Changes in the biocide susceptibility of Staphylococcus epidermidis and Escherichia coli cells associated with rapid attachment to plastic surfaces

The resistance change and stress response mechanisms of chlorine-resistant bacteria under microplastic stress in drinking water distribution system

The presence of both chlorine-resistant bacteria (CRB) and microplastics (MPs) in drinking water distribution systems (DWDS) poses a threat to water quality and human health. However, the risk of CRB bio evolution under the stress of MPs remains unclear. In this study, polypropylene (PP) and polyethylene (PE) were selected to study the adsorption and desorption behavior of sulfamethoxazole (SMX), and it was clear that MPs had the risk of carrying pollutants into DWDS and releasing them. The results of the antibiotic susceptibility test and disinfection experiment confirmed that MPs could enhance the resistance of CRB to antibiotics and disinfectants. Bacteria epigenetic resistance mechanisms were approached from multiple perspectives, including physiological and biochemical characteristics, as well as molecular regulatory networks. When MPs enter DWDS, CRB could attach to the surface of MPs and directly interact with both MPs and the antibiotics they release. This attachment process promoted changes in the composition and content of extracellular polymers (EPS) within cells, enhanced surface hydrophobicity, stimulated oxidative stress function, and notably elevated the relative abundance of certain antibiotic resistance genes (ARGs). This study elucidates the mechanism by which MPs alter the intrinsic properties of CRB, providing valuable insights into the effective avoidance of biological risks to water quality during CRB evolution.

Three dimensional printed biofilms: Fabrication, design and future biomedical and environmental applications

Three dimensional printing has emerged as a widely acceptable strategy for the fabrication of mammalian cell laden constructs with complex microenvironments for tissue engineering and regenerative medicine. More recently 3D printed living materials containing microorganisms have been developed and matured into living biofilms. The potential for engineered 3D biofilms as in vitro models for biomedical applications, such as antimicrobial susceptibility testing, and environmental applications, such as bioleaching, bioremediation, and wastewater purification, is extensive but the need for an in-depth understanding of the structure-function relationship between the complex construct and the microorganism response still exists. This review discusses 3D printing fabrication methods for engineered biofilms with specific structural features. Next, it highlights the importance of bioink compositions and 3D bioarchitecture design. Finally, a brief overview of current and potential applications of 3D printed biofilms in environmental and biomedical fields is discussed.

Microbial Biofilm: A Review on Formation, Infection, Antibiotic Resistance, Control Measures, and Innovative Treatment

Biofilm is complex and consists of bacterial colonies that reside in an exopolysaccharide matrix that attaches to foreign surfaces in a living organism. Biofilm frequently leads to nosocomial, chronic infections in clinical settings. Since the bacteria in the biofilm have developed antibiotic resistance, using antibiotics alone to treat infections brought on by biofilm is ineffective. This review provides a succinct summary of the theories behind the composition of, formation of, and drug-resistant infections attributed to biofilm and cutting-edge curative approaches to counteract and treat biofilm. The high frequency of medical device-induced infections due to biofilm warrants the application of innovative technologies to manage the complexities presented by biofilm.

Concomitant Effect of Quercetin and Its Copper Complex in the Development of Sustained-Release Nanoparticles of Polycaprolactone, Used for the Treatment of Skin Infection

The study aimed to improve the treatment of impetigo with naturally occurring quercetin and its copper-quercetin (Cu-Q) complex by preparing sustained-release (SR) nanoparticles of polycaprolactone (PCL). The solvent evaporation method was used for the copper-quercetin (Cu-Q) complex formation, and their PCL nanoparticles (PCL-NPs, Q-PCL-NPs, and Cu-Q-PCL-NPs) were prepared by the high-pressure homogenization method. Synthesis of nanoparticles was confirmed by their physicochemical and antibacterial properties of quercetin against Gram-positive as well as Gram-negative bacteria. The percentage loading efficiency of quercetin and release in 100 mM of phosphate buffer pH 7.4 and 5.5 at 37 °C was found to be more than 90% after 24 h with the zero-order release pattern. Minimum inhibitory concentration of nanoparticles was found to increase threefold in the case of Cu-Q-PCL-NPs may be due to the synergistic antibacterial behavior. Scanning electron microscopy showed spherical nanoparticles, and surface roughness was confirmed by atomic force microscopy analysis. Fortunately, no sign of irritation on rat skin even at 3%, was seen. In vitro antioxidant assay by 2,2-diphenyl-1-picrylhydrazyl reduction was found to be ≤80 ± 0.02% which confirmed their scavenging activity. Interestingly, for the ex vivo study, the tape-stripping model was applied against Staphylococcus aureus containing rats and showed the formation of the epidermal layer within 4-5 days. Confirmation of antibacterial activity of pure quercetin, from Cu-Q complex, and their SR release from Q-PCL-NPs and Cu-Q-PCL-NPs was considered an effective tool for the treatment of skin diseases and can be used as an alternative of already resistant ciprofloxacin in impetigo.

Mitigation and use of biofilms in space for the benefit of human space exploration

Biofilms are self-organized communities of microorganisms that are encased in an extracellular polymeric matrix and often found attached to surfaces. Biofilms are widely present on Earth, often found in diverse and sometimes extreme environments. These microbial communities have been described as recalcitrant or protective when facing adversity and environmental exposures. On the International Space Station, biofilms were found in human-inhabited environments on a multitude of hardware surfaces. Moreover, studies have identified phenotypic and genetic changes in the microorganisms under microgravity conditions including changes in microbe surface colonization and pathogenicity traits. Lack of consistent research in microgravity-grown biofilms can lead to deficient understanding of altered microbial behavior in space. This could subsequently create problems in engineered systems or negatively impact human health on crewed spaceflights. It is especially relevant to long-term and remote space missions that will lack resupply and service. Conversely, biofilms are also known to benefit plant growth and are essential for human health (i.e., gut microbiome). Eventually, biofilms may be used to supply metabolic pathways that produce organic and inorganic components useful to sustaining life on celestial bodies beyond Earth. This article will explore what is currently known about biofilms in space and will identify gaps in the aerospace industry's knowledge that should be filled in order to mitigate or to leverage biofilms to the advantage of spaceflight.

