Key role of teichoic acid net charge in Staphylococcus aureus colonization of artificial surfaces

Staphylococcal biofilms

Staphylococcus epidermidis and Staphylococcus aureus are the most frequent causes of nosocomial infections and infections on indwelling medical devices, which characteristically involve biofilms. Recent advances in staphylococcal molecular biology have provided more detailed insight into the basis of biofilm formation in these opportunistic pathogens. A series of surface proteins mediate initial attachment to host matrix proteins, which is followed by the expression of a cationic glucosamine-based exopolysaccharide that aggregates the bacterial cells. In some cases, proteins may function as alternative aggregating substances. Furthermore, surfactant peptides have now been recognized as key factors involved in generating the three-dimensional structure of a staphylococcal biofilm by cell-cell disruptive forces, which eventually may lead to the detachment of entire cell clusters. Transcriptional profiling experiments have defined the specific physiology of staphylococcal biofilms and demonstrated that biofilm resistance to antimicrobials is due to gene-regulated processes. Finally, novel animal models of staphylococcal biofilm-associated infection have given us important information on which factors define biofilm formation in vivo. These recent advances constitute an important basis for the development of anti-staphylococcal drugs and vaccines.

Localization and interactions of teichoic acid synthetic enzymes in Bacillus subtilis

The thick wall of gram-positive bacteria is a polymer meshwork composed predominantly of peptidoglycan (PG) and teichoic acids, both of which have a critical function in maintenance of the structural integrity and the shape of the cell. In Bacillus subtilis 168 the major teichoic acid is covalently coupled to PG and is known as wall teichoic acid (WTA). Recently, PG insertion/degradation over the lateral wall has been shown to occur in a helical pattern. However, the spatial organization of WTA assembly and its relationship with cell shape and PG assembly are largely unknown. We have characterized the localization of green fluorescent protein fusions to proteins involved in several steps of WTA synthesis in B. subtilis: TagB, -F, -G, -H, and -O. All of these localized similarly to the inner side of the cytoplasmic membrane, in a pattern strikingly similar to that displayed by probes of nascent PG. Helix-like localization patterns are often attributable to the morphogenic cytoskeletal proteins of the MreB family. However, localization of the Tag proteins did not appear to be substantially affected by single disruption of any of the three MreB homologues of B. subtilis. Bacterial and yeast two-hybrid experiments revealed a complex network of interactions involving TagA, -B, -E, -F, -G, -H, and -O and the cell shape determinants MreC and MreD (encoded by the mreBCD operon and presumably involved in the spatial organization of PG synthesis). Taken together, our results suggest that, in B. subtilis at least, the synthesis and export of WTA precursors are mediated by a large multienzyme complex that may be associated with the PG-synthesizing machinery.

Differential roles of poly-N-acetylglucosamine surface polysaccharide and extracellular DNA in Staphylococcus aureus and Staphylococcus epidermidis biofilms

Staphylococcus aureus and Staphylococcus epidermidis are major human pathogens of increasing importance due to the dissemination of antibiotic-resistant strains. Evidence suggests that the ability to form matrix-encased biofilms contributes to the pathogenesis of S. aureus and S. epidermidis. In this study, we investigated the functions of two staphylococcal biofilm matrix polymers: poly-N-acetylglucosamine surface polysaccharide (PNAG) and extracellular DNA (ecDNA). We measured the ability of a PNAG-degrading enzyme (dispersin B) and DNase I to inhibit biofilm formation, detach preformed biofilms, and sensitize biofilms to killing by the cationic detergent cetylpyridinium chloride (CPC) in a 96-well microtiter plate assay. When added to growth medium, both dispersin B and DNase I inhibited biofilm formation by both S. aureus and S. epidermidis. Dispersin B detached preformed S. epidermidis biofilms but not S. aureus biofilms, whereas DNase I detached S. aureus biofilms but not S. epidermidis biofilms. Similarly, dispersin B sensitized S. epidermidis biofilms to CPC killing, whereas DNase I sensitized S. aureus biofilms to CPC killing. We concluded that PNAG and ecDNA play fundamentally different structural roles in S. aureus and S. epidermidis biofilms.

Molecular basis of resistance to muramidase and cationic antimicrobial peptide activity of lysozyme in staphylococci

It has been shown recently that modification of peptidoglycan by O-acetylation renders pathogenic staphylococci resistant to the muramidase activity of lysozyme. Here, we show that a Staphylococcus aureus double mutant defective in O-acetyltransferase A (OatA), and the glycopeptide resistance-associated two-component system, GraRS, is much more sensitive to lysozyme than S. aureus with the oatA mutation alone. The graRS single mutant was resistant to the muramidase activity of lysozyme, but was sensitive to cationic antimicrobial peptides (CAMPs) such as the human lysozyme-derived peptide ₁₀₇R-A-W-V-A-W-R-N-R₁₁₅ (LP9), polymyxin B, or gallidermin. A comparative transcriptome analysis of wild type and the graRS mutant revealed that GraRS controls 248 genes. It up-regulates global regulators (rot, sarS, or mgrA), various colonization factors, and exotoxin-encoding genes, as well as the ica and dlt operons. A pronounced decrease in the expression of the latter two operons explains why the graRS mutant is also biofilm-negative. The decrease of the dlt transcript in the graRS mutant correlates with a 46.7% decrease in the content of esterified d-alanyl groups in teichoic acids. The oatA/dltA double mutant showed the highest sensitivity to lysozyme; this mutant completely lacks teichoic acid–bound d-alanine esters, which are responsible for the increased susceptibility to CAMPs and peptidoglycan O-acetylation. Our results demonstrate that resistance to lysozyme can be dissected into genes mediating resistance to its muramidase activity (oatA) and genes mediating resistance to CAMPs (graRS and dlt). The two lysozyme activities act synergistically, as the oatA/dltA or oatA/graRS double mutants are much more susceptible to lysozyme than each of the single mutants.

In humans, lysozyme plays an important role in the suppression of bacterial infections. However, some bacterial pathogens, such as Staphylococcus aureus, are completely resistant to lysozyme. Here we demonstrate that lysozyme acts on S. aureus in two ways: as a muramidase (cell wall lytic enzyme) and as a cationic antimicrobial peptide (CAMP). S. aureus has developed resistance mechanisms against both activities by modifying distinct cell wall structures. Modification of the peptidoglycan by O-acetylation (OatA) renders the cells resistant to the muramidase activity. Modification of teichoic acids by d-alanine esterification (Dlt) renders the cells resistant to lysozyme's CAMPs and other CAMPs. Transcriptome analysis of the glycopeptide resistance-associated (GraRS) two-component system revealed that this global regulator controls 248 genes such as other global regulators, colonization factors, or exotoxin-encoding genes. Since GraRS also upregulates the dlt operon, it was not surprising that in the graRS mutant teichoic acid d-alanylation is markedly decreased, which explains its increased sensitivity to CAMPs. By comparative analysis of mutants we were able to dissect genes that were responsive to the dual activities of lysozyme. Here we show how efficiently S. aureus is protected from the human defense system, which enables this pathogen to cause persistent infections.

