Antibiofilm activity of Actinobacillus pleuropneumoniae serotype 5 capsular polysaccharide

Micrococcal nuclease regulates biofilm formation and dispersal in methicillin-resistant Staphylococcus aureus USA300

Biofilm formation is an important virulence factor for methicillin-resistant Staphylococcus aureus (MRSA). The extracellular matrix of MRSA biofilms contains significant amounts of double-stranded DNA that hold the biofilm together. MRSA cells secrete micrococcal nuclease (Nuc1), which degrades double-stranded DNA. In this study, we used standard methodologies to investigate the role of Nuc1 in MRSA biofilm formation and dispersal. We quantified biofilm formation and extracellular DNA (eDNA) levels in broth and agar cultures. In some experiments, cultures were supplemented with sub-MIC amoxicillin to induce biofilm formation. Biofilm erosion was quantitated by culturing biofilms on rods and enumerating detached colony-forming units (CFUs), and biofilm sloughing was investigated by perfusing biofilms cultured in glass tubes with fresh broth and measuring the sizes of the detached cell aggregates. We found that an MRSA nuc1- mutant strain produced significantly more biofilm and more eDNA than a wild-type strain, both in the absence and presence of sub-MIC amoxicillin. nuc1- mutant biofilms grown on rods detached significantly less than wild-type biofilms. Detachment was restored by exogenous DNase or complementing the nuc1- mutant. In the sloughing assay, nuc1- mutant biofilms released cell aggregates that were significantly larger than those released by wild-type biofilms. Our results suggest that Nuc1 modulates biofilm formation, biofilm detachment, and the sizes of detached cell aggregates. These processes may play a role in the spread and subsequent survival of MRSA biofilms during biofilm-related infections.IMPORTANCEInfections caused by antibiotic-resistant bacteria known as methicillin-resistant Staphylococcus aureus (MRSA) are a significant problem in hospitals. MRSA forms adherent biofilms on implanted medical devices such as catheters and breathing tubes. Bacteria can detach from biofilms on these devices and spread to other parts of the body such as the blood or lungs, where they can cause life-threatening infections. In this article, researchers show that MRSA secretes an enzyme known as thermonuclease that causes bacteria to detach from the biofilm. This is important because understanding the mechanism by which MRSA detaches from biofilms could lead to the development of procedures to mitigate the problem.

Micrococcal nuclease regulates biofilm formation and dispersal in methicillin-resistant Staphylococcus aureus USA300

Biofilm formation is an important virulence factor for methicillin-resistant Staphylococcus aureus (MRSA). The extracellular matrix of MRSA biofilms contains significant amounts of double-stranded DNA. MRSA cells also secrete micrococcal nuclease (Nuc1) which degrades double-stranded DNA. In this study we used a nuc1 mutant strain to investigate the role of Nuc1 in MRSA biofilm formation and dispersal. Biofilm was quantitated in microplates using a crystal violet binding assay. Extracellular DNA (eDNA) was isolated from colony biofilms and analyzed by agarose gel electrophoresis. In some experiments, broth or agar was supplemented with sub-MIC amoxicillin to induce biofilm formation. Biofilm erosion was quantitated by culturing biofilms on rods, transferring the rods to fresh broth, and enumerating CFUs that detached from the rods. Biofilm sloughing was investigated by culturing biofilms in glass tubes perfused with broth and measuring the sizes of the detached cell aggregates. We found that a nuc1 mutant strain produced significantly more biofilm and more eDNA than a wild-type strain in both the absence and presence of sub-MIC amoxicillin, nuc1 mutant biofilms grown on rods detached significantly less than wild-type biofilms. Detachment was restored by exogenous DNase or a wild-type nuc1 gene on a plasmid. In the sloughing assay, nuc1 mutant biofilms released cell aggregates that were significantly larger than those released by wild-type biofilms. Our results suggest that Nuc1 modulates biofilm formation, biofilm detachment, and the sizes of detached cell aggregates. These processes may play a role in the spread and subsequent survival of MRSA biofilms during biofilm-related infections.

