CF infections.

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Journal

PubMed ID:: 15040259

DOI:: 10.1038/nrmicro821

ScienceOpen disciplines: Chemistry

Keywords: Adaptation, Physiological,Bacterial Adhesion,Biofilms,Elasticity,Endocarditis, Bacterial,complications,Equipment Contamination,Pneumonia, Bacterial,etiology,Viscosity

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ScienceOpen disciplines: Chemistry

Keywords: Adaptation, Physiological, Bacterial Adhesion, Biofilms, Elasticity, Endocarditis, Bacterial, complications, Equipment Contamination, Pneumonia, Bacterial, etiology, Viscosity

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