Biofilms: survival mechanisms of clinically relevant microorganisms

The pgaABCD locus of Escherichia coli promotes the synthesis of a polysaccharide adhesin required for biofilm formation

Production of a polysaccharide matrix is a hallmark of bacterial biofilms, but the composition of matrix polysaccharides and their functions are not widely understood. Previous studies of the regulation of Escherichia coli biofilm formation suggested the involvement of an unknown adhesin. We now establish that the pgaABCD (formerly ycdSRQP) locus affects biofilm development by promoting abiotic surface binding and intercellular adhesion. All of the pga genes are required for optimal biofilm formation under a variety of growth conditions. A pga-dependent cell-bound polysaccharide was isolated and determined by nuclear magnetic resonance analyses to consist of unbranched beta-1,6-N-acetyl-D-glucosamine, a polymer previously unknown from the gram-negative bacteria but involved in adhesion by staphylococci. The pga genes are predicted to encode envelope proteins involved in synthesis, translocation, and possibly surface docking of this polysaccharide. As predicted, if poly-beta-1,6-GlcNAc (PGA) mediates cohesion, metaperiodate caused biofilm dispersal and the release of intact cells, whereas treatment with protease or other lytic enzymes had no effect. The pgaABCD operon exhibits features of a horizontally transferred locus and is present in a variety of eubacteria. Therefore, we propose that PGA serves as an adhesin that stabilizes biofilms of E. coli and other bacteria.

The pgaABCD locus of Escherichia coli promotes the synthesis of a polysaccharide adhesin required for biofilm formation

Production of a polysaccharide matrix is a hallmark of bacterial biofilms, but the composition of matrix polysaccharides and their functions are not widely understood. Previous studies of the regulation of Escherichia coli biofilm formation suggested the involvement of an unknown adhesin. We now establish that the pgaABCD (formerly ycdSRQP) locus affects biofilm development by promoting abiotic surface binding and intercellular adhesion. All of the pga genes are required for optimal biofilm formation under a variety of growth conditions. A pga-dependent cell-bound polysaccharide was isolated and determined by nuclear magnetic resonance analyses to consist of unbranched beta-1,6-N-acetyl-D-glucosamine, a polymer previously unknown from the gram-negative bacteria but involved in adhesion by staphylococci. The pga genes are predicted to encode envelope proteins involved in synthesis, translocation, and possibly surface docking of this polysaccharide. As predicted, if poly-beta-1,6-GlcNAc (PGA) mediates cohesion, metaperiodate caused biofilm dispersal and the release of intact cells, whereas treatment with protease or other lytic enzymes had no effect. The pgaABCD operon exhibits features of a horizontally transferred locus and is present in a variety of eubacteria. Therefore, we propose that PGA serves as an adhesin that stabilizes biofilms of E. coli and other bacteria.

Quorum sensing in Staphylococcus aureus biofilms

Several serious diseases are caused by biofilm-associated Staphylococcus aureus, infections in which the accessory gene regulator (agr) quorum-sensing system is thought to play an important role. We studied the contribution of agr to biofilm development, and we examined agr-dependent transcription in biofilms. Under some conditions, disruption of agr expression had no discernible influence on biofilm formation, while under others it either inhibited or enhanced biofilm formation. Under those conditions where agr expression enhanced biofilm formation, biofilms of an agr signaling mutant were particularly sensitive to rifampin but not to oxacillin. Time lapse confocal scanning laser microscopy showed that, similar to the expression of an agr-independent fluorescent reporter, biofilm expression of an agr-dependent reporter was in patches within cell clusters and oscillated with time. In some cases, loss of fluorescence appeared to coincide with detachment of cells from the biofilm. Our studies indicate that the role of agr expression in biofilm development and behavior depends on environmental conditions. We also suggest that detachment of cells expressing agr from biofilms may have important clinical implications.

Bacterial biofilms: from the natural environment to infectious diseases

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.

Virulence factors and in vitro adherence of Enterococcus strains to urinary catheters

The ability to adhere in vitro to urinary catheters and the presence of enterococcal virulence factors was determined in 30 Enterococcus urinary isolates (12 E. faecalis, 12 E. faecium, 3 E. casseliflavus, 3 E. gallinarum). Silicone, siliconized latex and polyvinyl chloride (PVC) were examined by sonication quantitative culture technique and scanning electron microscope. As compared to E. faecalis and E. faecium, E. casseliflavus and E. gallinarum displayed lower adhesion to all synthetic materials. All the tests performed showed higher adherence of all tested strains to siliconized latex and silicone than to PVC. Biofilmforming ability was observed in 5 E. faecalis but in none of the remaining strains. The gene coding enterococcal surface protein (Esp) was detected in 7 E. faecalis and 6 E. faecium strains. Gelatinase was found in 1 E. faecalis, 2 E. faecium and hemolysins were found in 6 E. faecalis and 1 E. faecium strains. All E. casseliflavus and E. gallinarum strainswere negative for these traits. Hydrophobic type of cell surface (measured by its affinity for n-hexadecane) was shown in a few isolates. Bacterial adherence was not significantly associated with the above pathogenic factors.