Impact of benzalkonium chloride, benzethonium chloride and chloroxylenol on bacterial antimicrobial resistance

This review examined 3655 articles on benzalkonium chloride (BKC), benzethonium chloride (BZT) and chloroxylenol (CHO) aiming to understand their impact on antimicrobial resistance. Following the application of inclusion/exclusion criteria, only 230 articles were retained for analysis; 212 concerned BKC, with only 18 for CHO and BZT. Seventy-eight percent of studies used MIC to measure BKC efficacy. Very few studies defined the term 'resistance' and 85% of studies defined 'resistance' as <10-fold increase (40% as low as 2-fold) in MIC. Only a few in vitro studies reported on formulated products and when they did, products performed better. In vitro studies looking at the impact of BKC exposure on bacterial resistance used either a stepwise training protocol or exposure to constant BKC concentrations. In these, BKC exposure resulted in elevated MIC or/and MBC, often associated with efflux, and at time, a change in antibiotic susceptibility profile. The clinical relevance of these findings was, however, neither reported nor addressed. Of note, several studies reported that bacterial strains with an elevated MIC or MBC remained susceptible to the in-use BKC concentration. BKC exposure was shown to reduce bacterial diversity in complex microbial microcosms, although the clinical significance of such a change has not been established. The impact of BKC exposure on the dissemination of resistant genes (notably efflux) remains speculative, although it manifests that clinical, veterinary and food isolates with elevated BKC MIC carried multiple efflux pump genes. The correlation between BKC usage and gene carriage, maintenance and dissemination has also not been established. The lack of clinical interpretation and significance in these studies does not allow to establish with certainty the role of BKC on AMR in practice. The limited literature and BZT and CHO do not allow to conclude that these will impact negatively on emerging bacterial resistance in practice.

Capsule formation around breast implants

All implants are rapidly coated by the host with glycoproteins forming a thin capsule, and this is a normal response. Where an inflammatory stimulus such as infection is present, the capsule can thicken and become microvascularised and sometimes calcified. This inflammatory stimulus can take the form of leachable chemicals from the implant, or bacteria live or dead. The presence of live bacteria can lead to biofilm development, which is part of the chronic infective, inflammatory process. Staphylococcus epidermidis and Cutibacterium acnes have been implicated in chronic infection around breast implants, and some animal models suggest their involvement in capsule contracture. Molecular methods have revealed an array of microorganisms from samples of removed capsular material, though they are extremely sensitive to contamination. The relevance of the results to capsular contracture remains poorly understood. Bacteria of low virulence are shown associated with capsular contracture and calcification, and measures beyond those conventionally applied need to be investigated to limit perioperative contamination.

Effect of Polystyrene Microplastics of Different Sizes to Escherichia coli and Bacillus cereus

The toxicity of polystyrene (PS) particles of different sizes was investigated using Gram-negative Escherichia coli and Gram-positive Bacillus cereus. PS particles could inhibit the cell growth of E. coli but promote the cell growth of B. cereus, and this difference might be attributed to different composition in their cell walls and the different interactions between the two bacteria and PS particles. Direct adhesion of E. coli cells on the surface of 5 μm PS microbeads by flagella was observed, indicating the putative role of E. coli on biofilm formation of plastisphere. The regulations of malondialdehyde, lactate dehydrogenase and glutathione were similar between the two bacteria, so the difference in the toxicity effect of PS between the two bacteria was not caused by the antioxidant activity. The overall results of the present study could help to understand the responses of different bacteria to microplastic exposure.

Disinfectant testing for veterinary and agricultural applications: A review

Disinfectants for veterinary and livestock use, plus skin antiseptics, are critical elements for the control of infectious agents, including zoonotic and antimicrobial-resistant micro-organisms, in managed animal species. Such agents impact animal welfare, economic performance and human health. Testing of disinfectants is needed for safety, efficacy and quality control. The present review examines the principal types of test (carrier, suspension, surface and field) that have been developed or attempted, plus the features inherent in the respective tests, particularly with respect to variability. Elements of testing that have to be controlled, or which can be manipulated, are discussed in the context of real-world scenarios and anticipated applications. Current national and international testing regimes are considered, with an emphasis on the UK, continental Europe and North America, and with further detail provided in the Supporting Information. Challenges to disinfectant efficacy include: the nature of the biological targets (bacteria, fungi, yeasts, spores, viruses and prions), the need for economical and safe working concentrations, the physical and chemical nature of contaminated surfaces, constraints on contact times and temperatures, the presence of organic soil and other barrier or neutralising substances (including biofilms), and thoroughness of pre-cleaning and disinfectant application. The principal challenges with veterinary disinfectant testing are the control of test variability, and relating test results to likely performance in variable field conditions. Despite some ambitions to develop standardised field tests for disinfectants, aside from skin antiseptic trials the myriad problems such tests pose with respect to cost, reproducibility and generalisability remain intractable.

Zinc- and strontium- co-incorporated nanorods on titanium surfaces with favorable material property, osteogenesis, and enhanced antibacterial activity

Early infection and peri-implantitis after implant restoration are major reasons for dental implant failure. Implant-associated infections are majorly attributed to biofilm formation. In this study, co-incorporated zinc- (Zn-) and strontium- (Sr-) nanorod coating on sandblasted and acid-etched (SLA) titanium (SLA-Zn/Sr) was fabricated by hydrothermal synthesis. It was aimed at promoting osteogenesis while inhibiting biofilm formation. The nanorod-like particles (φ 30-50 nm) were found to be evenly formed on SLA-Zn/Sr (Zn: 1.49 ± 0.16 wt%; Sr: 21.69 ± 2.74 wt%) that was composed of well-crystallized ZnTiO₃ and SrTiO₃ phases. With a sufficient interface bonding strength (42.00 ± 3.00 MPa), SLA-Zn/Sr enhanced the corrosion resistance property of titanium. Besides, SLA-Zn/Sr promoted the cellular initial adhesion, proliferation and osteogenic differentiation of rBMSCs in vitro while inhibiting the adhesion of Staphylococcus aureus and Porphyromonas gingivalis . In addition, through down-regulating icaA gene expression, this novel surface reduced the secretion of polysaccharide intercellular adhesion (reduced by 87.9% compared to SLActive) to suppress the S. aureus biofilm formation. We, therefore, propose a new chemical modification on titanium for multifunctional implant material development. Due to the Zn/Sr co-doping in coating, material properties, early osteogenic effect and antibacterial ability of titanium can be simultaneously enhanced, which has the potential to be applied in dental implantation in the future.

