Defining motility in the Staphylococci

Cuminaldehyde synergistically enhances the antimicrobial and antibiofilm potential of gentamicin: A direction towards an effective combination for the control of biofilm-linked threats of Staphylococcus aureus

Staphylococcus aureus, a Gram-positive, coccus-shaped bacterium often causes several infections on human hosts by exploiting biofilm. This current work investigates a potential strategy to manage the threats of biofilm-linked infections by embracing a combinatorial approach involving cuminaldehyde (phytochemical) and gentamicin (antibiotic). Despite showing antimicrobial properties individually, cuminaldehyde and gentamicin could exhibit enhanced antimicrobial potential when used together against S. aureus. The fractional inhibitory concentration index (FICI = 0.36) suggested that the selected compounds (cuminaldehyde and gentamicin) offered synergistic interaction while showing antimicrobial potential against the same organism. A series of experiments indicated that the selected compounds (cuminaldehyde and gentamicin) showed substantial antibiofilm potential against S. aureus when combined. The increased antibiofilm potential was linked to the accumulation of reactive oxygen species (ROS) and increased cell membrane permeability. Additionally, the combination of the selected compounds (cuminaldehyde and gentamicin) also impeded the cell surface hydrophobicity of S. aureus, aiding in the prevention of biofilm formation. The present study also showed that combining the mentioned compounds (cuminaldehyde and gentamicin) notably reduced the secretion of several virulence factors from S. aureus. Furthermore, the current research showed that these compounds (cuminaldehyde and gentamicin) could also exhibit antibiofilm potential against the clinical strains of Methicillin-Resistant S. aureus (MRSA). Taken together, this innovative approach not only enhances the potential of existing standard antibiotics but also opens up new therapeutic possibilities for combating biofilm-related infections.

Innovative fast and low-cost method for the detection of living bacteria based on trajectory

Detection of pathogens is a major concern in many fields like medicine, pharmaceuticals, or agri-food. Most conventional detection methods require skilled staff and specific laboratory equipment for sample collection and analysis or are specific to a given pathogen. Thus, they cannot be easily integrated into a portable device. In addition, the time-to-response, including the sample collection, possible transport to the measurement equipment, and analysis, is often quite long, making real-time screening of a large number of samples impossible. This paper presents a new approach that better fulfills industry needs in terms of integrated real-time wide screening of a large number of samples. It combines optical imaging, object detection and tracking, and machine-learning-based classification. Three of the most common bacteria are selected for this study. For all of them, living bacteria are distinguished from inert and inorganic objects (1 μm latex beads) based on their trajectory, with a high degree of confidence. Discrimination between living and dead bacteria of the same species is also achieved. Finally, the method successfully detects abnormal concentrations of a given bacterium compared to a standard baseline solution. Although there is still room for improvement, these results provide a proof of concept for this technology, which has strong application potential in infection spread prevention.

Anti-biofilm mechanisms of action of essential oils by targeting genes involved in quorum sensing, motility, adhesion, and virulence: A review

Biofilms are a critical factor for food safety, causing important economic losses. Among the novel strategies for controlling biofilms, essential oils (EOs) can represent an environmentally friendly approach, able to act both on early and mature stages of biofilm formation. This review reports the anti-biofilm mechanisms of action of EOs against five pathogenic bacterial species known for their biofilm-forming ability. These mechanisms include disturbing the expression of genes related to quorum sensing (QS), motility, adhesion, and virulence. Biofilms and QS are interconnected processes, and EOs interfere with the communication system (e.g. regulating the expression of agrBDCA, luxR, luxS, and pqsA genes), thus influencing biofilm formation. In addition, QS is an important mechanism that regulates gene expression related to bacterial survival, virulence, and pathogenicity. Similarly, EOs also influence the expression of many virulence genes. Moreover, EOs exert their effects modulating the genes associated with bacterial adhesion and motility, for example those involved in curli (csg), fimbriae (fim, lpf), and flagella (fla, fli, flh, and mot) production, as well as the ica genes responsible for synthetizing polysaccharide intercellular adhesin. This review provides a comprehensive framework on the topic for a better understanding of EOs biofilm mechanisms of action.

Emergence of an unconventional Enterobacter cloacae-derived Iturin A C-15 as a potential therapeutic agent against methicillin-resistant Staphylococcus aureus

Antimicrobial resistance poses a significant global health threat by reducing the effectiveness of conventional antibiotics, particularly against pathogens like Methicillin-resistant Staphylococcus aureus (MRSA). This study investigates the antimicrobial potential of rhizospheric soil bacteria from Prosopis cineraria (Sangri) in the Thar Desert. Bacterial strains isolated from these samples were observed to produce secondary metabolites, notably, Iturin A C-15 cyclic lipopeptide (SS1-3-P) which was extracted from strain Enterobacter cloacae SS1-3 and was purified and characterized using reverse-phase HPLC, ESI-LC/MS, Nile-Red Assay, and FT-IR analysis. The presence of the Iturin A biosynthetic gene cluster was confirmed using gene-specific polymerase chain reaction and the biocompatibility of the purified product was assessed on HEK-293, WI38, and human RBCs. The potential of SS1-3-P to bind to and destroy MRSA membranes was validated using molecular dynamics simulation along with membranolysis and membrane depolarization assays. Antimicrobial assays like growth curve analysis, field emission scanning electron microscopy, and ROS generation confirmed the efficacy of SS1-3-P against clinical MRSA. Furthermore, the antibiofilm and anti-virulence properties of SS1-3-P were studied meticulously. Studies on NIH/3T3 cell lines and a murine excisional wound model showed significant wound-healing attributes of the lipopeptide. These results highlight the potential of desert ecosystems in developing effective antimicrobial therapies against recalcitrant nosocomial pathogens like MRSA.

Antibiotic susceptibility and phenotypic profile of Staphylococcus species isolated from different clinical samples from health facilities: A cross-sectional study

Background

Staphylococcus species are widely distributed in nature and found in various human body sites.

Objectives

To determine the antibiotic susceptibility pattern of Staphylococcus species isolated from different clinical samples.

Methods

This cross-sectional study was conducted on 400 clinical specimens from conveniently sampled patients seeking healthcare at two health facilities in sulaimani / Iraq. Bacterial isolation and identification were done using conventional techniques, after which the antibiotic susceptibility profile of Staphylococcus species commonly prescribed antibiotics used in treating infections at the facilities was done using the disc diffusion method. Finally, MecA, methicillin-resistant Staphylococcus aureus and macrolides-lincosamide and streptogramin genes with mupirocin-resistant, beta-lactamase and vancomycin-resistance phenotypes were identified.