Enterococcus durans endocarditis in a patient with transposition of the great vessels

A case of native valve endocarditis caused by Enterococcus durans in a patient with transposition of the great vessels is reported. The patient was treated initially with gentamicin and ceftriaxone; after isolation of enterococci, ceftriaxone was switched to ampicillin. The only virulence factors established in the strain were haemolytic activity and biofilm formation.

Attachment to and biofilm formation on abiotic surfaces by Acinetobacter baumannii: involvement of a novel chaperone-usher pili assembly system

Acinetobacter baumannii causes severe infections in compromised patients, survives on abiotic surfaces in hospital environments and colonizes different medical devices. In this study the analysis of the processes involved in surface attachment and biofilm formation by the prototype strain 19606 was initiated. This strain attaches to and forms biofilm structures on plastic and glass surfaces, particularly at the liquid-air interface of cultures incubated stagnantly. The cell aggregates, which contain cell stacks separated by water channels, formed under different culture conditions and were significantly enhanced under iron limitation. Electron and fluorescence microscopy showed that pili and exopolysaccharides are part of the cell aggregates formed by this strain. Electron microscopy of two insertion derivatives deficient in attachment and biofilm formation revealed the disappearance of pili-like structures and DNA sequencing analysis showed that the transposon insertions interrupted genes with the highest similarity to hypothetical genes found in Pseudomonas aeruginosa, Pseudomonas putida and Vibrio parahaemolyticus. Although the products of these genes, which have been named csuC and csuE, have no known functions, they are located within a polycistronic operon that includes four other genes, two of which encode proteins related to chaperones and ushers involved in pili assembly in other bacteria. Introduction of a copy of the csuE parental gene restored the adherence phenotype and the presence of pili on the cell surface of the csuE mutant, but not that of the csuC derivative. These results demonstrate that the expression of a chaperone-usher secretion system, some of whose components appear to be acquired from unrelated sources, is required for pili formation and the concomitant attachment to plastic surfaces and the ensuing formation of biofilms by A. baumannii cells.

Modeling antibiotic tolerance in biofilms by accounting for nutrient limitation

A mathematical model of biofilm dynamics was used to investigate the protection from antibiotic killing that can be afforded to microorganisms in biofilms based on a mechanism of localized nutrient limitation and slow growth. The model assumed that the rate of killing by the antibiotic was directly proportional to the local growth rate. Growth rates in the biofilm were calculated by using the local concentration of a single growth-limiting substrate with Monod kinetics. The concentration profile of this metabolic substrate was calculated by solving a reaction-diffusion problem. The model predicted the following features: stratified patterns of growth with zones of no growth in the biofilm interior, slow killing of biofilm microorganisms that was further retarded as the initial biofilm thickness increased, nonuniform spatial patterns of killing inside the biofilm, biofilm killing rates that decrease in a nonlinear way as the concentration of the growth-limiting substrate feeding the biofilm is decreased, and heightened tolerance when external mass transfer resistance is manifested. This modeling study also provides motivation for further investigation of a hypothetical cell state in which damaged cells score as nonviable but continue to consume substrate. The existence of such a cell state can further retard biofilm killing, according to the simulations. The results support the important contributions of nutrient limitation and slow growth to the antibiotic tolerance of microorganisms in biofilms.

Characterization of two Pseudomonas putida lipopeptide biosurfactants, putisolvin I and II, which inhibit biofilm formation and break down existing biofilms

Pseudomonas putida strain PCL1445 was isolated from roots of plants, grown on a site polluted with polycyclic aromatic hydrocarbons. PCL1445 produces biosurfactant activity at the end of the exponential growth phase. High-performance liquid chromatography (HPLC) analysis of supernatant extracts of PCL1445 showed two peaks with surface-tension reducing activity, tentatively assigned as biosurfactants putisolvin I and putisolvin II and was followed by structural analyses. A transposon mutant of PCL1445, strain PCL1436, which lacks the two surface-active peaks appeared to be mutated in an open reading frame (ORF) with amino acid homology to various lipopeptide synthetases. Structural analyses of the two biosurfactants of PCL1445 revealed that both are novel cyclic lipodepsipeptides with a hexanoic lipid chain connected to the N-terminus of a 12-amino-acid peptide moiety, in which the C-terminal carboxylic acid group forms an ester with the hydroxyl side-chain of Ser9. The difference between the two structures is located in the second amino acid from the C-terminus, being valine for putisolvin I, and leucine/isoleucine for putisolvin II. We show that these novel compounds lower the surface tension and influence the biofilm development on polyvinyl chloride (PVC). Biofilm formation of the bio-synthetic mutant PCL1436 was strongly increased containing more cells, which formed aggregates earlier as compared with wild-type PCL1445 biofilms. Using purified putisolvin I and II it was shown that biofilm formation of different Pseudomonas strains was inhibited and most interestingly, that both putisolvins are also able to break down existing Pseudomonas biofilms.

