A combination of assays reveals biomass differences in biofilms formed by Escherichia coli mutants

Application of BactTiter-Glo ATP bioluminescence assay for Mycobacterium tuberculosis detection

BACKGROUND

Tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB), remains a global health threat, necessitating faster and more accessible diagnostic methods. This study investigates critical parameters in the application of a commercial ATP bioluminescence assay for the detection of MTB.

METHOD

Our objective was to optimize the ATP bioluminescence protocol using BacTiter-Glo™ for MTB, investigating the impact of varying volumes of MTB suspension and reagent on assay sensitivity, evaluating ATP extraction methods, establishing calibration curves, and elucidating strain-specific responses to antimicrobial agents.

RESULTS

ATP extraction methods showed no significant improvement over controls. Calibration curves revealed a linear correlation between relative light units (RLU) and colony-forming units (CFU/mL), establishing low detection limits. Antimicrobial testing demonstrated strain-specific responses aligning with susceptibility and resistance patterns.

CONCLUSION

Our findings contribute to refining ATP bioluminescence protocols for enhanced MTB detection and susceptibility testing. Further refinements and validation efforts are warranted, holding promise for more efficient diagnostic platforms in the future.

Blocking bacterial appendage attachment to wastewater treatment membranes using anti-adhesins

Membrane bioreactors (MBRs) suffer from high operational and cleaning costs due to biofouling. The biofouling begins when the adhesins (an anchor-type epitope made up of polar and charged amino acids) on microbial appendages bind to the surface. Two different compounds-dodecyl-β-D-maltoside (DDM) and methyl α-d-mannopyranoside (MeαMan)-were investigated as possible biofilm mitigation tools due to their documented anti-adhesin properties in the biomedical field. DDM prevented up to 56.3, 87.0, and 67.6% of the formation of Pseudomonas putida, Escherichia coli and wastewater culture biofilms, respectively, in microplate experiments. MeαMan increased biofilm in the microplates. In a biofilm reactor setting, DDM was then applied on typical membrane materials, polyvinylidene fluoride, polyamide, polyether-sulfone, and polyacrylonitrile and prevented 79.4, 62.5, 81.3, and 68.2% of the detectable wastewater culture biofilm formation, respectively. The mechanism of anti-adhesion was the binding of the polar head of the DDM to the polar amino acids of the microbial appendages in conjunction with the orientation of the DDM as it binds different membrane materials. If the anti-adhesins are effective at increasing the distance of the bacteria from the membrane materials, they will serve as a new method for delaying biofouling.

Effective immobilization of heavy metals via reactive barrier by rhizosphere bacteria and their biofilms

As the portal of plants, rhizosphere microorganisms play an essential role in controlling the species, transformation, and bioavailability of heavy metals, yet the potential passivation mechanism is still unclear. In this study, two heavy metal resistant and growth-promoting rhizosphere bacteria were screened, and their mechanisms in dealing with external stress and immobilizing heavy metal were explored. The results showed that heavy metals inhibited the ability of Pseudomonas sp. H13 and Brevundomonas sp. H16 to promote plant growth, but stimulated the production of extracellular polysaccharides and inorganic labile sulfide, and enhanced biofilm formation, thereby significantly improved the removal efficiency of Cu²⁺, Zn²⁺, Cd²⁺, and Pb²⁺. Compared with H16, the biofilm of H13 disintegrated rapidly in the later stage, so more metal ions were adsorbed on the planktonic cells. The C-OH and PO groups related to polysaccharides play a crucial role in heavy metal adsorption, and the immobilization mechanism of the planktonic cell is mainly ion exchange and group complex, but for H16, intracellular enrichment cannot be ignored. Functional group complexes played a dominant role in biofilm, and the immobilized heavy metals were more difficult to release into the environment. This study highlighted the potential application prospects of biofilm bacteria in heavy metal remediation and explained the reactive barrier of rhizosphere bacteria to heavy metals.

Plant-based oral care product exhibits antibacterial effects on different stages of oral multispecies biofilm development in vitro

Background

Excessive biofilm formation on surfaces in the oral cavity is amongst the main reasons for severe infection development like periodontitis and peri-implantitis. Mechanical biofilm removal as well as the use of adjuvant antiseptics supports the prevention of pathogenic biofilm formation. Recently, the antibacterial effect of the oral care product REPHA-OS^®, based on medicinal plant extracts and essential oils, has been demonstrated on oral pathogens grown on agar plates. In the present study, the effectiveness of the product on medical relevant oral biofilm development should be demonstrated for the first time.

Methods

An established in vitro oral multispecies biofilm, composed of Streptococcus oralis, Actinomyces naeslundii, Veillonella dispar and Porphyromonas gingivalis, was used to analyze the antibacterial effect of different REPHA-OS^® concentrations on planktonic bacteria, biofilm formation and mature biofilms. It was quantified using metabolic activity assays and live/dead fluorescence staining combined with three-dimensional confocal laser-scanning microscopy. Additionally, effects on species distribution inside the biofilm were assessed by means of quantitative real-time PCR.

Results

REPHA-OS^® showed statistically significant antimicrobial effects on all stages of biofilm development: a minimal inhibitory concentration of 5% could be detected for both, for planktonic bacteria and for biofilm formation. Interestingly, only a slightly higher concentration of 10% was necessary to completely kill all bacteria in mature biofilms also. In contrast, an influence on the biofilm matrix or the species distribution could not be observed. The effect could be attributed to the herbal ingredients, not to the contained ethanol.

Conclusion

The strong antibacterial effect of REPHA-OS^® on different stages of oral biofilm development strengthens its application as an alternative adjuvant in oral care therapies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-021-01504-4.

Synergistic effect of biofilm growth and cadmium adsorption via compositional changes of extracellular matrix in montmorillonite system

The interaction of bacterial biofilm and clay minerals provides great potential for heavy metal remediation in contaminated soil, yet, little is known about how heavy metal, clay minerals and their combinations affect the bacterial biofilm performance and heavy metal adsorption. In this study, the response of biofilm development as well as Cd²⁺ adsorption in the presence of Cd²⁺ and montmorillonite has been deciphered. Low concentrations of Cd²⁺ and montmorillonite or their combinations enhanced biofilm formation by increasing polysaccharides proportion in the biofilm matrix, and the maximum adsorption capacity of Cd²⁺ by biofilm was increased by 1.5 times. Furthermore, the immobilization of Cd²⁺ by soil was significantly improved when S14-biofilm was introduced. Such results could gain deeper insight into bacterial survival tactics in the complex systems which makes major contribution to microbial remediation of heavy metal polluted environments.

