Development of a standard test to assess the resistance of Staphylococcus aureus biofilm cells to disinfectants

Alkylated EDTA potentiates antibacterial photodynamic activity of protoporphyrin

Antibiotic resistance has garnered significant attention due to the scarcity of new antibiotics in development. Protoporphyrin IX (PpIX)-mediated photodynamic therapy shows promise as a novel antibacterial strategy, serving as an alternative to antibiotics. However, the poor solubility of PpIX and its tendency to aggregate greatly hinder its photodynamic efficacy. In this study, we demonstrate that alkylated EDTA derivatives (aEDTA), particularly C14-EDTA, can enhance the solubility of PpIX by facilitating its dispersion in aqueous solutions. The combination of C14-EDTA and PpIX exhibits potent antibacterial activity against Staphylococcus aureus (S. aureus) when exposed to LED light irradiation. Furthermore, this combination effectively eradicates S. aureus biofilms, which are known to be strongly resistant to antibiotics, and demonstrates high therapeutic efficacy in an animal model of infected ulcers. Mechanistic studies reveal that C14-EDTA can disrupt PpIX crystallization, increase bacterial membrane permeability and sequester divalent cations, thereby improving the accumulation of PpIX in bacteria. This, in turn, enhances reactive oxygen species (ROS) production and the antibacterial photodynamic activity. Overall, this effective strategy holds great promise in combating antibiotic-resistant strains.

Reduced Pseudomonas aeruginosa Cell Size Observed on Planktonic Cultures Grown in the International Space Station

Bacterial growth and behavior have been studied in microgravity in the past, but little focus has been directed to cell size despite its impact on a myriad of processes, including biofilm formation, which is impactful regarding crew health. To interrogate this characteristic, supernatant aliquots of P. aeruginosa cultured on different materials and media on board the International Space Station (ISS) as part of the Space Biofilms Project were analyzed. For that experiment, P. aeruginosa was grown in microgravity-with matching Earth controls-in modified artificial urine medium (mAUMg-high Pi) or LB Lennox supplemented with KNO3, and its formation of biofilms on six different materials was assessed. After one, two, and three days of incubation, the ISS crew terminated subsets of the experiment by fixation in paraformaldehyde, and aliquots of the supernatant were used for the planktonic cell size study presented here. The measurements were obtained post-flight through the use of phase contrast microscopy under oil immersion, a Moticam 10+ digital camera, and the FIJI image analysis program. Statistical comparisons were conducted to identify which treatments caused significant differences in cell dimensions using the Kruskal-Wallis and Dunn tests. There were statistically significant differences as a function of material present in the culture in both LBK and mAUMg-high Pi. Along with this, the data were also grouped by gravitational condition, media, and days of incubation. Comparison of planktonic cells cultured in microgravity showed reduced cell length (from 4% to 10% depending on the material) and diameter (from 1% to 10% depending on the material) with respect to their matching Earth controls, with the caveat that the cultures may have been at different points in their growth curve at a given time. In conclusion, smaller cells were observed on the cultures grown in microgravity, and cell size changed as a function of incubation time and the material upon which the culture grew. We describe these changes here and possible implications for human space travel in terms of crew health and potential applications.

Fungal versus non-fungal supra-inguinal prosthetic vascular graft infections: A cohort study

OBJECTIVES

Fungal prosthetic vascular graft infections are rare and mainly supra-inguinal. Current guidelines are based on the few studies that have specifically investigated this population, with few risk factors described. The objective of this study is to compare fungal and non-fungal supra-inguinal prosthetic vascular graft infections (PVGI), describing their specificities, identifying risk factors, and evaluating outcomes.

PATIENTS AND METHODS

This is a single-center retrospective cohort study carried out at the Pitié-Salpêtrière Hospital in Paris, including all patients who were treated for a supra-inguinal PVGI between January 1st, 2009 and February 28th, 2021. Preoperative, intraoperative and postoperative data were compared between fungal and non-fungal PVGI.

RESULTS

Out of the 475 patients screened, 148 developed a supra-inguinal PVGI: 32 fungal and 116 non-fungal. Factors independently associated with fungal PVGI were presence of a prostheto-digestive fistula (OR 5.98; 95% CI 2.29-15.62) and preoperative antibiotic therapy of seven days or more (OR 2.87; 95% CI 1.12-7.38). Mortality rate at 180 days was significantly higher for fungal as compared to non-fungal PVGIs (38% vs. 16% p = 0.009) and for fungal PVGI with prostheto-digestive fistula. However, there was no statistically significant relation between mortality due to prostheto-digestive fistula in contrast with fungal PVGI alone (p = 0.21).

CONCLUSION

Prostheto-digestive fistula was strongly associated with fungal PVGI, which leads us to suggest that in such cases, an anti-fungal agent should be prescribed.

In Vitro Activities of Oxazolidinone Antibiotics Alone and in Combination with C-TEMPO against Methicillin-Resistant Staphylococcus aureus Biofilms

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are a global health concern. The propensity of MRSA to form biofilms is a significant contributor to its pathogenicity. Strategies to treat biofilms often involve small molecules that disperse the biofilm into planktonic cells. Linezolid and, by extension, theoxazolidinones have been developed to treat infections caused by Gram-positive bacteria such as MRSA. However, the clinical development of these antibiotics has mainly assessed the susceptibility of planktonic cells to the drug. Previous studies evaluating the anti-biofilm activity of theoxazolidinones have mainly focused on the biofilm inhibition of Enterococcus faecalis and methicillin-sensitive Staphylococcus aureus, with only a few studies investigating the activity of oxazolidinones for eradicating established biofilms for these species. Very little is known about the ability of oxazolidinones to eradicate MRSA biofilms. In this work, five oxazolidinones were assessed against MRSA biofilms using a minimum biofilm eradication concentration (MBEC) assay. All oxazolidinones had inherent antibiofilm activity. However, only ranbezolid could completely eradicate MRSA biofilms at clinically relevant concentrations. The susceptibility of the MRSA biofilms to ranbezolid was synergistically enhanced by coadministration with the nitroxide biofilm dispersal agent C-TEMPO. We presume that ranbezolid acts as a dual warhead drug, which combines the mechanism of action of the oxazolidinones with a nitric oxide donor or cytotoxic drug.