Impact of environmental and genetic factors on biofilm formation by the probiotic strain Lactobacillus rhamnosus GG

Lactobacillus rhamnosus GG (ATCC 53103) is one of the clinically best-studied probiotic organisms. Moreover, L. rhamnosus GG displays very good in vitro adherence to epithelial cells and mucus. Here, we report that L. rhamnosus GG is able to form biofilms on abiotic surfaces, in contrast to other strains of the Lactobacillus casei group tested under the same conditions. Microtiter plate biofilm assays indicated that in vitro biofilm formation by L. rhamnosus GG is strongly modulated by culture medium factors and conditions related to the gastrointestinal environment, including low pH; high osmolarity; and the presence of bile, mucins, and nondigestible polysaccharides. Additionally, phenotypic analysis of mutants affected in exopolysaccharides (wzb), lipoteichoic acid (dltD), and central metabolism (luxS) showed their relative importance in biofilm formation by L. rhamnosus GG.

Effect of shear stress on growth, adhesion and biofilm formation of Pseudomonas aeruginosa with antibiotic-induced morphological changes

The aim of this study was to investigate the effect of shear stress and antibiotic-induced morphological changes on the growth, adhesion and biofilm formation ability of Pseudomonas aeruginosa. A modified microtitre plate assay was used to quantify adhesion, biofilm formation and planktonic culture density of P. aeruginosa ATCC 27853 under the effect of 0.5x minimal inhibitory concentrations (MICs) of piperacillin/tazobactam, imipenem and meropenem. Hydrodynamic conditions were achieved by orbital shaking at 250 rpm with the presence of a glass bead in each microtitre well. These conditions decreased adhesion and biofilm formation abilities, increased planktonic culture density over 1h and decreased planktonic culture density over 16 h for bacteria with antibiotic-induced morphological changes in comparison with static conditions. Our results demonstrate the importance of using a high-throughput dynamic model to assess the adhesion and biofilm formation behaviour of P. aeruginosa with antibiotic-induced morphological changes and suggest the possible use of sub-MIC antibiotics in clinical applications to prevent infections acquired by haematogenous spread. This dynamic model provides a better simulation of in vivo conditions of adhesion and biofilm formation of P. aeruginosa with altered morphologies induced by beta-lactam antibiotics.

Inhibition of staphylococcal biofilm formation by nitrite

Several environmental stresses have been demonstrated to increase polysaccharide intercellular adhesin (PIA) synthesis and biofilm formation by the human pathogens Staphylococcus aureus and Staphylococcus epidermidis. In this study we characterized an adaptive response of S. aureus SA113 to nitrite-induced stress and show that it involves concomitant impairment of PIA synthesis and biofilm formation. Transcriptional analysis provided evidence that nitrite, either as the endogenous product of respiratory nitrate reduction or after external addition, causes repression of the icaADBC gene cluster, mediated likely by IcaR. Comparative microarray analysis revealed a global change in gene expression during growth in the presence of 5 mM sodium nitrite and indicated a response to oxidative and nitrosative stress. Many nitrite-induced genes are involved in DNA repair, detoxification of reactive oxygen and nitrogen species, and iron homeostasis. Moreover, preformed biofilms could be eradicated by the addition of nitrite, likely the result of the formation of toxic acidified nitrite derivatives. Nitrite-mediated inhibition of S. aureus biofilm formation was abrogated by the addition of nitric oxide (NO) scavengers, suggesting that NO is directly or indirectly involved. Nitrite also repressed biofilm formation of S. epidermidis RP62A.

A Staphylococcus aureus ypfP mutant with strongly reduced lipoteichoic acid (LTA) content: LTA governs bacterial surface properties and autolysin activity

Many Gram-positive bacteria produce lipoteichoic acid (LTA) polymers whose physiological roles have remained a matter of debate because of the lack of LTA-deficient mutants. The ypfP gene responsible for biosynthesis of a glycolipid found in LTA was deleted in Staphylococcus aureus SA113, causing 87% reduction of the LTA content. Mass spectrometry and nuclear magnetic resonance spectroscopy revealed that the mutant LTA contained a diacylglycerol anchor instead of the glycolipid, whereas the remaining part was similar to the wild-type polymer except that it was shorter. The LTA mutant strain revealed no major changes in patterns of cell wall proteins or autolytic enzymes compared with the parental strain indicating that LTA may be less important in S. aureus protein attachment than previously thought. However, the autolytic activity of the mutant was strongly reduced demonstrating a role of LTA in controlling autolysin activity. Moreover, the hydrophobicity of the LTA mutant was altered and its ability to form biofilms on plastic was completely abrogated indicating a profound impact of LTA on physicochemical properties of bacterial surfaces. We propose to consider LTA and its biosynthetic enzymes as targets for new antibiofilm strategies.

Bacterial cell attachment, the beginning of a biofilm

The ability of bacteria to attach to surfaces and develop into a biofilm has been of considerable interest to many groups in numerous industries, including the medical and food industry. However, little is understood in the critical initial step seen in all biofilm development, the initial bacterial cell attachment to a surface. This initial attachment is critical for the formation of a bacterial biofilm, as all other cells within a biofilm structure rely on the interaction between surface and bacterial cell for their survival. This review examines what are believed to be some of the most important aspects involved in bacterial attachment to a surface.

Role of solution chemistry and ion valence on the adhesion kinetics of groundwater and marine bacteria

The role of solution chemistry on bacterial adhesion has been investigated using a radial stagnation point flow (RSPF) system. This experimental system utilized an optical microscope and an image-capturing device to directly observe the deposition kinetics of a groundwater bacterium, Burkholderia cepacia G4g, and a marine bacterium, Halomonas pacifica g. Experiments were carried out under well-controlled hydrodynamic and solution chemistry conditions, allowing for the sensitivity of bacterial adhesion behavior to be examined under a range of ionic strength and valence (KCl vs CaCl2) simulating groundwater and marine environments. Complimentary cell characterization techniques were conducted to evaluate the electrophoretic mobility, hydrophobicity, surface charge density, and viability of the bacteria under the same range of conditions. Solution chemistry was found to have a marked effect on the electrokinetic and surface properties of bacteria and the quartz collector, as well as on the resulting rate of bacterial deposition. Comparable adhesion trends were observed for B. cepacia G4g and H. pacifica g. Specifically, the deposition rates of the two bacteria species in both KCl and CaCl2 solutions increased with ionic strength, a trend consistent with traditional Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, which considers the combination of van der Waals and electrostatic double-layer interaction forces. However, in some cases, experimental results showed bacterial deposition behavior to deviate from DLVO predictions. On the basis of the systematic investigation of bacterial cell characteristics, it was found that Ca2+ ions play a distinct role on bacterial surface charge, hydrophobicity, and deposition behaviors. It is further suggested that bacterial adhesion is determined by the combined influence of DLVO interactions, electrosteric interactions associated with solution chemistry, and the hydrodynamics of the deposition system.