Into the well-A close look at the complex structures of a microtiter biofilm and the crystal violet assay

The microtiter assay is one of the most widely used methods for assessing biofilm formation. Though it has high throughput, this assay is known for its substantial deviation from experiment to experiment, and even from well to well. Since the assay constitutes one of the pillars of biofilm research, it was decided to examine the wells of a microtiter plate directly during growth, treatment, and the steps involved in crystal violet (CV) measurements. An inverted Zeiss LSM 880 confocal laser scanning microscope was used to visualize and quantify biomass directly in the wells of the microtiter plate. Green fluorescent protein-tagged Pseudomonas aeruginosa, PAO1, and live/dead stains were used to assess the structure, state, and position of biomass build-up. Microscopic observations were compared with colony-forming unit (CFU) and CV measurements. The development and the structured architecture of biomass was observed in real-time in the wells. Three-dimensional images of biomass were obtained from all of the microtiter wells; these showed variations from well to well. CV staining showed large variations in remaining biomass, depending on the method selected to remove the supernatant prior to CV staining (i.e. pipetting or manually discarding the fluid by inversion, washed or unwashed wells). Colony-forming unit counts or live/dead staining used to evaluate biomass with or without antibiotic treatment proved imprecise due to aggregation, limited removal of biomass, and overestimation of dead staining. The highly structured microenvironment of biomass in microtiter wells needs to be considered when designing and analyzing experiments. When using microtiter plates, stochastic variation due to growth and handling may lead to flawed conclusions. It is therefore recommended that this assay be used as a screening tool rather than as a stand-alone experimental tool.

Antibiotics versus biofilm: an emerging battleground in microbial communities

Biofilm is a complex structure of microbiome having different bacterial colonies or single type of cells in a group; adhere to the surface. These cells are embedded in extracellular polymeric substances, a matrix which is generally composed of eDNA, proteins and polysaccharides, showed high resistance to antibiotics. It is one of the major causes of infection persistence especially in nosocomial settings through indwelling devices. Quorum sensing plays an important role in regulating the biofilm formation. There are many approaches being used to control infections by suppressing its formation but CRISPR-CAS (gene editing technique) and photo dynamic therapy (PDT) are proposed to be used as therapeutic approaches to subside bacterial biofim infections, especially caused by deadly drug resistant bad bugs.

Silica-gentamicin nanohybrids: combating antibiotic resistance, bacterial biofilms, and in vivo toxicity

INTRODUCTION

Antibiotic resistance is a growing concern in health care. Methicillin-resistant Staphylococcus aureus (MRSA), forming biofilms, is a common cause of resistant orthopedic implant infections. Gentamicin is a crucial antibiotic preventing orthopedic infections. Silica-gentamicin (SiO2-G) delivery systems have attracted significant interest in preventing the formation of biofilms. However, compelling scientific evidence addressing their efficacy against planktonic MRSA and MRSA biofilms is still lacking, and their safety has not extensively been studied.

MATERIALS AND METHODS

In this work, we have investigated the effects of SiO2-G nanohybrids against planktonic MRSA as well as MRSA and Escherichia coli biofilms and then evaluated their toxicity in zebrafish embryos, which are an excellent model for assessing the toxicity of nanotherapeutics.

RESULTS

SiO2-G nanohybrids inhibited the growth and killed planktonic MRSA at a minimum concentration of 500 µg/mL. SiO2-G nanohybrids entirely eradicated E. coli cells in biofilms at a minimum concentration of 250 µg/mL and utterly deformed their ultrastructure through the deterioration of bacterial shapes and wrinkling of their cell walls. Zebrafish embryos exposed to SiO2-G nanohybrids (500 and 1,000 µg/mL) showed a nonsignificant increase in mortality rates, 13.4±9.4 and 15%±7.1%, respectively, mainly detected 24 hours post fertilization (hpf). Frequencies of malformations were significantly different from the control group only 24 hpf at the higher exposure concentration.

CONCLUSION

Collectively, this work provides the first comprehensive in vivo assessment of SiO2-G nanohybrids as a biocompatible drug delivery system and describes the efficacy of SiO2-G nanohybrids in combating planktonic MRSA cells and eradicating E. coli biofilms.

Effect of shear stress on the reduction of bacterial adhesion to antifouling polymers

In this work, two antifouling polymer brushes were tested at different shear stress conditions to evaluate their performance in reducing the initial adhesion of Escherichia coli. Assays were performed using a parallel plate flow chamber and a shear stress range between 0.005 and 0.056 Pa. These shear stress values are found in different locations in the human body where biomedical devices are placed. The poly(MeOEGMA) and poly(HPMA) brushes were characterized and it was shown that they can reduce initial adhesion up to 90% when compared to glass. Importantly, the performance of these surfaces was not affected by the shear stress, which is an indication that they do not collapse under this shear stress range. The brushes displayed a similar behavior despite the differences in their chemical composition and surface energy. Both surfaces have shown ultra-low adsorption of macromolecules from the medium when tested with relevant biological fluids (urine and serum). This indicates that these surfaces can potentially be used in biomedical devices to reduce initial bacterial colonization and eventually reduce biofilm formation on these devices.

In vitro studies of the antibacterial activity of Copaifera spp. oleoresins, sodium hypochlorite, and peracetic acid against clinical and environmental isolates recovered from a hemodialysis unit

Background

Patients submitted to hemodialysis therapy are more susceptible to infection, especially to infection by Gram-positive bacteria. Various research works have attempted to discover new antimicrobial agents from plant extracts and other natural products.