Food grade disinfectants based on hydrogen peroxide/peracetic acid and sodium hypochlorite interfere with the adhesion of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Listeria monocytogenes to stainless steel of differing surface roughness

This study aimed to evaluate the potential of the bacterium Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Listeria monocytogenes to adhere to stainless steel discs with differing degrees of surface roughness (Ra = 25.20-961.90 nm). Stainless steel is a material commonly used in the food industry for processing equipment, which is regularly exposed to cleaning procedures. The investigation included the commercial disinfectants hydrogen peroxide/peracetic acid and sodium hypochlorite which were evaluated for their antibacterial and anti-adhesion activity. The adhesion was assessed by the standard plate count method, while the broth microdilution method CLSI M07-A10 was used to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the disinfectants. Based on the MIC values, both disinfectants exerted significant inhibitory effects with MIC values for hydrogen peroxide/peracetic acid and sodium hypochlorite of 250 µg ml-1 and 500 µg ml-1, respectively. Whereas the MBC values were equal to the MIC for all bacteria except for E. coli with values 2-fold higher than the MIC. Obtained results also revealed that all tested bacteria were able to adhere to stainless steel surfaces, although differences were found for strains and surface roughness. The lowest adhesion rate of each strain was recorded on the roughest stainless steel disc at a Ra of 961.90 nm. Further, at a concentration of 1 MIC, the disinfectant sodium hypochlorite reduced initial bacterial adhesion to stainless steel surfaces to a significantly greater extent than the disinfectant hydrogen peroxide/peracetic acid. These findings are consistent with the results obtained by Scanning Electron Microscopy (SEM) analysis, which indicates the great applicability of the tested disinfectants for the control of bacterial adhesion in the food industry.

Risk factor-based clustering of Listeria monocytogenes in food processing environments using principal component analysis

Listeria monocytogenes has a range of strategies that allow it to persist as biofilms in food processing environments (FPE), making it a pathogen of concern to the food industry. The properties of these biofilms are highly variable among strains, and this significantly affects the risk of food contamination. The present study therefore aims to conduct a proof-of-concept study to cluster strains of L. monocytogenes by risk potential using principal component analysis, a multivariate approach. A set of 22 strains, isolated from food processing environments, were typed by serogrouping and pulsed-field gel electrophoresis, showing a relatively high diversity. They were characterized in terms of several biofilm properties that might pose a potential risk of food contamination. The properties studied were tolerance to benzalkonium chloride (BAC), the structural parameters of biofilms (biomass, surface area, maximum and average thickness, surface to biovolume ratio and roughness coefficient) measured by confocal laser scanning microscopy and (3) transfer of biofilm cells to smoked salmon. The PCA correlation circle revealed that the tolerance of biofilms to BAC was positively correlated with roughness, but negatively with biomass parameters. On the contrary, cell transfers were not related to three-dimensional structural parameters, which suggests the role of other variables yet unexplored. Additionally, hierarchical clustering grouped strains into three different clusters. One of them included the strains with high tolerance to BAC and roughness. Another one consisted of strains with enhanced transfer ability, whereas the third cluster contained those that stood out for the thickness of biofilms. The present study represents a novel and effective way to classify L. monocytogenes strains according to biofilm properties that condition the potential risk of reaching the consumer through food contamination. It would thus allow the selection of strains representative of different worst-case scenarios for future studies in support of QMRA and decision-making analysis.

Precise Localization and Simultaneous Bacterial Eradication of Biofilms Based on Nanocontainers with Successive Responsive Property toward pH and ATP

The bacterial colonization of surfaces and subsequent biofilm formation are a great threat in medical therapy and clinical diagnosis. The complex internal structure and composition sets an enormous obstacle for the localization and removal of biofilms. In this study, we proposed a novel biofilm-targeted nanocontainer with successive responsive property toward pH and ATP for precise localization and simultaneous bacterial eradication, with an acidic and adenosine triphosphate (ATP)-rich microenvironment within biofilms, formed due to the accumulation of fatty acids and ATP in the three-dimensional enclosed structure, integrated as two successive indicators to improve the precision of biofilm identification and removal. The biofilm-targeted nanocontainer was composed of a ATP-responsive zeolitic imidazolate framework-90 (ZIF-90) core loaded with Rho 6G and doxorubicin hydrochloride (DOX) encapsulated in the pH-responsive amorphous calcium carbonate/poly(acrylic acid) (ACC/PAA) shell. In the presence of biofilms, the ACC/PAA shell and ZIF-90 core were successively degraded by the accumulated H⁺ and ATP within biofilms, resulting in the release of fluorescence indicators and antimicrobial agents. On the other hand, to meet the application requirements of different biofilm scenarios, the pH response ability of the nanocontainers could be adjusted by changing the metallic ions (Ni²⁺, Zn²⁺, and Cu²⁺) doped into the structure of the ACC/PAA shell. Owing to excellent water dispersion of the pH/ATP double-responsive ZIF-90@Zn-ACC/PAA nanocontainer, precise localization and simultaneous bacterial eradication was successfully realized via a simple spray process. The successive pH/ATP two-step unlocking processes endowed the nanocontainers high precision for localization and simultaneous eradication of biofilms, which made the proposed nanocontainers high promising in food safety and medical treatment.

Propionate and Butyrate Inhibit Biofilm Formation of Salmonella Typhimurium Grown in Laboratory Media and Food Models

Salmonella is among the most frequently isolated foodborne pathogens, and biofilm formed by Salmonella poses a potential threat to food safety. Short-chain fatty acids (SCFAs), especially propionate and butyrate, have been demonstrated to exhibit a beneficial effect on promoting intestinal health and regulating the host immune system, but their anti-biofilm property has not been well studied. This study aims to investigate the effects of propionate or butyrate on the biofilm formation and certain virulence traits of Salmonella. We investigated the effect of propionate or butyrate on the biofilm formation of Salmonella enterica serovar Typhimurium (S. Typhimurium) SL1344 grown in LB broth or food models (milk or chicken juice) by crystal violet staining methods. Biofilm formation was significantly reduced in LB broth and food models and the reduction was visualized using a scanning electron microscope (SEM). Biofilm metabolic activity was attenuated in the presence of propionate or butyrate. Meanwhile, both SCFAs decreased AI-2 quorum sensing based on reporter strain assay. Butyrate, not propionate, could effectively reduce bacterial motility. Bacterial adhesion to and invasion of Caco-2 cells were also significantly inhibited in the presence of both SCFAs. Finally, two SCFAs downregulated virulence genes related to biofilm formation and invasion through real-time polymerase chain reaction (RT-PCR). These findings demonstrate the potential application of SCFAs in the mitigation of Salmonella biofilm in food systems, but future research mimicking food environments encountered during the food chain is necessitated.