Different patterns of biofilm formation in Staphylococcus aureus under food-related stress conditions

Staphylococcus aureus and its biofilm formation are recognized as a serious clinical problem. S. aureus is also a food borne pathogen, and little is known regarding biofilm formation of food-related strains. We have studied biofilm formation of both food-related and clinical S. aureus strains grown under different stress conditions (temperature, sodium chloride, glucose and ethanol) relevant for food processing. Strong biofilm formers were identified among food-related S. aureus strains, and biofilm formation was affected by environmental conditions relevant for the food industry. The results showed that temperatures suboptimal for growth increased the production of biofilm. The combined presence of sodium chloride and glucose enhanced the biofilm formation. Both temperature and osmolarity affected the expression of several biofilm associated genes (e.g. icaA and rbf). Variations in gene expression (e.g. icaA, agrA and sigB) between strains were also observed. Our results support the existence of both ica-dependent and ica-independent mechanisms of biofilm production in S. aureus. The phenotypic and genotypic results showed highly diverse and complex patterns of biofilm formation in S. aureus. This clearly demonstrates that caution must be exercised before drawing general conclusions about gene expression in S. aureus in relation to regulation of biofilm formation. The results are relevant for food safety as they indicate that food processing conditions could promote biofilm formation by S. aureus.

Functional analysis of D-alanylation of lipoteichoic acid in the probiotic strain Lactobacillus rhamnosus GG

Lipoteichoic acid (LTA) is a macroamphiphile molecule which performs several functions in gram-positive bacteria, such as maintenance of cell wall homeostasis. D-alanylation of LTA requires the proteins encoded by the dlt operon, and this process is directly related to the charge properties of this polymer strongly contributing to its function. The insertional inactivation of dltD of the probiotic strain Lactobacillus rhamnosus GG (ATCC 53103) resulted in the complete absence of D-alanyl esters in the LTA as confirmed by nuclear magnetic resonance analysis. This was reflected in modifications of the bacterial cell surface properties. The dltD strain showed 2.4-fold-increased cell length, a low survival capacity in response to gastric juice challenge, an increased sensitivity to human beta-defensin-2, an increased rate of autolysis, an increased capacity to initiate growth in the presence of an anionic detergent, and a decreased capacity to initiate growth in the presence of cationic peptides compared to wild-type results. However, in vitro experiments revealed no major differences for adhesion to human intestinal epithelial cells, biofilm formation, and immunomodulation. These properties are considered to be important for probiotics. The role of the dlt operon in lactobacilli is discussed in view of these results.

ica and beyond: biofilm mechanisms and regulation in Staphylococcus epidermidis and Staphylococcus aureus

Recent progress in elucidating the role of the icaADBC-encoded polysaccharide intercellular adhesin (PIA) or polymeric N-acetyl-glucosamine (PNAG) in staphylococcal biofilm development has in turn contributed significantly to our understanding of the pathogenesis of device-related infections. Nevertheless, our understanding of how the ica locus and PIA/PNAG biosynthesis are regulated is far from complete and many questions remain. Moreover, beyond ica, evidence is now emerging for the existence of ica-independent biofilm mechanisms in both Staphylococcus aureus and Staphylococcus epidermidis. Teichoic acids, which are a major carbohydrate component of the S. epidermidis biofilm matrix and the major cell wall autolysin, play an important role in the primary attachment phase of biofilm development, whereas the cell surface biofilm-associated protein and accumulation-associated protein are capable of mediating intercellular accumulation. These findings raise the exciting prospect that other surface proteins, which typically function as antigenic determinants or in binding to extracellular matrix proteins, may also act as biofilm adhesins. Given the impressive array of surface proteins expressed by S. aureus and S. epidermidis, future research into their potential role in biofilm development either independent of PIA/PNAG or in cooperation with PIA/PNAG will be of particular interest.

A new device for rapid evaluation of biofilm formation potential by bacteria

This work describes the implementation of a new assay named the BioFilm Ring Test to evaluate the ability of bacteria to form biofilms. This assay is based on the immobilisation (or not) of magnetic beads embedded by bacterial aggregates or mats (patented concept). It is realised on modified polystyrene 96-wells microtiter plates with individual 8-wells slides. The kinetic of biofilm formation of four bacterial species, Listeria monocytogenes, Escherichia coli, Staphylococcus carnosus and Staphylococcus xylosus was evaluated with this new device by comparison with the standard crystal violet staining method of sessile cells. In parallel, the biofilm growth was visualized by Scanning Electron Microscopy (SEM) observations. The BioFilm Ring Test gave similar but faster results than the crystal violet method. Moreover, the new assay was easier to implement, more reproducible and allowed high throughput screenings due to limited manipulations (no washing and staining steps) and rapid and accurate measurements of magnetic bead immobilisation by sessile bacterial cells.

Correlation between fundamental binding forces and clinical prognosis of Staphylococcus aureus infections of medical implants

Atomic force microscopy was used to "fish" for binding reactions between a fibronectin-coated probe (i.e., substrate simulating an implant device) and each of 15 different isolates of Staphylococcus aureus obtained from either patients with an infected cardiac prosthesis (invasive group) or healthy human subjects (control group). There is a strong distinction (p = 0.01) in the binding-force signature observed for the invasive versus control populations. This observation suggests that a microorganism's "force taxonomy" may provide a fundamental and practical indicator of the pathogen-related risk that infections pose to patients with implanted medical devices.

Colony spreading in Staphylococcus aureus

Wild-type Staphylococcus aureus rapidly expands on the surface of soft agar plates. The rates of expansion and the shapes of the resultant giant colonies were distinct for different strains of laboratory stocks and clinical isolates. The colony spreading abilities did not correlate with the biofilm-forming abilities in these strains. Insertional disruption of the dltABCD operon, which functions at the step of D-alanine addition to teichoic acids, and of the tagO gene, which is responsible for the synthesis of wall teichoic acids, decreased the colony spreading ability. The results indicate that wall teichoic acids and D-alanylation of teichoic acids are required for colony spreading.