Results

Staphylococcus aureus was the prevalent isolated species (n = 197, 49.3%), followed by Staphylococcus hemolyticus (n = 115, 28.8%), Staphylococcus epidermidis (n = 49, 12.3%), Staphylococcus hominis (n = 9.0, 2.3%), Staphylococcus sciuri (n = 8.0, 2.0%) and Staphylococcus lentus (n = 4.0, 1.0%). All isolated species resisted Penicillin G, Ampicillin, Cefotaxime and Cefoxitin. Most of the isolates, 89.5% (n = 358) had the beta-lactamase phenotype, 18.0% (n = 72) had the MecA gene, 2.8% (n = 11) the Mupirocin-resistant phenotype, and 2.0% (n = 8.0) the vancomycin-resistance phenotype. Additionally, 12 isolates had both methicillin-resistant Staphylococcus aureus (66.7%) and macrolides-lincosamide and streptogramin (65.2%) genes. The majority of the patients, 43% (n = 172) were >50 years old and 52.25% (n = 209) males. Also, most samples were from patients with urinary tract infection (n = 73), wound (n = 71), blood (n = 35), sputum (n = 29), pus (n = 28), seminal fluid (n = 27), cerebrospinal fluid (n = 1.0) and stool (n = 1.0). Most isolates that had the MSLb gene were highly significantly resistant to both Clindamycin (94.6%) and Erythromycin (84.7%) (p < 0.001).

Conclusions

Staphylococcus aureus was the predominant Staphylococcus species isolated from the clinical samples, most of which were resistant to most commonly prescribed antibiotics and had developed resistant genes and phenotypes.

The Development of a Biomimetic Model of Bacteria Migration on Indwelling Urinary Catheter Surfaces

The aim of this study was to develop a novel biomimetic in vitro extraluminal migration model to observe the migration of bacteria along indwelling urinary catheters within the urethra and assess the efficacy of a prototype chlorhexidine diacetate (CHX) coating to prevent this migration. The in vitro urethra model utilised chromogenic agar. A catheter was inserted into each in vitro urethra. One side of the urethra was then inoculated with bacteria to replicate a contaminated urethral meatus. The models were then incubated for 30 days (d), with the migration distance recorded each day. Four indwelling catheter types were used to validate the in vitro urethra model and methodology. Using the biomimetic in vitro urethra model, E. coli and S. aureus migrated the entire length of a control catheter within 24-48 h (h). In the presence of a prototype CHX coating, full migration of the channel was prevented for 30 d. The results of this study support the hypothesis that catheter-associated urinary tract infections (CAUTIs) could be prevented by targeting catheter-mediated extraluminal microbial migration from outside of the urinary tract into the bladder.

Mucin-induced surface dispersal of Staphylococcus aureus and Staphylococcus epidermidis via quorum-sensing dependent and independent mechanisms

Nasopharyngeal carriage of staphylococci spreads potentially pathogenic strains into (peri)oral regions and increases the chance of cross-infections. Some laboratory strains can also move rapidly on hydrated agar surfaces, but the biological relevance of these observations is not clear. Using soft-agar [0.3% (wt/vol)] plate assays, we demonstrate the rapid surface dispersal of (peri)oral isolates of Staphylococcus aureus and Staphylococcus epidermidis and closely related laboratory strains in the presence of mucin glycoproteins. Mucin-induced dispersal was a stepwise process initiated by the passive spreading of the growing colonies followed by their rapid branching (dendrites) from the colony edge. Although most spreading strains used mucin as a growth substrate, dispersal was primarily dependent on the lubricating and hydrating properties of the mucins. Using S. aureus JE2 as a genetically tractable representative, we demonstrate that mucin-induced dendritic dispersal, but not colony spreading, is facilitated by the secretion of surfactant-active phenol-soluble modulins (PSMs) in a process regulated by the agr quorum-sensing system. Furthermore, the dendritic dispersal of S. aureus JE2 colonies was further stimulated in the presence of surfactant-active supernatants recovered from the most robust (peri)oral spreaders of S. aureus and S. epidermidis. These findings suggest complementary roles for lubricating mucins and staphylococcal PSMs in the active dispersal of potentially pathogenic strains from perioral to respiratory mucosae, where gel-forming, hydrating mucins abound. They also highlight the impact that interspecies interactions have on the co-dispersal of S. aureus with other perioral bacteria, heightening the risk of polymicrobial infections and the severity of the clinical outcomes.

IMPORTANCE

Despite lacking classical motility machinery, nasopharyngeal staphylococci spread rapidly in (peri)oral and respiratory mucosa and cause cross-infections. We describe laboratory conditions for the reproducible study of staphylococcal dispersal on mucosa-like surfaces and the identification of two dispersal stages (colony spreading and dendritic expansion) stimulated by mucin glycoproteins. The mucin type mattered as dispersal required the surfactant activity and hydration provided by some mucin glycoproteins. While colony spreading was a passive mode of dispersal lubricated by the mucins, the more rapid and invasive form of dendritic expansion of Staphylococcus aureus and Staphylococcus epidermidis required additional lubrication by surfactant-active peptides (phenol-soluble modulins) secreted at high cell densities through quorum sensing. These results highlight a hitherto unknown role for gel-forming mucins in the dispersal of staphylococcal strains associated with cross-infections and point at perioral regions as overlooked sources of carriage and infection by staphylococci.