Molecular Epidemiology of Plasmid-Mediated Types 1 and 3 Fimbriae Associated with Biofilm Formation in Multidrug Resistant Escherichia coli from Diseased Food Animals in Guangdong, China

Types 1 and 3 fimbriae in Enterobacteriaceae play versatile roles in bacterial physiology including attachment, invasion, cell motility as well as with biofilm formation and urinary tract infections. Herein, we investigated the prevalence and transmission of plasmid-mediated types 1 and 3 fimbriae from 1753 non-duplicate Enterobacteriaceae from diseased food Animals. We identified 123 (7.01%) strong biofilm producers and all was identified as E. coli. WGS analysis of 43 selected strong biofilm producers revealed that they harbored multiple ARGs, including ESBLs, PMQR and mcr-1. The gene clusters mrkABCDF and fimACDH encoding types 1 and 3 fimbriae, respectively, were identified among 43 (34.96%) and 7 (5.7%) of 123 strong biofilm isolates, respectively. These two operons were able to confer strong biofilm-forming ability to an E. coli weak-biofilm forming laboratory strain. Plasmid analysis revealed that mrk and fim operons were found to co-exist with ARGs and were primarily located on IncX1 and IncFII plasmids with similar backbones, respectively. mrkABCDF operons was present in all of 9457 Klebsiella pneumoniae using archived WGS data, and shared high homology to those on plasmids of 8 replicon types and chromosomes from 6 Enterobacteriaceae species from various origins and countries. In contrast, fimACDH operons was present in most of Enterobacter cloacae (62.15%), and shared high homology to those with only a small group of plasmids and Enterobacteriaceae species. This is the first comprehensive report of the prevalence, transmission and homology of plasmid-encoded type 1 and 3 fimbriae among the Enterobacteriaceae. Our findings indicated that plasmid-encoded mrkABCDF and fimACDH were major contributors to enhanced biofilm formation among E. coli and these two operons, in particular mrk could be as a potential anti-biofilm target. IMPORTANCE Biofilms allow bacteria to tolerate disinfectants and antimicrobials, as well as mammalian host defenses, and are therefore difficult to treat clinically. Most research concerning biofilm-related infections is typically focused on chromosomal biofilm-associated factors, including types 1 and 3 fimbriae of biofilm-forming Enterobacterium. However, the transmission and homology of the mobile types 1 and 3 fimbriae among Enterobacteriaceae is largely unknown. The findings revealed that the plasmid-encoded type 3 fimbriae encoded by mrkABCDF and type 1 fimbriae encoded by fimACDH were major contributors to enhancing biofilm formation among strong biofilm E. coli from diseased food producing animals. Additionally, mrk operon with high homology at an amino acid sequence was present both on plasmids of various replicon types and on chromosomes from diverse Enterobacteriaceae species from numerous origins and countries. These findings provide important information on the transmission of the mobile types 1 and 3 fimbriae among Enterobacteriaceae, indicating a potential antibiofilm target.

Felodipine enhances aminoglycosides efficacy against implant infections caused by methicillin-resistant Staphylococcus aureus, persisters and biofilms

Methicillin-resistant Staphylococcus aureus (MRSA), biofilms, and persisters are three major factors leading to recurrent and recalcitrant implant infections. Although antibiotics are still the primary treatment for chronic implant infections in clinical, only few drugs are effective in clearing persisters and formed biofilms. Here, felodipine, a dihydropyridine calcium channel blocker, was reported for the first time to have antibacterial effects against MRSA, biofilm, and persisters. Even after continuous exposure to sub-lethal concentrations of felodipine, bacteria are less likely to develop resistance. Besides, low doses of felodipine enhances the antibacterial activity of gentamicin by inhibiting the expression of protein associated with aminoglycoside resistance (aacA-aphD). Next, biofilm eradication test and persisters killing assay suggested felodipine has an excellent bactericidal effect against formed biofilms and persisters. Furthermore, the result of protein profiling, and quantitative metabonomics analysis indicated felodipine reduce MRSA virulence (agrABC), biofilm formation and TCA cycle. Then, molecular docking showed felodipine inhibit the growth of persisters by binding to the H pocket of ClpP protease, which could lead to substantial protein degradation. Furthermore, murine infection models suggested felodipine in combination with gentamicin alleviate bacterial burden and inflammatory response. In conclusion, low dose of felodipine might be a promising agent for biomaterial delivery to enhance aminoglycosides efficacy against implant infections caused by MRSA, biofilm, and persisters.

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Felodipine inhibits MRSA gene expression associated with aminoglycoside resistance and biofilm formation.

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Felodipine eradicates formed biofilm and persisters on the surface of implants.

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Felodipine induces proteolysis of MRSA and decreases energy metabolism.

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Felodipine in combination with gentamicin alleviates murine periprosthetic joint infection.

The Association between Biofilm Formation and Antimicrobial Resistance with Possible Ingenious Bio-Remedial Approaches

Biofilm has garnered a lot of interest due to concerns in various sectors such as public health, medicine, and the pharmaceutical industry. Biofilm-producing bacteria show a remarkable drug resistance capability, leading to an increase in morbidity and mortality. This results in enormous economic pressure on the healthcare sector. The development of biofilms is a complex phenomenon governed by multiple factors. Several attempts have been made to unravel the events of biofilm formation; and, such efforts have provided insights into the mechanisms to target for the therapy. Owing to the fact that the biofilm-state makes the bacterial pathogens significantly resistant to antibiotics, targeting pathogens within biofilm is indeed a lucrative prospect. The available drugs can be repurposed to eradicate the pathogen, and as a result, ease the antimicrobial treatment burden. Biofilm formers and their infections have also been found in plants, livestock, and humans. The advent of novel strategies such as bioinformatics tools in treating, as well as preventing, biofilm formation has gained a great deal of attention. Development of newfangled anti-biofilm agents, such as silver nanoparticles, may be accomplished through omics approaches such as transcriptomics, metabolomics, and proteomics. Nanoparticles’ anti-biofilm properties could help to reduce antimicrobial resistance (AMR). This approach may also be integrated for a better understanding of biofilm biology, guided by mechanistic understanding, virtual screening, and machine learning in silico techniques for discovering small molecules in order to inhibit key biofilm regulators. This stimulated research is a rapidly growing field for applicable control measures to prevent biofilm formation. Therefore, the current article discusses the current understanding of biofilm formation, antibiotic resistance mechanisms in bacterial biofilm, and the novel therapeutic strategies to combat biofilm-mediated infections.

Characterization of the Lytic Phage Flora With a Broad Host Range Against Multidrug-Resistant Escherichia coli and Evaluation of Its Efficacy Against E. coli Biofilm Formation

Escherichia coli is a gram-negative bacterium that is distributed widely throughout the world; it is mainly found in contaminated food, the poultry industry, and animal feces. The emergence of antibiotic-resistant E. coli poses a threat to human and animal health, which has led to renewed interest in phage-based therapy. E. coli biofilm control and prevention are of great importance. In this study, the isolated phages Flora and KM18 were found to belong to the family Myoviridae; the optimal preservation buffer was pH = 6~7, and the phage genome sizes were 168,909 (Flora) and 168,903 (KM18) bp. Phage Flora had a broader lytic spectrum than KM18. Phage Flora had a better antibiofilm effect than kanamycin sulfate in high-concentration E. coli cultures. A combination of the phage Flora and kanamycin sulfate showed better antibiofilm effects than Flora or kanamycin sulfate alone in low-concentration E. coli cultures. These characteristics can serve as a guideline for the selection of effective candidates for phage therapy, in this case antibiotic-resistant E. coli control in the poultry industry.