Methods

The present study aimed to assess the antibacterial activities of Copaifera duckei, C. reticulata, and C. oblongifolia oleoresins; sodium hypochlorite; and peracetic acid against clinical and environmental isolates recovered from a Hemodialysis Unit. The Minimum Inhibitory Concentration and the Fractionated Inhibitory Concentration Index were determined; the ability of the tested compounds/extracts to inhibit biofilm formation was evaluated by calculating the MICB50 and IC50.

Results

C. duckei was the most efficient among the assayed Copaifera species, and its oleoresin was more effective than peracetic acid and sodium hypochlorite. Copaifera oleoresins and disinfectants did not act synergistically at any of the tested combinations. Certain of C. duckei oleoresin, peracetic acid, and sodium hypochlorite concentrations inhibited biofilm formation and eradicated 50% of the biofilm population.

Conclusion

C. duckei oleoresin is a potential candidate for disinfectant formulations. Based on these results and given the high incidence of multi-resistant bacteria in hemodialysis patients, it is imperative that new potential antibacterial agents like C. duckei oleoresin, which is active against Staphylococcus, be included in disinfectant formulations.

Discrepancies between Cyclic and Linear Antimicrobial Peptide Actions on the Spectrochemical and Nanomechanical Fingerprints of a Young Biofilm

Antimicrobial peptides (AMPs) are currently known for their potential as an alternative to conventional antibiotics and new weapons against drug-resistant bacteria and biofilms. In the present work, the mechanism of action of a cyclic (colistin) and a linear (catestatin) AMP on a young E. coli biofilm was deciphered from the molecular to the cellular scale. To this end, infrared spectroscopy (attenuated total reflection-Fourier transform infrared) assisted by chemometric analysis was combined with fluorescence and atomic force microscopies to address the very different behaviors of both AMPs. Indeed, the colistin dramatically damaged the bacterial cell wall and the metabolism even though its action was not homogeneous over the whole bacterial population and repopulation can be observed after peptide removal. Conversely, catestatin did not lead to major damages in the bacterial morphology but its action was homogeneous over the whole bacterial population and the cells were unable to regrow after the peptide treatment. Our results strongly suggested that contrary to the cyclic molecule, the linear one is able to cause irreversible damages in the bacterial membrane concomitantly to a strong impact on the bacterial metabolism.

A post-planktonic era of in vitro infectious models: issues and changes addressed by a clinically relevant wound like media

Medical science is pitted against an ever-increasing rise in antibiotic tolerant microorganisms. Concurrently, during the past decade, biofilms have garnered much attention within research and clinical practice. Although the significance of clinical biofilms is becoming very apparent, current methods for diagnostics and direction of therapy plans in many hospitals do not reflect this knowledge; with many of the present tools proving to be inadequate for accurately mimicking the biofilm phenomenon. Based on current findings, we address some of the fundamental issues overlooked by clinical labs: the paradigm shifts that need to occur in assessing chronic wounds; better simulation of physiological conditions in vitro; and the importance of incorporating polymicrobial populations into biofilm models. In addition, this review considers using a biofilm relevant in vitro model for cultivating and determining the antibiotic tolerance and susceptibility of microorganisms associated with chronic wounds. This model presents itself as a highly rapid and functional tool that can be utilized by hospitals in an aim to improve bedside treatments.

An Activity of Thioacyl Derivatives of 4-Aminoquinolinium Salts towards Biofilm Producing and Planktonic Forms of Coagulase-Negative Staphylococci

Microorganisms present in different environments have developed specific mechanisms of settling on various abiotic and biotic surfaces by forming a biofilm. It seems to be well justified to search for new compounds enabling biofilm reduction, which is highly resistant to antibiotics. This study was thus an initial assessment of the antibacterial activity of two new quinoline derivatives of a structure of 3-thioacyl 1-methyl 4-arylaminoquinolinium salts against coagulase-negative staphylococci (CoNS) isolated from a hospital environment, in a form of both biofilms and in planktonic form. Thirty-three stains of CoNS isolated from the hospital environment (air, surfaces) and seven reference strains from the ATCC collection were selected for the study. The mean MIC value for 1-methyl-3-benzoylthio-4-(4-chlorophenylamino)quinolinum chloride (4-chlorophenylamino derivative) was 42.60 ± 19.91 μg/mL, and in the case of strains subjected to 1-methyl-3-benzoylthio-4-(4-fluorophenylamino)quinolinum chloride (4-fluorophenylamino derivative) activity, the mean MIC value was 43.20 ± 14.30 μg/mL. The mean concentration of 4-chlorophenylamino derivative that inhibited biofilm formation was 86.18 ± 30.64 μg/mL. The mean concentration of 4-fluorophenylamino derivatives that inhibited biofilm formation was higher and amounted to 237.09 ± 160.57 μg/mL. Based on the results, both derivatives of the examined compounds exhibit high antimicrobial activity towards strains growing both in planktonic and biofilm form.

Green biocides, a promising technology: current and future applications to industry and industrial processes

The study of biofilms has skyrocketed in recent years due to increased awareness of the pervasiveness and impact of biofilms. It costs the USA literally billions of dollars every year in energy losses, equipment damage, product contamination and medical infections. But biofilms also offer huge potential for cleaning up hazardous waste sites, filtering municipal and industrial water and wastewater, and forming biobarriers to protect soil and groundwater from contamination. The complexity of biofilm activity and behavior requires research contributions from many disciplines such as biochemistry, engineering, mathematics and microbiology. The aim of this review is to provide a comprehensive analysis of emerging novel antimicrobial techniques, including those using myriad organic and inorganic products as well as genetic engineering techniques, the use of coordination complex molecules, composite materials and antimicrobial peptides and the use of lasers as such or their modified use in combination treatments. This review also addresses advanced and recent modifications, including methodological changes, and biocide efficacy enhancing strategies. This review will provide future planners of biofilm control technologies with a broad understanding and perspective on the use of biocides in the field of green developments for a sustainable future.