Cross-sectional analysis of clinical and environmental isolates of Pseudomonas aeruginosa: biofilm formation, virulence, and genome diversity

Chronic lung infections with Pseudomonas aeruginosa biofilms are associated with refractory and fatal pneumonia in cystic fibrosis (CF). In this study, a group of genomically diverse P. aeruginosa isolates were compared with the reference strain PAO1 to assess the roles of motility, twitching, growth rate, and overproduction of a capsular polysaccharide (alginate) in biofilm formation. In an in vitro biofilm assay system, P. aeruginosa displayed strain-specific biofilm formation that was not solely dependent on these parameters. Compared with non-CF isolates, CF isolates expressed two opposing growth modes: reduced planktonic growth versus efficient biofilm formation. Planktonic cells of CF isolates showed elevated sensitivity to hydrogen peroxide, a reactive oxygen intermediate, and decreased lung colonization in an aerosol infection mouse model. Despite having identical genomic profiles, CF sequential isolates produced different amounts of biofilm. While P. aeruginosa isolates exhibited genomic diversity, the genome size of these isolates was estimated to be 0.4 to 19% (27 to 1,184 kb) larger than that of PAO1. To identify these extra genetic materials, random amplification of polymorphic DNA was coupled with PAO1-subtractive hybridization. Three loci were found within the genomes of two CF isolates encoding one novel homolog involved in retaining a Shigella virulence plasmid (mvpTA) and two divergent genes that function in removing negative supercoiling (topA) and biosynthesis of pyoverdine (PA2402). Together, P. aeruginosa biodiversity could provide one cause for the variation of morbidity and mortality in CF. P. aeruginosa may possess undefined biofilm adhesins that are important to the development of an antibiofilm therapeutic target.

The effect of systemic antibiotics on the microbiological diagnosis of experimental foreign body infections caused by S taphylococcus epidermidis

Qualitative broth culture and quantitative culture on agar were compared with quantitative polymerase chain reaction (PCR) for the diagnosis of foreign body infections (FBI) in a rat model with and without exposure to systemic antibiotics (teicoplanin and rifampin). The 3 methods had a similar and high yield without antibiotics. Antibiotics decreased the number of CFU/foreign body and increased the number of culture-negative foreign bodies and the variability of the results in quantitative culture. The yield of broth culture remained high under antibiotics although prolonged incubation (2-5 days) was required. The yield of the PCR was equivalent or even superior (for teicoplanin) to the yield of broth culture. Quantitative PCR had a higher yield and lower variability than quantitative culture and was not affected by antibiotics. The simultaneous isolation of RNA from all samples indicated viability of the bacteria. Quantitative PCR seems a promising method for the diagnosis of FBI.

Esp-independent biofilm formation by Enterococcus faecalis

Enterococcus faecalis is a gram-positive opportunistic pathogen known to form biofilms in vitro. In addition, this organism is often isolated from biofilms on the surfaces of various indwelling medical devices. However, the molecular mechanisms regulating biofilm formation in these clinical isolates are largely unknown. Recent work has suggested that a specific cell surface protein (Esp) of E. faecalis is critical for biofilm formation by this organism. However, in the same study, esp-deficient strains of E. faecalis were found to be capable of biofilm formation. To test the hypothesis that Esp is dispensable for biofilm formation by E. faecalis, we used microtiter plate assays and a chemostat-based biofilm fermentor assay to examine biofilm formation by genetically well-defined, non-Esp-expressing strains. Our results demonstrate that in vitro biofilm formation occurs, not only in the absence of esp, but also in the absence of the entire pathogenicity island that harbors the esp coding sequence. Using scanning electron microscopy to evaluate biofilms of E. faecalis OG1RF grown in the fermentor system, biofilm development was observed to progress through multiple stages, including attachment of individual cells to the substratum, microcolony formation, and maturation into complex multilayered structures apparently containing water channels. Microtiter plate biofilm analyses indicated that biofilm formation or maintenance was modulated by environmental conditions. Furthermore, our results demonstrate that expression of a secreted metalloprotease, GelE, enhances biofilm formation by E. faecalis. In summary, E. faecalis forms complex biofilms by a process that is sensitive to environmental conditions and does not require the Esp surface protein.

Planktonic or biofilm growth affects survival, hydrophobicity and protein expression patterns of a pathogenic Campylobacter jejuni strain

The effect of planktonic or biofilm modes of growth on survival, hydrophobicity and cellular protein expression patterns of a pathogenic Campylobacter jejuni strain were determined. This was achieved by growing the strain in brain heart infusion broth (with 1% yeast extract), or attached to glass beads in the same medium, at 37 degrees C for 48 h under microaerophilic conditions. Cells from the broth or the bead surfaces were stored at different temperatures (4, 10, 25 and 37 degrees C) for 28 days in phosphate buffered saline (PBS) and monitored at appropriate time intervals for culturable numbers and hydrophobicity by standard methods. In addition, cells were inoculated onto the surface of two processed meat products (a bologna and a summer sausage) vacuum packaged and stored at 4 degrees C for 28 days. Numbers of culturable cells were monitored at appropriate time intervals by standard methods. Cells from the broth or the bead surfaces were also examined for protein expression using two-dimensional protein electrophoresis. Results indicated that numbers of culturable cells in phosphate buffered saline decreased from approximately 6 log colony forming units (cfu) g(-1) to undetectable levels within 14-day storage in a temperature dependent manner. Hydrophobicity of broth grown cells decreased from 15% to 0% adherence to xylene over the same time in a temperature independent manner. Cells grown in a biofilm mode initially displayed a <0.3% adherence to xylene which was maintained during storage. Furthermore, cells grown in the biofilm mode decreased in number more rapidly on storage in buffer than their counterparts grown in broth. Numbers of culturable cells on meat decreased from approximately 5 log cfu g(-1) to undetectable levels within 14-day storage in a product dependent manner, with the most rapid decrease observed for the more acidic summer sausage. Cells grown in a biofilm mode decreased in number more rapidly on storage than broth grown cells. The protein expression patterns differed between planktonic and biofilm cells with seven unique and 12 up-regulated protein spots expressed in a growth mode specific manner. A number of the differentially expressed spots were tentatively identified, by comparison to existing literature, as surface- and stress-associated proteins. Despite the elicitation of some putative stress proteins, this study importantly indicates that biofilm cells of C. jejuni are less resistant to stress than their planktonic counterparts and may lack a sophisticated adaptive stress-resistance response. These findings have implication in determining the risks of infection associated with C. jejuni contamination on food.

