Trends in Microbiology
Survival strategies of infectious biofilms
Introduction
Since the discovery of penicillin in 1938, antibiotics have proven tremendously successful in controlling acute bacterial infections. Microbiologists have learned to predict antibiotic effects in vivo by evaluating the minimal inhibitory concentration (MIC) and the minimal bactericidal concentration (MBC) in vitro. MIC and MBC assess the effect of antibiotics against planktonic organisms in the exponential phase of growth and therefore correctly predict antibiotic efficacy against rapidly dividing bacteria in acute infections, such as septicemia. In this review we will concern ourselves with the growing number of chronic and device-related infections in which antibiograms of the causative organism show sensitivity to standard antibiotics in readily attainable concentrations, but the infection fails to be cleared. Microscopic evaluations of these refractory infections have revealed bacteria growing as surface-adherent biofilms. The key characteristic of these slime-embedded bacterial communities – and the topic of this review - is their tolerance to antimicrobials and host defenses. Biofilm tolerance is of major clinical importance because more than 60% of the bacterial infections currently treated by physicians in the developed world are considered to involve biofilm formation (Table 1) [1]. Successful treatment in these cases depends on long-term, high-dose antibiotic therapies and the removal of any foreign-body material.
Section snippets
Bacterial sanctuaries
Biofilms are inherently protected from host defenses and antibiotics. Secreted antibodies fail to penetrate biofilms because of matrix binding [2], and secreted catalase protects aggregated bacteria by preventing full penetration of hydrogen peroxide into the biofilm [3]. Host-specific differences in the balance between T-helper 1 (Th1) and Th2-weighted immune responses (Box 1) might determine both the healing rates of biofilm infections and the extent of collateral damage to host tissues due
Physiology determines antibiotic susceptibility
Biofilm formation occurs as a result of a sequence of events: microbial surface attachment, cell proliferation, matrix production and detachment [18]. This process is partially controlled by quorum sensing, an interbacterial communication mechanism that is dependent on population density and is associated with radical (more than 50%) changes in protein expression patterns [18]. Mature biofilms demonstrate a complex 3-dimensional structure with numerous microenvironments differing with respect
Learning from planktonic cultures
The physiology of bacteria in the depths of a biofilm shows striking similarities to stationary-phase planktonic cells. Both are affected by nutrient limitation and high cell densities and express similar degrees of antibiotic tolerance 22, 23. The impact of individual factors on antibiotic susceptibility can be illustrated with a set of experiments performed in planktonic culture (Box 2). The experiments showed that antibiotic tolerance is mediated by starvation, but also stressed the
Bacterial adaptations to stress and damage
In addition to the passive protection against antibiotics and host defenses provided by metabolic inactivity, bacteria actively adapt to stress. For example, biofilm organisms increase their capacity to withstand and neutralize monochloramine [29], stimulate catalase production [3], or induce the expression of chromosomal betalactamases [9] following prolonged treatment with the respective substances. Bacteria in biofilms and planktonic cultures can turn on stress-response genes and switch to
Genomics and proteomics
The observation of antimicrobial tolerance in biofilms that are too thin to represent a relevant diffusion barrier for metabolic substrates 46, 47 proposes that starvation-induced dormancy is not the only reason for antimicrobial tolerance. This observation led to the hypothesis of a genetically controlled biofilm-specific phenotype. This concept is of particular interest because the control of key biofilm genes would offer excellent options to overcome tolerance.
A multitude of strategies have
Concluding remarks
In the industrialized world, acute bacterial infections caused by rapidly proliferating planktonic cells (e.g. Salmonella typhi) have been gradually replaced by chronic infections owing to environmental organisms (e.g. Staphylococcus epidermidis) growing as biofilms. The failure of conventional culture techniques to predict antibiotic susceptibilities of biofilm communities explains part of our failure to eradicate biofilm-related infections. Furthermore, the biofilm mode-of-growth represents a
Acknowledgements
This work was supported by the Swiss National Science Foundation grant 81BE-69256 (C.F.) and the National Institutes of Health RO1 grant GM60052–02 (P.S.). From the Center for Biofilm Engineering, we thank S. Wilson and P. Perry for excellent technical assistance with the experiments described in Box 2 and P. Dirckx for graphic assistance.
References (65)
Persister cells and tolerance to antimicrobials
FEMS Microbiol. Lett.