Bacterial biofilms: a diagnostic and therapeutic challenge

Bacteria have traditionally been regarded as individual organisms growing in homogeneous planktonic populations. However, bacteria in natural environments usually form communities of surface-adherent organisms embedded in an extracellular matrix, called biofilms. Current antimicrobial strategies often fail to control bacteria in the biofilm mode of growth. Treatment failure is particularly frequent in association with intracorporeal or transcutaneous medical devices and compromised host immunity. The rising prevalence of these risk factors over the last decades has paralleled the increase in biofilm infections. This review discusses the shortcomings of current therapies against biofilms both in theory and with clinical examples. Biofilm characteristics are described with a focus on new diagnostic and therapeutic targets.

Evaluation of detergents and contact time on biofilm removal from flexible endoscopes

BACKGROUND

The formation of endoscopic biofilm reduces the results of cleaning and disinfection and may increase nosocomial infection. This study aims to evaluate the effects of various detergents and different contact time on the removal of biofilm on flexible endoscopes based on an artificial biofilm model.

METHOD

Endoscopic biofilm model was established and treated with various detergents (detergent 1, Rapid Multi-Enzyme; detergent 2, Scopezime; and detergent 3, Intercept) for 3, 5, and 7 minutes. Escherichia coli viable counts and biofilm changes were measured by colony counting and electron microscopy scanning, respectively.

RESULTS

Statistical differences were observed between various detergents and the control group (P < .001) but not among the different contact time groups (3, 5, and 7 minutes, P > .05). Multiple comparisons showed that statistical differences in residual biofilm bacteria were observed between the detergents and the control (P < .001). Significant differences (P < .001) in residual biofilm bacteria existed between the 2 enzymatic detergents and the nonenzymatic detergent group, whereas no significant difference was observed between the 2 enzymatic detergents (P > .05). No crossover effect was observed between various detergent groups, contact time, and the control group (P > .05). Electron microscopy scanning revealed that, after various detergents and contact time of 3, 5, and 7 minutes, the residual biofilm in the enzymatic detergent group was significantly more than that of the nonenzymatic detergent group. No significant difference was observed among the groups with the same detergent and different contact time.

CONCLUSION

Significantly more biofilm bacteria and biofilms were found in the enzymatic detergent groups compared with the nonenzymatic detergent group, whereas no significant difference was observed among 3, 5, and 7 minutes groups.

Antimicrobial effect of alexidine and chlorhexidine against Enterococcus faecalis infection

A previous study demonstrated that alexidine has greater affinity for the major virulence factors of bacteria than chlorhexidine. The aim of this study was to compare the antimicrobial activity of 1% alexidine with that of 2% chlorhexidine using Enterococcus faecalis-infected dentin blocks. Sixty bovine dentin blocks were prepared and randomly divided into six groups of 10 each. E. faecalis was inoculated on 60 dentin blocks using the Luppens apparatus for 24 h and then the dentin blocks were soaked in 2% chlorhexidine or 1% alexidine solutions for 5 and 10 min, respectively. Sterile saline was used as a control. The antimicrobial efficacy was assessed by counting the number of bacteria adhering to the dentin surface and observing the degradation of bacterial shape or membrane rupture under a scanning electron microscope. Significantly fewer bacteria were observed in the 2% chlorhexidine- or 1% alexidine-soaked groups than in the control group (P<0.05). However, there was no significant difference in the number of bacteria adhering to the dentinal surface between the two experimental groups or between the two soaking time groups (P>0.05). Ruptured or antiseptic-attached bacteria were more frequently observed in the 10-min-soaked chlorhexidine and alexidine groups than in the 5-min-soaked chlorhexidine and alexidine groups. In conclusion, 10-min soaking with 1% alexidine or 2% chlorhexidine can be effective against E. faecalis infection.

Antimicrobial effect of alexidine and chlorhexidine against Enterococcus faecalis infection

A previous study demonstrated that alexidine has greater affinity for the major virulence factors of bacteria than chlorhexidine. The aim of this study was to compare the antimicrobial activity of 1% alexidine with that of 2% chlorhexidine using Enterococcus faecalis-infected dentin blocks. Sixty bovine dentin blocks were prepared and randomly divided into six groups of 10 each. E. faecalis was inoculated on 60 dentin blocks using the Luppens apparatus for 24 h and then the dentin blocks were soaked in 2% chlorhexidine or 1% alexidine solutions for 5 and 10 min, respectively. Sterile saline was used as a control. The antimicrobial efficacy was assessed by counting the number of bacteria adhering to the dentin surface and observing the degradation of bacterial shape or membrane rupture under a scanning electron microscope. Significantly fewer bacteria were observed in the 2% chlorhexidine- or 1% alexidine-soaked groups than in the control group (P<0.05). However, there was no significant difference in the number of bacteria adhering to the dentinal surface between the two experimental groups or between the two soaking time groups (P>0.05). Ruptured or antiseptic-attached bacteria were more frequently observed in the 10-min-soaked chlorhexidine and alexidine groups than in the 5-min-soaked chlorhexidine and alexidine groups. In conclusion, 10-min soaking with 1% alexidine or 2% chlorhexidine can be effective against E. faecalis infection.

Characterising the structure of photosynthetic biofilms using fluid dynamic gauging

A new configuration of the fluid dynamic gauging technique for measuring soft layers on surfaces was used to monitor the growth of a cyanobacterium, Synechococcus sp. WH 5701, on stainless steel (SS), glass and an indium tin oxide (ITO) on a polyethylene terephthalate (PET) substratum. The biofilm thickness increased steadily over 4 weeks and exhibited noticeable changes in microstructure and strength. The biofilms all exhibited a two-layer structure, with a compact layer next to the substratum and a loose layer above. Biofilms on ITO or SS exhibited cohesive failure when removed by fluid shear whereas those on glass exhibited adhesive failure. The technique is able to elucidate various aspects of biofilm behaviour, as illustrated by the action of a biocide (NaOCl) on a mature biofilm.