Quorum sensing in Staphylococcus infections

Quorum sensing via the accessory gene regulator (agr) system has been assigned a central role in the pathogenesis of staphylococci, particularly Staphylococcus aureus. While the control of virulence gene expression in vitro by agr has been relatively straightforward to describe, regulation of both the quorum response itself and virulence genes in vivo is considerably more complex. The quorum response is highly dependent upon the environment in which the organism is grown and is strongly influenced by additional regulators that respond to signals other than cell density. There is increasing evidence that the agr phenotype may influence the behavior and pathogenesis of biofilm-associated S. aureus and S. epidermidis and may contribute to the chronic nature of some biofilm-associated infections.

Quorum sensing and biofilm formation in Streptococcal infections

Members of the bacterial genus Streptococcus are responsible for causing a wide variety of infections in humans. Many Streptococci use quorum-sensing systems to regulate several physiological properties, including the ability to incorporate foreign DNA, tolerate acid, form biofilms, and become virulent. These quorum-sensing systems are primarily made of small soluble signal peptides that are detected by neighboring cells via a histidine kinase/response regulator pair.

Quorum sensing in Staphylococcus infections

Quorum sensing via the accessory gene regulator (agr) system has been assigned a central role in the pathogenesis of staphylococci, particularly Staphylococcus aureus. While the control of virulence gene expression in vitro by agr has been relatively straightforward to describe, regulation of both the quorum response itself and virulence genes in vivo is considerably more complex. The quorum response is highly dependent upon the environment in which the organism is grown and is strongly influenced by additional regulators that respond to signals other than cell density. There is increasing evidence that the agr phenotype may influence the behavior and pathogenesis of biofilm-associated S. aureus and S. epidermidis and may contribute to the chronic nature of some biofilm-associated infections.

Suppression of bacterial biofilm formation by iron limitation

The concentration of iron that permits bacterial differentiation generally differs from that needed for vegetative cell growth. An undesirable manifestation of differentiation is biofilm formation. The process in some, but not all, bacterial systems requires a higher level of iron than is needed for growth and it is suppressed by specific iron chelators. Human transferrin and lactoferrin, as well as at least six low molecular mass iron chelators, are now available for possible screening and clinical development as inhibitors of bacterial biofilm formation.

Biocide use and antibiotic resistance: the relevance of laboratory findings to clinical and environmental situations

Antibiotics are used as chemotherapeutic drugs, and biocides are used as antiseptics, disinfectants, and preservatives. Several factors affect biocidal activity, notably concentration, period of contact, pH, temperature, the presence of interfering material, and the types, numbers, location, and condition of microorganisms. Bacterial cells as part of natural or artificial (laboratory) biofilm communities are much less susceptible than planktonic cells to antibiotics and biocides. Assessment of biocidal activity by bactericidal testing is more relevant than by determination of minimum inhibitory concentrations. Biocides and antibiotics may show some similarities in their mechanisms of action and common mechanisms of bacterial insusceptibility may apply, but there are also major differences. In the laboratory, bacteria can become less susceptible to some biocides. Decreased resistance may be stable or unstable and may be accompanied by a low-level increase in antibiotic resistance. Laboratory studies are useful for examining stress responses and basic mechanisms of action and of bacterial insusceptibility to antibacterial agents. Translation of such findings to the clinical and environmental situations to provide evidence of a possible relation between biocide use and clinical antibiotic resistance is difficult and should be viewed with caution.

Variation in biofilm formation among strains of Listeria monocytogenes

Contamination of food by Listeria monocytogenes is thought to occur most frequently in food-processing environments where cells persist due to their ability to attach to stainless steel and other surfaces. Once attached these cells may produce multicellular biofilms that are resistant to disinfection and from which cells can become detached and contaminate food products. Because there is a correlation between virulence and serotype (and thus phylogenetic division) of L. monocytogenes, it is important to determine if there is a link between biofilm formation and disease incidence for L. monocytogenes. Eighty L. monocytogenes isolates were screened for biofilm formation to determine if there is a robust relationship between biofilm formation, phylogenic division, and persistence in the environment. Statistically significant differences were detected between phylogenetic divisions. Increased biofilm formation was observed in Division II strains (serotypes 1/2a and 1/2c), which are not normally associated with food-borne outbreaks. Differences in biofilm formation were also detected between persistent and nonpersistent strains isolated from bulk milk samples, with persistent strains showing increased biofilm formation relative to nonpersistent strains. There were no significant differences detected among serotypes. Exopolysaccharide production correlated with cell adherence for high-biofilm-producing strains. Scanning electron microscopy showed that a high-biofilm-forming strain produced a dense, three-dimensional structure, whereas a low-biofilm-forming strain produced a thin, patchy biofilm. These data are consistent with data on persistent strains forming biofilms but do not support a consistent relationship between enhanced biofilm formation and disease incidence.