Isolation and characterization of biofilm formation-defective mutants of Staphylococcus aureus

Staphylococcus aureus produces biofilm and this mode of colonization facilitates infections that are often difficult to treat and engender high morbidity and mortality. We have exploited bacteriophage Mu transposition methods to create an insertional mutant library in a highly biofilm-forming S. aureus clinical isolate. Our screen identified 38 insertions in 23 distinct genes together with one intergenic region that significantly reduced biofilm formation. Nineteen insertions were mapped in loci not previously known to affect biofilm in this organism. These include insertions in codY, srrA, mgrA, and fmtA, a putative DEAD-box helicase, two members of the zinc-metallo-beta lactamase/beta-CASP family, and a hypothetical protein with a GGDEF motif. Fifteen insertions occurred in the icaADBC operon, which produces intercellular adhesion antigen (PIA) and is important for biofilm formation in many strains of S. aureus and Staphylococcus epidermidis. Obtaining a high proportion of independent Em-Mu disruptions in icaADBC demonstrated both the importance of PIA for biofilm formation in this clinical strain and the strong validation of the screening procedure that concomitantly uncovered additional mutants. All non-ica mutants were further analyzed by immunoblotting and biochemical fractionation for perturbation of PIA and wall teichoic acid. PIA levels were diminished in the majority of non-ica insertional mutants. Three mutant strains were chosen and were functionally complemented for restored biofilm formation by transformation with plasmids carrying the cloned wild-type gene under the control of a xylose-inducible promoter. This is a comprehensive collection of biofilm-defective mutants that underscores the multifactorial genetic program underlying the establishment of biofilm in this insidious pathogen.

Opsonic antibodies to Enterococcus faecalis strain 12030 are directed against lipoteichoic acid

A teichoic acid (TA)-like polysaccharide in Enterococcus faecalis has previously been shown to induce opsonic antibodies that protect against bacteremia after active and passive immunization. Here we present new data providing a corrected structure of the antigen and the epitope against which the opsonic antibodies are directed. Capsular polysaccharide isolated from E. faecalis strain 12030 by enzymatic digestion of peptidoglycan and chromatography (enzyme-TA) was compared with lipoteichoic acid (LTA) extracted using butanol and purified by hydrophobic-interaction chromatography (BuOH-LTA). Structural determinations were carried out by chemical analysis and nuclear magnetic resonance spectroscopy. Antibody specificity was assessed by enzyme-linked immunosorbent assay and the opsonophagocytosis assay. After alanine ester hydrolysis, there was structural identity between enzyme-TA and BuOH-LTA of the TA-parts of the two molecules. The basic enterococcal LTA structure was confirmed: 1,3-poly(glycerol phosphate) nonstoichiometrically substituted at position C-2 of the glycerol residues with d-Ala and kojibiose. We also detected a novel substituent at position C-2, [D-Ala-->6]-alpha-D-Glcp-(1-->2-[D-Ala-->6]-alpha-D-Glcp-1-->). Antiserum raised against enzyme-TA bound equally well to BuOH-LTA and dealanylated BuOH-LTA as to the originally described enzyme-TA antigen. BuOH-LTA was a potent inhibitor of opsonophagocytic killing by the antiserum to enzyme-TA. Immunization with antibiotic-killed whole bacterial cells did not induce a significant proportion of antibodies directed against alanylated epitopes on the TA, and opsonic activity was inhibited completely by both alanylated and dealanylated BuOH-LTA. In summary, the E. faecalis strain 12030 enzyme-TA is structurally and immunologically identical to dealanylated LTA. Opsonic antibodies to E. faecalis 12030 are directed predominantly to nonalanylated epitopes on the LTA molecule.

Molecular mechanisms of bacterial resistance to antimicrobial peptides

Cationic antimicrobial peptides (CAMPs) are integral compounds of the antimicrobial arsenals in virtually all kinds of organisms, with important roles in microbial ecology and higher organisms' host defense. Many bacteria have developed countermeasures to limit the efficacy of CAMPs such as defensins, cathelicidins, kinocidins, or bacteriocins. The best-studied bacterial CAMP resistance mechanisms involve electrostatic repulsion of CAMPs by modification of cell envelope molecules, proteolytic cleavage of CAMPs, production of CAMP-trapping proteins, or extrusion of CAMPs by energy-dependent efflux pumps. The repertoire of CAMPs produced by a given host organism and the efficiency of microbial CAMP resistance mechanisms appear to be crucial in host-pathogen interactions, governing the composition of commensal microbial communities and the virulence of bacterial pathogens. However, all CAMP resistance mechanisms have limitations and bacteria have never succeeded in becoming fully insensitive to a broad range of CAMPs. CAMPs or conserved CAMP resistance factors are discussed as new mediators and targets, respectively, of novel and sustainable anti-infective strategies.

Alanine esters of enterococcal lipoteichoic acid play a role in biofilm formation and resistance to antimicrobial peptides

Enterococcus faecalis is among the predominant causes of nosocomial infections. Surface molecules like d-alanine lipoteichoic acid (LTA) perform several functions in gram-positive bacteria, such as maintenance of cationic homeostasis and modulation of autolytic activities. The aim of the present study was to evaluate the effect of d-alanine esters of teichoic acids on biofilm production and adhesion, autolysis, antimicrobial peptide sensitivity, and opsonic killing. A deletion mutant of the dltA gene was created in a clinical E. faecalis isolate. The absence of d-alanine in the LTA of the dltA deletion mutant was confirmed by nuclear magnetic resonance spectroscopy. The wild-type strain and the deletion mutant did not show any significant differences in growth curve, morphology, or autolysis. However, the mutant produced significantly less biofilm when grown in the presence of 1% glucose (51.1% compared to that of the wild type); adhesion to eukaryotic cells was diminished. The mutant absorbed 71.1% of the opsonic antibodies, while absorption with the wild type resulted in a 93.2% reduction in killing. Sensitivity to several cationic antimicrobial peptides (polymyxin B, colistin, and nisin) was considerably increased in the mutant strain, confirming similar results from other studies of gram-positive bacteria. Our data suggest that the absence of d-alanine in LTA plays a role in environmental interactions, probably by modulating the net negative charge of the bacterial cell surface, and therefore it may be involved in the pathogenesis of this organism.

Spx is a global effector impacting stress tolerance and biofilm formation in Staphylococcus aureus

In Bacillus subtilis, Spx was recently characterized as a novel type of global regulator whose activity is regulated by the redox status of the cells. In the present study, we demonstrate that inactivation of Spx in the important pathogen Staphylococcus aureus renders the cells hypersensitive to a wide range of stress conditions including high and low temperature, high osmolarity, and hydrogen peroxide. Moreover, growth was restricted under nonstress conditions. Two-dimensional gel electrophoresis revealed that the proteome of the spx mutant differs substantially from the proteome of wild-type cells, supporting the finding that Spx is also a global regulator in S. aureus. More specifically, we demonstrated that Spx is required for transcription of trxB, encoding thioredoxin reductase, under all growth conditions examined. As trxB is essential in S. aureus, we speculate that the severely reduced trxB transcription could account for some of the growth defects of the spx mutant. Inactivation of spx also enhanced biofilm formation. S. aureus biofilm formation is associated with the production of the polysaccharide intercellular adhesin encoded by the ica operon. Interestingly, our data indicate that the augmented capacity of the spx mutant to form biofilms is due to Spx modulating the expression of icaR, encoding a repressor of the structural ica genes (icaABCD). In summary, we conclude that Spx fulfills an important role for growth, general stress protection, and biofilm formation in S. aureus.