Novel regulators of the csgD gene encoding the master regulator of biofilm formation in Escherichia coli K-12

Under stressful conditions, Escherichia coli forms biofilm for survival by sensing a variety of environmental conditions. CsgD, the master regulator of biofilm formation, controls cell aggregation by directly regulating the synthesis of Curli fimbriae. In agreement of its regulatory role, as many as 14 transcription factors (TFs) have so far been identified to participate in regulation of the csgD promoter, each monitoring a specific environmental condition or factor. In order to identify the whole set of TFs involved in this typical multi-factor promoter, we performed in this study ‘promoter-specific transcription-factor’ (PS-TF) screening in vitro using a set of 198 purified TFs (145 TFs with known functions and 53 hitherto uncharacterized TFs). A total of 48 TFs with strong binding to the csgD promoter probe were identified, including 35 known TFs and 13 uncharacterized TFs, referred to as Y-TFs. As an attempt to search for novel regulators, in this study we first analysed a total of seven Y-TFs, including YbiH, YdcI, YhjC, YiaJ, YiaU, YjgJ and YjiR. After analysis of curli fimbriae formation, LacZ-reporter assay, Northern-blot analysis and biofilm formation assay, we identified at least two novel regulators, repressor YiaJ (renamed PlaR) and activator YhjC (renamed RcdB), of the csgD promoter.

Dynamics of Dissolution, Killing, and Inhibition of Dental Plaque Biofilm

The present study aims to establish a standardized model that makes it possible to evaluate the dynamic dissolution of biofilm, killing of biofilm microbes and inhibition of growth of biofilm by disinfecting solutions. Biofilm was grown from dental plaque bacteria on collagen-coated hydroxyapatite (HA) disks for 3 days or 3 weeks under anaerobic conditions. Biofilms were stained with the LIVE/DEAD viability stain and subjected to sterile water, 2% sodium hypochlorite (NaOCl), 6% NaOCl, or 2% chlorhexidine (CHX) for 32 min. Dynamic change in fluorescence on bacterial cells and extracellular polymeric substance (EPS) during the exposure was analyzed using Alexa Fluor 647-labeled dextran conjugate and a live-cell imaging confocal laser scanning microscopy (LC-CLSM). The biofilm structures after treatments were visualized by scanning electron microscopy (SEM). The treated biofilms on HA disks were collected and subjected to colony forming unit (CFU) counting. Another set of sterile HA disks were coated with CHX prior to the monitoring of plaque biofilm growth for 12 h. The LC-CLSM results showed that NaOCl dissolved biofilm effectively, more so at a higher concentration and longer exposure time. Six percent NaOCl was the most effective at dissolving and killing bacteria (e.g., 99% bacterial reduction in 3-day-old biofilm and 95% bacterial reduction in 3-week-old biofilm in 32 min) followed by 2% NaOCl and CHX. Sodium hypochlorite dissolved over 99.9% of the EPS whereas CHX only slightly reduced the EPS biovolume in 32 min. CFU results indicated that the dispersed biofilm bacteria are more resistant than planktonic bacteria to disinfectants. SEM showed the disruption of biofilm after exposures to CHX and NaOCl. The use of 2% CHX and sterile water did not result in biofilm dissolution. However, prior exposure of the HA disks to 2 and 0.2% CHX for 3 min prevented biofilm from growing on the HA disk surfaces for at least 12 h. This new platform has the potential to aid in a better understanding of the antibiofilm properties of oral disinfectants.

Detecting Escherichia coli Biofilm Development Stages on Gold and Titanium by Quartz Crystal Microbalance

Bacterial biofilms are responsible for persistent infections and biofouling, raising serious concerns in both medical and industrial processes. These motivations underpin the need to develop methodologies to study the complex biological structures of biofilms and prevent their formation on medical implants, tools, and industrial apparatuses. Here, we report the detailed comparison of Escherichia coli biofilm development stages (adhesion, maturation, and dispersion) on gold and titanium surfaces by monitoring the changes in both frequency and dissipation of a quartz crystal microbalance (QCM) device, a cheap and reliable microgravimetric sensor which allows the real-time and label-free characterization of various stages of biofilm development. Although gold is the most common electrode material used for QCM sensors, the titanium electrode is also readily available for QCM sensors; thus, QCM sensors with different metal electrodes serve as a simple platform to probe how pathogens interact with different metal substrates. The QCM outcomes are further confirmed by atomic force microscopy and crystal violet staining, thus validating the effectiveness of this surface sensitive sensor for microbial biofilm research. Moreover, because QCM technology can easily modify the substrate types and coatings, QCM sensors also provide well-controlled experimental conditions to study antimicrobial surface treatments and eradication procedures, even on mature biofilms.

Regulatory role of pyruvate-sensing BtsSR in biofilm formation by Escherichia coli K-12

Pyruvate, the key regulator in connection of a variety of metabolic pathways, influences transcription of the Escherichia coli genome through controlling the activity of two pyruvate-sensing two-component systems (TCSs), BtsSR and PyrSR. Previously, we identified the whole set of regulatory targets of PyrSR with low-affinity to pyruvate. Using gSELEX screening system, we found here that BtsSR with high-affinity to pyruvate regulates more than 100 genes including as many as 13 transcription factors genes including the csgD gene encoding the master regulator of biofilm formation. CsgD regulates more than 20 target genes including the csg operons encoding the Curli fimbriae. In addition, we identified the csgBAC as one of the regulatory targets of BtsR, thus indicating the involvement of two pyruvate-dependent regulatory pathways of the curli formation: indirect regulation by CsgD; and direct regulation by BtsR. Based on the findings of the whole set of regulatory targets by two pyruvate-sensing BtsR and PyrR, we further propose an innovative concept that the pyruvate level-dependent regulation of different gene sets takes place through two pyruvate-sensing TCS systems, high-affinity BtsSR and low-affinity PyrSR to pyruvate.

Detecting Gold Biomineralization by Delftia acidovorans Biofilms on a Quartz Crystal Microbalance

The extensive use of gold in sensing, diagnostics, and electronics has led to major concerns in solid waste management since gold and other heavy metals are nonbiodegradable and can easily accumulate in the environment. Moreover, gold ions are extremely reactive and potentially harmful for humans. Thus, there is an urgent need to develop reliable methodologies to detect and possibly neutralize ionic gold in aqueous solutions and industrial wastes. In this work, by using complementary measurement techniques such as quartz crystal microbalance (QCM), atomic force microscopy, crystal violet staining, and optical microscopy, we investigate a promising biologically induced gold biomineralization process accomplished by biofilms of bacterium Delftia acidovorans. When stressed by Au³⁺ ions, D. acidovorans is able to neutralize toxic soluble gold by excreting a nonribosomal peptide, which forms extracellular gold nanonuggets via complexation with metal ions. Specifically, QCM, a surface-sensitive transducer, is employed to quantify the production of these gold complexes directly on the D. acidovorans biofilm in real time. Detailed kinetics obtained by QCM captures the condition for maximized biomineralization yield and offers new insights underlying the biomineralization process. To the best of our knowledge, this is the first study providing an extensive characterization of the gold biomineralization process by a model bacterial biofilm. We also demonstrate QCM as a cheap, user-friendly sensing platform and alternative to standard analytical techniques for studies requiring high-resolution quantitative details, which offers promising opportunities in heavy-metal sensing, gold recovery, and industrial waste treatment.