Anti-Bacterial Adhesion on Abiotic and Biotic Surfaces of the Exopolysaccharide from the Marine Bacillus licheniformis B3-15

The eradication of bacterial biofilm represents a crucial strategy to prevent a clinical problem associated with microbial persistent infection. In this study we evaluated the ability of the exopolysaccharide (EPS) B3-15, produced by the marine Bacillus licheniformis B3-15, to prevent the adhesion and biofilm formation of Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 29213 on polystyrene and polyvinyl chloride surfaces. The EPS was added at different times (0, 2, 4 and 8 h), corresponding to the initial, reversible and irreversible attachment, and after the biofilm development (24 or 48 h). The EPS (300 µg/mL) impaired the initial phase, preventing bacterial adhesion even when added after 2 h of incubation, but had no effects on mature biofilms. Without exerting any antibiotic activity, the antibiofilm mechanisms of the EPS were related to the modification of the (i) abiotic surface properties, (ii) cell-surface charges and hydrophobicity, and iii) cell-to-cell aggregation. The addition of EPS downregulated the expression of genes (lecA and pslA of P. aeruginosa and clfA of S. aureus) involved in the bacterial adhesion. Moreover, the EPS reduced the adhesion of P. aeruginosa (five logs-scale) and S. aureus (one log) on human nasal epithelial cells. The EPS could represent a promising tool for the prevention of biofilm-related infections.

Antibiofilm activity from endophyte bacteria, Vibrio cholerae strains, and actinomycetes isolates in liquid and solid culture

Background

Biofilm-associated infections are a global threat to our economy and human health; as such, development of antibiofilm compounds is an urgent need. Our previous study identified eleven environmental isolates of endophyte bacteria, actinomycetes, and two strains of Vibrio cholerae as having strong antibiofilm activity, but only tested crude extracts from liquid culture. Here we grew the same bacteria in solid culture to induce the formation of colony biofilms and the expression of genes that may ultimately produce antibiofilm compounds. This research aimed to compare antibiofilm inhibition and destruction activities between liquid and solid cultures of these eleven environmental isolates against the biofilms of representative pathogenic bacteria.

Results

We measured antibiofilm activity using the static antibiofilm assay and crystal violet staining. The majority of our isolates exhibited higher inhibitory antibiofilm activity in liquid media, including all endophyte bacteria, V. cholerae V15a, and actinomycetes strains (CW01, SW03, CW17). However, for V. cholerae strain B32 and two actinomycetes bacteria (TB12 and SW12), the solid crude extracts showed higher inhibitory activity. Regarding destructive antibiofilm activity, many endophyte isolates and V. cholerae strains showed no significant difference between culture methods; the exceptions were endophyte bacteria isolate JerF4 and V. cholerae B32. The liquid extract of isolate JerF4 showed higher destructive activity relative to the corresponding solid culture extract, while for V. cholerae strain B32 the solid extract showed higher activity against some biofilms of pathogenic bacteria.

Conclusions

Culture conditions, namely solid or liquid culture, can influence the activity of culture extracts against biofilms of pathogenic bacteria. We compared the antibiofilm activity and presented the data that majority of isolates showed a higher antibiofilm activity in liquid culture. Interestingly, solid extracts from three isolates (B32, TB12, and SW12) have a better inhibition or/and destruction antibiofilm activity compared to their liquid culture. Further research is needed to characterize the activities of specific metabolites in solid and liquid culture extracts and to determine the mechanisms of their antibiofilm actions.

Biosynthesis of Silver Nanoparticles Using the Biofilm Supernatant of Pseudomonas aeruginosa PA75 and Evaluation of Their Antibacterial, Antibiofilm, and Antitumor Activities

Purpose

As an under-explored biomaterial, bacterial biofilms have a wide range of applications in the green synthesis of nanomaterials. The biofilm supernatant of Pseudomonas aeruginosa PA75 was used to synthesize novel silver nanoparticles (AgNPs). BF75-AgNPs were found to possess several biological properties.

Methods

In this study, we biosynthesized BF75-AgNPs using biofilm supernatant as the reducing agent, stabilizer, and dispersant and investigated their biopotential in terms of antibacterial, antibiofilm, and antitumor activities.