Influence of topology on bacterial social interaction

The environmental topology of complex structures is used by Escherichia coli to create traveling waves of high cell density, a prelude to quorum sensing. When cells are grown to a moderate density within a confining microenvironment, these traveling waves of cell density allow the cells to find and collapse into confining topologies, which are unstable to population fluctuations above a critical threshold. This was first observed in mazes designed to mimic complex environments, then more clearly in a simpler geometry consisting of a large open area surrounding a square (250 x 250 microm) with a narrow opening of 10-30 microm. Our results thus show that under nutrient-deprived conditions bacteria search out each other in a collective manner and that the bacteria can dynamically confine themselves to highly enclosed spaces.

Bacterial biofilms: an emerging link to disease pathogenesis

The role of biofilms in the pathogenesis of some chronic human infections is now widely accepted. However, the criteria used to determine whether a given infection is caused by biofilms remain unclear. In this chapter we discuss three infections that are caused by biofilms--infectious kidney stones, bacterial endocarditis, and cystic fibrosis lung infections--and focus on the role of the biofilm in disease pathogenesis. Biofilms are also important as environmental reservoirs for pathogens, and the biofilm growth mode may provide organisms with survival advantages in natural environments and increase their virulence. The consequences of pathogens living in environmental biofilms and an analysis of some specific environmental biofilm systems are presented.

Antibiotic-loaded cement in revision joint replacement

The infected joint replacement remains a difficult clinical challenge. Antibiotic-loaded cement provides one therapeutic solution that combines mechanical stability and antibiotic delivery.

Molecular and antibiofilm approaches to prosthetic joint infection

The majority of patients with prosthetic joint replacement (arthroplasty) experience dramatic relief of pain and restoration of satisfactory joint function. In the United States, more than.5 million people have a primary arthroplasty each year. Less than 10% of prosthesis recipients have complications develop during their lifetime, commonly as a result of aseptic biomechanical failure, followed by prosthetic joint infection. The pathogenesis of prosthetic joint infection is related to bacteria in biofilms, in which they are protected from antimicrobial killing and host responses rendering these infections difficult to eradicate. Current microbiology laboratory methods for diagnosis of prosthetic joint infection depend on isolation of a pathogen by culture. However, these methods have neither ideal sensitivity nor ideal specificity. Therefore, culture-independent molecular methods have been used to improve the diagnosis of prosthetic joint infection. In the research setting, detection of 16S ribosomal deoxyribonucleic acid by polymerase chain reaction has been used in the molecular diagnosis of prosthetic joint infection. Various antibiofilm strategies directed at disruption of adherent bacteria are the focus of intense research to improve the detection of biofilm organisms and their eradication. In this article, molecular and antibiofilm approaches to prosthetic joint infection are reviewed.

State of the art: why do the lungs of patients with cystic fibrosis become infected and why can't they clear the infection?

Cystic Fibrosis (CF) lung disease, which is characterized by airway obstruction, chronic bacterial infection, and an excessive inflammatory response, is responsible for most of the morbidity and mortality. Early in life, CF patients become infected with a limited spectrum of bacteria, especially P. aeruginosa. New data now indicate that decreased depth of periciliary fluid and abnormal hydration of mucus, which impede mucociliary clearance, contribute to initial infection. Diminished production of the antibacterial molecule nitric oxide, increased bacterial binding sites (e.g., asialo GM-1) on CF airway epithelial cells, and adaptations made by the bacteria to the airway microenvironment, including the production of virulence factors and the ability to organize into a biofilm, contribute to susceptibility to initial bacterial infection. Once the patient is infected, an overzealous inflammatory response in the CF lung likely contributes to the host's inability to eradicate infection. In response to increased IL-8 and leukotriene B₄ production, neutrophils infiltrate the lung where they release mediators, such as elastase, that further inhibit host defenses, cripple opsonophagocytosis, impair mucociliary clearance, and damage airway wall architecture. The combination of these events favors the persistence of bacteria in the airway. Until a cure is discovered, further investigations into therapies that relieve obstruction, control infection, and attenuate inflammation offer the best hope of limiting damage to host tissues and prolonging survival.

Prophylactic efficacy of topical temporin A and RNAIII-inhibiting peptide in a subcutaneous rat Pouch model of graft infection attributable to staphylococci with intermediate resistance to glycopeptides

BACKGROUND

Bacteria that adhere to implanted medical devices play an important role in industry and in modern medicine. Staphylococci are among the most common pathogens that cause biomaterial infections. Vascular prosthetic graft infection is one of the most feared complications that the vascular surgeon treats, frequently resulting in prolonged hospitalization, organ failure, amputation, and death. A rat model was used to investigate the topical efficacies of temporin A and the quorum-sensing inhibitor RNAIII-inhibiting protein (RIP) as prophylactic agents of vascular prosthetic graft infections caused by Staphylococcus aureus and Staphylococcus epidermidis with intermediate resistance to glycopeptides.