(2004)Aging in bacteria
Curr. Opin. Microbiol.
(2002)Gene expression and protein levels of the stationary phase sigma factor, RpoS, in continuously-fed Pseudomonas aeruginosa biofilms
FEMS Microbiol. Lett.
(2001)Phenotypic switching of antibiotic resistance circumvents permanent costs in Staphylococcus aureus
Curr. Biol.
(2001)Bacterial biofilms: a common cause of persistent infections
Science
(1999)Measurement of local diffusion coefficients in biofilms by micro-injection and confocal microscopy
Biotechnol. Bioeng.
(1997)Effect of catalase on hydrogen peroxide penetration into Pseudomonas aeruginosa biofilms
Appl. Environ. Microbiol.
(2000)The immune response to chronic Pseudomonas aeruginosa lung infection in cystic fibrosis patients is predominantly of the Th2 type
APMIS
(2000)Production of mucoid microcolonies by Pseudomonas aeruginosa within infected lungs in cystic fibrosis
Infect. Immun.
(1980)Polysaccharide intercellular adhesin (PIA) protects Staphylococcus epidermidis against major components of the human innate immune system
Cell. Microbiol.
(2004)
Intracellular bacterial biofilm-like pods in urinary tract infections
Science
Role of Nutrient Limitation and Stationary-Phase Existence in Klebsiella pneumoniae Biofilm Resistance to Ampicillin and Ciprofloxacin
Antimicrob. Agents Chemother.
Dynamics and spatial distribution of beta-lactamase expression in Pseudomonas aeruginosa biofilms
Antimicrob. Agents Chemother.
Contributions of antibiotic penetration, oxygen limitation, and low metabolic activity to tolerance of Pseudomonas aeruginosa biofilms to ciprofloxacin and tobramycin
Antimicrob. Agents Chemother.
Factors compromising antibiotic activity against biofilms of Staphylococcus epidermidis
Eur.J. Clin. Microbiol. Infect. Dis.
Effects of slime produced by clinical isolates of coagulase-negative staphylococci on activities of various antimicrobial agents
Antimicrob. Agents Chemother.
A genetic basis for Pseudomonas aeruginosa biofilm antibiotic resistance
Nature
Antibiotic efflux pumps in prokaryotic cells: occurrence, impact on resistance and strategies for the future of antimicrobial therapy
J. Antimicrob. Chemother.
Multidrug efflux pumps: expression patterns and contribution to antibiotic resistance in Pseudomonas aeruginosa biofilms
Antimicrob. Agents Chemother.
Exopolysaccharide production is required for development of Escherichia coli K-12 biofilm architecture
J. Bacteriol.
Functional role of mucoid exopolysaccharide (alginate) in antibiotic-induced and polymorphonuclear leukocyte-mediated killing of Pseudomonas aeruginosa
Infect. Immun.
Pseudomonas aeruginosa displays multiple phenotypes during development as a biofilm
J. Bacteriol.
Nonuniform spatial patterns of respiratory activity within biofilms during disinfection
Appl. Environ. Microbiol.
Clonal variation in maximum specific growth rate and susceptibility towards antimicrobials
J. Appl. Microbiol.
Biofilms and planktonic cells of Pseudomonas aeruginosa have similar resistance to killing by antimicrobials
J. Bacteriol.
Detachment characteristics and oxacillin resistance of Staphylococcus aureus biofilm emboli in an in-vitro infection model
J. Bacteriol.
Cell density-dependent starvation survival of Rhizobium leguminosarum bv. phaseoli: identification of the role of an N-acyl homoserine lactone in adaptation to stationary-phase survival
J. Bacteriol.
Global adaptations resulting from high population densities in Escherichia coli cultures
J. Bacteriol.
Comparison of respiratory activity and culturability during monochloramine disinfection of binary population biofilms
Appl. Environ. Microbiol.
Antibacterial action of ciprofloxacin
Antimicrob. Agents Chemother.
Role of rifampin for treatment of orthopedic implant-related staphylococcal infections: a randomized controlled trial. Foreign-Body Infection (FBI) Study Group
JAMA
Evidence of Bacterial Adaptation to Monochloramine in Pseudomonas aeruginosa Biofilms and Evaluation of Biocide Action Model
Biotechnol. Bioeng.
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