Results

The synthesized BF75-AgNPs demonstrated a typical face-centered cubic crystal structure; they were well dispersed; and they were spherical with a size of 13.899 ± 4.036 nm. The average zeta potential of the BF75-AgNPs was -31.0 ± 8.1 mV. The BF75-AgNPs exhibited strong antibacterial activities against the methicillin-resistant Staphylococcus aureus (MRSA), extended-spectrum beta-lactamase Escherichia coli (ESBL-EC), extensively drug-resistant Klebsiella pneumoniae (XDR-KP), and carbapenem-resistant Pseudomonas aeruginosa (CR-PA). Moreover, the BF75-AgNPs had a strong bactericidal effect on XDR-KP at 1/2 × MIC, and the expression level of reactive oxygen species (ROS) in bacteria was significantly increased. A synergistic effect was observed when the BF75-AgNPs and colistin were used for the co-treatment of two colistin-resistant XDR-KP strains, with fractional inhibitory concentration index (FICI) values of 0.281 and 0.187, respectively. Furthermore, the BF75-AgNPs demonstrated a strong biofilm inhibition activity and mature biofilm bactericidal activity against XDR-KP. The BF75-AgNPs also exhibited a strong antitumor activity against melanoma cells and low cytotoxicity against normal epidermal cells. In addition, the BF75-AgNPs increased the proportion of apoptotic cells in two melanoma cell lines, and the proportion of late apoptotic cells increased with BF75-AgNP concentration.

Conclusion

This study suggests that BF75-AgNPs synthesized from biofilm supernatant have broad prospects for antibacterial, antibiofilm, and antitumor applications.

Conventional vs. Innovative Protocols for the Extraction of Polysaccharides from Macroalgae

Macroalgae are one of the most environmentally friendly resources, and their industrial by-products should also be sustainable. Algal polysaccharides represent valuable products, and the definition of new eco-sustainable extraction processes, ensuring a safe and high-quality product, is a new goal in the context of reducing the carbon footprint. The aim of the present work was to determine the influence of the extraction methodology on the properties and structure of the polysaccharides, comparing conventional and innovative microwave-assisted methods. We focused on extraction times, yield, chemical composition and, finally, biological activities of raw polymers from three macroalgal species of Chlorophyta, Rhodophyta and Phaeophyceae. The main objective was to design a sustainable process in terms of energy and time savings, with the aim of developing subsequent application at the industrial level. Extraction efficacy was likely dependent on the physico-chemical polysaccharide properties, while the use of the microwave did not affect their chemical structure. Obtained results indicate that the innovative method could be used as an alternative to the conventional one to achieve emulsifiers and bacterial antiadhesives for several applications. Natural populations of invasive algae were used rather than cultivated species in order to propose the valorization of unwanted biomasses, which are commonly treated as waste, converting them into a prized resource.

Probing Antimicrobial Halloysite/Biopolymer Composites with Electron Microscopy: Advantages and Limitations

Halloysite is a tubular clay nanomaterial of the kaolin group with a characteristic feature of oppositely charged outer and inner surfaces, allowing its selective spatial modification. The natural origin and specific properties of halloysite make it a potent material for inclusion in biopolymer composites with polysaccharides, nucleic acids and proteins. The applications of halloysite/biopolymer composites range from drug delivery and tissue engineering to food packaging and the creation of stable enzyme-based catalysts. Another important application field for the halloysite complexes with biopolymers is surface coatings resistant to formation of microbial biofilms (elaborated communities of various microorganisms attached to biotic or abiotic surfaces and embedded in an extracellular polymeric matrix). Within biofilms, the microorganisms are protected from the action of antibiotics, engendering the problem of hard-to-treat recurrent infectious diseases. The clay/biopolymer composites can be characterized by a number of methods, including dynamic light scattering, thermo gravimetric analysis, Fourier-transform infrared spectroscopy as well as a range of microscopic techniques. However, most of the above methods provide general information about a bulk sample. In contrast, the combination of electron microscopy with energy-dispersive X-ray spectroscopy allows assessment of the appearance and composition of biopolymeric coatings on individual nanotubes or the distribution of the nanotubes in biopolymeric matrices. In this review, recent contributions of electron microscopy to the studies of halloysite/biopolymer composites are reviewed along with the challenges and perspectives in the field.