Multi-Faceted Antimicrobial Efficacy of a Quinoline-Derived Bidentate Copper(II) Ligand Complex and Its Hydrogel Encapsulated Formulation in Methicillin-Resistant Staphylococcus aureus Inhibition and Wound Management

The emergence of antimicrobial resistance, exemplified by methicillin-resistant Staphylococcus aureus (MRSA), poses a grave threat to public health globally. Over time, MRSA has evolved resistance to multiple antibiotics, challenging conventional treatment strategies. The relentless adaptability of MRSA underscores the urgent need for innovative and targeted antimicrobial approaches to combat this resilient pathogen. Ancient knowledge and practices, along with scientific evidence, have established that metallic copper, and its organic coordination complexes can act as potential antibacterial substances. In search of a smart and effective antimicrobial against MRSA, we designed, synthesized, and characterized a bidentate copper(II) ligand complex (SG-Cu) utilizing a comprehensive array of analytical techniques, including ESI-MS, elemental analysis, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy, and others. Antibacterial efficacy and mechanism of action of the complex were assessed through bacterial growth analyses, bacterial membrane perturbation assays, ROS elicitation assays, and field emission scanning electron microscopy. SG-Cu was found to maintain robust biocompatibility against the mammalian cell lines HEK-293, WI-38, and NIH/3T3. Remarkably, SG-Cu demonstrated significant biofilm disruptive tendency evidenced by the retardation of sliding motility, reduction in slime production, reduction in biofilm viability, and enhanced biofilm eradication, both in vitro and in urinary catheters. In vivo studies on murine excisional wounds, with SG-Cu impregnated in a palmitic acid conjugated NAVSIQ hexapeptide (PA-NV) hydrogel, revealed the sustained release of SG-Cu from the gel matrix, facilitating accelerated wound healing and effective wound disinfection. This multifaceted investigation highlights the potential of SG-Cu as a versatile option for combating MRSA infections and promoting wound healing, solidifying its claim to be developed into a viable therapeutic.

Antimicrobial and Antibiofilm Potential of Flourensia retinophylla against Staphylococcus aureus

Staphylococcus aureus is a Gram-positive bacteria with the greatest impact in the clinical area, due to the high rate of infections and deaths reaching every year. A previous scenario is associated with the bacteria's ability to develop resistance against conventional antibiotic therapies as well as biofilm formation. The above situation exhibits the necessity to reach new effective strategies against this pathogen. Flourensia retinophylla is a medicinal plant commonly used for bacterial infections treatments and has demonstrated antimicrobial effect, although its effect against S. aureus and bacterial biofilms has not been investigated. The purpose of this work was to analyze the antimicrobial and antibiofilm potential of F. retinophylla against S. aureus. The antimicrobial effect was determined using an ethanolic extract of F. retinophylla. The surface charge of the bacterial membrane, the K+ leakage and the effect on motility were determined. The ability to prevent and remove bacterial biofilms was analyzed in terms of bacterial biomass, metabolic activity and viability. The results showed that F. retinophylla presents inhibitory (MIC: 250 µg/mL) and bactericidal (MBC: 500 µg/mL) activity against S. aureus. The MIC extract increased the bacterial surface charge by 1.4 times and the K+ concentration in the extracellular medium by 60%. The MIC extract inhibited the motility process by 100%, 61% and 40% after 24, 48 and 72 h, respectively. The MIC extract prevented the formation of biofilms by more than 80% in terms of biomass production and metabolic activity. An extract at 10 × MIC reduced the metabolic activity by 82% and the viability by ≈50% in preformed biofilms. The results suggest that F. retinophylla affects S. areus membrane and the process of biofilm formation and removal. This effect could set a precedent to use this plant as alternative for antimicrobial and disinfectant therapies to control infections caused by this pathogen. In addition, this shrub could be considered for carrying out a purification process in order to identify the compounds responsible for the antimicrobial and antibiofilm effect.

Visible-light photoactivated proanthocyanidin and kappa-carrageenan coating with anti-adhesive properties against clinically relevant bacteria

The increase of bacterial resistance to antibiotics is a growing concern worldwide and the search for new therapies could cost billions of dollars and countless lives. Inert surfaces are major sources of contamination due to easier adhesion and formation of bacterial biofilms, hindering the disinfection process. Therefore, the objective of this study was to develop a photoactivatable and anti-adhesive kappa-carrageenan coating using proanthocyanidin as a photosensitizer. The complete reduction (>5-log10 CFU/cm3) of culturable cells of Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa pathogens was achieved after 30 min of exposure to visible light (420 nm; 30 mW/cm2) with 5 % (w/v) of the photosensitizer. Cell membrane damage was confirmed by measuring potassium leakage, epifluorescence microscopy and bacterial motility analysis. Overall, visible light irradiation on coated solid surfaces mediated by proanthocyanidin showed no cytotoxicity and inactivated clinically important pathogens through the generation of reactive oxygen species, inhibiting bacterial initial adhesion. The developed coating is a promising alternative for a wide range of applications related to surface disinfection and food biopreservation.

Escherichia coli has an undiscovered ability to inhibit the growth of both Gram-negative and Gram-positive bacteria

The ability for bacteria to form boundaries between neighboring colonies as the result of intra-species inhibition has been described for a limited number of species. Here, we report that intra-species inhibition is more common than previously recognized. We demonstrated that swimming colonies of four Escherichia coli strains and six other bacteria form inhibitory zones between colonies, which is not caused by nutrient depletion. This phenomenon was similarly observed with non-flagellated bacteria. We developed a square-streaking pattern assay which revealed that Escherichia coli BW25113 inhibits the growth of other E. coli, and surprisingly, other Gram-positive and negative bacteria, including multi-drug resistant clinical isolates. Altogether, our findings demonstrate intra-species inhibition is common and might be used by E. coli to inhibit other bacteria. Our findings raise the possibility for a common mechanism shared across bacteria for intra-species inhibition. This can be further explored for a potential new class of antibiotics.

The potential of therapeutic hyperthermia to eradicate Staphylococcus aureus bacteria; an in vitro study

Staphylococcus aureus is one of the most common infectious agents, causing morbidity and mortality worldwide. Most pathogenic bacteria are classified in the group of mesophilic bacteria and the optimal growth temperature of these bacteria changes between 33 and 41 °C. Increased temperature can inhibit bacterial growth and mobility, which in turn, can trigger autolysis and cause cell wall damage. Hyperthermia treatment is defined as a heat-mediated treatment method applied using temperatures higher than body temperature. Nowadays, this treatment method is used especially in the treatment of tumours. Hyperthermia treatment is divided into two groups: mild hyperthermia and ablative or high-temperature hyperthermia. Mild hyperthermia is a therapeutic technique in which tumour tissue is heated above body temperature to produce a physiological or biological effect but is often not aimed at directly causing significant cell death. The goal of this method is to achieve temperatures of 40-45 °C in human tissues for up to 2 h. Hyperthermia can be used in the treatment of infections caused by such bacterial pathogens. In addition, using hyperthermia in combination with antimicrobial drugs may result in synergistic effects and reduce resistance issues. In our study, we used two different temperature levels (37 °C and 45 °C). We assessed growth inhibition, some virulence factors, alteration colony morphologies, and antimicrobial susceptibility for several antibiotics with three methods (Kirby-Bauer, E-test and broth microdilution) under hyperthermia. In the study, we observed that hyperthermia affected the urease enzyme, antibiotic sensitivity levels showed synergy with hyperthermia, and changes occurred in colony diameters and affected bacterial growth. We hypothesise that hyperthermia might be a new therapeutic option for infectious diseases as a sole agent or in combination with different antimicrobials.