Lecithin-based novel cationic nanocarriers (LeciPlex) I: fabrication, characterization and evaluation

Aims: In the present investigation, the feasibility of fabricating novel self-assembled cationic nanocarriers (LeciPlex) containing cetyltrimethylammonium bromide (CTAB) or didodecyldimethylammonium bromide (DDAB) and soybean lecithin using pharmaceutically acceptable biocompatible solvents such as 2-Pyrrolidone (Soluphor P®) and diethyleneglycol monoethyl ether (Transcutol®) was established. Materials & Methods: The interaction between DDAB/CTAB and soybean lecithin in the nanocarriers was confirmed by differential scanning calorimetry and in vitro antimicrobial studies. The positive charge on the nanocarriers was confirmed by zeta potential analysis. Results: Transmission electron microscopy analysis could not reveal sufficient information regarding the internal structure of the nanocarriers, whereas cryotransmission electron microscopy studies indicated that these novel nanocarriers have unilamellar structure. Small-angle neutron scattering studies confirmed interaction of cationic surfactant (DDAB) and lecithin in the nanocarriers and confirmed the presence of unilamellar nanostructures. Conclusion: Various hydrophobic drugs could be encapsulated in the CTAB/DDAB-based lecithin nanocarriers (CTAB–LeciPlex or DDAB–LeciPlex) irrespective of their difference in log p-values. In vitro antimicrobial studies on triclosan-loaded LeciPlex confirmed entrapment of triclosan in the nanocarriers. The ability of CTAB–LeciPlex and DDAB–LeciPlex to condense plasmid DNA was established using agarose gel electrophoresis. DDAB–LeciPlex could successfully transfect pDNA in HEK-293 cells indicating potential in gene delivery.

Original submitted: 20/8/2010; Revised submitted: 14/12/2010

Antimicrobial tolerance and the significance of persister cells in recalcitrant chronic wound biofilms

The application of antimicrobials in the management of wounds is a complex procedure requiring appropriate clinical decision making, judgment and a thorough understanding of antimicrobial therapies, together with their potential disadvantages. There is considerable direct and indirect evidence for the presence of bacterial biofilms in the chronic wound bed, and it has been demonstrated that bacteria within these biofilms may exhibit both specific and nonspecific antimicrobial tolerance. The antimicrobial tolerance of biofilms is a major concern in the treatment of both infected and nonhealing chronic wounds and an understanding of the mechanisms involved is of fundamental importance in managing wound infections and developing future wound management strategies. The aim of this review is therefore to provide an overview of our current understanding of the mechanisms by which bacteria in wound biofilms can resist conventional antibiotic and antibacterial therapies which is very important to wound healing.

Chapter 4: In vitro biofilm models: an overview

Observing naturally occurring biofilms in situ or ex situ has revealed the wide distribution of sessile microbial communities. The ubiquity, variety and complexity of biofilms is now widely accepted by microbiologists. While they are associated with many beneficial functions such as nutrient cycling, bioremediation and colonization resistance, adverse effects including recalcitrance, their involvement in industrial fouling, contamination and infection have made biofilms a priority research topic. We know that most biofilms, other than within certain infections and laboratory flasks, are composed of multiple species and that there is arguably no unifying biofilm architecture. Biofilms do however share certain properties including the presence of gradients of nutrients, gasses and metabolic products, relatively increased cell density, deposition of extracellular polymeric substances and marked recalcitrance towards antimicrobial treatments. Much of our understanding of biofilm physiology and micro-ecology originates from experiments using in vitro biofilm models. Broadly speaking, such models may be used to replicate environmental conditions within the laboratory or to focus on selected variables such a growth rate or fluid flow, etc. This chapter provides an overview of some commonly used biofilm models including microtitre plate systems, flow cells, the constant depth film fermenter, annular reactors and the perfused biofilm fermenter. While perfused biofilm fermenters, in particular, enable growth rate to be controlled within thin, relatively homogenous, quasi steady-state biofilms through modulation of flow rate nutrient availability, other models provide representative modelling of in situ conditions where steady states may be uncommon.

The effect of multiple cycles of contamination, detergent washing, and disinfection on the development of biofilm in endoscope tubing

BACKGROUND

Patient soil and bacterial biofilm in patient-ready endoscope channels can adversely impact the efficacy of detergent and disinfectant, thereby increasing the risk of nosocomial infection. Biofilm bacteria are firmly attached to one another and to the substrate by exopolysaccharide, making them difficult to remove. We analyzed the effect of 20 wash/contamination cycles on biofilm formation.

MATERIALS

Pseudomonas aeruginosa biofilm-covered endoscope tubing was soaked in water (control), an enzymatic cleaner, or a nonenzymatic cleaner (Matrix) for 10 minutes and decontaminated in a washer-disinfector machine. Media containing P aeruginosa was then recycled to simulate contamination in clinical practice.

RESULTS

SEM analysis showed that loosely attached biofilm was removed under the high flow rates in the washer-disinfector. The control tubing remained 100% covered with biofilm, which became thicker with increased recontamination cycles. Washing in the enzymatic detergent retarded the redevelopment of biofilm. The nonenzymatic cleaner (Matrix) continued to remove more biofilm with an increasing number of wash/contamination cycles. At the 20th cycle, 90% of the tubing was biofilm-free.

CONCLUSION

Washing endoscopes under high flow rates with some detergents removes established biofilm and retards biofilm generation, emphasizing the importance of cleaning before disinfection. Continued research into the physicochemical mechanisms of biofilm adherence and removal is needed to optimize detergents.

In vitro study of the effect of cationic biocides on bacterial population dynamics and susceptibility

Cationic biocides (CBs) are widely used in domestic and public hygiene and to control biofouling and microbial contamination in industry. The increased use of biocides has led to concern regarding possible reductions in biocide effectiveness. Domestic drain microcosms were stabilized for 5 months and then exposed to polyhexamethylene biguanide (PHMB) at 0.1, 0.2, and 0.4g liter(-1) over 6 months and characterized throughout by differential culture, together with eubacterial-specific PCR-denaturing gradient gel electrophoresis. Additionally, MICs and minimal bactericidal concentrations (MBCs) for bacteria previously isolated from a domestic drain (n = 18) and the human skin (n = 13) were determined before, during, and after escalating, sublethal exposure (14 passages) to two quaternary ammonium compounds (QAC1 and QAC2), the bisbiguanide chlorhexidine (CHX), and PHMB. Exposure of the drain microcosm to PHMB did not decrease the total viable count although significant (P < 0.01) decreases in recovery were observed for the gram-positive cocci with associated clonal expansion of pseudomonads (from ca. 0.1% of the population to ca. 10%). This clonal expansion was also manifested as elevations in bacteria that could grow in the presence of PHMB, CHX, and QAC1. Decreases in susceptibility (greater than twofold) occurred for 10/31 of the test bacteria for QAC1, 14/31 for QAC2, 10/31 for CHX, and 7/31 for PHMB. Exposure of microcosms to PHMB targeted gram-positive species and caused the clonal expansion of pseudomonads. In terms of prolonged-sublethal passage on CBs, exposure to all the biocides tested resulted in susceptibility decreases for a proportion of test bacteria, but refractory clones were not generated.