Methods Used for the Eradication of Staphylococcal Biofilms

Staphylococcus aureus is considered one of the leading pathogens responsible for community and healthcare-associated infections. Among them, infections caused by methicillin-resistant strains (MRSA) are connected with ineffective or prolonged treatment. The therapy of staphylococcal infections faces many difficulties, not only because of the bacteria's resistance to antibiotics and the multiplicity of virulence factors it produces, but also due to its ability to form a biofilm. The present review focuses on several approaches used for the assessment of staphylococcal biofilm eradication. The methods described here are successfully applied in research on the prevention of biofilm-associated infections, as well as in their management. They include not only the evaluation of the antimicrobial activity of novel compounds, but also the methods for biomaterial functionalization. Moreover, the advantages and limitations of different dyes and techniques used for biofilm characterization are discussed. Therefore, this review may be helpful for those scientists who work on the development of new antistaphylococcal compounds.

Efficacy of β-phenylethylamine as a novel anti-microbial and application as a liquid catheter flush

With this study, we introduce a liquid flush for catheters and other tubing-based applications that consists of a solution of β-phenylethylamine (PEA) in tryptic soy broth. The initial experiments in multiwell polystyrene plates were conducted with Escherichia coli K-12 to assess the effectiveness of PEA at reducing planktonic growth, as well as the biomass and adenosine triphosphate (ATP) content of biofilm; PEA reduced these growth parameters as a function of increasing concentration. This effect was also seen in mutants of PEA catabolism, which leads us to believe that the PEA effect is due to PEA itself and not one of its degradation products. Since PEA reduced planktonic growth and biofilm when added at the time of inoculation, as well as at later time points, we propose PEA as a novel compound for the prevention and treatment of biofilm. PEA reduced planktonic growth and the ATP content of the biofilm for five bacterial pathogens, including an enterohemorrhagic E. coli, two uropathogenic E. coli, Pseudomonas aeruginosa and Staphylococcus aureus. A major finding of this study is the reduction of the ATP content of biofilm that formed in silicone tubing by periodic flushes of PEA. This experiment was performed to model antibiotic-lock treatment of an intravenous catheter. It was found that 10 mg ml^-1 of PEA reduced the ATP content of biofilm of five bacterial strains by 96.3 % or more after 2 weeks of incubation and three treatments with PEA. For P. aeruginosa, the reduction in ATP content was paralleled by an identical percentage reduction in viable cells in the biofilm.

Activity of a novel antimicrobial peptide against Pseudomonas aeruginosa biofilms

With the increasing recognition of biofilms in human disease, the development of novel antimicrobial therapies is of critical importance. For example, in patients with cystic fibrosis (CF), the acquisition of host-adapted, chronic Pseudomonas aeruginosa infection is associated with a decline in lung function and increased mortality. Our objective was to test the in vitro efficacy of a membrane-active antimicrobial peptide we designed, termed 6K-F17 (sequence: KKKKKK-AAFAAWAAFAA-NH₂), against multidrug resistant P. aeruginosa biofilms. This peptide displays high antimicrobial activity against a range of pathogenic bacteria, yet is non-hemolytic to human erythrocytes and non-toxic to human bronchial epithelial cells. In the present work, P. aeruginosa strain PAO1, and four multidrug resistant (MDR) isolates from chronically infected CF individuals, were grown as 48-hour biofilms in a static biofilm slide chamber model. These biofilms were then exposed to varying concentrations of 6K-F17 alone, or in the presence of tobramycin, prior to confocal imaging. Biofilm biovolume and viability were assessed. 6K-F17 was able to kill biofilms - even in the presence of sputum - and greatly reduce biofilm biovolume in PAO1 and MDR isolates. Strikingly, when used in conjunction with tobramycin, low doses of 6K-F17 significantly potentiated tobramycin killing, leading to biofilm destruction.

bifA Regulates Biofilm Development of Pseudomonas putida MnB1 as a Primary Response to H2O2 and Mn2

Pseudomonas putida (P. putida) MnB1 is a widely used model strain in environment science and technology for determining microbial manganese oxidation. Numerous studies have demonstrated that the growth and metabolism of P. putida MnB1 are influenced by various environmental factors. In this study, we investigated the effects of hydrogen peroxide (H₂O₂) and manganese (Mn²⁺) on proliferation, Mn²⁺ acquisition, anti-oxidative system, and biofilm formation of P. putida MnB1. The related orthologs of 4 genes, mco, mntABC, sod, and bifA, were amplified from P. putida GB1 and their involvement were assayed, respectively. We found that P. putida MnB1 degraded H₂O₂, and quickly recovered for proliferation, but its intracellular oxidative stress state was maintained, with rapid biofilm formation after H₂O₂ depletion. The data from mco, mntABC, sod and bifA expression levels by qRT-PCR, elucidated a sensitivity toward bifA-mediated biofilm formation, in contrary to intracellular anti-oxidative system under H₂O₂ exposure. Meanwhile, Mn²⁺ ion supply inhibited biofilm formation of P. putida MnB1. The expression pattern of these genes showed that Mn²⁺ ion supply likely functioned to modulate biofilm formation rather than only acting as nutrient substrate for P. putida MnB1. Furthermore, blockade of BifA activity by GTP increased the formation and development of biofilms during H₂O₂ exposure, while converse response to Mn²⁺ ion supply was evident. These distinct cellular responses to H₂O₂ and Mn²⁺ provide insights on the common mechanism by which environmental microorganisms may be protected from exogenous factors. We postulate that BifA-mediated biofilm formation but not intracellular anti-oxidative system may be a primary protective strategy adopted by P. putida MnB1. These findings will highlight the understanding of microbial adaptation mechanisms to distinct environmental stresses.

Preliminary study on the tick population of Benin wildlife at the moment of its invasion by the Rhipicephalus microplus tick (Canestrini, 1888)

BACKGROUND AND AIM

Rhipicephalus microplus (Rm) is one of the most problematic livestock tick species in the world. Its rapid propagation and resistance to acaricides make it control difficult in the sub-region and Benin particularly. The aim of this work was to check its presence in wildlife and to confirm the possible role of reservoir wildlife may play in the propagation of the parasite. This will help to design more efficient control strategy.

MATERIALS AND METHODS

This study was conducted from February to March 2017 in the National Parks of Benin (Pendjari and W Park) and wildfowl's assembly and selling point in Benin. Ticks were manually picked with forceps from each animal after slaughtering by hunters then stored in 70° ethanol. Collected ticks were counted and identified in the laboratory using the identification key as described by Walker.