Nosocomial infections by Staphylococcus epidermidis: how a commensal bacterium turns into a pathogen

Staphylococcus epidermidis is a commensal bacterium of the human skin. However, S. epidermidis and other coagulase-negative staphylococci (CNS) emerge also as common nosocomial pathogens infecting immunocompromized patients carrying medical devices. Antibiotic resistance and the ability of many nosocomial S. epidermidis isolates to form biofilms on inert surfaces make these infections hard to treat. Epidemiological analyses using multilocus sequence typing (MLST) and genetic studies suggest that S. epidermidis isolates in the hospital environment differ from those obtained outside of medical facilities with respect to biofilm formation, antibiotic resistance, and the presence of mobile DNA elements. Since S. epidermidis isolates exhibit high genome flexibility, they are now regarded as reservoirs for the evolution and spread of resistance traits within nosocomial bacterial communities.

A functional dlt operon, encoding proteins required for incorporation of d-alanine in teichoic acids in gram-positive bacteria, confers resistance to cationic antimicrobial peptides in Streptococcus pneumoniae

Streptococcus pneumoniae is one of the few species within the group of low-G +C gram-positive bacteria reported to contain no d-alanine in teichoic acids, although the dltABCD operon encoding proteins responsible for d-alanylation is present in the genomes of two S. pneumoniae strains, the laboratory strain R6 and the clinical isolate TIGR4. The annotation of dltA in R6 predicts a protein, d-alanine-d-alanyl carrier protein ligase (Dcl), that is shorter at the amino terminus than all other Dcl proteins. Translation of dltA could also start upstream of the annotated TTG start codon at a GTG, resulting in the premature termination of dltA translation at a stop codon. Applying a novel integrative translation probe plasmid with Escherichia coli 'lacZ as a reporter, we could demonstrate that dltA translation starts at the upstream GTG. Consequently, S. pneumoniae R6 is a dltA mutant, whereas S. pneumoniae D39, the parental strain of R6, and Rx, another derivative of D39, contained intact dltA genes. Repair of the stop codon in dltA of R6 and insertional inactivation of dltA in D39 and Rx yielded pairs of dltA-deficient and dltA-proficient strains. Subsequent phenotypic analysis showed that dltA inactivation resulted in enhanced sensitivity to the cationic antimicrobial peptides nisin and gallidermin, a phenotype fully consistent with those of dltA mutants of other gram-positive bacteria. In addition, mild alkaline hydrolysis of heat-inactivated whole cells released d-alanine from dltA-proficient strains, but not from dltA mutants. The results of our study suggest that, as in many other low-G+C gram-positive bacteria, teichoic acids of S. pneumoniae contain d-alanine residues in order to protect this human pathogen against the actions of cationic antimicrobial peptides.

Cation-induced transcriptional regulation of the dlt operon of Staphylococcus aureus

Lipoteichoic and wall teichoic acids (TA) are highly anionic cell envelope-associated polymers containing repeating polyglycerol/ribitol phosphate moieties. Substitution of TA with D-alanine is important for modulation of many cell envelope-dependent processes, such as activity of autolytic enzymes, binding of divalent cations, and susceptibility to innate host defenses. D-Alanylation of TA is diminished when bacteria are grown in medium containing increased NaCl concentrations, but the effects of increased salt concentration on expression of the dlt operon encoding proteins mediating D-alanylation of TA are unknown. We demonstrate that Staphylococcus aureus transcriptionally represses dlt expression in response to high concentrations of Na(+) and moderate concentrations of Mg(2+) and Ca(2+) but not sucrose. Changes in dlt mRNA are induced within 15 min and sustained for several generations of growth. Mg(2+)-induced dlt repression depends on the ArlSR two-component system. Northern blotting, reverse transcription-PCR, and SMART-RACE analyses suggest that the dlt transcript begins 250 bp upstream of the dltA start codon and includes an open reading frame immediately upstream of dltA. Chloramphenicol transacetylase transcriptional fusions indicate that a region encompassing the 171 to 325 bp upstream of dltA is required for expression and Mg(2+)-induced repression of the dlt operon in S. aureus.

Staphylococci and implant surfaces: a review

Surfaces of internal fracture fixation implants are generally designed to encourage soft- and/or hard-tissue adherence, eventually leading to tissue or osseo integration. Unfortunately, this feature may also encourage bacterial adhesion. About half of the two million cases of nosocomial infections per year in the US are associated with indwelling devices. In the UK, implant-associated infections are estimated to cost pound 7-11 million per year, and with the rise in antibiotic-resistant bacteria, are an important issue. Soft-tissue infections and osteomyelitis are serious complications associated with implants, particularly open fractures, external fixation devices, and intramedullary nailing. Consequences of implant-associated infections include prolonged hospitalization with systemic antibiotic therapy, several revision procedures, possible amputation, and even death. This review discusses the issue of implant-associated infections and some of the methods used to prevent bacterial adhesion to osteosynthesis implants.

Effect of d-Alanylation of (Lipo)Teichoic Acids ofStaphylococcus aureuson Host Secretory Phospholipase A2Action before and after Phagocytosis by Human Neutrophils

Invading bacteria such as Staphylococcus aureus induce mobilization of professional phagocytes (e.g., neutrophils) and extracellular antibacterial proteins (e.g., group IIA phospholipase A2 (gIIA PLA2)). Accumulation of gIIA PLA2 in inflammatory fluids confers potent extracellular antistaphylococcal activity and at lower concentrations promotes bacterial phospholipid degradation during phagocytosis of S. aureus by human neutrophils. D-alanylation of (lipo) teichoic acids of S. aureus increases bacterial resistance to gIIA PLA2 approximately 100-fold, raising the possibility that the resistance of ingested S. aureus to related gV and gX secretory PLA2 present in human neutrophil granules depends on D-alanylation mediated by the dlt operon. However, we show that isogenic wild-type and dltA S. aureus are equally resistant to gV/X PLA2 during phagocytosis and when exposed to the purified enzymes. The fates of wild-type and dltA S. aureus exposed to serum and human neutrophils differed significantly only when extracellular gIIA PLA2 was also present before phagocytosis. The extreme potency of the gIIA PLA2 toward dltA S. aureus suggests that even small amounts of this extracellular enzyme mobilized early in inflammation could contribute substantially to the overall cytotoxicity of acute inflammatory exudates toward S. aureus when D-alanylation of (lipo)teichoic acids is limiting.

Commensal isolates of methicillin-resistant Staphylococcus epidermidis are also well equipped to produce biofilm on polystyrene surfaces

OBJECTIVES

To study biofilm production and to detect icaAD, atlE and aap genes in 137 isolates of methicillin-resistant Staphylococcus epidermidis (MRSE) obtained from healthy individuals from the community (35 isolates), from hospitalized patients at the Antônio Pedro University Hospital (25 isolates) and from individuals from a home-care system (HCS; 77 isolates).