The effects of rotating magnetic field and antiseptic on in vitro pathogenic biofilm and its milieu

The application of various magnetic fields for boosting the efficacy of different antimicrobial molecules or in the character of a self-reliant antimicrobial agent is considered a promising approach to eradicating bacterial biofilm-related infections. The purpose of this study was to analyze the phenomenon of increased activity of octenidine dihydrochloride-based antiseptic (OCT) against Staphylococcus aureus and Pseudomonas aeruginosa biofilms in the presence of the rotating magnetic field (RMF) of two frequencies, 5 and 50 Hz, in the in vitro model consisting of stacked agar discs, placed in increasing distance from the source of the antiseptic solution. The biofilm-forming cells' viability and morphology as well as biofilm matrix structure and composition were analyzed. Also, octenidine dihydrochloride permeability through biofilm and porous agar obstacles was determined for the RMF-exposed versus unexposed settings. The exposure to RMF or OCT apart did not lead to biofilm destruction, contrary to the setting in which these two agents were used together. The performed analyses revealed the effect of RMF not only on biofilms (weakening of cell wall/membranes, disturbed morphology of cells, altered biofilm matrix porosity, and composition) but also on its milieu (altered penetrability of octenidine dihydrochloride through biofilm/agar obstacles). Our results suggest that the combination of RMF and OCT can be particularly promising in eradicating biofilms located in such areas as wound pockets, where physical obstacles limit antiseptic activity.

Effect of Flexibility and Size of Nanofabricated Topographies on the Mechanobactericidal Efficacy of Polymeric Surfaces

Driven by the growing threat of antimicrobial resistance, the design of intrinsically bactericidal surfaces has been gaining significant attention. Proposed surface topography designs are often inspired by naturally occurring nanopatterns on insect wings that mechanically damage bacteria via membrane deformation. The stability of and the absence of chemicals in such surfaces support their facile and sustainable employment in avoiding surface-born pathogen transmission. Recently, the deflection of controllably nanofabricated pillar arrays has been shown to strongly affect bactericidal activity, with the limits of mechanical effectiveness of such structures remaining largely unexplored. Here, we examine the limits of softer, commonly used polymeric materials and investigate the interplay between pillar nanostructure sizing and flexibility for effective antibacterial functionality. A facile, scalable, UV nanoimprint lithography method was used to fabricate nanopillar array topographies of variable sizes and flexibilities. It was found that bacterial death on nanopillars in the range of diameters ≤100 nm and Young's moduli ≥1.3 GPa is increased by 3.5- to 5.6-fold, while thicker or softer pillars did not reduce bacterial viability. To further support our findings, we performed a finite element analysis of pillar deformation. It revealed that differences in the amount of stress exerted on bacterial membranes, generated from the stored elastic energy in flexible pillars, contribute to the observed bactericidal performance.

Combined an acoustic pressure simulation of ultrasonic radiation and experimental studies to evaluate control efficacy of high-intensity ultrasound against Staphylococcus aureus biofilm

This study evaluated efficacy of high-intensity ultrasound (HIU) on controlling or stimulating Staphylococcus aureus biofilm. Acoustic pressure distribution on the surface of glass slide cultivated S. aureus biofilm was first simulated as a standardized parameter to reflect sono-effect. When the power of HIU was 240 W with acoustic pressure of -1.38×105 Pa, a reasonably high clearance rate of S. aureus biofilm was achieved (96.02%). As an all-or-nothing technique, the HIU did not cause sublethal or injury of S. aureus but inactivate the cell directly. A further evaluation of HIU-induced stimulation of biofilm was conducted at a low power level (i.e. 60 W with acoustic pressure of -6.91×104 Pa). The low-power-long-duration HIU treatment promoted the formation of S. aureus biofilm and enhanced its resistance as proved by transcriptional changes of genes in S. aureus, including up-regulations of rbf, sigB, lrgA, icaA, icaD, and down-regulation of icaR. These results indicate that the choose of input power is determined during the HIU-based cleaning and processing. Otherwise, the growth of S. aureus and biofilm formation are stimulated when treats by an insufficiently high power of HIU.

Isolation and Characterization of a Lytic Staphylococcus aureus Phage WV against Staphylococcus aureus Biofilm

BACKGROUND

Staphylococcus aureus is a Gram-positive, pathogenic bacterium that causes a wide range of symptoms in humans and can form biofilm, which is a multicellular community of microorganisms that attaches to nonbiological and biological surfaces.

METHODS

Here, we aimed to isolate and characterize an S. aureus phage and examine the bactericidal activity alone and in conjunction with streptomycin treatment.

RESULTS

We isolated a virulent phage, WV, from a slaughterhouse in Jiangsu, China. This strain belonged to the family Myoviridae and presented a genome size of 141,342 bp. The optimal pH of the preservation buffer was 6-7, optimal growth temperature was 37°C, and optimal multiplicity of infection was 0.01. Phage WV can sterilize most clinical strains of S. aureus that had been isolated from clinical patients in the First People's Hospital of the Yunnan Province. Against low-concentration S. aureus culture, streptomycin demonstrated a greater antibiofilm effect than that of phage WV. By contrast, in high-concentration S. aureus culture, phage WV demonstrated greater antibiofilm effect than that of streptomycin. The use of phage WV and streptomycin together had a substantially greater overall antibiofilm effect than that achieved using either component alone.

CONCLUSION

This study provides strong evidence for the effectiveness of phage application for the reduction of S. aureus biofilm growth and suggests that phages can be considered as a viable alternative to antibiotics in clinical settings.

Mimicking biofilm formation and development: Recent progress in in vitro and in vivo biofilm models

Biofilm formation in living organisms is associated to tissue and implant infections, and it has also been linked to the contribution of antibiotic resistance. Thus, understanding biofilm development and being able to mimic such processes is vital for the successful development of antibiofilm treatments and therapies. Several decades of research have contributed to building the foundation for developing in vitro and in vivo biofilm models. However, no such thing as an "all fit" in vitro or in vivo biofilm models is currently available. In this review, in addition to presenting an updated overview of biofilm formation, we critically revise recent approaches for the improvement of in vitro and in vivo biofilm models.

Transfer rates of pathogenic bacteria during pork processing

We examined the rates of pathogenic bacterial cross-contamination from gloves to meat and from meat to gloves during pork processing under meat-handling scenarios in transfer rate experiments of inoculated pathogens. The inoculated pork contained ~5-6 Log₁₀ CFU/g pathogenic bacteria like Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Listeria monocytogenes (L. monocytogenes), and Salmonella enterica subsp. enterica (Sal. enteritidis). On cotton gloves, after cutting the pork, the cutting board, knife, and cotton gloves showed 3.07-3.50, 3.29-3.92 and 4.48-4.86 Log₁₀ CFU/g bacteria. However, when using polyethylene gloves, fewer bacteria (3.12-3.75, 3.20-3.33, and 3.07-3.97 Log₁₀ CFU/g, respectively) were transferred. When four pathogens (6 Log₁₀ CFU/g) were inoculated onto the gloves, polyethylene gloves showed a lower transition rate (cutting board 2.47-3.40, knife 2.01-3.98, and polyethylene glove 2.40-2.98 Log₁₀ CFU/g) than cotton gloves. For cotton gloves, these values were 3.46-3.96, 3.37-4.06, and 3.55-4.00 Log₁₀ CFU/g, respectively. Use of cotton gloves, polyethylene gloves, knives and cutting boards for up to 10 hours in a meat butchering environment has not exceeded HACCP regulations. However, after 10 h of use, 3.09, 3.27, and 2.94 Log₁₀ CFU/g of plate count bacteria were detected on the cotton gloves, cutting board, and knives but polyethylene gloves showed no bacterial count. Our results reveal the transfer efficiency of pathogenic bacteria and that gloved hands may act as a transfer route of pathogenic bacteria between meat and hands. The best hand hygiene was achieved when wearing polyethylene gloves. Thus, use of polyethylene rather than cotton gloves reduces cross-contamination during meat processing.