RESULTS

Overall, seven species of ticks (Amblyomma variegatum, Boophilus decoloratus, Rm, Boophilus spp., Hyalomma spp., Rhipicephalus sanguineus, Rhipicephalus spp.) were identified on nine wild animal species sampled (Cane rat, wildcat, Hare, Doe, Cricetoma, Buffalo, Buffon Cobe, and Bushbuck and Warthog). The average number of ticks varies from 3 to 6 between animal species, 3 to 7 between localities visited, and 2 to 5 between tick species. However, these differences are statistically significant only for localities. Considering tick species and animal species, the parasite load of Rm and Rhipicephalus spp. is higher; the buffalo being more infested. The analysis of deviance reveals that the abundance of ticks observed depends only on the observed localities (p>0.05). However, the interactions between animal species and localities on the one hand and between animal and tick species on the other hand, although not significant, have influenced the abundance of ticks as they reduce the residual deviance after their inclusion in the model.

CONCLUSIONS

This study reported the presence of Rm in wildlife of Benin and confirmed its role in the maintenance and spread of the parasites. It is, therefore, an important risk factor that we must not neglect in the epidemiological surveillance and ticks control strategies in the West African sub-region and particularly in Benin.

Bacteriophage Isolated from Sewage Eliminates and Prevents the Establishment of Escherichia Coli Biofilm

Purpose: Biofilm growth exerts a negative impact on industry and health, necessitating the development of strategies to control. The objective of this work was study the lytic activity of the phage isolated from the sewage network in the formation and degradation of Escherichia coli biofilms.

Methods: E. coli cultures were incubated in 96-well polystyrene microplates under controlled conditions to evaluate the biofilm formation. The E. coli cultures and established biofilms were treated with the suspensions of the vB_EcoM-UFV017 (EcoM017) bacteriophage obtained from sewage for 24 hours. The E. coli bacterial density was measured using absorbance at 600 nm and the biofilms were measured by crystal violet staining. Polystyrene coupons were used as support for Scanning Electron Microscopy and Confocal Microscopy to evaluate biofilm formation.

Results: The E. coli strains formed biofilms in polystyrene microplates after 48 hours’ incubation. The highest EcoM017 phage titer, in the prevention and degradation experiments, reduced the bacterial growth and the quantity of biofilm formed by E. coli in 90.0% and 87.5%, respectively. The minimum dose capable of reducing the biofilms of this bacterium was 10¹ PFU/mL after 24 hours. The preformed E. coli biofilm mass was reduced 79% post exposure to the phage in the degradation assay. Microscopic analysis confirmed the results obtained in the plates assays.

Conclusion: The EcoM017 phage prevented biofilm formation and degraded the E. coli-established ones. The EcoM017 phage isolated from sewage can reduce bacterial attachment and lyse the E. coli associated biofilm cells, offering biotechnological potential applicability for this phage.

Stress Tolerance-Related Genetic Traits of Fish Pathogen Flavobacterium psychrophilum in a Mature Biofilm

Flavobacterium psychrophilum is the causative agent of bacterial cold-water disease and rainbow trout fry syndrome, and hence this bacterium is placed among the most important salmonid pathogens in the freshwater aquaculture industry. Since bacteria in biofilms differ substantially from free-living counterparts, this study sought to find the main differences in gene expression between sessile and planktonic states of F. psychrophilum LM-02-Fp and NCMB1947^T, with focus on stress-related changes in gene expression occurring during biofilm formation. To this end, biofilm and planktonic samples were analyzed by RNA sequencing to detect differentially expressed candidate genes (DECGs) between the two growth states, and decreasing the effects of interstrain variation by considering only genes with log₂-fold changes ≤ −2 and ≥ 2 at Padj-values ≤ 0.001 as DECGs. Overall, 349 genes accounting for ~15% of total number of genes expressed in transcriptomes of F. psychrophilum LM-02-Fp and NCMB1947^T (n = 2327) were DECGs between biofilm and planktonic states. Approximately 83 and 81% of all up- and down-regulated candidate genes in mature biofilms, respectively, were assigned to at least one gene ontology term; these were primarily associated with the molecular function term “catalytic activity.” We detected a potential stress response in mature biofilms, characterized by a generalized down-regulation of DECGs with roles in the protein synthesis machinery (n = 63, primarily ribosomal proteins) and energy conservation (seven ATP synthase subunit genes), as well as an up-regulation of DECGs involved in DNA repair (ruvC, recO, phrB1, smf, and dnaQ) and oxidative stress response (cytochrome C peroxidase, probable peroxiredoxin, and a probable thioredoxin). These results support the idea of a strategic trade-off between growth-related processes and cell homeostasis to preserve biofilm structure and metabolic functioning. In addition, LDH-based cytotoxicity assays and an intraperitoneal challenge model for rainbow trout fry agreed with the transcriptomic evidence that the ability of F. psychrophilum to form biofilms could contribute to the virulence. Finally, the reported changes in gene expression, as induced by the plankton-to-biofilm transition, represent the first transcriptomic guideline to obtain insights into the F. psychrophilum biofilm lifestyle that could help understand the prevalence of this bacterium in aquaculture settings.

Rifampicin-Manuka Honey Combinations Are Superior to Other Antibiotic-Manuka Honey Combinations in Eradicating Staphylococcus aureus Biofilms

Chronic wound infections are a major burden to both society and the health care industry. Bacterial biofilms are the major cause of chronic wound infections and are notoriously recalcitrant to treatments with antibiotics, making them difficult to eradicate. Thus, new approaches are required to combat biofilms in chronic wounds. One possible approach is to use drug combination therapies. Manuka honey has potent broad-spectrum antibacterial activity and has previously shown synergistic activity in combination with antibiotics against common wound pathogens, including Staphylococcus aureus. In addition, manuka honey exhibits anti-biofilm activity, thereby warranting the investigation of its potential as a combination therapy with antibiotics for the topical treatment of biofilm-related infections. Here we report the first use of MacSynergy II to investigate the response of established S. aureus (strain NCTC 8325) biofilms to treatment by combinations of Medihoney (medical grade manuka honey) and conventional antibiotics that are used for preventing or treating infections: rifampicin, oxacillin, fusidic acid, clindamycin, and gentamicin. Using checkerboard microdilution assays, viability assays and MacSynergy II analysis we show that the Medihoney-rifampicin combination was more effective than combinations using the other antibiotics against established staphylococcal biofilms. Medihoney and rifampicin were strongly synergistic in their ability to reduce both biofilm biomass and the viability of embedded S. aureus cells at a level that is likely to be significant in vivo. Other combinations of Medihoney and antibiotic produced an interesting array of effects: Medihoney-fusidic acid treatment showed minor synergistic activity, and Medihoney-clindamycin, -gentamicin, and -oxacillin combinations showed overall antagonistic effects when the honey was used at sub-inhibitory concentration, due to enhanced biofilm formation at these concentrations which could not be counteracted by the antibiotics. However, these combinations were not antagonistic when honey was used at the inhibitory concentration. Confocal scanning laser microscopy confirmed that different honey-antibiotic combination treatments could eradicate biofilms. Our results suggest that honey has potential as an adjunct treatment with rifampicin for chronic wounds infected with staphylococcal biofilms. We also show that MacSynergy II allows a comprehensive examination of the synergistic effects of honey-antibiotic combinations, and can help to identify doses for clinical use.