Antibiofilm Activity of Antarctic Sponge-Associated Bacteria against Pseudomonas aeruginosa and Staphylococcus aureus

Bioprospecting in unusual marine environments provides an innovative approach to search novel biomolecules with antibiofilm activity. Antarctic sponge-associated bacteria belonging to Colwellia, Pseudoalteromonas, Shewanella and Winogradskyella genera were evaluated for their ability to contrast the biofilm formation by Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 29213, as model organisms. All strains were able to produce biofilm at both 4 and 25 °C, with the highest production being for Colwellia, Shewanella and Winogradskyella strains at 4 °C after 24 h. Antibiofilm activity of cell-free supernatants (CFSs) differed among strains and on the basis of their incubation temperature (CFSs4°C and CFSs25°C). The major activity was observed by CFSs4°C against S. aureus and CFSs25°C against P. aeruginosa, without demonstrating a bactericidal effect on their growth. Furthermore, the antibiofilm activity of crude extracts from Colwellia sp. GW185, Shewanella sp. CAL606, and Winogradskyella sp. CAL396 was also evaluated and visualized by confocal laser scanning microscopic images. Results based on the surface-coating assay and surface tension measurements suggest that CFSs and the crude extracts may act as biosurfactants inhibiting the first adhesion of P. aeruginosa and S. aureus. The CFSs and the novel biopolymers may be useful in applicative perspectives for pharmaceutical and environmental purposes.

Synergistic antimicrobial combination of carvacrol and thymol impairs single and mixed-species biofilms of Candida albicans and Staphylococcus epidermidis

Candida albicans and Staphylococcus epidermidis are important opportunistic human pathogens, which form mixed-species biofilms and cause recalcitrant device associated infections in clinical settings. Further to many reports suggesting the therapeutic potential of plant-derived monoterpenoids, this study investigated the interaction of the monoterpenoids carvacrol (C) and thymol (T) against mono- and mixed-species growth of C. albicans and S. epidermidis. C and T exhibited synergistic antimicrobial activity. The time-kill study and post-antimicrobial effect results revealed the effective microbicidal action of the C + T combination. Filamentation, surface coating assays and live-dead staining of biofilms determined the anti-hyphal, antiadhesion, and anti-biofilm activities of the C + T combination, respectively. Notably, this combination killed highly tolerant persister cells of mono-species and mixed-species biofilms and demonstrated less risk of resistance development. The collective data suggest that the C + T combination could act as an effective therapeutic agent against biofilm associated mono-species and mixed-species infections of C. albicans and S. epidermidis.

Antibiofilm activity of symbiotic Bacillus species associated with marine gastropods

Purpose

Generally, symbiotic marine bacteria are renowned for the synthesis of compounds with bioactive properties, and this has been documented in many previous studies. Therefore, the present study was aimed to isolate novel bacterial symbionts of gastropods that have the ability to synthesize bioactive compounds. These bioactive compounds could be used effectively as antibiofilm agents in order to overcome the problems associated with biofilm.

Methods

The bacteria associated with the surface of marine gastropods were isolated and characterized. Following this, the bacterial metabolites were extracted and their antibiofilm effect was evaluated on biofilm-forming bacteria on artificial substrates. Moreover, the biofilm-forming bacterium Alteromonas sp. was treated with the extracts of symbiotic bacteria in order to evaluate the influence of extracts over the synthesis of extracellular polymeric substance (EPS). Besides, the biologically active chemical constituents of the extracts were separated using thin-layer chromatography and subjected to gas chromatography and mass spectrometry (GC-MS) analysis for characterization.

Results

Three bacterial strains belonging to the species Bacillus firmus, Bacillus cereus and Bacillus subtilis were identified from the bacterial community associated with the gastropods. The antibiofilm assays revealed that the extract of three symbiotic bacteria significantly (p < 0.05) reduced the biofilm formation by the marine bacterium Alteromonas sp. on artificial materials. Also, the EPS synthesis by Alteromonas sp. was significantly inhibited due to symbiotic bacterial extract treatment. The chemical composition of the bioactive fraction isolated from the symbiotic bacteria extract revealed that most of the detected compounds were belonging to aromatic acid, fatty acid and carboxylic acid.

Conclusion

The results of this study clearly revealed that the bacteria belonging to the above listed Bacillus species can be considered as a promising source of natural antibiofilm agents.