METHODS

Biofilm production was determined in vitro using polystyrene inert surfaces. icaAD, atlE and aap genes were detected using PCR. Hybridization experiments were also carried out to confirm some PCR results. Antimicrobial susceptibility testing was carried out using the NCCLS methods.

RESULTS

Although many of the commensal MRSE isolates produced biofilms, the percentage of biofilm producers was significantly higher (P = 0.0107) among hospital isolates (76%) than among isolates from the community (60%) and from the HCS (57%). An association was observed between multiresistance and biofilm production for isolates obtained from healthy individuals from the community and from household contacts from the HCS (P < 0.0001). The concomitant presence of the ica operon and atlE and aap genes was associated with the strong biofilm-producer phenotype (P < 0.0001).

CONCLUSION

Because many of the commensal MRSE isolates obtained from nares produced biofilms and carried icaAD, aap and atlE genes, biofilms or such genetic elements should not be used as markers for clinical significance. The biofilm environment seems to increase genetic exchanges and hence may contribute to multiresistance phenotypes.

The genetics of staphylococcal biofilm formation--will a greater understanding of pathogenesis lead to better management of device-related infection?

Staphylococcus epidermidis and Staphylococcus aureus are common causes of biofilm-mediated prosthetic device-related infection. The polysaccharide adhesion mechanism encoded by the ica operon is currently the best understood mediator of biofilm development, and represents an important virulence determinant. More recently, the contributions of other virulence regulators, including the global regulators agr, sarA and sigmaB, to the biofilm phenotype have also been investigated. Nevertheless, little has changed at the bedside; the clinical and laboratory diagnosis of device-related infection can be difficult, and biofilm resistance frequently results in failure of therapy. This review assesses the way in which advances in the understanding of biofilm genetics may impact on the clinical management of device-related infection.

Influence of growth phase on bacterial deposition: interaction mechanisms in packed-bed column and radial stagnation point flow systems

The influence of bacterial growth stage on cell deposition kinetics has been examined using a mutant of Escherichia coli K12. Two experimental techniques--a packed-bed column and a radial stagnation point flow (RSPF) system--were employed to determine bacterial deposition rates onto quartz surfaces over a wide range of solution ionic strengths. Stationary-phase cells were found to be more adhesive than mid-exponential phase cells in both experimental systems. The divergence in deposition behavior was notably more pronounced in the RSPF than in the packed-bed system. For instance, in the RSPF system, the deposition rate of the stationary-phase cells at 0.03 M ionic strength was 14 times greater than that of the mid-exponential cells. The divergence in the packed-bed system was most significant at 0.01 M, where the deposition rate for the stationary-phase cells was nearly 4 times greater than for the mid-exponential cells. To explain the observed adhesion behavior, the stationary and mid-exponential bacterial cells were characterized for their size, surface charge density, electrophoretic mobility, viability, and hydrophobicity. On the basis of this analysis, it is suggested that the stationary cells have a more heterogeneous distribution of charged functional groups on the bacterial surface than the mid-exponential cells, which results in higher deposition kinetics. Furthermore, because the RSPF system enumerates only bacterial cells retained in primary minima, whereas the packed column captures mostly cells deposited in secondary minima, the difference in the stationary and mid-exponential cell deposition kinetics is much more pronounced in the RSPF system.

Staphylococcus aureus develops an alternative, ica-independent biofilm in the absence of the arlRS two-component system

The biofilm formation capacity of Staphylococcus aureus clinical isolates is considered an important virulence factor for the establishment of chronic infections. Environmental conditions affect the biofilm formation capacity of S. aureus, indicating the existence of positive and negative regulators of the process. The majority of the screening procedures for identifying genes involved in biofilm development have been focused on genes whose presence is essential for the process. In this report, we have used random transposon mutagenesis and systematic disruption of all S. aureus two-component systems to identify negative regulators of S. aureus biofilm development in a chemically defined medium (Hussain-Hastings-White modified medium [HHWm]). The results of both approaches coincided in that they identified arlRS as a repressor of biofilm development under both steady-state and flow conditions. The arlRS mutant exhibited an increased initial attachment as well as increased accumulation of poly-N-acetylglucosamine (PNAG). However, the biofilm formation of the arlRS mutant was not affected when the icaADBC operon was deleted, indicating that PNAG is not an essential compound of the biofilm matrix produced in HHWm. Disruption of the major autolysin gene, atl, did not produce any effect on the biofilm phenotype of an arlRS mutant. Epistatic experiments with global regulators involved in staphylococcal-biofilm formation indicated that sarA deletion abolished, whereas agr deletion reinforced, the biofilm development promoted by the arlRS mutation.

Inhibition of the D-alanine:D-alanyl carrier protein ligase from Bacillus subtilis increases the bacterium's susceptibility to antibiotics that target the cell wall

The surface charge as well as the electrochemical properties and ligand binding abilities of the Gram-positive cell wall is controlled by the D-alanylation of the lipoteichoic acid. The incorporation of D-Ala into lipoteichoic acid requires the D-alanine:D-alanyl carrier protein ligase (DltA) and the carrier protein (DltC). We have heterologously expressed, purified, and assayed the substrate selectivity of the recombinant proteins DltA with its substrate DltC. We found that apo-DltC is recognized by both endogenous 4'-phosphopantetheinyl transferases AcpS and Sfp. After the biochemical characterization of DltA and DltC, we designed an inhibitor (D-alanylacyl-sulfamoyl-adenosine), which is able to block the D-Ala adenylation by DltA at a K(i) value of 232 nM vitro. We also performed in vivo studies and determined a significant inhibition of growth for different Bacillus subtilis strains when the inhibitor is used in combination with vancomycin.

Extracellular carbohydrate-containing polymers of a model biofilm-producing strain, Staphylococcus epidermidis RP62A

Staphylococcus aureus and coagulase-negative staphylococci, primarily Staphylococcus epidermidis, are recognized as a major cause of nosocomial infections associated with the use of implanted medical devices. It has been established that clinical isolates often produce a biofilm, which is involved in adherence to biomaterials and provides enhanced resistance of bacteria against host defenses and antibiotic treatments. It has been thought that the staphylococcal biofilm contains two polysaccharides, one responsible for primary cell adherence to biomaterials (polysaccharide/adhesin [PS/A]) and an antigen that mediates bacterial aggregation (polysaccharide intercellular adhesin [PIA]). In the present paper we present an improved procedure for preparation of PIA that conserves its labile substituents and avoids contamination with by-products. Based on structural analysis of the polysaccharide antigens and a thorough overview of the previously published data, we concluded that PIA from S. epidermidis is structurally identical to the recently described poly-beta-(1-->6)-N-acetylglucosamine from PS/A-overproducing strain S. aureus MN8m. We also show that another carbohydrate-containing polymer, extracellular teichoic acid (EC TA), is an essential component of S. epidermidis RP62A biofilms. We demonstrate that the relative amounts of extracellular PIA and EC TA produced depend on the growth conditions. Moderate shaking or static culture in tryptic soy broth favors PIA production, while more EC TA is produced in brain heart infusion medium.