Effects of humic acid on the interactions between zinc oxide nanoparticles and bacterial biofilms

The effects of humic acid (HA) on interactions between ZnO nanoparticles (ZnO NPs) and Pseudomonas putida KT2440 biofilms at different maturity stages were investigated. Three stages of biofilm development were identified according to bacterial adenosine triphosphate (ATP) activity associated with biofilm development process. In the initial biofilm stage 1, the ATP content of bacteria was reduced by more than 90% when biofilms were exposed to ZnO NPs. However, in the mature biofilm stages 2 and 3, the ATP content was only slightly decreased. Biofilms at stage 3 exhibited less susceptibility to ZnO NPs than biofilms at stage 2. These results suggest that more mature biofilms have a significantly higher tolerance to ZnO NPs compared to young biofilms. In addition, biofilms with intact extracellular polymeric substances (EPS) showed higher tolerance to ZnO NPs than those without EPS, indicating that EPS play a key role in alleviating the toxic effects of ZnO NPs. In both pure ZnO NPs and ZnO-HA mixtures, dissolved Zn²⁺ originating from the NPs significantly contributed to the overall toxicity. The presence of HA dramatically decreased the toxicity of ZnO NPs due to the binding of Zn²⁺ on HA. The combined results from this work suggest that the biofilm maturity stages and environmental constituents (such as humic acid) are important factors to consider when evaluating potential risks of NPs to ecological systems.

Dependence of toxicity of silver nanoparticles on Pseudomonas putida biofilm structure

Susceptibility of biofilms with different physical structures to silver nanoparticles (AgNPs) was studied. Biofilms of Pseudomonas putida KT2440 were formed in batch conditions under different carbon sources (glucose, glutamic acid, and citrate), glucose concentrations (5 and 50 mM), and incubation temperatures (25 and 30 °C). The biofilms were observed using confocal laser scanning microscopy for their physical characteristics (biomass amount, thickness, biomass volume, surface to volume ratio, and roughness coefficient). The biofilms forming under different growth conditions exhibited different physical structures. The biofilm thickness and the roughness coefficient were found negatively and positively correlated with the biofilm susceptibility to AgNPs, respectively. The effect of AgNPs on biofilms was low (1-log reduction of cell number) when the biofilms had high biomass amount, high thickness, high biomass volume, low surface to volume ratio, and low roughness coefficient. Furthermore, the extracellular polymeric substance (EPS) stripping process was applied to confirm the dependence of susceptibility to AgNPs on the structure of biofilm. After the EPS stripping process, the biofilms forming under different conditions showed reduction in thickness and biomass volume, and increases in surface to volume ratio and roughness coefficient, which led to more biofilm susceptibility to AgNPs. The results of this study suggest that controlling the growth conditions to alter the biofilm physical structure is a possible approach to reduce the impact of AgNPs on biofilms in engineered and natural systems.

Identification and characterization of AckA-dependent protein acetylation in Neisseria gonorrhoeae

Neisseria gonorrhoeae, the causative agent of gonorrhea, has a number of factors known to contribute to pathogenesis; however, a full understanding of these processes and their regulation has proven to be elusive. Post-translational modifications (PTMs) of bacterial proteins are now recognized as one mechanism of protein regulation. In the present study, Western blot analyses, with an anti-acetyl-lysine antibody, indicated that a large number of gonococcal proteins are post-translationally modified. Previous work has shown that N^ε-lysine acetylation can occur non-enzymatically with acetyl-phosphate (AcP) as the acetyl donor. In the current study, an acetate kinase mutant (1291ackA), which accumulates AcP, was generated in N. gonorrhoeae. Broth cultures of N. gonorrhoeae 1291wt and 1291ackA were grown, proteins extracted and digested, and peptides containing acetylated-lysines (K-acetyl) were affinity-enriched from both strains. Mass spectrometric analyses of these samples identified a total of 2686 unique acetylation sites. Label-free relative quantitation of the K-acetyl peptides derived from the ackA and wild-type (wt) strains demonstrated that 109 acetylation sites had an ackA/wt ratio>2 and p-values <0.05 in at least 2/3 of the biological replicates and were designated as “AckA-dependent”. Regulated K-acetyl sites were found in ribosomal proteins, central metabolism proteins, iron acquisition and regulation proteins, pilus assembly and regulation proteins, and a two-component response regulator. Since AckA is part of a metabolic pathway, comparative growth studies of the ackA mutant and wt strains were performed. The mutant showed a growth defect under aerobic conditions, an inability to grow anaerobically, and a defect in biofilm maturation. In conclusion, the current study identified AckA-dependent acetylation sites in N. gonorrhoeae and determined that these sites are found in a diverse group of proteins. This work lays the foundation for future studies focusing on specific acetylation sites that may have relevance in gonococcal pathogenesis and metabolism.

Bioluminescence assay for cell viability

Theoretical aspects of the adenosine triphosphate bioluminescence assay based on the use of the firefly luciferin-luciferase system are considered, as well as its application for assessing cell viability in microbiology, sanitation, medicine, and ecology. Various approaches for the analysis of individual or mixed cultures of microorganisms are presented, and capabilities of the method for investigation of biological processes in live cells including necrosis, apoptosis, as well as for investigation of the dynamics of metabolism are described.

Quantifying implant-associated biofilms: Comparison of microscopic, microbiologic and biochemical methods

Biofilm-associated infections pose severe problems in modern implant medicine. Screening for new implant materials with antibacterial properties requires reliable quantification of colonizing bacteria. There are many different methods to quantify biofilms on solid surfaces in vitro, employing different (bio-)chemical/microbiological reference parameters. It is therefore difficult to compare studies with different quantification techniques. Here, we have evaluated commonly used microscopic, microbiologic and biochemical methods to quantify bacterial biofilms, in order to clarify their comparability and applicability. Two bacterial species frequently involved in biofilm-associated infections, Staphylococcus aureus and Aggregatibacter actinomycetemcomitans, were used as model organisms; their initial adhesion and biofilm formation on titanium and on antibacterial copper were analyzed using the following methods: LIVE/DEAD fluorescence staining and confocal laser-scanning microscopy, ultrasonic or a newly developed enzymatic detachment followed by standard plate counting (CFU method), a resazurin-based assay, the BacTiter-Glo™ assay and crystal violet staining. The methods differed greatly in complexity, reliability and the applicability to initial adhesion and biofilm formation. To screen biofilm formation on a multitude of surfaces, the resazurin-based and the BacTiterGlo™ assay are well suited. LIVE/DEAD staining and confocal laser-scanning microscopy can be applied for a more detailed analysis of both, initial adhesion and biofilm formation. When using the CFU method for screening purposes, the introduced enzymatic detachment procedure is to be favored over ultrasonic detachment. There is not one single method, which is suitable for all purposes. The appropriate biofilm quantification method has to be chosen on the basis of the specific scientific question.