Polysaccharide Galactan Inhibits Pseudomonas aeruginosa Biofilm Formation but Protects Pre-formed Biofilms from Antibiotics

Microorganisms residing within a biofilm become more tolerant to antibiotics and other types of adverse impact, and biofilm formation by pathogenic bacteria is an important problem of current medicine. Polysaccharides that prevent biofilm formation are among the promising candidates to help tackle this problem. Earlier we demonstrated the ability of a potato polysaccharide galactan to inhibit biofilm formation by a Pseudomonas aeruginosa clinical isolate. Here we investigate the effect of potato galactan on P. aeruginosa biofilms in more detail. Microscopic analysis indicated that the galactan did not interfere with the adhesion of bacterial cells to the substrate but prevented the build-up of bacterial biomass. Moreover, the galactan not only inhibited biofilm formation, but partially destroyed pre-formed biofilms. Presumably, this activity of the galactan was due to the excessive aggregation of bacterial cells, which prohibited the formation and maintenance of proper biofilm architecture, or due to some other mechanisms of biofilm structure remodeling. This led to an unexpected effect, i.e., P. aeruginosa biofilms treated with an antibiotic and the galactan retained more viable bacterial cells compared to biofilms treated with the antibiotic alone. Galactan is the first polysaccharide demonstrated to exert such effect on bacterial biofilms.

Mucins trigger dispersal of Pseudomonas aeruginosa biofilms

Mucus is a biological gel that lines all wet epithelia in the body, including the mouth, lungs, and digestive tract, and has evolved to protect the body from pathogenic infection. However, microbial pathogenesis is often studied in mucus-free environments that lack the geometric constraints and microbial interactions in physiological three-dimensional mucus gels. We developed fluid-flow and static test systems based on purified mucin polymers, the major gel-forming constituents of the mucus barrier, to understand how the mucus barrier influences bacterial virulence, particularly the integrity of Pseudomonas aeruginosa biofilms, which can become resistant to immune clearance and antimicrobial agents. We found that mucins separate the cells in P. aeruginosa biofilms and disperse them into suspension. Other viscous polymer solutions did not match the biofilm disruption caused by mucins, suggesting that mucin-specific properties mediate the phenomenon. Cellular dispersion depended on functional flagella, indicating a role for swimming motility. Taken together, our observations support a model in which host mucins are key players in the regulation of microbial virulence. These mucins should be considered in studies of mucosal pathogenesis and during the development of novel strategies to treat biofilms.

Biofilms are an important survival strategy for pathogenic bacteria including Pseudomonas aeruginosa and whilst mucins play a role the regulation of microbial virulence, microbial pathogenesis on mucosal tissues is often studied in mucin-free contexts. Here, Katharina Ribbeck and colleagues at the Massachusetts Institute of Technology used native purified mucin polymers and examined their effects on the integrity of Pseudomonas aeruginosa biofilms. The mucins dissolved the biofilms by separating the bacteria, which was not observed in other viscous alternative substances examined, but this did rely on functional bacterial motility. Here the authors provide evidence that mucins are involved in suppressing bacterial virulence and should be included in systems used to assess bacterial pathogenesis on mucosal tissues.

Commensal coagulase-negative Staphylococcus from the udder of healthy cows inhibits biofilm formation of mastitis-related pathogens

Bovine mastitis, considered the most important cause of economic losses in the dairy industry, is a major concern in veterinary medicine. Staphylococcus aureus and coagulase-negative staphylococci (CNS) are the main pathogens associated with intramammary infections, and bacterial biofilms are suspected to be responsible for the persistence of this disease. CNS from the udder are not necessarily associated with intramammary infections. In fact, some commensal CNS have been shown to have biological activities. This issue led us to screen exoproducts from commensal Staphylococcus chromogenes for anti-biofilm activity against different mastitis pathogens. The cell-free supernatant from S. chromogenes LN1 (LN1-CFS) was confirmed to display a non-biocidal inhibition of pathogenic biofilms. The supernatant was subjected to various treatments to estimate the nature of the biofilm-inhibiting compounds. The results showed that the bioactive compound >5KDa in mass is sensitive to thermal treatment and proteinase K digestion, suggesting its protein properties. LN1-CFS was able to significantly inhibit S. aureus and CNS biofilm formation in a dose-independent manner and without affecting the viability of bovine cells. These findings reveal a new activity of the udder microflora of healthy animals. Studies are underway to purify and identify the anti-biofilm biocompound and to evaluate its biological activity in vivo.