Cell Adhesion, Elasticity, and Rupture Forces Guide Microbial Cell Death on Nanostructured Antimicrobial Titanium Surfaces

Naturally occurring and synthetic nanostructured surfaces have been widely reported to resist microbial colonization. The majority of these studies have shown that both bacterial and fungal cells are killed upon contact and subsequent surface adhesion to such surfaces. This occurs because the presence of high-aspect-ratio structures can initiate a self-driven mechanical rupture of microbial cells during the surface adsorption process. While this technology has received a large amount of scientific and medical interest, one important question still remains: what factors drive microbial death on the surface? In this work, the interplay between microbial-surface adhesion, cell elasticity, cell membrane rupture forces, and cell lysis at the microbial-nanostructure biointerface during adsorptive processes was assessed using a combination of live confocal laser scanning microscopy, scanning electron microscopy, in situ amplitude atomic force microscopy, and single-cell force spectroscopy. Specifically, the adsorptive behavior and nanomechanical properties of live Gram-negative (Pseudomonas aeruginosa) and Gram-positive (methicillin-resistant Staphylococcus aureus) bacterial cells, as well as the fungal species Candida albicans and Cryptococcus neoformans, were assessed on unmodified and nanostructured titanium surfaces. Unmodified titanium and titanium surfaces with nanostructures were used as model substrates for investigation. For all microbial species, cell elasticity, rupture force, maximum cell-surface adhesion force, the work of adhesion, and the cell-surface tether behavior were compared to the relative cell death observed for each surface examined. For cells with a lower elastic modulus, lower force to rupture through the cell, and higher work of adhesion, the surfaces had a higher antimicrobial activity, supporting the proposed biocidal mode of action for nanostructured surfaces. This study provides direct quantification of the differences observed in the efficacy of nanostructured antimicrobial surface as a function of microbial species indicating that a universal, antimicrobial surface architecture may be hard to achieve.

Resveratrol-Encapsulated Glutathione-Modified Robust Mesoporous Silica Nanoparticles as an Antibacterial and Antibiofilm Coating Agent for Medical Devices

The emergence of various lethal bacterial infections and their adherence to medical devices are major public health concerns. The increased bacterial exposure and titer are accompanied by the inappropriate use of antibiotics that sometimes lead to antibiotic resistance, and therefore, a drug-free antibacterial approach is required. Several nanoparticles (NPs) have been developed as antibacterial and antibiofilm coating agents, which can overcome different drug resistance mechanisms by inhibiting the important processes related to bacterial virulence potential. However, developing safe and biocompatible nanomaterials (NMs) for these applications has remained a major challenge due to their poorly understood mechanism of action. In this work, biogenic silica NPs were modified with glutathione (GSH) to form GSH@SNP (∼80 ± 15 nm) for targeting the bacterial cell surface and biofilm. GSH@SNP was loaded with resveratrol to obtain Res_GSH@SNP (∼124 ± 15 nm) that enhances the antibacterial activity of the NPs against Staphylococcus aureus and Escherichia coli by ∼51 and ∼49%, respectively, compared to GSH@SNP. Res_GSH@SNP is responsible for binding to the bacterial cell surface receptors that interrupt the cell membrane potential, leading to reactive oxygen species (ROS) generation, membrane disruption, and DNA damage and eventually resulting in antibacterial activity. Moreover, the antibiofilm activity of Res_GSH@SNP has been found to result from the interaction of the NPs with the abundant carbohydrates present on the biofilm surface. To check the practical utility of Res_GSH@SNP, these were further evaluated as an antibacterial and antibiofilm coating agent for urinary catheters and were found to be effective even after multiple washes. Res_GSH@SNP has been found to exhibit ∼80 ± 1.4% cytocompatibility toward fibroblast NIH-3T3 cells. Overall, this study is expected to pave the way for the development of biocompatible NP-based coating agents for medical devices.

Bacterial-fungal interactions promote parallel evolution of global transcriptional regulators in a widespread Staphylococcus species

Experimental studies of microbial evolution have largely focused on monocultures of model organisms, but most microbes live in communities where interactions with other species may impact rates and modes of evolution. Using the cheese rind model microbial community, we determined how species interactions shape the evolution of the widespread food- and animal-associated bacterium Staphylococcus xylosus. We evolved S. xylosus for 450 generations alone or in co-culture with one of three microbes: the yeast Debaryomyces hansenii, the bacterium Brevibacterium aurantiacum, and the mold Penicillium solitum. We used the frequency of colony morphology mutants (pigment and colony texture phenotypes) and whole-genome sequencing of isolates to quantify phenotypic and genomic evolution. The yeast D. hansenii strongly promoted diversification of S. xylosus. By the end of the experiment, all populations co-cultured with the yeast were dominated by pigment and colony morphology mutant phenotypes. Populations of S. xylosus grown alone, with B. aurantiacum, or with P. solitum did not evolve novel phenotypic diversity. Whole-genome sequencing of individual mutant isolates across all four treatments identified numerous unique mutations in the operons for the SigB, Agr, and WalRK global regulators, but only in the D. hansenii treatment. Phenotyping and RNA-seq experiments highlighted altered pigment and biofilm production, spreading, stress tolerance, and metabolism of S. xylosus mutants. Fitness experiments revealed antagonistic pleiotropy, where beneficial mutations that evolved in the presence of the yeast had strong negative fitness effects in other biotic environments. This work demonstrates that bacterial-fungal interactions can have long-term evolutionary consequences within multispecies microbiomes by facilitating the evolution of strain diversity.

Impact of cell-free supernatant of lactic acid bacteria on Staphylococcus aureus biofilm and its metabolites

Introduction

A safe bio-preservative agent, lactic acid bacteria (LAB) can inhibit the growth of pathogenic bacteria and spoilage organisms. Its cell-free supernatant (LAB-CFS), which is rich in bioactive compounds, is what makes LAB antibacterial work.

Methods

This study focused on the changes in biofilm activity and related metabolic pathways of S. aureus treated with lactic acid bacteria planktonic CFS (LAB-pk-CFS) and biofilm state (LAB-bf-CFS).