Isolation, characterization, and application of Salmonella paratyphi phage KM16 against Salmonella paratyphi biofilm

Salmonella biofilm prevention and control is of great importance. This study, investigated the use of the isolated phage KM16 belonging to the family Myoviridae in the order Caudovirales. The phage genome size was 170,126 bp. Almost all phages were adsorbed to the host within 20 min. KM16 had a latent period of 70 min followed by a rise period of 40 min. Phage KM16 had the ability to lytically infect 10 out of the 12 clinical strains of S. paratyphi tested. Phylogenetic analysis indicated that the S. paratyphi 16S rRNA, crispr 1 and fimA genes correlated with the lytic spectrum of phage KM16. The lytic spectrum of phage KM16 correlated with Salmonella pili (fimA), and Salmonella pili were the recognition site for phage adsorption to the host. Phage KM16 (MOI = 0.1) had a better anti-biofilm effect than kanamycin sulfate (10 ug ml^-1) in high-concentration Salmonella cultures.

Isolation and Characterization of a Lytic Salmonella paratyphi Phage and Its Antibiofilm Activity Individually or Collaborative with Kanamycin Sulfate

Salmonella is among the most serious of foodborne pathogens worldwide and distributed widely in the natural environment; in addition, it has caused severe medical problems and foodborne diseases. Bacterial biofilm was the multicellular community of microorganisms that attached to nonbiological and biological surfaces. Phages and their derivatives are ideal candidates for replacing and compensating antibiotic resistance problems in the future. In this study, a virulent phage of KM15 was isolated from pig slaughterhouse sump samples in Kunming, China. It belonged to the Siphoviridae family, and optimal growth temperature was 42°C, the pH of optimal preservation buffer was 6-7, optimal multiplicity of infection was 0.0001, and the genome size was 41,869 bp. The Salmonella paratyphi A and Salmonella paratyphi B have a broad spectrum of antibiotic resistance and were isolated from clinical patients in the First People's Hospital of Yunnan Province; fortunately, most of them can be lysed by phage KM15. Collaboration of phage KM15 and kanamycin sulfate has a better antibiofilm effect than KM15 and kanamycin sulfate alone, in low-concentration bacterial culture; KM15 has better antibiofilm effect than kanamycin sulfate in high-concentration bacterial culture. The data of this study provided a strong evidence of application of phage to reduce the growth of Salmonella biofilm, which was important for public health.

Bactericidal Characteristics of Bioinspired Nontoxic and Chemically Stable Disordered Silicon Nanopyramids

Controlling bacterial growth using artificial nanostructures inspired from natural species is of immense importance in biomedical applications. In the present work, a low cost, fast processing, and scalable anisotropic wet etching technique is developed to fabricate the densely packed disordered silicon nanopyramids (SiNPs) with nanosized sharp tips. The bactericidal characteristics of SiNPs are assessed against strains implicated in nosocomial and biomaterial-related infections. Compared to the bare silicon with no antibacterial activities, SiNPs of 1.85 ± 0.28 μm height show 55 and 75% inhibition of Escherichia coli (Gram-negative) and Bacillus subtilis (Gram-positive) bacteria, whereas the silicon nanowires (SiNWs) fabricated using a metal-assisted chemical etching method show 50 and 58% inhibition of E. coli and B. subtilis. The mechanistic studies using a scanning electron microscope and live/dead bacterial cell assay reveal cell rupture and predominance of dead cells on contact with SiNPs and SiNWs, which confirms their bactericidal effects. Chemical stability and cell viability studies demonstrate the biocompatible nature of SiNP and SiNW surfaces. Owing to their capability to kill both Gram-negative and positive bacteria and minimal toxicity to murine fibroblast cells, SiNPs can be used as an antibacterial coating on medical devices to prevent nosocomial and biomaterial-related infections.

Antimicrobial Activity and Prevention of Bacterial Biofilm Formation of Silver and Zinc Oxide Nanoparticle-Containing Polyester Surfaces at Various Concentrations for Use

Food contact surfaces are primary sources of bacterial contamination in food industry processes. With the objective of preventing bacterial adhesion and biofilm formation on surfaces, this study evaluated the antimicrobial activity of silver (Ag-NPs) and zinc oxide (ZnO-NPs) nanoparticle-containing polyester surfaces (concentration range from 400 ppm to 850 ppm) using two kinds of bacteria, Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli), and the prevention of bacterial biofilm formation using the pathogen Listeria monocytogenes. The results of antimicrobial efficacy (reductions ≥ 2 log CFU/cm2) showed that at a concentration of 850 ppm, ZnO-NPs were effective against only E. coli (2.07 log CFU/cm2). However, a concentration of 400 ppm of Ag-NPs was effective against E. coli (4.90 log CFU/cm2) and S. aureus (3.84 log CFU/cm2). Furthermore, a combined concentration of 850 ppm Ag-NPs and 400 ppm ZnO-NPs showed high antimicrobial efficacy against E. coli (5.80 log CFU/cm2) and S. aureus (4.11 log CFU/cm2). The results also showed a high correlation between concentration levels and the bacterial activity of Ag-ZnO-NPs (R2 = 0.97 for S. aureus, and R2 = 0.99 for E. coli). They also showed that unlike individual action, the joint action of Ag-NPs and ZnO-NPs has high antimicrobial efficacy for both types of microorganisms. Moreover, Ag-NPs prevent the biofilm formation of L. monocytogenes in humid conditions of growth at concentrations of 500 ppm. Additional studies under different conditions are needed to test the durability of nanoparticle containing polyester surfaces with antimicrobial properties to optimize their use.

Continuous flow system for biofilm formation using controlled concentrations of Pseudomonas putida from chicken carcass and coupled to electrochemical impedance detection

Most studies dealing with monitoring the dynamics of biofilm formation use microbial suspensions at high concentrations. These conditions do not always represent food or water distribution systems. A continuous flow system capable of controlling the concentration of the microbial suspension stream from 10⁴ to 10⁶ CFU ml^-1 is reported. Pseudomonas putida biofilms formed using 100-fold, 1,000-fold or 10,000-fold diluted bacterial suspensions were monitored in-line by electrochemical impedance spectroscopy (EIS) and total plate counts. Randles equivalent circuit model and a modified Randles model with biofilm elements were used to fit the EIS data. In Randles equivalent circuit, the charge transfer resistance decreased as the biofilm formed. The log colony counts of the biofilm correlated to the charge transfer resistance. In the biofilm model, the biofilm resistance and the double layer capacitance decreased as the biofilm formed. The log colony counts of the biofilm correlated to the biofilm resistance.