Endophytic Nocardiopsis sp. from Zingiber officinale with both antiphytopathogenic mechanisms and antibiofilm activity against clinical isolates

Novel and potential antimicrobial compounds are essential to tackle the frequently emerging multidrug-resistant pathogens and also to develop environment friendly agricultural practices. In the current study, endophytic actinomycetes from rhizome of Zingiber officinale were explored in terms of its diversity and bioactive properties. Fourteen different organisms were isolated, identified and screened for activity against Pythium myriotylum and human clinical pathogens. Among these, Nocardiopsis sp. ZoA1 was found to have highest inhibition with excellent antibacterial effects compared to standard antibiotics. Remarkable antibiofilm property was also shown by the extract of ZoA1. Its antifungal activity against Pythium and other common phytopathogens was also found to be promising as confirmed by scanning electron microscopic analysis. By PCR-based sequence analysis of phz E gene, the organism was confirmed for the genetic basis of phenazine biosynthesis. Further GC-MS analysis of Nocardiopsis sp. revealed the presence of various compounds including Phenol, 2,4-bis (1,1-dimethylethyl) and trans cinnamic acid which can have significant role in the observed result. The current study is the first report on endophytic Nocardiopsis sp. from ginger with promising applications. In vivo treatment of Nocardiopsis sp. on ginger rhizome has revealed its inhibition towards the colonization of P. myriotylum which makes the study to have promises to manage the severe diseases in ginger like rhizome rot.

Anti-biofilm Activity as a Health Issue

The formation and persistence of surface-attached microbial communities, known as biofilms, are responsible for 75% of human microbial infections (National Institutes of Health). Biofilm lifestyle confers several advantages to the pathogens, notably during the colonization process of medical devices and/or patients’ organs. In addition, sessile bacteria have a high tolerance to exogenous stress including anti-infectious agents. Biofilms are highly competitive communities and some microorganisms exhibit anti-biofilm capacities such as bacterial growth inhibition, exclusion or competition, which enable them to acquire advantages and become dominant. The deciphering and control of anti-biofilm properties represent future challenges in human infection control. The aim of this review is to compare and discuss the mechanisms of natural bacterial anti-biofilm strategies/mechanisms recently identified in pathogenic, commensal and probiotic bacteria and the main synthetic strategies used in clinical practice, particularly for catheter-related infections.

Effects of Low-Dose Amoxicillin on Staphylococcus aureus USA300 Biofilms

Previous studies showed that sub-MIC levels of β-lactam antibiotics stimulate biofilm formation in most methicillin-resistant Staphylococcus aureus (MRSA) strains. Here, we investigated this process by measuring the effects of sub-MIC amoxicillin on biofilm formation by the epidemic community-associated MRSA strain USA300. We found that sub-MIC amoxicillin increased the ability of USA300 cells to attach to surfaces and form biofilms under both static and flow conditions. We also found that USA300 biofilms cultured in sub-MIC amoxicillin were thicker, contained more pillar and channel structures, and were less porous than biofilms cultured without antibiotic. Biofilm formation in sub-MIC amoxicillin correlated with the production of extracellular DNA (eDNA). However, eDNA released by amoxicillin-induced cell lysis alone was evidently not sufficient to stimulate biofilm. Sub-MIC levels of two other cell wall-active agents with different mechanisms of action-d-cycloserine and fosfomycin-also stimulated eDNA-dependent biofilm, suggesting that biofilm formation may be a mechanistic adaptation to cell wall stress. Screening a USA300 mariner transposon library for mutants deficient in biofilm formation in sub-MIC amoxicillin identified numerous known mediators of S. aureus β-lactam resistance and biofilm formation, as well as novel genes not previously associated with these phenotypes. Our results link cell wall stress and biofilm formation in MRSA and suggest that eDNA-dependent biofilm formation by strain USA300 in low-dose amoxicillin is an inducible phenotype that can be used to identify novel genes impacting MRSA β-lactam resistance and biofilm formation.