Results

The findings demonstrated that the LAB-CFS treatment considerably slowed Staphylococcus aureus (S. aureus) growth and prevented it from forming biofilms. Additionally, it inhibits the physiological traits of the S. aureus biofilm, including hydrophobicity, motility, eDNA, and PIA associated to the biofilm. The metabolites of S. aureus biofilm treated with LAB-CFS were greater in the LAB-bf-CFS than they were in the LAB-pk-CFS, according to metabolomics studies. Important metabolic pathways such amino acids and carbohydrates metabolism were among the most noticeably altered metabolic pathways.

Discussion

These findings show that LAB-CFS has a strong potential to combat S. aureus infections.

Mechanobiology as a tool for addressing the genotype-to-phenotype problem in microbiology

The central hypothesis of the genotype-phenotype relationship is that the phenotype of a developing organism (i.e., its set of observable attributes) depends on its genome and the environment. However, as we learn more about the genetics and biochemistry of living systems, our understanding does not fully extend to the complex multiscale nature of how cells move, interact, and organize; this gap in understanding is referred to as the genotype-to-phenotype problem. The physics of soft matter sets the background on which living organisms evolved, and the cell environment is a strong determinant of cell phenotype. This inevitably leads to challenges as the full function of many genes, and the diversity of cellular behaviors cannot be assessed without wide screens of environmental conditions. Cellular mechanobiology is an emerging field that provides methodologies to understand how cells integrate chemical and physical environmental stress and signals, and how they are transduced to control cell function. Biofilm forming bacteria represent an attractive model because they are fast growing, genetically malleable and can display sophisticated self-organizing developmental behaviors similar to those found in higher organisms. Here, we propose mechanobiology as a new area of study in prokaryotic systems and describe its potential for unveiling new links between an organism's genome and phenome.

Discovery of AI-2 Quorum Sensing Inhibitors Targeting the LsrK/HPr Protein-Protein Interaction Site by Molecular Dynamics Simulation, Virtual Screening, and Bioassay Evaluation

Quorum sensing (QS) is a cell-to-cell communication mechanism that regulates bacterial pathogenicity, biofilm formation, and antibiotic sensitivity. Among the identified quorum sensing, AI-2 QS exists in both Gram-negative and Gram-positive bacteria and is responsible for interspecies communication. Recent studies have highlighted the connection between the phosphotransferase system (PTS) and AI-2 QS, with this link being associated with protein-protein interaction (PPI) between HPr and LsrK. Here, we first discovered several AI-2 QSIs targeting the LsrK/HPr PPI site through molecular dynamics (MD) simulation, virtual screening, and bioassay evaluation. Of the 62 compounds purchased, eight compounds demonstrated significant inhibition in LsrK-based assays and AI-2 QS interference assays. Surface plasmon resonance (SPR) analysis confirmed that the hit compound 4171-0375 specifically bound to the LsrK-N protein (HPr binding domain, KD = 2.51 × 10^-5 M), and therefore the LsrK/HPr PPI site. The structure-activity relationships (SARs) emphasized the importance of hydrophobic interactions with the hydrophobic pocket and hydrogen bonds or salt bridges with key residues of LsrK for LsrK/HPr PPI inhibitors. These new AI-2 QSIs, especially 4171-0375, exhibited novel structures, significant LsrK inhibition, and were suitable for structural modification to search for more effective AI-2 QSIs.

Antibacterial, antibiofilm, and anti-quorum sensing activities of pyocyanin against methicillin-resistant Staphylococcus aureus: in vitro and in vivo study

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) infections are considered a major public health problem, as the treatment options are restricted. Biofilm formation and the quorum sensing (QS) system play a pivotal role in S. aureus pathogenicity. Hence, this study was performed to explore the antibacterial effect of pyocyanin (PCN) on MRSA as well as its effect on MRSA biofilm and QS.

RESULTS

Data revealed that PCN exhibited strong antibacterial activity against all test MRSA isolates (n = 30) with a MIC value equal to 8 µg/ml. About 88% of MRSA biofilms were eradicated by PCN treatment using the crystal violet assay. The disruption of MRSA biofilm was confirmed using confocal laser scanning microscopy, which showed a reduction in bacterial viability (approximately equal to 82%) and biofilm thickness (approximately equal to 60%). Additionally, the disruption of the formation of microcolonies and the disturbance of the connection between bacterial cells in the MRSA biofilm after PCN treatment were examined by scanning electron microscopy. The 1/2 and 1/4 MICs of PCN exerted promising anti-QS activity without affecting bacterial viability; Agr QS-dependent virulence factors (hemolysin, protease, and motility), and the expression of agrA gene, decreased after PCN treatment. The in silico analysis confirmed the binding of PCN to the AgrA protein active site, which blocked its action. The in vivo study using the rat wound infection model confirmed the ability of PCN to modulate the biofilm and QS of MRSA isolates.

CONCLUSION

The extracted PCN seems to be a good candidate for treating MRSA infection through biofilm eradication and Agr QS inhibition.

Tuning the arrangement of lamellar nanostructures: achieving the dual function of physically killing bacteria and promoting osteogenesis

Bacteria killing behavior based on physical effects is preferred for biomedical implants because of the negligible associated side effects. However, our current understanding of the antibacterial activity of nanostructures remains limited and, in practice, nanoarchitectures that are created on orthopedics should also promote osteogenesis simultaneously. In this study, tilted and vertical nanolamellar structures are fabricated on semi-crystalline polyether-ether-ketone (PEEK) via argon plasma treatment with or without pre-annealing. The two types of nanolamellae can physically kill the bacteria that come into contact with them, but the antibacterial mechanisms between the two are different. Specifically, the sharp edges of the vertically aligned nanolamellae can penetrate and damage the bacterial membrane, whereas bacteria are stuck on the tilted nanostructures and are stretched, leading to eventual destruction. The tilted nanolamellae are more desirable than the vertically aligned ones from the perspective of peri-implant bone regeneration. Our study not only reveals the role of the arrangement of nanostructures in orthopedic applications but also provides new information about different mechanisms of physical antibacterial activity.