METHODS AND RESULTS

Graft infections were established in the back subcutaneous tissue of adult male Wistar rats by implantation of Dacron prostheses 1 cm2 followed by topical inoculation with 2x10(7) colony-forming units of bacterial strains. The study included, for each staphylococcal strain, a control group (no graft contamination), a contaminated group that did not receive antibiotic prophylaxis, and 6 contaminated groups that received grafts soaked with temporin A, RIP, rifampin, temporin A plus RIP, RIP plus rifampin, or temporin A plus RIP. The infection was evaluated by quantitative agar culture. When tested alone, temporin A and RIP showed comparable efficacies, and their efficacies were significantly higher than that of rifampin against both strains. All combinations showed efficacies significantly higher than that of each single compound. The combinations of temporin A and RIP exerted the strongest antistaphylococcal efficacies, eliminating infection by 100%.

CONCLUSIONS

The results of the present study make these molecules potentially useful for antimicrobial chemoprophylaxis in vascular surgery.

Mechanism of fluconazole resistance in Candida albicans biofilms: phase-specific role of efflux pumps and membrane sterols

Candida albicans biofilms are formed through three distinct developmental phases and are associated with high fluconazole (FLU) resistance. In the present study, we used a set of isogenic Candida strains lacking one or more of the drug efflux pumps Cdr1p, Cdr2p, and Mdr1p to determine their role in FLU resistance of biofilms. Additionally, variation in sterol profile as a possible mechanism of drug resistance was investigated. Our results indicate that parent and mutant strains formed similar biofilms. However, biofilms formed by double and triple mutants were more susceptible to FLU at 6 h (MIC = 64 and 16 microg/ml, respectively) than the wild-type strain (MIC > 256 microg/ml). At later time points (12 and 48 h), all the strains became resistant to this azole (MIC > or = 256 microg/ml), indicating lack of involvement of efflux pumps in resistance at late stages of biofilm formation. Northern blot analyses revealed that Candida biofilms expressed CDR and MDR1 genes in all the developmental phases, while planktonic cells expressed these genes only at the 12- and 48-h time points. Functionality of efflux pumps was assayed by rhodamine (Rh123) efflux assays, which revealed significant differences in Rh123 retention between biofilm and planktonic cells at the early phase (P = 0.0006) but not at later stages (12 and 48 h). Sterol analyses showed that ergosterol levels were significantly decreased (P < 0.001) at intermediate and mature phases, compared to those in early-phase biofilms. These studies suggest that multicomponent, phase-specific mechanisms are operative in antifungal resistance of fungal biofilms.

Intracellular bacterial biofilm-like pods in urinary tract infections

Escherichia coli entry into the bladder is met with potent innate defenses, including neutrophil influx and epithelial exfoliation. Bacterial subversion of innate responses involves invasion into bladder superficial cells. We discovered that the intracellular bacteria matured into biofilms, creating pod-like bulges on the bladder surface. Pods contained bacteria encased in a polysaccharide-rich matrix surrounded by a protective shell of uroplakin. Within the biofilm, bacterial structures interacted extensively with the surrounding matrix, and biofilm associated factors had regional variation in expression. The discovery of intracellular biofilm-like pods explains how bladder infections can persist in the face of robust host defenses.

Waterborne pathogens and dental waterlines

Humans, like every other living thing on Earth, have evolved in a world dominated by many billions of microscopic life forms. Most of the time, we live in a state of harmony (or even mutualism) with our invisible coinhabitants. When this balance becomes disturbed however, the consequences can be devastating. Infectious diseases including malaria, tuberculosis, and AIDS remain the world's greatest mass murderers. Dental workers strive to reduce infection risks for their patients through infection control measures that reduce or eliminate potentially pathogenic agents in the clinical environment. As increasing numbers of patients with varying degrees of immune suppression present for dental treatment, the need to ensure an aseptic treatment environment will become a higher priority for the dental profession. The possibility that exposure to aerosols contaminated with endotoxin might exacerbate asthma or cause chronic respiratory problems in dental health care workers should be investigated. Although direct evidence of widespread complications among patients or occupationally acquired illness among dental workers is presently lacking, reducing the numbers of microorganisms present in dental treatment water is consistent with other empiric measures that form the basis of infection-control practice.

RNA III inhibiting peptide inhibits in vivo biofilm formation by drug-resistant Staphylococcus aureus

Staphylococcus aureus is a prevalent cause of bacterial infections associated with indwelling medical devices. RNA III inhibiting peptide (RIP) is known to inhibit S. aureus pathogenesis by disrupting quorum-sensing mechanisms. RIP was tested in the present study for its ability to inhibit S. aureus biofilm formation in a rat Dacron graft model. The activity of RIP was synergistic with those of antibiotics for the complete prevention of drug-resistant S. aureus infections.

Asymptomatic bacteriuria: when to screen and when to treat

Asymptomatic bacteriuria is common. Populations with structural or functional abnormalities of the genitourinary tract may have an exceedingly high prevalence of bacteriuria, but even healthy individuals frequently have positive urine cultures. Asymptomatic bacteriuria is seldom associated with adverse outcomes. Pregnant women and individuals who are to undergo traumatic genitourinary interventions are at risk for complications of bacteriuria and benefit from screening and treatment programs. Although screening is recommended for renal transplant recipients, the benefits for these patients are less clear. For other populations, including most bacteriuric individuals, negative outcomes attributable to asymptomatic bacteriuria have not been described. Treatment of asymptomatic bacteriuria in these patients is not beneficial and, in fact, may be associated with harmful outcomes, such as increased short-term frequency of symptomatic infection, adverse drug effects, and reinfection with organisms of increased antimicrobial resistance. Screening for asymptomatic bacteriuria and treatment is recommended for only selected groups where benefit has been shown. Many research questions still need to be addressed. Different populations have unique risk factors, and the benefits and risks of different management approaches for asymptomatic bacteriuria must continue to be addressed systematically in appropriate clinical trials.