Surface Polysaccharide Mutants Reveal that Absence of O Antigen Reduces Biofilm Formation of Actinobacillus pleuropneumoniae

Actinobacillus pleuropneumoniae is a Gram-negative bacterium belonging to the Pasteurellaceae family and the causative agent of porcine pleuropneumonia, a highly contagious lung disease causing important economic losses. Surface polysaccharides, including lipopolysaccharides (LPS) and capsular polysaccharides (CPS), are implicated in the adhesion and virulence of A. pleuropneumoniae, but their role in biofilm formation is still unclear. In this study, we investigated the requirement for these surface polysaccharides in biofilm formation by A. pleuropneumoniae serotype 1. Well-characterized mutants were used: an O-antigen LPS mutant, a truncated core LPS mutant with an intact O antigen, a capsule mutant, and a poly-N-acetylglucosamine (PGA) mutant. We compared the amount of biofilm produced by the parental strain and the isogenic mutants using static and dynamic systems. Compared to the findings for the biofilm of the parental or other strains, the biofilm of the O antigen and the PGA mutants was dramatically reduced, and it had less cell-associated PGA. Real-time PCR analyses revealed a significant reduction in the level of pgaA, cpxR, and cpxA mRNA in the biofilm cells of the O-antigen mutant compared to that in the biofilm cells of the parental strain. Specific binding between PGA and LPS was consistently detected by surface plasmon resonance, but the lack of O antigen did not abolish these interactions. In conclusion, the absence of the O antigen reduces the ability of A. pleuropneumoniae to form a biofilm, and this is associated with the reduced expression and production of PGA.

Characterization of Biofilm Formation in [Pasteurella] pneumotropica and [Actinobacillus] muris Isolates of Mouse Origin

[Pasteurella] pneumotropica biotypes Jawetz and Heyl and [Actinobacillus] muris are the most prevalent Pasteurellaceae species isolated from laboratory mouse. However, mechanisms contributing to their high prevalence such as the ability to form biofilms have not been studied yet. In the present investigation we analyze if these bacterial species can produce biofilms in vitro and investigate whether proteins, extracellular DNA and polysaccharides are involved in the biofilm formation and structure by inhibition and dispersal assays using proteinase K, DNase I and sodium periodate. Finally, the capacity of the biofilms to confer resistance to antibiotics is examined. We demonstrate that both [P.] pneumotropica biotypes but not [A.] muris are able to form robust biofilms in vitro, a phenotype which is widely spread among the field isolates. The biofilm inhibition and dispersal assays by proteinase and DNase lead to a strong inhibition in biofilm formation when added at the initiation of the biofilm formation and dispersed pre-formed [P.] pneumotropica biofilms, revealing thus that proteins and extracellular DNA are essential in biofilm formation and structure. Sodium periodate inhibited the bacterial growth when added at the beginning of the biofilm formation assay, making difficult the assessment of the role of β-1,6-linked polysaccharides in the biofilm formation, and had a biofilm stimulating effect when added on pre-established mature biofilms of [P.] pneumotropica biotype Heyl and a majority of [P.] pneumotropica biotype Jawetz strains, suggesting that the presence of β-1,6-linked polysaccharides on the bacterial surface might attenuate the biofilm production. Conversely, no effect or a decrease in the biofilm quantity was observed by biofilm dispersal using sodium periodate on further biotype Jawetz isolates, suggesting that polysaccharides might be incorporated in the biofilm structure. We additionally show that [P.] pneumotropica cells enclosed in biofilms were less sensitive to treatment with amoxicillin and enrofloxacin than planktonic bacteria. Taken together, these findings provide a first step in understanding of the biofilm mechanisms in [P.] pneumotropica, which might contribute to elucidation of colonization and pathogenesis mechanisms for these obligate inhabitants of the mouse mucosa.

Putting on the brakes: Bacterial impediment of wound healing

The epithelium provides a crucial barrier to infection, and its integrity requires efficient wound healing. Bacterial cells and secretomes from a subset of tested species of bacteria inhibited human and porcine corneal epithelial cell migration in vitro and ex vivo. Secretomes from 95% of Serratia marcescens, 71% of Pseudomonas aeruginosa, 29% of Staphylococcus aureus strains, and other bacterial species inhibited epithelial cell migration. Migration of human foreskin fibroblasts was also inhibited by S. marcescens secretomes indicating that the effect is not cornea specific. Transposon mutagenesis implicated lipopolysaccharide (LPS) core biosynthetic genes as being required to inhibit corneal epithelial cell migration. LPS depletion of S. marcescens secretomes with polymyxin B agarose rendered secretomes unable to inhibit epithelial cell migration. Purified LPS from S. marcescens, but not from Escherichia coli or S. marcescens strains with mutations in the waaG and waaC genes, inhibited epithelial cell migration in vitro and wound healing ex vivo. Together these data suggest that S. marcescens LPS is sufficient for inhibition of epithelial wound healing. This study presents a novel host-pathogen interaction with implications for infections where bacteria impact wound healing and provides evidence that secreted LPS is a key factor in the inhibitory mechanism.