Associations of Ambient Environmental Conditions with Growth and Dissemination of Staphylococcus epidermidis on the Surface of Teatcups from Sheep Milking Parlours

The growth of two isolates of Staphylococcus epidermidis (one that was forming biofilm and one that was not) on new or used teatcups made of silicone for use in milking parlours for sheep, was assessed for 24 h after the application by smearing on the surface of the teatcup. Staphylococci were applied by smearing on an area of 0.0003142 (3.142 × 10−4) m2 on material obtained from the teatcups and their growth and expansion further on were monitored for 24 h at varying ambient conditions: temperature 21 °C or 31 °C and humidity 60% or 80%. No differences were evident between the two isolates in the frequency of recoveries in any of the conditions tested (p > 0.75 for all comparisons). Recovery rates were higher in humidity 80% compared to humidity 60%: 1678/2016 (83.2%) versus 1282/2016 (63.6%) (p < 0.0001), and in temperature 31 °C compared to temperature 21 °C: 1525/2016 (75.6%) versus 1435/2016 (71.2%) (p = 0.001). Recovery rates were also higher from new teatcups compared to used ones only in humidity 60%: 744/1008 (73.8%) versus 538/1008 (53.4%) (p < 0.0001). Humidity 80% was associated with higher speed of linear dissemination of the isolates on teatcup surface compared to humidity 60%: 0.000000640 (6.40 × 10−7) m s−1 versus 0.000000322 (3.22 × 10−7) m s−1 (+98.8%) (p < 0.0001); no such association was seen with higher temperature: 0.000000509 (5.09 × 10−7) m s−1 versus 0.000000453 (4.53 × 10−7) m s−1 for temperature 31 °C and 21 °C (+12.4%) (p = 0.29). As part of precision livestock farming, differing approaches can be instituted in accord with varying climatic conditions in different farms, as well as within the same farm with the change of seasons.

Hitchhiking motility of Staphylococcus aureus involves the interaction between its wall teichoic acids and lipopolysaccharide of Pseudomonas aeruginosa

Staphylococcus aureus, which lacks pili and flagella, is nonmotile. However, it hitchhikes motile bacteria, such as Pseudomonas aeruginosa, to migrate in the environment. This study demonstrated that the hitchhiking motility of S. aureus SA113 was reduced after the tagO, which encodes an enzyme for wall teichoic acids (WTA) synthesis, was deleted. The hitchhiking motility was restored after the mutation was complemented by transforming a plasmid expressing TagO into the mutant. We also showed that adding purified lipopolysaccharide (LPS) to a culture that contains S. aureus SA113 and P. aeruginosa PAO1, reduced the movement of S. aureus, showing that WTA and LPS are involved in the hitchhiking motility of S. aureus. This study also found that P. aeruginosa promoted the movement of S. aureus in the digestive tract of Caenorhabditis elegans and in mice. In conclusion, this study reveals how S. aureus hitchhikes P. aeruginosa for translocation in an ecosystem. The results from this study improve our understanding on how a nonmotile pathogen moves in the environment and spreads in animals.

Recent advances in experimental design and data analysis to characterize prokaryotic motility

Bacterial motility plays a key role in important cell processes such as chemotaxis and biofilm formation, but is challenging to quantify due to the small size of the individual microorganisms and the complex interplay of biological and physical factors that influence motility phenotypes. Swimming, the first type of motility described in bacteria, still remains largely unquantified. Light microscopy has enabled qualitative characterization of swimming patterns seen in different strains, such as run and tumble, run-reverse-flick, run and slow, stop and coil, and push and pull, which has allowed for elucidation of the underlying physics. However, quantifying these behaviors (e.g., identifying run distances and speeds, turn angles and behavior by surfaces or cell-cell interactions) remains a challenging task. A qualitative and quantitative understanding of bacterial motility is needed to bridge the gap between experimentation, omics analysis, and bacterial motility theory. In this review, we discuss the strengths and limitations of how phase contrast microscopy, fluorescence microscopy, and digital holographic microscopy have been used to quantify bacterial motility. Approaches to automated software analysis, including cell recognition, tracking, and track analysis, are also discussed with a view to providing a guide for experimenters to setting up the appropriate imaging and analysis system for their needs.

Study of SarA by DNA Affinity Capture Assay (DACA) Employing Three Promoters of Key Virulence and Resistance Genes in Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA), one of the most well-known human pathogens, houses many virulence factors and regulatory proteins that confer resistance to diverse antibiotics. Although they have been investigated intensively, the correlations among virulence factors, regulatory proteins and antibiotic resistance are still elusive. We aimed to identify the most significant global MRSA regulator by concurrently analyzing protein-binding and several promoters under same conditions and at the same time point. DNA affinity capture assay (DACA) was performed with the promoters of mecA, sarA, and sarR, all of which significantly impact survival of MRSA. Here, we show that SarA protein binds to all three promoters. Consistent with the previous reports, ΔsarA mutant exhibited weakened antibiotic resistance to oxacillin and reduced biofilm formation. Additionally, production and activity of many virulence factors such as phenol-soluble modulins (PSM), α-hemolysin, motility, staphyloxanthin, and other related proteins were decreased. Comparing the sequence of SarA with that of clinical strains of various lineages showed that all sequences were highly conserved, in contrast to that observed for AgrA, another major regulator of virulence and resistance in MRSA. We have demonstrated that SarA regulates antibiotic resistance and the expression of various virulence factors. Our results warrant that SarA could be a leading target for developing therapeutic agents against MRSA infections.

Biocompatibility and biocidal effects of modified polylactide composites

Polylactide (PLA) materials treated with antimicrobial fillers represent a suitable alternative to the production of medical devices. Their advantage is that they can prevent the growth of microorganisms and the formation of microbial biofilms on the surface and around composites. The work is focused on the evaluation of biocompatibility and biocide effect of PLA composite films filled with vermiculite and graphene oxide modified with silver (Ag⁺ and Ag nanoparticles), hexadecylpyridinium (HDP) and hexadecyltrimethylammonium (HDTMA) cations and their degradation leachates monitored at 1-3-6-month intervals. The antimicrobial effect of the leachates was detected by microdilution methods on gram-negative (Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis), gram-positive (Staphylococcus aureus, Streptococcus salivarius) bacteria and yeast (Candida albicans). The biocidal effect of composites on biofilm formation on the surface of composites was monitored by Christensen method and autoaggregation and motility tests. The biocompatibility of the composite and the leachates was assessed by 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) cytotoxicity assay. The evaluation of the antimicrobial effect of the leachates demonstrated that leachates of PLA composite filled with graphene oxide and Ag⁺ showed a stronger antimicrobial effect than leachates of PLA composite filled with vermiculite and Ag⁺ and Ag nanoparticles. The leachates of PLA composites containing vermiculite with HDP and HDTMA cations had a higher antimicrobial effect on G⁺ bacteria and yeast than G^- bacteria. Bacterial growth, biofilm formation, autoaggregation and motility of the tested bacteria were most inhibited by the composite with vermiculite and Ag⁺ and Ag nanoparticles. Even after a 6-month degradation of this composite, bacterial growth and biofilm formation continued to be strongly inhibited up to 42 and 91%, respectively. The cytotoxic effect was proved only in the leachate of the composite with vermiculite containing HDP after 6 months of its degradation. Tests evaluating the biocompatibility of materials have shown that the vermiculite is the most preferred carrier and can be used in the future to bind other compounds. The study confirmed that PLA composite filled with vermiculite and Ag⁺ and Ag nanoparticles was the most stable and effective composite with the best biocompatible and biocidal properties.