Effects of Monotypic and Binary Mixtures of Metal Oxide Nanoparticles on Microbial Growth in Sandy Soil Collected from Artificial Recharge Sites

The potential effects of monotypic and binary metal oxide nanoparticles (NPs, ZnO, NiO, Co₃O₄ and TiO₂) on microbial growth were evaluated in sandy soil collected from artificial recharge sites. Microbial growth was assessed based on adenosine triphosphate (ATP) content, dehydrogenase activity (DHA), and viable cell counts (VCC). Microbial growth based on ATP content and VCC showed considerable differences depending on NP type and concentration, whereas DHA did not significantly change. In general, ZnO NPs showed the strongest effect on microbial growth in all measurements, showing an EC50 value of 10.9 mg/L for ATP content. The ranking (EC50) of NPs based on their effect on microbial growth assessed by ATP content and VCC was ZnO > Co₃O₄ > NiO > TiO₂. Upon exposure to binary NP mixtures, synergistic and additive modes of action were observed for ATP content and VCC, respectively. The ranges of observed (P(O)) and expected (P(E)) activity were 83%-92% and 78%-82% of the control (p-value 0.0010) based on ATP content and 78%-95% and 72%-94% of the control (p-value 0.8813) based on VCC under the tested conditions, respectively. The results indicate that the effects of NP mixtures on microbial growth in the sandy soil matrix were as great, or greater, than those of single NPs. Therefore, understanding the effects of single NPs and NP mixtures is essential for proper ecological risk assessment. Additionally, these findings demonstrate that the evaluation of NP effects may be profoundly influenced by the method of microbial growth measurement.

Effect of silver nanoparticles on Pseudomonas putida biofilms at different stages of maturity

This study determined the effect of silver nanoparticles (AgNPs) on Pseudomonas putida KT2440 biofilms at different stages of maturity. Three biofilm stages (1-3, representing early to late stages of development) were identified from bacterial adenosine triphosphate (ATP) activity under static (96-well plate) and dynamic conditions (Center for Disease Control and Prevention biofilm reactor). Extracellular polymeric substance (EPS) levels, measured using crystal violet and total carbohydrate assays, and expression of the EPS-associated genes, csgA and alg8, supported the conclusion that biofilms at later stages were older than those at earlier stages. More mature biofilms (stages 2 and 3) showed little to no reduction in ATP activity following exposure to AgNPs. In contrast, the same treatment reduced ATP activity by more than 90% in the less mature stage 1 biofilms. Regardless of maturity, biofilms with EPS stripped off were more susceptible to AgNPs than controls with intact EPS, demonstrating that EPS is critical for biofilm tolerance of AgNPs. The findings from this study show that stage of maturity is an important factor to consider when studying effect of AgNPs on biofilms.

Simultaneous monitoring of Staphylococcus aureus growth in a multi-parametric microfluidic platform using microscopy and impedance spectroscopy

We describe the design, construction, and characterization of a scalable microfluidic platform that allows continuous monitoring of biofilm proliferation under shear stress conditions. Compared to other previous end-point assay studies, our platform offers the advantages of integration into multiple environments allowing simultaneous optical microscopy and impedance spectroscopy measurements. In this work we report a multi-parametric sensor that can monitor the growth and activity of a biofilm. This was possible by combining two interdigitated microelectrodes (IDuEs), and punctual electrodes to measure dissolved oxygen, K+, Na+ and pH. The IDuE has been optimized to permit sensitive and reliable impedance monitoring of Staphylococcus aureus V329 growth with two- and four-electrode measurements. We distinguished structural and morphological changes on intact cellular specimens using four-electrode data modeling. We also detected antibiotic mediated effects using impedance. Results were confirmed by scanning electrode microscopy and fluorescence microscopy after live/dead cell staining. The bacitracin mediated effects detected with impedance prove that the approach described can be used for guiding the development of novel anti-biofilm agents to better address bacterial infection.

Evaluation of different microtiter plate-based methods for the quantitative assessment of Staphylococcus aureus biofilms

AIM

To quantitatively assess Staphylococcus aureus biofilms.

MATERIALS & METHODS

In addition to the qualitative Congo red agar (CRA) method, we used the bioluminescence (BLM), safranine (SAF), crystal violet (CRV) and resazurin (RES) high-throughput microtiter plate-based quantitative assays.

RESULTS

60.47% (26/43) of S. aureus clinical isolates were weak biofilm producers. The CRA method detected positive-slime phenotypes (13.95%), but was unable to distinguish weak from negative producers. BLM assays demonstrated significant correlations with RES (highest), CRV and SAF (lowest). Lower coefficient of variation values indicate precision. BLM scored highest precision (coefficient of variation = 0.013) followed by RES, SAF and CRV.

CONCLUSION

BLM and RES detect live biomass in S. aureus biofilms (for physiological studies). SAF and CRV detect live/dead bacteria plus biofilm matrix (for monitoring overall biofilm architecture, not only its cell viability). Reliable assays are essential for effective biofilm therapy.

Dissolved organic nitrogen and its biodegradable portion in a water treatment plant with ozone oxidation

Biodegradability of dissolved organic nitrogen (DON) has been studied in wastewater, freshwater and marine water but not in drinking water. Presence of biodegradable DON (BDON) in water prior to and after chlorination may promote formation of nitrogenous disinfectant by-products and growth of microorganisms in the distribution system. In this study, an existing bioassay to determine BDON in wastewater was adapted and optimized, and its application was tested on samples from four treatment stages of a water treatment plant including ozonation and biologically active filtration. The optimized bioassay was able to detect BDON in 50 μg L(-1) as N of glycine and glutamic solutions. BDON in raw (144-275 μg L(-1) as N), softened (59-226 μg L(-1) as N), ozonated (190-254 μg L(-1) as N), and biologically filtered (17-103 μg L(-1) as N) water samples varied over a sampling period of 2 years. The plant on average removed 30% of DON and 68% of BDON. Ozonation played a major role in increasing the amount of BDON (31%) and biologically active filtration removed 71% of BDON in ozonated water.

OmpR and RcsB abolish temporal and spatial changes in expression of flhD in Escherichia coli biofilm

BACKGROUND

Biofilms are communities of bacteria that are characterized by specific phenotypes, including an increased resistance towards anti-microbials and the host immune system. This calls for the development of novel biofilm prevention and treatment options to combat infectious disease. In Escherichia coli, numerous global regulators have been implicated in the control of biofilm associated cell surface organelles. These include the flagellar regulator FlhD/FlhC, the osmoregulator EnvZ/OmpR, and the colanic acid activator RcsCDB. Using flow cell technology and fluorescence microscopy, we determined the temporal expression from flhD::gfp, ompR::gfp, and rcsB::gfp in E. coli biofilm, as well as the impact of the negative regulation of flhD by OmpR and RcsB. Spatial gene expression was investigated from flhD::gfp.