Disinfectant test against monoculture and mixed-culture biofilms composed of technological, spoilage and pathogenic bacteria: bactericidal effect of essential oil and hydrosol of Satureja thymbra and comparison with standard acid-base sanitizers

AIMS

To assess the antimicrobial action of three natural-derived products (essential oil, decoction and hydrosol of Satureja thymbra) against biofilms, composed of useful, spoilage and pathogenic bacteria (formed as monoculture or/and mixed-culture), and to compare their efficiency with three standard acid and alkaline chemical disinfectants.

METHODS AND RESULTS

Two acids (hydrochloric and lactic, pH 3), one alkali (sodium hydroxide, pH 11), the essential oil of S. thymbra (1% v/v) and the two by-products of the essential oil purification procedure (the decoction and the hydrosol fraction of essential oil, 100%), were tested against biofilms formed by five bacterial species, either as monospecies, or as mixed-culture of all species. The tested bacterial species were Staphylococcus simulans and Lactobacillus fermentum (useful technological bacteria), Pseudomonas putida (spoilage bacterium), Salmonella enterica and Listeria monocytogenes (pathogenic bacteria). Biofilms were left to be formed on stainless steel coupons for 5 days at 16 degrees C, before the application of disinfection treatments, for 60 and 180 min. The disinfection efficiency was evaluated by detaching the remaining viable biofilm cells and enumerating them by agar plating, as well as by automated conductance measurements (using Rapid Automated Bacterial Impedance Technique). Both these methods revealed that the essential oil and the hydrosol of S. thymbra exhibited a strong antimicrobial action against both monospecies and mixed-culture biofilms. Surprisingly, the efficiency of the other three acid-base disinfectants was not adequate, although a long antimicrobial treatment was applied (180 min).

CONCLUSIONS

The essential oil of S. thymbra (1%), as well as its hydrosol fraction (100%), presents sufficient bactericidal effect on bacterial biofilms formed on stainless steel.

SIGNIFICANCE AND IMPACT OF THE STUDY

Use of natural antimicrobial agents could provide alternative or supplemented ways for the disinfection of microbial-contaminated industrial surfaces.

The Listeria monocytogenes homolog of the Escherichia coli era gene is involved in adhesion to inert surfaces

Two transposon-insertional mutants of Listeria monocytogenes showing smaller viable surface-attached cell populations after disinfection with N,N-didecyl-N,N-dimethylammonium chloride were identified. In both mutants, transposon Tn917-lac was found to be inserted into the same gene, lmo1462, which is homologous to the essential Escherichia coli era gene. Both L. monocytogenes lmo1462-disrupted mutants displayed lower growth rates, as was also shown for several E. coli era mutants, and the lmo1462 gene was able to complement the growth defect of an E. coli era mutant. We showed that the disruption of lmo1462 decreased the ability of L. monocytogenes cells to adhere to stainless steel. Our results suggest that this era-like gene is involved in adhesion and contributes to the presence of L. monocytogenes on surfaces.

Role of the rapA gene in controlling antibiotic resistance of Escherichia coli biofilms

By using a high-throughput screening method, a mutant of a uropathogenic Escherichia coli strain affected in the rapA gene was isolated. The mutant formed normal-architecture biofilms but showed decreased penicillin G resistance, although the mutation did not affect planktonic cell resistance. Transcriptome analysis showed that 22 genes were down-regulated in the mutant biofilm. One of these genes was yhcQ, which encodes a putative multidrug resistance pump. Mutants with mutations in this gene also formed biofilms with decreased resistance, although the effect was less pronounced than that of the rapA mutation. Thus, an additional mechanism(s) controlled by a rapA-regulated gene(s) was involved in wild-type biofilm resistance. The search for this mechanism was guided by the fact that another down-regulated gene in rapA biofilms, yeeZ, is suspected to be involved in extra cell wall-related functions. A comparison of the biofilm matrix of the wild-type and rapA strains revealed decreased polysaccharide quantities and coverage in the mutant biofilms. Furthermore, the (fluorescent) functional penicillin G homologue Bocillin FL penetrated the mutant biofilms more readily. The results strongly suggest a dual mechanism for the wild-type biofilm penicillin G resistance, retarded penetration, and effective efflux. The results of studies with an E. coli K-12 strain pointed to the same conclusion. Since efflux and penetration can be general resistance mechanisms, tests were conducted with other antibiotics. The rapA biofilm was also more sensitive to norfloxacin, chloramphenicol, and gentamicin.

Caries-related plaque microcosm biofilms developed in microplates

In vivo dental plaque biofilms consist of complex communities of oral bacteria that are a challenge to replicate in vitro. The aim of this investigation was to establish human dental plaque microcosms in microplates to reflect conditions that are relevant to dental caries. Microcosm plaque biofilms were initiated from the saliva of two different donors, grown for up to 10 days in 24-welled microplates on Thermanox coverslips in various types of artificial saliva with and without sucrose, which were replaced daily. Microbiota composition of 40 species associated with oral health and dental caries was monitored in the plaques using Checkerboard DNA-DNA hybridization analysis. pH was measured as an indicator of cariogenic potential. The composition of the saliva inocula was different, and yielded plaque microcosms with different composition and growth responses to sucrose. Artificial saliva type and presence of sucrose, and the resulting growth and pH conditions, modified the growth of individual species and hence the ecological profile of the microplate plaques during development. Complex population shifts were observed during development, and older plaques comprised predominantly facultative anaerobic species. Sucrose supplementation limited the decline of Streptococci over time but did not increase the abundance of mutans Streptococci. Sucrose at 0.15% increased levels of caries-associated species including Lactobacillus fermentum, Lactobacillus acidophilus and Actinomyces gerensceriae; these were further increased with sucrose at 0.5%, in addition to Actinomyces israelii, Rothia dentocariosa and Capnocytophaga gingivalis. The microplate plaques demonstrated complex community dynamics that appeared to reflect the maturation of natural plaques, and sucrose induced a cariogenic plaque composition and pH.