Clp ATPases are required for stress tolerance, intracellular replication and biofilm formation in Staphylococcus aureus

The Hsp100/Clp ATPases constitute a family of closely related proteins of which some members function solely as chaperones whereas others additionally can associate with the unrelated ClpP peptidase forming a Clp proteolytic complex. We have investigated the role of four Clp ATPases in the versatile pathogen, Staphylococcus aureus. Previously, we showed that ClpX is required for expression of major virulence factors and for virulence of S. aureus, but not for survival during heat shock. In the present study, we have inactivated clpC, clpB and clpL and, while none of these mutations affected toxin production, both ClpC and ClpB and to a minor extent ClpL were required for intracellular multiplication within bovine mammary epithelial cells. These defects were paralleled by an inability of the clpC mutant to grow at high temperature and of the clpB mutant to induce thermotolerance indicating that the protective functions of these proteins are required both at high temperature and during infection. By primer extension analysis and footprint studies, we show that expression of clpC and clpB is controlled by the negative heat-shock regulator, CtsR, and that ClpC is required for its repressor activity. Thus, ClpC is a likely sensor of stress encountered during both environmental stress and infection. In addition to virulence factor production the ability to form biofilms is of importance to S. aureus as a nosocomial pathogen. Interestingly, biofilm formation was reduced in the absence of ClpX or ClpC whereas it was enhanced in the absence of ClpP. Thus, our data show that Clp proteolytic complexes and the Clp ATPases control several key processes of importance to the success of S. aureus as a pathogen.

Bacterial evasion of innate host defenses--the Staphylococcus aureus lesson

Bacterial pathogens such as Staphylococcus aureus use highly efficient mechanisms to evade recognition and elimination by the innate immune system. S. aureus produces sophisticated anti-inflammatory molecules and it employs several mechanisms protecting the bacteria against host cationic antimicrobial molecules such as defensin-like peptides and bacteriolytic enzymes such as lysozyme. Cell wall teichoic acids and lipoteichoic acids, complex Gram-positive surface polymers, and modified membrane lipids such as lysylphosphatidylglycerol are crucial in defensin resistance and other important aspects of staphylococcal virulence such as nasal colonization and biofilm formation on biomaterials. Certain S. aureus genes conferring escape from innate host defenses are conserved in many human pathogens suggesting that the underlying mechanisms are of general significance in bacterial virulence.

Quantitative analysis of adhesion and biofilm formation on hydrophilic and hydrophobic surfaces of clinical isolates of Staphylococcus epidermidis

Staphylococcus epidermidis is now well established as a major nosocomial pathogen associated with infections of indwelling medical devices. The major virulence factor of these organisms is their ability to adhere to devices and form biofilms. However, it has not been established that adherence and biofilm formation are closely linked phenotypes for clinical isolates. In this study, the initial adhesion to different materials (acrylic and glass) of 9 clinical isolates of S. epidermidis, along with biofilm-positive and biofilm-negative control strains, was assayed using physico-chemical interactions to analyze the basis for bacterial adherence to the substratum. X-ray photo electron spectroscopy (XPS) analysis of the cell surface elemental composition was also performed in an attempt to find a relationship between chemical composition and adhesion capabilities. Biofilm formation on the two surfaces was evaluated by dry weight measurements. Human erythrocytes were used to evaluate the ability of S. epidermidis strains to cause hemagglutination, an indicator of the production of a poly-N-acetyl glucosamine cell surface polysaccharide also involved in biofilm formation. The clinical isolates exhibited different cell wall physico-chemical properties, resulting in differing abilities to adhere to surfaces. Adhesion to hydrophobic substrata for all strains occurred to a greater extent than that to hydrophilic surfaces. Bacterial cell hydrophobicity seemed to have little or no influence on adhesion. X-ray photoelectron spectroscopy analysis showed a high ratio of oxygen/carbon for all strains, which is a common characteristic of S. epidermidis species. No relevant relationship was found between XPS data and adhesion values. All strains forming biofilms were able to agglutinate erythrocytes. However, no direct relationship was found between the amount of biofilm formed and the initial adhesion extent. These results indicate that high levels of initial adherence do not necessarily lead to thick biofilm formation. These two aspects of the pathogenesis of medical device related-infection may need to be evaluated independently to ascertain the contribution of each to the virulence of S. epidermidis causing device-related infections.

In vitro activity of vancomycin, quinupristin/dalfopristin, and linezolid against intact and disrupted biofilms of staphylococci

Shed cells or disrupted parts of the biofilm may enter the circulation causing serious and very hard to treat biofilm-associated infections. The activity of antimicrobial agents against the shed cells/disrupted biofilms is largely unknown.

Structural elucidation of the extracellular and cell-wall teichoic acids of Staphylococcus epidermidis RP62A, a reference biofilm-positive strain

The ability to adhere to artificial surfaces and form biofilms is considered as a virulence factor of Staphylococcus epidermidis, one of the major causes of nocosomial infections, especially those related to implanted medical devices. Cell-wall teichoic acid is known to play an important role in biofilm formation of staphylococci. The structure of the cell wall and extracellular teichoic acids of S. epidermidis RP62A, a reference biofilm-positive strain, was studied by NMR spectroscopy and capillary electrophoresis-mass spectrometry. Their structures were found to be a (1-->3)-linked poly(glycerol phosphate), substituted at the 2-position of glycerol residues with alpha-Glc, alpha-GlcNAc, D-Ala and alpha-Glc6Ala. D-Alanyl acylation of a sugar hydroxyl group seems to be a novel structural feature of teichoic acids from staphylococci.

Heterogeneous Binding of Lipoteichoic Acid to the Surface of Titanium Dioxide as Determined with31P Solid-State NMR Spectroscopy

The adsorption of lipoteichoic acid onto the surface of titanium dioxide is shown to be heterogeneous. 31P CPMAS solid-state NMR reveals two distinct phosphate species. The chemical shift anisotropy, asymmetry parameter, and rotating-frame spin-lattice relaxation suggest that 50% of the phosphates are bound to the surface. The remaining phosphates also exhibit restricted molecular motion, but do not have a direct surface bond.

Comparative evaluation of coagulase-negative staphylococci (CoNS) adherence to acrylic by a static method and a parallel-plate flow dynamic method

The main goal of this work was to evaluate the adhesion to acrylic of several clinical strains of Staphylococcus epidermidis and Staphylococcus haemolyticus using both static and dynamic adhesion methods, and to compare the results obtained with these two methods. Adhesion was evaluated using the static slide method with different washing procedures, and the parallel plate flow chamber method. The extent of S. epidermidis adhesion, assessed by both methods, was greater than that of S. haemolyticus. The number of bacteria which adhered using the static method was lower than that using the dynamic method. It was found that the simple static method, when performed with an accurate washing procedure, can be as effective as the dynamic flow method for assessing differences in the adherence capacity of strains. Although the dynamic flow method yielded more overall information, its greater complexity and cost may not always justify its use for certain experimental comparisons. This investigation has shown that simple static adhesion methods, when performed accurately, can be used to evaluate differences in adhesion capacity.