An iTRAQ-Based Comparative Proteomics Analysis of the Biofilm and Planktonic States of Aeromonas veronii TH0426

Aeromonas veronii is a virulent fish pathogen that causes extensive economic losses in the aquaculture industry worldwide. In this study, a virulent strain of A. veronii TH0426 was used to establish an in vitro biofilm model. The results show that the biofilm-forming abilities of A. veronii TH0426 were similar in different media, peaking under conditions of 20 °C and pH 6. Further, isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative proteomics methods were used to compare the differential expression of A. veronii between the biofilm and planktonic cells. The results show alterations in 277 proteins, with 130 being upregulated and 147 downregulated. Pathway analysis and GO (Gene Ontology) annotations indicated that these proteins are mainly involved in metabolic pathways and the biosynthesis of secondary metabolites and antibiotics. These proteins are the main factors affecting the adaptability of A. veronii to its external environment. MRM (multiple reaction 27 monitoring) and qPCR (qPCR) were used to verify the differential proteins of the selected A. veronii. This is the first report on the biofilm and planktonic cells of A. veronii, thus contributing to studying the infection and pathogenesis of A. veronii.

Bacterial Biofilm Eradication Agents: A Current Review

Most free-living bacteria can attach to surfaces and aggregate to grow into multicellular communities encased in extracellular polymeric substances called biofilms. Biofilms are recalcitrant to antibiotic therapy and a major cause of persistent and recurrent infections by clinically important pathogens worldwide (e.g., Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus). Currently, most biofilm remediation strategies involve the development of biofilm-inhibition agents, aimed at preventing the early stages of biofilm formation, or biofilm-dispersal agents, aimed at disrupting the biofilm cell community. While both strategies offer some clinical promise, neither represents a direct treatment and eradication strategy for established biofilms. Consequently, the discovery and development of biofilm eradication agents as comprehensive, stand-alone biofilm treatment options has become a fundamental area of research. Here we review our current understanding of biofilm antibiotic tolerance mechanisms and provide an overview of biofilm remediation strategies, focusing primarily on the most promising biofilm eradication agents and approaches. Many of these offer exciting prospects for the future of biofilm therapeutics for a large number of infections that are currently refractory to conventional antibiotics.

Bacterial Adhesion on Femtosecond Laser-Modified Polyethylene

In this study, femtosecond laser-induced sub-micrometer structures are generated to modify polyethylene (PE) surface topographies. These surfaces were subjected to bacterial colonization studies with Escherichia coli and Staphylococcus aureus as test strains. The results reveal that the nanostructures do not influence S. aureus coverage, while the adhesion of E. coli is reduced.

Studies of Black Diamond as an antibacterial surface for Gram Negative bacteria: the interplay between chemical and mechanical bactericidal activity

'Black silicon' (bSi) samples with surfaces covered in nanoneedles of length ~5 µm were fabricated using a plasma etching process and then coated with a conformal uniform layer of diamond using hot filament chemical vapour deposition to produce 'black diamond' (bD) nanostructures. The diamond needles were then chemically terminated with H, O, NH2 or F using plasma treatment, and the hydrophilicity of the resulting surfaces were assessed using water droplet contact-angle measurements, and scaled in the order O > H ≈NH2 >F, with the F-terminated surface being superhydrophobic. The effectiveness of these differently terminated bD needles in killing the Gram-negative bacterium E. coli was semi-quantified by Live/Dead staining and fluorescence microscopy, and visualised by environmental scanning electron microscopy. The total number of adhered bacteria was consistent for all the nanostructured bD surfaces at around 50% of the value for the flat diamond control. This, combined with a chemical bactericidal effect of 20-30%, shows that the nanostructured bD surfaces supported significantly fewer viable E. coli than flat surfaces. Moreover, the bD surfaces were particularly effective at preventing the establishment of bacterial aggregates - a precursor to biofilm formation. The percentage of dead bacteria also decreased as a function of hydrophilicity. These results are consistent with a predominantly mechanical mechanism for bacteria death based on the stretching and disruption of the cell membrane, combined with an additional effect from the chemical nature of the surface.

Lactobacillus plantarum Lipoteichoic Acid Inhibits Oral Multispecies Biofilm

INTRODUCTION

Apical periodontitis is an inflammatory disease in the periradicular region of teeth that results from infection by multispecies bacterial biofilm residing in the root canal system. In this study, we investigated whether Lactobacillus plantarum lipoteichoic acid (Lp.LTA) could inhibit multispecies oral pathogenic bacterial biofilm formation.

METHODS

Highly pure and structurally intact Lp.LTA was purified from L. plantarum. Actinomyces naeslundii, Lactobacillus salivarius, Streptococcus mutans, and Enterococcus faecalis were co-cultured to form oral multispecies biofilm in the presence or absence of Lp.LTA on culture plates or human dentin slices. Preformed biofilm was treated with or without Lp.LTA, followed by additional treatment with intracanal medicaments such as calcium hydroxide or chlorhexidine digluconate. Confocal microscopy and crystal violet assay were performed to determine biofilm formation. Biofilm on human dentin slices was visualized with a scanning electron microscope.

RESULTS

Biofilm formation of multispecies bacteria on the culture dishes was dose-dependently reduced by Lp.LTA compared with the nontreatment control group. Lp.LTA also inhibited multispecies biofilm formation on the dentin slices in a dose-dependent manner. Interestingly, Lp.LTA was shown to reduce preformed multispecies biofilm compared with the nontreatment group. Moreover, Lp.LTA potentiated the effectiveness of the intracanal medicaments in the removal of preformed multispecies biofilm.

CONCLUSIONS

These results suggest that Lp.LTA is a potential anti-biofilm agent for treatment or prevention of oral infectious disease, including apical periodontitis, which is mainly caused by multispecies bacterial biofilm.

Measuring Antimicrobial Efficacy against Biofilms: a Meta-analysis

Through a statistical meta-analysis of published data on antimicrobial efficacy against biofilms formed by two common bacterial species, it was concluded that the particular experimental method used is the most important factor determining the outcome of the test. An expected dose-response relationship (greater killing with higher doses or longer treatment times) was observed for data sets derived from a single method but was not observed when data from multiple studies using diverse methods were pooled. Method-specific properties such as the surface area/volume ratio, areal biofilm cell density, and microbial species were shown to influence quantitative measurements of biofilm killing. A better appreciation of the method characteristics that affect antibiofilm efficacy tests could aid decision-making related to investment in research and development and regulatory approvals for biofilm control strategies. The following recommendations are offered to those working in research and development related to biofilm control: (i) report the log reduction, surface area/volume ratio, and biofilm areal cell density; (ii) include data for a benchmark agent, making sure that this agent performs competitively at the dose tested; (iii) measure the dose-response relationship, i.e., make measurements at multiple treatment concentrations or dose durations; and (iv) use a standardized method in addition to research methods.