Inhibitory effect of silver nanoparticle fabricated urinary catheter on colonization efficiency of Coagulase Negative Staphylococci

Multiple antibiotic resistance and diverse mechanisms for biofilm formation make Coagulase Negative Staphylococci (CoNS) to cause infections associated with insertion of medical devices. As the infectious life style of CoNS pose difficult to treat conditions, materials with multitargeted antimicrobial effect can offer promising ways to modify the surface of devices to limit microbial growth. The broad spectrum of antimicrobial properties shown by silver nanoparticles (AgNPs) make it as an excellent candidate to act on device surface as persistent antimicrobial structures. In the current study, AgNPs assembled by soil bacteria under visible light at room temperature were analysed for its physical properties by UV-Vis spectroscopy, FTIR, SEM, HR-TEM and EDS and they also showed significant antimicrobial and antibiofilm properties against selected members of CoNS like Staphylococcus epidermidis and Staphylococcus haemolyticus. Very interestingly, further analysis on antibacterial mechanism of AgNPs showed their remarkable ability to cause disorganization of bacterial cell membrane. Further, surface engineering application of AgNPs on urinary catheter showed its excellent potential to prevent the attachment and colonization of CoNS which make result of study with significantly novel medical applications.

Environmental bacteria produce abundant and diverse antibiofilm compounds

AIMS

The aim of this study was to isolate novel antibiofilm compounds produced by environmental bacteria.

METHODS AND RESULTS

Cell-free extracts were prepared from lawns of bacteria cultured on agar. A total of 126 bacteria isolated from soil, cave and river habitats were employed. Extracts were tested for their ability to inhibit Staphylococcus aureus biofilm in a 96-well microtitre plate assay. A total of 55/126 extracts (44%) significantly inhibited Staph. aureus biofilm. Seven extracts were selected for further analysis. The antibiofilm activities in all seven extracts exhibited unique patterns of molecular mass, chemical polarity, heat stability and spectrum of activity against Staph. aureus, Staphylococcus epidermidis and Pseudomonas fluorescens, suggesting that these seven antibiofilm activities were mediated by unique chemical compounds with different mechanisms of action.

CONCLUSIONS

Environmental bacteria produce abundant and diverse antibiofilm compounds.

SIGNIFICANCE AND IMPACT OF THE STUDY

Screening cell-free extracts is a useful method for identifying secreted compounds that regulate biofilm formation. Such compounds may represent a novel source of antibiofilm agents for technological development.

Anti-biofilm activity: a function of Klebsiella pneumoniae capsular polysaccharide

Competition and cooperation phenomena occur within highly interactive biofilm communities and several non-biocides molecules produced by microorganisms have been described as impairing biofilm formation. In this study, we investigated the anti-biofilm capacities of an ubiquitous and biofilm producing bacterium, Klebsiella pneumoniae. Cell-free supernatant from K. pneumoniae planktonic cultures showed anti-biofilm effects on most Gram positive bacteria tested but also encompassed some Gram negative bacilli. The anti-biofilm non-bactericidal activity was further investigated on Staphylococcus epidermidis, by determining the biofilm biomass, microscopic observations and agglutination measurement through a magnetic bead-mediated agglutination test. Cell-free extracts from K. pneumoniae biofilm (supernatant and acellular matrix) also showed an influence, although to a lesser extend. Chemical analyses indicated that the active molecule was a high molecular weight polysaccharide composed of five monosaccharides: galactose, glucose, rhamnose, glucuronic acid and glucosamine and the main following sugar linkage residues [→ 2)-α-L-Rhap-(1 →]; [→ 4)-α-L-Rhap-(1 →]; [α-D-Galp-(1 →]; [→ 2,3)-α-D-Galp-(1 →]; [→ 3)-β-D-Galp-(1 →] and, [→ 4)-β-D-GlcAp-(1 →]. Characterization of this molecule indicated that this component was more likely capsular polysaccharide (CPS) and precoating of abiotic surfaces with CPS extracts from different serotypes impaired the bacteria-surface interactions. Thus the CPS of Klebsiella would exhibit a pleiotropic activity during biofilm formation, both stimulating the initial adhesion and maturation steps as previously described, but also repelling potential competitors.