A small subpopulation of blastospores in candida albicans biofilms exhibit resistance to amphotericin B associated with differential regulation of ergosterol and beta-1,6-glucan pathway genes

The resistance of Candida albicans biofilms to a broad spectrum of antimicrobial agents has been well documented. Biofilms are known to be heterogeneous, consisting of microenvironments that may induce formation of resistant subpopulations. In this study we characterized one such subpopulation. C. albicans biofilms were cultured in a tubular flow cell (TF) for 36 h. The relatively large shear forces imposed by draining the TF removed most of the biofilm, which consisted of a tangled mass of filamentous forms with associated clusters of yeast forms. This portion of the biofilm exhibited the classic architecture and morphological heterogeneity of a C. albicans biofilm and was only slightly more resistant than either exponential- or stationary-phase planktonic cells. A submonolayer fraction of blastospores that remained on the substratum was resistant to 10 times the amphotericin B dose that eliminated the activity of the planktonic populations. A comparison between planktonic and biofilm populations of transcript abundance for genes coding for enzymes in the ergosterol (ERG1, -3, -5, -6, -9, -11, and -25) and beta-1,6-glucan (SKN and KRE1, -5, -6, and -9) pathways was performed by quantitative RT-PCR. The results indicate a possible association between the high level of resistance exhibited by the blastospore subpopulation and differential regulation of ERG1, ERG25, SKN1, and KRE1. We hypothesize that the resistance originates from a synergistic effect involving changes in both the cell membrane and the cell wall.

A three-dimensional computer model of four hypothetical mechanisms protecting biofilms from antimicrobials

Four hypothetical mechanisms for protection of biofilms against antimicrobials were incorporated into a three-dimensional model of biofilm growth and development. The model integrated processes of substrate utilization, diffusion, growth, cell migration, death, and detachment in a cellular automaton framework. Compared to simulations of unprotected biofilms, each of the protective mechanisms provided some tolerance to antimicrobial action. When the mechanisms were compared to each other, the behaviors of the four protective mechanisms produced distinct shapes of killing curves, nonuniform spatial patterns of survival and cell type distribution, and anticipated susceptibility patterns for dispersed biofilm cells. The differences between the protective mechanisms predicted in these simulations could guide the design of experiments to discriminate antimicrobial tolerance mechanisms in biofilms. Each of the mechanisms could be a plausible avenue of biofilm protection.

Antimicrobial susceptibility of Staphylococcus aureus and Staphylococcus epidermidis biofilms isolated from infected total hip arthroplasty cases

BACKGROUND

It is difficult to treat implant-related infections because bacteria form biofilms on implants. Biofilms protect the organisms from the host's immune system and prevent penetration of antimicrobial agents. We investigated the susceptibility of six strains isolated from infected total hip arthroplasty (THA) cases to six antimicrobial agents.

METHODS

Six Staphylococcus aureus and S. epidermidis strains isolated from infected THA cases and S. aureus ACTT 25923, positive strains of biofilms, were used in this study. Biofilms were developed on 96-well titer plates. After 7 days the nutrient solution was aspirated, and wells were rinsed three times with sterile water. A series of doubling dilutions of each antimicrobial agent (16, 32, 64, 128, 256, 512, and 1024 microg/ml) in trypticase soy broth were added to the wells. The plates were incubated at 37 degrees C. After 24 h, the contents were aspirated and wells were rinsed three times with sterile water. The surfaces of wells were vigorously scraped with a sterile swab and applied to sheep blood agar plates at 37 degrees C in an aerobic chamber for 24 h. The minimum bactericidal concentrations (MBCs) were determined as the lowest concentration of antibiotic resulting in 100% reduction of viable cells compared to the antibiotic-free control. Biofilms were produced on stainless steel washers, and the time-course changes were observed by scanning electron microscopy (SEM).

RESULTS

Planktonic bacteria were sensitive to the antimicrobial agents, but biofilm bacteria were markedly resistant. SEM revealed that biofilms grew larger with time.

CONCLUSIONS

The MBCs of antimicrobial agents for biofilms bacteria were higher than those of planktonic bacteria. Therefore, it is suggested that implant-related infection is difficult to treat with antimicrobial agents alone.

Destruction of Deinococcus geothermalis biofilm by photocatalytic ALD and sol-gel TiO2 surfaces

The aim of the present work was to explore possibilities of photocatalytic TiO2 coating for reducing biofilms on non-living surfaces. The model organism, Deinococcus geothermalis, known to initiate growth of durable, colored biofilms on machine surfaces in the paper industry, was allowed to form biofilms on stainless steel, glass and TiO2 film coated glass or titanium. Field emission electron microscopy revealed that the cells in the biofilm formed at 45 degrees C under vigorous shaking were connected to the surface by means of numerous adhesion threads of 0.1-0.3 microm in length. Adjacent cells were connected to one another by threads of 0.5-1 microm in length. An ultrastructural analysis gave no indication for the involvement of amorphous extracellular materials (e.g., slime) in the biofilm. When biofilms on photocatalytic TiO2 surfaces, submerged in water, were exposed to 20 W h m(-2) of 360 nm light, both kinds of adhesion threads were completely destroyed and the D. geothermalis cells were extensively removed (from >10(7) down to below 10(6) cells cm(-2)). TiO2 films prepared by the sol-gel technique were slightly more effective than those prepared by the ALD technique. Doping of the TiO2 with sulfur did not enhance its biofilm-destroying capacity. The results show that photocatalytic TiO2 surfaces have potential as a self-cleaning technology for warm water using industries.