RESULTS

The temporal gene expression profile for flhD yielded an early peak at 12 h, a minimum of expression at 35 h, and a second increase in expression towards 51 h of biofilm development. In contrast, the ompR profile showed a peak at 35 h. A mutation in ompR abolished time dependence of flhD expression after the initial growth period of 12 h. Intriguingly, rcsB expression did not correlate inversely with flhD expression, yet a mutation in rcsB abolished time dependence of flhD expression as well. Spatially, expression of flhD was highest in the outermost layer of the biofilm in the parent strain. In ompR and rcsB mutants, flhD was expressed throughout the biofilm. Mutations in both, ompR and rcsB increased flhD expression throughout all temporal and spatial experiments. This increase was paralleled by reductions in biofilm amounts at four tested time points.

CONCLUSION

Our data lead to the conclusion that FlhD/FlhC and its regulation by OmpR and RcsB may be our first target mechanism for the development of novel biofilm prevention and treatment techniques.

ß-Phenylethylamine as a novel nutrient treatment to reduce bacterial contamination due to Escherichia coli O157:H7 on beef meat

Bacterial infection by Escherichia coli O157:H7 through the consumption of beef meat or meat products is an ongoing problem, in part because bacteria develop resistances towards chemicals aimed at killing them. In an approach that uses bacterial nutrients to manipulate bacteria into behaviors or cellular phenotypes less harmful to humans, we screened a library of 95 carbon and 95 nitrogen sources for their effect on E. coli growth, cell division, and biofilm formation. In the initial screening experiment using the Phenotype MicroArray(TM) technology from BioLog (Hayward, CA), we narrowed the 190 starting nutrients down to eight which were consecutively tested as supplements in liquid beef broth medium. Acetoacetic acid (AAA) and ß-phenylethylamine (PEA) performed best in this experiment. On beef meat pieces, PEA reduced the bacterial cell count by 90% after incubation of the PEA treated and E. coli contaminated meat pieces at 10°C for one week.

Physiological consequences of mutations in the htpG heat shock gene of Escherichia coli

Mutation of the heat shock gene, htpG, causes severe defects of several cellular functions in Escherichia coli. A null htpG mutant constructed by gene replacement was impaired in the biosynthesis and secretion of several enzymes, and in biofilm formation and proteolysis. A significant decrease in the activity of β-lactamase in the ΔhtpG mutant was observed at 42°C. The alkaline phosphatase activity in sonicates of cells propagated at this raised temperature was lower in the ΔhtpG mutant than in the wild-type strain. The ability of the ΔhtpG mutant to degrade abnormal proteins was also impaired compared with the wild-type, but was increased at 42°C. Assays based on bioluminescence and crystal violet staining demonstrated that biofilm formation was diminished in the ΔhtpG mutant at the elevated temperature. All these defects can be complemented upon introducing htpG wild allele.

A novel inducer of Roseobacter motility is also a disruptor of algal symbiosis

Silicibacter sp. strain TM1040, a member of the Roseobacter clade, forms a symbiosis with unicellular phytoplankton, which is inextricably linked to the biphasic "swim or stick" lifestyle of the bacteria. Mutations in flaC bias the population toward the motile phase. Renewed examination of the FlaC(-) strain (HG1016) uncovered that it is composed of two different cells: a pigmented type, PS01, and a nonpigmented cell, PS02, each of which has an identical mutation in flaC. While monocultures of PS01 and PS02 had few motile cells (0.6 and 6%, respectively), coculturing the two strains resulted in a 10-fold increase in the number of motile cells. Cell-free supernatants from coculture or wild-type cells were fully capable of restoring motility to PS01 and PS02, which was due to increased fliC3 (flagellin) transcription, FliC3 protein levels per cell, and flagella synthesis. The motility-inducing compound has an estimated mass of 226 Da, as determined by mass spectrometry, and is referred to as Roseobacter Motility Inducer (RMI). Mutations affecting genes involved in phenyl acetic acid synthesis significantly reduced RMI, while defects in tropodithietic acid (TDA) synthesis had marginal or no effect on RMI. RMI biosynthesis is induced by p-coumaric acid, a product of algal lignin degradation. When added to algal cultures, RMI caused loss of motility, cell enlargement, and vacuolization in the algal cells. RMI is a new member of the roseobacticide family of troponoid compounds whose activities affect roseobacters, by shifting their population toward motility, as well as their phytoplankton hosts, through an algicidal effect.

A novel regulator RcdA of the csgD gene encoding the master regulator of biofilm formation in Escherichia coli

The FixJ/LuxR family transcription factor CsgD is a master regulator of biofilm formation in Escherichia coli. Previously, we identified more than 10 transcription factors that participate in regulation of the csgD promoter. After genomic SELEX screening of regulation targets, an uncharacterized TetR-type transcription factor YbjK was found to be involved in regulation of the csgD promoter. In addition, a number of stress-response genes were found to be under the direct control of YbjK. Taken together, we propose to rename it to RcdA (regulator of csgD). One unique feature of RcdA is its mode of DNA binding. Gel shift, DNase-I footprinting, and atomic force microscopic (AFM) analyses indicated that RcdA is a DNA-binding protein with a high level of cooperativity, with which it covers the entire surface of probe DNA through protein–protein interaction and moreover it induces the formation of aggregates of DNA–RcdA complexes.

The role of activated acetate intermediates in the control of Escherichia coli biofilm amounts

A previous study postulated that acetate metabolism was a metabolic sensory mechanism that related information about E. coli's environment to the formation of biofilms (Prüβ et al., Arch. Microbiol. 2010). Considering that mutants in pta ackA (no acetyl phosphate) and ackA (high acetyl phosphate) exhibited similarly increased biofilm amounts and three dimensional structures, the hypothesis for this study was that acetyl Co-A was a more likely mediator of the acetate effect than acetyl phosphate. The effect of acetate metabolism on biofilm amounts was detailed by using single carbon sources rather than the previously used mixed amino acid medium, as well as mutations in additional genes that contribute to acetate metabolism (ldhA, pflA, pflB). In summary, the mutations in ackA, pta ackA, and ldhA increased biofilm amounts in the presence of maltose, D-trehalose, D-mannose, and L-rhamnose, all of which get converted to acetyl-CoA. The ackA mutant also exhibited increased biofilm amounts in the presence of inosine and thymidine. The mutation in pflA decreased biofilm amounts in the presence of maltotriose, uridine, D-serine, and acetate. Since ackA, pta ackA, and ldhA mutants are expected to exhibit increased intracellular acetyl-CoA levels, and pflA and pflB mutants likely exhibit decreased acetyl-CoA concentrations, we believe that acetyl-CoA is the activated acetate intermediate that controls biofilm amounts.