Biofilms and catheter-associated urinary tract infections

Urinary catheter-related infections are commonly seen in several different patient populations and lead to substantial morbidity. The overall health care costs caused by these infections are sizable given how often urinary catheters are used in acute care settings, extended care facilities, and in persons with injured spinal cords. Recent attention has appropriately focused on biofilm development on the catheter surface because biofilm has important implications for the pathogenesis, treatment, and prevention of catheter-related infection. Because the most important risk factor for infection is duration of catheterization, indwelling urethral catheterization should be avoided or at least limited whenever possible. Additional methods to prevent this infection include aseptic insertion and maintenance use of a closed drainage system, anti-infective catheters in patients at high-risk for infection, and systemic antibiotics in select patients. Alternative urinary collection strategies may be appropriate in certain patient groups. Specifically, condom catheters should be considered in men likely to be adherent with this urinary collection method, suprapubic catheters should be considered in patients requiring long-term indwelling drainage, and intermittent catheterization seems appropriate in patients with injured spinal cords. Future research should focus on additional methods for preventing this common infection.

Adhesive surface proteins of Erysipelothrix rhusiopathiae bind to polystyrene, fibronectin, and type I and IV collagens

Erysipelothrix rhusiopathiae is a gram-positive bacterium that causes erysipelas in animals and erysipeloid in humans. We found two adhesive surface proteins of E. rhusiopathiae and determined the nucleotide sequences of the genes, which were colocalized and designated rspA and rspB. The two genes were present in all of the serovars of E. rhusiopathiae strains examined. The deduced RspA and RspB proteins contain the C-terminal anchoring motif, LPXTG, which is preceded by repeats of consensus amino acid sequences. The consensus sequences are composed of 78 to 92 amino acids and repeat 16 and 3 times in RspA and RspB, respectively. Adhesive surface proteins of other gram-positive bacteria, including Listeria monocytogenes adhesin-like protein, Streptococcus pyogenes protein F2 and F2-like protein, Streptococcus dysgalactiae FnBB, and Staphylococcus aureus Cna, share the same consensus repeats. Furthermore, the N-terminal regions of RspA and RspB showed characteristics of the collagen-binding domain that was described for Cna. RspA and RspB were expressed in Escherichia coli as histidine-tagged fusion proteins and purified. The recombinant proteins showed a high degree of capacity to bind to polystyrene and inhibited the binding of E. rhusiopathiae onto the abiotic surface in a dose dependent manner. In a solid-phase binding assay, both of the recombinant proteins bound to fibronectin, type I and IV collagens, indicating broad spectrum of their binding ability. It was suggested that both RspA and RspB were exposed on the cell surface of E. rhusiopathiae, as were the bacterial cells agglutinated by the anti-RspA immunoglobulin G (IgG) and anti-RspB IgG. RspA and RspB were present both in surface-antigen extracts and the culture supernatants of E. rhusiopathiae Fujisawa-SmR (serovar 1a) and SE-9 (serovar 2). The recombinant RspA, but not RspB, elicited protection in mice against experimental challenge. These results suggest that RspA and RspB participate in initiation of biofilm formation through their binding abilities to abiotic and biotic surfaces.

Global gene expression in Escherichia coli biofilms

It is now apparent that microorganisms undergo significant changes during the transition from planktonic to biofilm growth. These changes result in phenotypic adaptations that allow the formation of highly organized and structured sessile communities, which possess enhanced resistance to antimicrobial treatments and host immune defence responses. Escherichia coli has been used as a model organism to study the mechanisms of growth within adhered communities. In this study, we use DNA microarray technology to examine the global gene expression profile of E. coli during sessile growth compared with planktonic growth. Genes encoding proteins involved in adhesion (type 1 fimbriae) and, in particular, autoaggregation (Antigen 43) were highly expressed in the adhered population in a manner that is consistent with current models of sessile community development. Several novel gene clusters were induced upon the transition to biofilm growth, and these included genes expressed under oxygen-limiting conditions, genes encoding (putative) transport proteins, putative oxidoreductases and genes associated with enhanced heavy metal resistance. Of particular interest was the observation that many of the genes altered in expression have no current defined function. These genes, as well as those induced by stresses relevant to biofilm growth such as oxygen and nutrient limitation, may be important factors that trigger enhanced resistance mechanisms of sessile communities to antibiotics and hydrodynamic shear forces.