Rapid Bacterial Motility Monitoring Using Inexpensive 3D-Printed OpenFlexure Microscopy Allows Microfluidic Antibiotic Susceptibility Testing

Antibiotic susceptibility testing is vital to tackle the emergence and spread of antimicrobial resistance. Inexpensive digital CMOS cameras can be converted into portable digital microscopes using 3D printed x-y-z stages. Microscopic examination of bacterial motility can rapidly detect the response of microbes to antibiotics to determine susceptibility. Here, we present a new simple microdevice-miniature microscope cell measurement system for multiplexed antibiotic susceptibility testing. The microdevice is made using melt-extruded plastic film strips containing ten parallel 0.2 mm diameter microcapillaries. Two different antibiotics, ceftazidime and gentamicin, were prepared in Mueller-Hinton agar (0.4%) to produce an antibiotic-loaded microdevice for simple sample addition. This combination was selected to closely match current standard methods for both antibiotic susceptibility testing and motility testing. Use of low agar concentration permits observation of motile bacteria responding to antibiotic exposure as they enter capillaries. This device fits onto the OpenFlexure 3D-printed digital microscope using a Raspberry Pi computer and v2 camera, avoiding need for expensive laboratory microscopes. This inexpensive and portable digital microscope platform had sufficient magnification to detect motile bacteria, yet wide enough field of view to monitor bacteria behavior as they entered antibiotic-loaded microcapillaries. The image quality was sufficient to detect how bacterial motility was inhibited by different concentrations of antibiotic. We conclude that a 3D-printed Raspberry Pi-based microscope combined with disposable microfluidic test strips permit rapid, easy-to-use bacterial motility detection, with potential for aiding detection of antibiotic resistance.

Mechanical Stabilization of a Bacterial Adhesion Complex

The adhesions between Gram-positive bacteria and their hosts are exposed to varying magnitudes of tensile forces. Here, using an ultrastable magnetic tweezer-based single-molecule approach, we show the catch-bond kinetics of the prototypical adhesion complex of SD-repeat protein G (SdrG) to a peptide from fibrinogen β (Fgβ) over a physiologically important force range from piconewton (pN) to tens of pN, which was not technologically accessible to previous studies. At 37 °C, the lifetime of the complex exponentially increases from seconds at several pN to ∼1000 s as the force reaches 30 pN, leading to mechanical stabilization of the adhesion. The dissociation transition pathway is determined as the unbinding of a critical β-strand peptide (“latch” strand of SdrG that secures the entire adhesion complex) away from its binding cleft, leading to the dissociation of the Fgβ ligand. Similar mechanical stabilization behavior is also observed in several homologous adhesions, suggesting the generality of catch-bond kinetics in such bacterial adhesions. We reason that such mechanical stabilization confers multiple advantages in the pathogenesis and adaptation of bacteria.

The Effect of Hypochlorous Acid on the Filtration Performance and Bacterial Decontamination of N95 Filtering Facemask Respirators

BACKGROUND

Stabilized Hypochlorous acid (HOCl) is increasingly used as a hospital disinfectant and antiseptic, yet its effect on N95 filtration facemask respirators (FFR) is unknown. These FFRs could also contribute to fomite-based transmission of nosocomial infections if worn for extended use between patient rooms.

METHODS

Filtration performance of N95 FFR fabric swatches was assessed after various levels of HOCl exposure. N95 swatches were then contaminated with 10⁸ E. coli or 10⁸ Staph aureus and treated with HOCl solution, 70% ethyl alcohol, or normal saline. Surviving bacterial numbers were assessed by plate counts.

RESULTS

The size-dependent filtration efficiency of HOCl-sprayed N95 FFR fabric ranged from 96 to 100%, showing no significant change. Flow resistance testing revealed almost no change compared to control. Submersion in HOCl, but not spraying, had an excellent bactericidal effect on contaminated swatches.

DISCUSSION

The role of the outer hydrophobic layer of N95 FFRs is discussed regarding the effects of HOCl on filtration and bacterial decontamination.

CONCLUSION

N95 material, sprayed with or briefly submerged in HOCl, maintained its filtration function. HOCl delivery by spray pump, however, would not accomplish decontamination of extended use FFRs between patient encounters. HOCl submersion of intact FFRs, contaminated with various hospital pathogens, is worth further study.

4-Chloro-2-Isopropyl-5-Methylphenol Exhibits Antimicrobial and Adjuvant Activity against Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) causes severe infections and poses a global healthcare challenge. The utilization of novel molecules which confer synergistical effects to existing MRSA-directed antibiotics is one of the well-accepted strategies in lieu of de novo development of new antibiotics. Thymol is a key component of the essential oil of plants in the Thymus and Origanum genera. Despite the absence of antimicrobial potency, thymol is known to inhibit MRSA biofilm formation. However, the anti-MRSA activity of thymol analogs is not well characterized. Here, we assessed the antimicrobial activity of several thymol derivatives and found that 4-chloro-2-isopropyl-5-methylphenol (chlorothymol) has antimicrobial activity against MRSA and in addition it also prevents biofilm formation. Chlorothymol inhibited staphyloxanthin production, slowed MRSA motility, and altered bacterial cell density and size. This compound also showed a synergistic antimicrobial activity with oxacillin against highly resistant S. aureus clinical isolates and biofilms associated with these isolates. Our results demonstrate that chlorinated thymol derivatives should be considered as a new lead compound in anti-MRSA therapeutics.