Effect of subinhibitory concentration of piperacillin/tazobactam on Pseudomonas aeruginosa

Subinhibitory concentrations (sub-MICs) of antibiotics, although not able to kill bacteria, can modify their physico-chemical characteristics and the architecture of their outermost surface and may interfere with some bacterial functions. This study investigated the ability of sub-MIC piperacillin/tazobactam (P/T) to interfere with the bacterial virulence parameters of adhesiveness, cell-surface hydrophobicity, motility, biofilm formation and sensitivity to oxidative stress. Antimicrobial activity against five Pseudomonas aeruginosa clinical isolates, representative of clonal lineages of 96 strains of nosocomial origin, and six control strains (ATCC 27853, PAO1, AK1, MT1562, PT623, PAO1algC) was evaluated in vitro using the NCCLS microdilution method. The effects of sub-MIC on bacterial adhesion and biofilm formation were studied using a modified microtitre plate assay. The relative cell-surface hydrophobicity of P. aeruginosa strains was determined by measuring their ability to adhere to n-hexadecane. P. aeruginosa that had been exposed overnight to P/T and incubated with P/T in the plate were also screened for their ability to swim using flagella and to twitch and for their sensitivity to oxidative stress. The results obtained showed that the impact of sub-MIC P/T on bacterial characteristics was different for the various strains of P. aeruginosa. There was a change in bacterial morphology and hydrophobicity that could explain a significant decrease in adhesion values in all clinical isolates and controls tested, a decrease in biofilm formation, a significant increase in sensitivity to oxidative stress, a significant decrease in flagellum-mediated swimming and a decrease in type IV fimbriae-mediated twitching. The results obtained indicate that sub-MIC P/T interferes with the pathogenic potential of P. aeruginosa.

Identification of AbrB-regulated genes involved in biofilm formation by Bacillus subtilis

Bacillus subtilis is a ubiquitous soil bacterium that forms biofilms in a process that is negatively controlled by the transcription factor AbrB. To identify the AbrB-regulated genes required for biofilm formation by B. subtilis, genome-wide expression profiling studies of biofilms formed by spo0A abrB and sigH abrB mutant strains were performed. These data, in concert with previously published DNA microarray analysis of spo0A and sigH mutant strains, led to the identification of 39 operons that appear to be repressed by AbrB. Eight of these operons had previously been shown to be repressed by AbrB, and we confirmed AbrB repression for a further six operons by reverse transcription-PCR. The AbrB-repressed genes identified in this study are involved in processes known to be regulated by AbrB, such as extracellular degradative enzyme production and amino acid metabolism, and processes not previously known to be regulated by AbrB, such as membrane bioenergetics and cell wall functions. To determine whether any of these AbrB-regulated genes had a role in biofilm formation, we tested 23 mutants, each with a disruption in a different AbrB-regulated operon, for the ability to form biofilms. Two mutants had a greater than twofold defect in biofilm formation. A yoaW mutant exhibited a biofilm structure with reduced depth, and a sipW mutant exhibited only surface-attached cells and did not form a mature biofilm. YoaW is a putative secreted protein, and SipW is a signal peptidase. This is the first evidence that secreted proteins have a role in biofilm formation by Bacillus subtilis.

Lysostaphin disrupts Staphylococcus aureus and Staphylococcus epidermidis biofilms on artificial surfaces

Staphylococci often form biofilms, sessile communities of microcolonies encased in an extracellular matrix that adhere to biomedical implants or damaged tissue. Infections associated with biofilms are difficult to treat, and it is estimated that sessile bacteria in biofilms are 1,000 to 1,500 times more resistant to antibiotics than their planktonic counterparts. This antibiotic resistance of biofilms often leads to the failure of conventional antibiotic therapy and necessitates the removal of infected devices. Lysostaphin is a glycylglycine endopeptidase which specifically cleaves the pentaglycine cross bridges found in the staphylococcal peptidoglycan. Lysostaphin kills Staphylococcus aureus within minutes (MIC at which 90% of the strains are inhibited [MIC(90)], 0.001 to 0.064 microg/ml) and is also effective against Staphylococcus epidermidis at higher concentrations (MIC(90), 12.5 to 64 microg/ml). The activity of lysostaphin against staphylococci present in biofilms compared to those of other antibiotics was, however, never explored. Surprisingly, lysostaphin not only killed S. aureus in biofilms but also disrupted the extracellular matrix of S. aureus biofilms in vitro on plastic and glass surfaces at concentrations as low as 1 microg/ml. Scanning electron microscopy confirmed that lysostaphin eradicated both the sessile cells and the extracellular matrix of the biofilm. This disruption of S. aureus biofilms was specific for lysostaphin-sensitive S. aureus, as biofilms of lysostaphin-resistant S. aureus were not affected. High concentrations of oxacillin (400 microg/ml), vancomycin (800 microg/ml), and clindamycin (800 microg/ml) had no effect on the established S. aureus biofilms in this system, even after 24 h. Higher concentrations of lysostaphin also disrupted S. epidermidis biofilms.

The ability of biofilm formation does not influence virulence of Staphylococcus aureus and host response in a mouse tissue cage infection model

The virulence of Staphylococcus aureus Sa113 (SA113) and an isogenic ica deletion mutant (ica-), deficient in the production of polysaccharide intercellular adhesin (PIA), which is crucial for biofilm formation, was compared in a mouse tissue cage infection model. The minimal infective doses for the induction of persistent tissue infections in C57BL/6 mice were 10(3) CFU for both SA113 and the ica- mutant. Bacterial growth, initial adherence to surfaces within the implants and the course of inflammation including growth-dependent host TNF and MIP-2 release, influx of phagocytes and an accumulation of dead leukocytes were similar as well. Since SA113 expressed PIA in vivo, we could demonstrate that PIA and the lack of biofilm formation did not influence the capacity of S. aureus to induce persistent infections and did not modulate host responses in the mouse tissue cage model.

Influence of origin of isolates, especially endocarditis isolates, and various genes on biofilm formation by Enterococcus faecalis

Endocarditis isolates of Enterococcus faecalis produced biofilm significantly more often than nonendocarditis isolates, and 39% of 79 versus 6% of 84 isolates produced strong biofilm (P < 0.0001). esp was not required, but its presence was associated with higher amounts of biofilm (P < 0.001). Mutants disrupted in dltA, efaA, ace, lsa, and six two-component regulatory systems were largely unaltered, while disruptions in epa (encoding enterococcal polysaccharide antigen), atn (encoding an autolysin), gelE (encoding gelatinase), and fsr (encoding the E. faecalis regulator) [corrected] resulted in fewer attached bacteria, as determined using phase-contrast microscopy, and less biofilm (P < 0.0001).