Quantifying dental biofilm growth using cross-polarization optical coherence tomography

AIMS

Quantifying the ex vivo growth of complex multispecies dental biofilms using cross-polarization 1310-nm optical coherence tomography (CP-OCT) system was investigated.

METHODS AND RESULTS

Bacterial microcosms, which were derived from plaque samples of paediatric subjects, were incubated in a biofilm reactor system containing discs of different dental materials for 72 h with daily sucrose pulsing (5×). CP-OCT analysis of biofilm mass was validated with crystal violet (CV) assays at various growth stages of these complex biofilms. CP-OCT was able to filter out the back-reflected signals of water layers in the hydrated biofilm and allowed for direct biofilm quantification. The overall depth-resolved scattering intensity of the biofilm showed very strong positive correlation with CV assay quantification (Spearman's ρ = 0.92) during the growth phase of the biofilm.

CONCLUSION

CP-OCT was able to quantify the mass of the biofilm by measuring the overall depth-resolved scattering of the biofilm.

SIGNIFICANCE AND IMPACT OF THE STUDY

CP-OCT has the ability to nondestructively monitor biofilm growth and elucidate the growth characteristics of these microcosms on different dental material compositions.

The polyketide Pks1 contributes to biofilm formation in Mycobacterium tuberculosis

Infections caused by biofilms are abundant and highly persistent, displaying phenotypic resistance to high concentrations of antimicrobials and modulating host immune systems. Tuberculosis (TB), caused by Mycobacterium tuberculosis, shares these qualities with biofilm infections. To identify genetic determinants of biofilm formation in M. tuberculosis, we performed a small-scale transposon screen using an in vitro pellicle biofilm assay. We identified five M. tuberculosis mutants that were reproducibly attenuated for biofilm production relative to that of the parent strain H37Rv. One of the most attenuated mutants is interrupted in pks1, a polyketide synthase gene. When fused with pks15, as in some M. tuberculosis isolates, pks1 contributes to synthesis of the immunomodulatory phenolic glycolipids (PGLs). However, in strains such as H37Rv with split pks15 and pks1 loci, PGL is not produced and pks1 has no previously defined role. We showed that pks1 complementation restores biofilm production independently of the known role of pks1 in PGL synthesis. We also assessed the relationship among biofilm formation, the pks15/1 genotype, and M. tuberculosis phylogeography. A global survey of M. tuberculosis clinical isolates revealed surprising sequence variability in the pks15/1 locus and substantial variation in biofilm phenotypes. Our studies identify novel M. tuberculosis genes that contribute to biofilm production, including pks1. In addition, we find that the ability to make pellicle biofilms is common among M. tuberculosis isolates from throughout the world, suggesting that this trait is relevant to TB propagation or persistence.

Regulation of cell division, biofilm formation, and virulence by FlhC in Escherichia coli O157:H7 grown on meat

To understand the continuous problems that Escherichia coli O157:H7 causes as food pathogen, this study assessed global gene regulation in bacteria growing on meat. Since FlhD/FlhC of E. coli K-12 laboratory strains was previously established as a major control point in transducing signals from the environment to several cellular processes, this study compared the expression pattern of an E. coli O157:H7 parent strain to that of its isogenic flhC mutant. This was done with bacteria that had been grown on meat. Microarray experiments revealed 287 putative targets of FlhC. Real-time PCR was performed as an alternative estimate of transcription and confirmed microarray data for 13 out of 15 genes tested (87%). The confirmed genes are representative of cellular functions, such as central metabolism, cell division, biofilm formation, and pathogenicity. An additional 13 genes from the same cellular functions that had not been hypothesized as being regulated by FlhC by the microarray experiment were tested with real-time PCR and also exhibited higher expression levels in the flhC mutant than in the parent strain. Physiological experiments were performed and confirmed that FlhC reduced the cell division rate, the amount of biofilm biomass, and pathogenicity in a chicken embryo lethality model. Altogether, this study provides valuable insight into the complex regulatory network of the pathogen that enables its survival under various environmental conditions. This information may be used to develop strategies that could be used to reduce the number of cells or pathogenicity of E. coli O157:H7 on meat by interfering with the signal transduction pathways.

Environmental and genetic factors that contribute to Escherichia coli K-12 biofilm formation

Biofilms are communities of bacteria whose formation on surfaces requires a large portion of the bacteria's transcriptional network. To identify environmental conditions and transcriptional regulators that contribute to sensing these conditions, we used a high-throughput approach to monitor biofilm biomass produced by an isogenic set of Escherichia coli K-12 strains grown under combinations of environmental conditions. Of the environmental combinations, growth in tryptic soy broth at 37 degrees C supported the most biofilm production. To analyze the complex relationships between the diverse cell-surface organelles, transcriptional regulators, and metabolic enzymes represented by the tested mutant set, we used a novel vector-item pattern-mining algorithm. The algorithm related biofilm amounts to the functional annotations of each mutated protein. The pattern with the best statistical significance was the gene ontology 'pyruvate catabolic process,' which is associated with enzymes of acetate metabolism. Phenotype microarray experiments illustrated that carbon sources that are metabolized to acetyl-coenzyme A, acetyl phosphate, and acetate are particularly supportive of biofilm formation. Scanning electron microscopy revealed structural differences between mutants that lack acetate metabolism enzymes and their parent and confirmed the quantitative differences. We conclude that acetate metabolism functions as a metabolic sensor, transmitting changes in environmental conditions to biofilm biomass and structure.

Using enzymes to remove biofilms of bacterial isolates sampled in the food-industry

The aim of this study was to analyze the cleaning efficiency of polysaccharidases and proteolytic enzymes against biofilms of bacterial species found in food industry processing lines and to study enzyme effects on the composition of extracellular polymeric substances (EPS) and biofilm removal in a Clean-in-Place (CIP) procedure. The screening of 7 proteases and polysaccharidases for removal of biofilms of 16 bacterial species was first evaluated using a microtiter plate assay. The alkaline pH buffer removed more biofilm biomass as well as affecting a larger range of bacterial species. The two serine proteases and alpha-amylase were the most efficient enzymes. Proteolytic enzymes promoted biofilm removal of a larger range of bacterial species than polysaccharidases. Using three isolates derived from two bacterial species widely found in food processing lines (Pseudomonas fluorescens and the Bacillus cereus group), biofilms were developed on stainless steel slides and enzymatic solutions were used to remove the biofilms using CIP procedure. Serine proteases were more efficient in removing cells of Bacillus biofilms than polysaccharidases. However, polysaccharidases were more efficient in removing P. fluorescens biofilms than serine proteases. Solubilization of enzymes with a buffer containing surfactants, and dispersing and chelating agents enhanced the efficiency of polysaccharidases and proteases respectively in removing biofilms of Bacillus and P. fluorescens. A combination of enzymes targeting several components of EPS, surfactants, dispersing and chelating agents would be an efficient alternative to chemical cleaning agents.