Growth substrate may influence biofilm susceptibility to antibiotics

The CDC biofilm reactor is a robust culture system with high reproducibility in which biofilms can be grown for a wide variety of analyses. Multiple material types are available as growth substrates, yet data from biofilms grown on biologically relevant materials is scarce, particularly for antibiotic efficacy against differentially supported biofilms. In this study, CDC reactor holders were modified to allow growth of biofilms on collagen, a biologically relevant substrate. Susceptibility to multiple antibiotics was compared between biofilms of varying species grown on collagen versus standard polycarbonate coupons. Data indicated that in 13/18 instances, biofilms on polycarbonate were more susceptible to antibiotics than those on collagen, suggesting that when grown on a complex substrate, biofilms may be more tolerant to antibiotics. These outcomes may influence the translatability of antibiotic susceptibility profiles that have been collected for biofilms on hard plastic materials. Data may also help to advance information on antibiotic susceptibility testing of biofilms grown on biologically relevant materials for future in vitro and in vivo applications.

Antifungal activities against Candida albicans, of cell-free supernatants obtained from probiotic Pediococcus acidilactici HW01

OBJECTIVE

The aim of this study was to investigate the antifungal activities of cell-free supernatants of a probiotic strain, Pediococcus acidilactici HW01, against Candida albicans.

DESIGN

C. albicans was cultured in the presence of different concentration of cell-free supernatants obtained from P. acidilactici HW01 (HW01 CFS) and the growth of C. albicans was determined. C. albicans was incubated with HW01 CFS for 24 h and the biofilm formation of C. albicans was determined by staining crystal violet and by using a scanning electron microscope. Biofilm quantification was determined by 2, 3-Bis (2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) assay.

RESULTS

HW01 CFS inhibitedC. albicans growth, whereas bacteriocin, which is a well-known antimicrobial peptide of lactic acid bacteria, failed to inhibit C. albicans growth. Pre-treatment and simultaneous treatment with HW01 CFS exhibited a significant inhibition of C. albicans biofilm. Although post-treatment with HW01 CFS did not disrupt the established biofilm of C. albicans at 3 h-incubation, significant reduced C. albicans biofilm was observed after 6 h-incubation in the presence of HW01 CFS.

CONCLUSION

These results suggested that the CFS fromP. acidilactici HW01 was revealed as an effective antifungal agent against C. albicans by reducing the growth and biofilm formation.

Growth, Viability, and Death of Planktonic and Biofilm Sphingomonas desiccabilis in Simulated Martian Brines

Aqueous solutions on Mars are theorized to contain very different ion compositions than those on Earth. To determine the effect of such solutions on typical environmental micro-organisms, which could be released from robotic spacecraft or human exploration activity, we investigated the resistance of Sphingomonas desiccabilis to brines that simulate the composition of martian aqueous environments. S. desiccabilis is a desiccation-resistant, biofilm-forming microbe found in desert crusts. The viability of cells in both planktonic and biofilm forms was measured after exposure to simulated martian brines. Planktonic cells showed a loss of viability over the course of several hours in almost all of the seven brines tested. Biofilms conferred greater resistance to all the brines, including those with low water activity and pH, but even cells in biofilms showed a complete loss of viability in <6 h in the harsher brines and in <2 days in the less harsh brines. One brine, however, allowed the microbes to maintain viability over several days, despite having a water activity and pH lower and ionic strength higher than brines that reduced viability over the same timescales, suggesting important ion-specific effects. These data show that biofilm-forming cells have a greater capacity to resist martian aqueous extremes, but that evaporative or deliquescent brines are likely to be destructive to many organisms over relatively short timescales, with implications for the habitability of Mars and for micro-organisms dispersed by robotic or human explorers.

In Vitro Evaluation of a Hypochlorous Acid Hygiene Solution on Established Biofilms

OBJECTIVES

The purpose of this study was to determine whether a commercial formulation of hypochlorous acid hygiene solution (0.01%), Avenova, can destroy existing biofilms formed by ocular clinical bacterial isolates, including blepharitis isolates of Staphylococcus aureus and coagulase-negative staphylococci, and a keratitis isolate of Pseudomonas aeruginosa.

METHODS

Biofilms grown in bacterial growth media on disposable contact lens cases were challenged with hypochlorous acid hygiene solution. At various time points, surviving bacteria were quantified by serial dilution and colony counts. Staphylococcus aureus biofilms formed on glass were challenged using a hypochlorous acid hygiene solution and imaged using vital staining and confocal laser scanning microscopy.

RESULTS

Bactericidal activity (≥3 Log10; 99.9%) was observed for all tested bacterial species after a 30-min exposure. Staphylococcus aureus biofilms had a bactericidal level of killing by 10 min (P<0.01), Staphylococcus capitis by 5 min (P<0.001), Staphylococcus epidermidis by 30 min (P<0.001), and P. aeruginosa by 10 min (P<0.01). Confocal microscopy and crystal violet staining analysis of bacterial biofilms treated with hypochlorous acid solution both demonstrated that biofilm bacteria were readily killed, but biofilm structure was largely maintained.

CONCLUSIONS

Hypochlorous acid (0.01%) hygiene solution was able to achieve bactericidal levels of killing of bacteria in biofilms but did not disrupt biofilm structures. Susceptibility of tested staphylococcal blepharitis isolates varied by species, with S. capitis being the most susceptible and S. epidermidis being the least susceptible.

Enzymes Catalyzing the TCA- and Urea Cycle Influence the Matrix Composition of Biofilms Formed by Methicillin-Resistant Staphylococcus aureus USA300

In methicillin-sensitive Staphylococcus aureus (MSSA), the tricarboxylic acid (TCA) cycle is known to negatively regulate production of the major biofilm-matrix exopolysaccharide, PIA/PNAG. However, methicillin-resistant S. aureus (MRSA) produce a primarily proteinaceous biofilm matrix, and contribution of the TCA-cycle therein remains unclear. Utilizing USA300-JE2 Tn-mutants (NARSA) in genes encoding TCA- and urea cycle enzymes for transduction into a prolific biofilm-forming USA300 strain (UAS391-Ery^s), we studied the contribution of the TCA- and urea cycle and of proteins, eDNA and PIA/PNAG, to the matrix. Genes targeted in the urea cycle encoded argininosuccinate lyase and arginase (argH::Tn and rocF::Tn), and in the TCA-cycle encoded succinyl-CoA synthetase, succinate dehydrogenase, aconitase, isocitrate dehydrogenase, fumarate hydratase class II, and citrate synthase II (sucC::Tn, sdhA/B::Tn, acnA::Tn, icd::Tn, fumC::Tn and gltA::Tn). Biofilm formation was significantly decreased under no flow and flow conditions by argH::Tn, fumC::Tn, and sdhA/B::Tn (range OD₄₉₂ 0.374−0.667; integrated densities 2.065−4.875) compared to UAS391-Ery^S (OD₄₉₂ 0.814; integrated density 10.676) (p ≤ 0.008). Cellular and matrix stains, enzymatic treatment (Proteinase K, DNase I), and reverse-transcriptase PCR-based gene-expression analysis of fibronectin-binding proteins (fnbA/B) and the staphylococcal accessory regulator (sarA) on pre-formed UAS391-Ery^s and Tn-mutant biofilms showed: (i) < 1% PIA/PNAG in the proteinaceous/eDNA matrix; (ii) increased proteins under no flow and flow in the matrix of Tn mutant biofilms (on average 50 and 51 (±11)%) compared to UAS391-Ery^s (on average 22 and 25 (±4)%) (p < 0.001); and (iii) down- and up-regulation of fnbA/B and sarA, respectively, in Tn-mutants compared to UAS391-Ery^S (0.62-, 0.57-, and 2.23-fold on average). In conclusion, we show that the biofilm matrix of MRSA-USA300 and the corresponding Tn mutants is PIA/PNAG-independent and are mainly composed of proteins and eDNA. The primary impact of TCA-cycle inactivation was on the protein component of the biofilm matrix of MRSA-USA300.