Antibiotic lock-technique for the treatment of catheter-related bloodstream infections

The management of central venous catheter-related bloodstream infections (CRBSI), though still debated, requires the removal of the line in most cases: we investigated the efficacy of an alternative approach, based on higher concentrations of antibiotics locked within the catheter lumen, in an open, pilot study aimed at preserving the line in place and at eradicating the infection. Thirty consecutive patients carrying a central line over 10 days and who fulfilled criteria for ascertained diagnosis of bacterial CRBSI, had the catheter "locked" with antimicrobials therein; all patients also received systemic antibiotic therapy within the first 48 hours. Subsequently, 15 patients underwent locks alone, and 15 locks plus systemic therapy. Twenty-eight out of 30 (93.3%) patients retained the catheter in place, appearing to be cleared of infection and no treatment-related untoward events were observed. Locks should be considered as effective as line removal in the management of bacterial CRBSI in unselected patients, and could thus provide advantages in terms of resource sparing and lowered antibiotic pressure in the hospital setting.

The genetics of nontuberculous mycobacterial infection

The molecular aetiology of familial susceptibility to disseminated mycobacterial disease, usually involving weakly pathogenic strains of mycobacteria, has now been elucidated in more than 30 families. Mutations have been identified in five genes in the interleukin-12-dependent interferon-gamma pathway, highlighting the importance of this pathway in human mycobacterial immunity. Knowledge derived from the study of these rare patients contributes to our understanding of the immune response to common mycobacterial pathogens such as Mycobacterium tuberculosis and Mycobacterium leprae, which remain major public health problems globally. This knowledge can be applied to the rational development of novel therapies and vaccines for these important mycobacterial diseases.

Transcriptional organization and regulation of the Escherichia coli K30 group 1 capsule biosynthesis (cps) gene cluster

Escherichia coli group 1 capsules are important virulence determinants, yet little is known about the transcriptional organization or regulation of their biosynthetic (cps) operons. Transcription of the prototype serotype K30 cluster is modulated by the JUMPStart-RfaH antitermination mechanism, with the cps promoter being localized to a region immediately upstream of the JUMPStart sequence. A putative stem-loop structure located within the K30 cps cluster separates conserved genes with products that are required for surface expression of capsule from serotype-specific genes encoding enzymes for polymer repeat-unit synthesis and polymerization. This putative stem-loop structure significantly reduces transcription in a termination-probe vector and may contribute to differential expression of the cps genes. Previous work indicated that increased amounts of group 1 capsular polysaccharide synthesis resulted from the overexpression of the Rcs (regulator of capsule synthesis) proteins. However, neither overexpression of the transcriptional activator RcsB nor an rcsB::aadA chromosomal insertion altered the level of transcription measured by cps::lacZ fusions. In the group 1 strains examined, an RcsAB box was found immediately upstream of galF, a gene involved in the production of sugar nucleotide precursors. Overexpression of RcsB was found to result in a threefold increase in transcription of a galF::lacZ chromosomal fusion. Moreover, overexpression of GalF gave rise to a two- to threefold increase in cell-free as well as cell-associated capsule, without affecting cps::lacZ activity. These results indicate that transcription of the E. coli group 1 capsule cluster itself is not regulated by the Rcs system and may, in fact, be constitutive. However, the Rcs system can potentially influence levels of capsular polysaccharide production by increasing galF transcription and influencing the available pool of biosynthetic precursors.

Candida biofilms and their role in infection

Pathogenic fungi in the genus Candida can cause both superficial and serious systemic disease, and are now recognized as major agents of hospital-acquired infection. Many Candida infections involve the formation of biofilms on implanted devices such as indwelling catheters or prosthetic heart valves. Biofilms of Candida albicans formed in vitro on catheter material consist of matrix-enclosed microcolonies of yeasts and hyphae, arranged in a bilayer structure. The biofilms are resistant to a range of antifungal agents currently in clinical use, including amphotericin B and fluconazole, and there appear to be multiple resistance mechanisms. Recent studies with mixed biofilms containing Candida and bacterial species suggest that extensive and striking interactions occur between the prokaryotic and eukaryotic cells in these adherent populations.

Bacterial outer membrane and cell wall penetration and cell destruction by polluting chemical agents and physical conditions

In the environment, bacteria and other microorganisms are subjected to a variety of constantly changing chemical and physical agencies. Chemical ones include antimicrobial compounds (both biocides and antibiotics), pollutants, drugs, cosmetic and pharmaceutical ingredients and pesticides. The physical agents include desiccation and drying, osmotic pressure, hydrostatic pressure, temperature and pH changes and radiations (ultraviolet, sunlight, ionizing). Bacteria must thus adapt to survive these inimicable conditions. Organisms such as bacterial spores usually survive, whereas other types of microorganisms may be much more susceptible. Depending on the type of organism, the bacterial cell wall, outer membrane or the spore outer layers may act as permeability barriers to the intracellular uptake of antibiotics and biocides. Some antibacterial agents interact with, and damage or modify, the outer components. Physical agencies are known to damage the cytoplasmic membrane or to produce alterations in DNA or proteins or enzymes. Nevertheless, significant damage to the cell wall or outer membrane may also occur. Four types of organisms are considered: cocci, mycobactria, Gram-negative bacteria and bacterial spores. The nature of the damage inflicted on, or in some cases prevented by, their outer cell layers is discussed for each type of organism.

Are there biofilm-specific physiological pathways beyond a reasonable doubt?

The development of surface-attached communities called biofilms is often thought to be a regulated developmental process involving profound biofilm-specific modifications. Despite intense scrutiny and a growing body of evidence correlating changes in gene expression with the switch from planktonic-to-biofilm lifestyle, an integrated view of biofilm formation is still missing.