Comparison of antibacterial activity of alexidine alone or as a final irrigant with sodium hypochlorite and chlorhexidine

Aims:

To compare the antibacterial activity of alexidine (ALX) alone or as a final irrigant in combination with sodium hypochlorite (NaOCl), with the most common canal irrigants, NaOCl and chlorhexidine (CHX).

Materials and methods:

Ninety-four root fragments from extracted human teeth were infected with Enterococcus faecalis for 24 h and then distributed into 4 groups of 20 fragments each. The NaOCl, CHX and ALX groups were immersed in 1 ml of 2.5% NaOCl, 2% CHX, and 1% ALX for 10 min, respectively. The samples of the NaOCl+ALX group were immersed in 1 ml of 2.5% NaOCl for 10 min followed by 1% ALX for 10 min. Bacteriological samples were taken, cultured, and the colony-forming units were counted.

Results:

There was no significant differences among the experimental groups (P>0.05) except for the comparisons CHX versus ALX and NaOCl+ALX versus ALX (P=0.004). ALX alone was the worst irrigant. CHX and NaOCl+ALX eradicated all bacteria. All experimental groups were significantly more effective than the control group immersed in saline (P<0.05).

Conclusions:

The antibacterial effect of ALX alone was inferior to 2% CHX and 2.5% NaOCl. However, the combination of NaOCl with ALX as a final irrigant eradicated the biofilms.

Natural and bioinspired nanostructured bactericidal surfaces

Bacterial antibiotic resistance is becoming more widespread due to excessive use of antibiotics in healthcare and agriculture. At the same time the development of new antibiotics has effectively ground to a hold. Chemical modifications of material surfaces have poor long-term performance in preventing bacterial build-up and hence approaches for realising bactericidal action through physical surface topography have become increasingly important in recent years. The complex nature of the bacteria cell wall interactions with nanostructured surfaces represents many challenges while the design of nanostructured bactericidal surfaces is considered. Here we present a brief overview of the bactericidal behaviour of naturally occurring and bio-inspired nanostructured surfaces against different bacteria through the physico-mechanical rupture of the cell wall. Many parameters affect this process including the size, shape, density, rigidity/flexibility and surface chemistry of the surface nanotextures as well as factors such as bacteria specificity (e.g. gram positive and gram negative) and motility. Different fabrication methods for such bactericidal nanostructured surfaces are summarised.

Phenotypic and genetic heterogeneity within biofilms with particular emphasis on persistence and antimicrobial tolerance

Phenotypic changes or phase variation within biofilms is an important feature of bacterial dormant life. Enhanced resistance to antimicrobials is one of the distinct features displayed by a fraction of cells within biofilms. It is believed that persisters are mainly responsible for this phenotypic heterogeneity. However, there is still an unresolved debate on the formation of persisters. In this short review, we highlight all known genomic and proteomic changes encountered by bacterial cells within biofilms. We have also described all phenotypic changes displayed by bacterial cells within biofilms with particular emphasis on enhanced antimicrobial tolerance of biofilms with particular reference to persisters. In addition, all currently known models of persistence have been succinctly discussed.

Ciprofloxacin-nitroxide hybrids with potential for biofilm control

As bacterial biofilms display extreme tolerance to conventional antibiotic treatments, it has become imperative to develop new antibacterial strategies with alternative mechanisms of action. Herein, we report the synthesis of a series of ciprofloxacin-nitroxide conjugates and their corresponding methoxyamine derivatives in high yield. This was achieved by linking various nitroxides or methoxyamines to the secondary amine of the piperazine ring of ciprofloxacin using amide bond coupling. Biological evaluation of the prepared compounds on preformed P. aeruginosa biofilms in flow cells revealed substantial dispersal with ciprofloxacin-nitroxide hybrid 25, and virtually complete killing and removal (94%) of established biofilms in the presence of ciprofloxacin-nitroxide hybrid 27. Compounds 25-28 were shown to be non-toxic in both human embryonic kidney 293 (HEK 293) cells and human muscle rhabdomyosarcoma (RD) cells at concentrations up to 40 μM. Significantly, these hybrids demonstrate the potential of antimicrobial-nitroxide agents to overcome the resistance of biofilms to antimicrobials via stimulation of biofilm dispersal or through direct cell killing.

New Weapons to Fight Old Enemies: Novel Strategies for the (Bio)control of Bacterial Biofilms in the Food Industry

Biofilms are microbial communities characterized by their adhesion to solid surfaces and the production of a matrix of exopolymeric substances, consisting of polysaccharides, proteins, DNA and lipids, which surround the microorganisms lending structural integrity and a unique biochemical profile to the biofilm. Biofilm formation enhances the ability of the producer/s to persist in a given environment. Pathogenic and spoilage bacterial species capable of forming biofilms are a significant problem for the healthcare and food industries, as their biofilm-forming ability protects them from common cleaning processes and allows them to remain in the environment post-sanitation. In the food industry, persistent bacteria colonize the inside of mixing tanks, vats and tubing, compromising food safety and quality. Strategies to overcome bacterial persistence through inhibition of biofilm formation or removal of mature biofilms are therefore necessary. Current biofilm control strategies employed in the food industry (cleaning and disinfection, material selection and surface preconditioning, plasma treatment, ultrasonication, etc.), although effective to a certain point, fall short of biofilm control. Efforts have been explored, mainly with a view to their application in pharmaceutical and healthcare settings, which focus on targeting molecular determinants regulating biofilm formation. Their application to the food industry would greatly aid efforts to eradicate undesirable bacteria from food processing environments and, ultimately, from food products. These approaches, in contrast to bactericidal approaches, exert less selective pressure which in turn would reduce the likelihood of resistance development. A particularly interesting strategy targets quorum sensing systems, which regulate gene expression in response to fluctuations in cell-population density governing essential cellular processes including biofilm formation. This review article discusses the problems associated with bacterial biofilms in the food industry and summarizes the recent strategies explored to inhibit biofilm formation, with special focus on those targeting quorum sensing.