Transition metal complex laminated bioactive implant alleviates Methicillin Resistant Staphylococcus aureus virulence

Orthopedic implant infections cause a serious threat after implantation. The major source of implant infection is biofilms which are highly tolerant to antibiotics due to the presence of rigid biofilm matrix. Hence to overcome biofilm mediated implant infections, we developed a novel antibiofilm agent, palladium (II) thiazolinyl picolinamide complex (Pd(II)-E). From our study, it was found that Pd(II)-E have profound biofilm inhibition activity and also reduced various virulence factors of Methicillin resistant Staphylococcus aureus (MRSA) including slime synthesis, Phenol soluble modulin (PSM) mediated spreading, Exopolysaccharides production and staphyloxanthin synthesis. Further, Pd(II)-E was coated over the titanium plates which was confirmed using EDX (Energy Dispersive X-Ray) analysis. The Pd(II)-E coated plates were able to prevent the biofilm formation on them which was evident under a Scanning electron microscope (SEM) and several virulent genes were found to be downregulated in the biofilms on the coated titanium plates which confirmed by qPCR. From our findings, it was found that Pd(II)-E coated titanium implants would be an effective alternate approach for preventing biofilm mediated implant infections.

Ultrafast and Multiplexed Bacteriophage Susceptibility Testing by Surface Plasmon Resonance and Phase Imaging of Immobilized Phage Microarrays

In the context of bacteriophage (phage) therapy, there is an urgent need for a method permitting multiplexed, parallel phage susceptibility testing (PST) prior to the formulation of personalized phage cocktails for administration to patients suffering from antimicrobial-resistant bacterial infections. Methods based on surface plasmon resonance imaging (SPRi) and phase imaging were demonstrated as candidates for very rapid (<2 h) PST in the broth phase. Biosensing layers composed of arrays of phages 44AHJD, P68, and gh-1 were covalently immobilized on the surface of an SPRi prism and exposed to liquid culture of either Pseudomonas putida or methicillin-resistant Staphylococcus aureus (i.e., either the phages’ host or non-host bacteria). Monitoring of reflectivity reveals susceptibility of the challenge bacteria to the immobilized phage strains. Investigation of phase imaging of lytic replication of gh-1 demonstrates PST at the single-cell scale, without requiring phage immobilization. SPRi sensorgrams show that on-target regions increase in reflectivity more slowly, stabilizing later and to a lower level compared to off-target regions. Phage susceptibility can be revealed in as little as 30 min in both the SPRi and phase imaging methods.

Investigating the microbial and metalloprotease sequestration properties of superabsorbent wound dressings

Exudate production is a natural part of the wound healing process, however levels of exudate need to be appropriately managed to maintain a moist wound environment which supports healing. An overly-exuding wound creates an environment favourable to bacterial growth. In recent years, a significant increase in commercially available superabsorbent dressings have become available which claim to absorb and retain excess exudate and its components. However, the effectiveness of these dressings in sequestering and retaining bacteria and host-derived proteins has not been compared. We have therefore investigated several superabsorbent dressings for their ability to absorb and retain bacteria (Staphylococcus aureus and Pseudomonas aeruginosa), their impact on bacterial viability, and their ability to sequester matrix metalloproteinases (MMP)-2 and 9 over 7 days. Whilst all dressings could sequester bacteria, some dressings internalised bacteria more effectively. There was considerable variation in bacterial viability within the dressings’ core, as well as differences in bacterial retention. Some dressings effectively internalised and retained bacteria over time, whereas other dressings retained significantly less. These differences were reflected visually using scanning electron microscopy. Most dressings fully sequestered MMP-2 and 9. These data illustrate differences in the ability of superabsorbent dressings to absorb and retain exudate and its components.

Methods to Evaluate Bacterial Motility and Its Role in Bacterial–Host Interactions

Bacterial motility is a widespread characteristic that can provide several advantages for the cell, allowing it to move towards more favorable conditions and enabling host-associated processes such as colonization. There are different bacterial motility types, and their expression is highly regulated by the environmental conditions. Because of this, methods for studying motility under realistic experimental conditions are required. A wide variety of approaches have been developed to study bacterial motility. Here, we present the most common techniques and recent advances and discuss their strengths as well as their limitations. We classify them as macroscopic or microscopic and highlight the advantages of three-dimensional imaging in microscopic approaches. Lastly, we discuss methods suited for studying motility in bacterial–host interactions, including the use of the zebrafish model.

Bactericidal and antibiofilm properties of Rumex japonicus Houtt. on multidrug-resistant Staphylococcus aureus isolated from milk

Multidrug-resistant (MDR) Staphylococcus aureus and its biofilm formation have been challenging to control in milk and dairy industries. Biofilms formed by Staph. aureus may result in the failure of antibacterial agents and disinfectants to penetrate the biofilm in an attempt to control contamination. Novel natural antibacterial agents are required to combat MDR bacteria and biofilms. In this study, we evaluated the bactericidal, antibiofilm, and antimotility effects of Rumex japonicus Houtt. (RJH) extract on MDR Staph. aureus isolated from milk. The RJH extract exhibited good antibacterial activity against MDR strains with minimum inhibitory concentrations (MIC) ranging from 0.78 to 6.25 mg/mL and minimum bactericidal concentrations ranging from 3.125 to 12.5 mg/mL. The extract showed strong inhibition of biofilm formation (81.9%) at sub-MIC value and eradication of biofilm at higher concentrations. The motility of Staph. aureus was effectively blocked by the extract. Major compounds emodin, chrysophanol, and physcion were identified in RJH extract using HPLC-linear trap quadrupole (LTQ)/Orbitrap-mass spectrometry. The extract was nontoxic to human epithelial cell lines such as Caco-2 and HT-29 cell lines at concentrations ranging from 0.1 to 0.5 mg/mL, and from 0.1 to 0.75 mg/mL, respectively. These findings suggest that RJH extract could be an alternative to synthetic preservatives in milk and dairy products.

Comparative Study of the Difference in Behavior of the Accessory Gene Regulator (Agr) in USA300 and USA400 Community-Associated Methicillin-Resistant Staphylococcus aureus (CA-MRSA)

Community-associated Methicillin-Resistant Staphylococcus aureus (CA-MRSA) is notorious as a leading cause of soft tissue infections. Despite several studies on the Agr regulator, the mechanisms of action of Agr on the virulence factors in different strains are still unknown. To reveal the role of Agr in different CA-MRSA, we investigated the LACΔagr mutant and the MW2Δagr mutant by comparing LAC (USA300), MW2 (USA400), and Δagr mutants. The changes of Δagr mutants in sensitivity to oxacillin and several virulence factors such as biofilm formation, pigmentation, motility, and membrane properties were monitored. LACΔagr and MW2Δagr mutants showed different oxacillin sensitivity and biofilm formation compared to the LAC and MW2 strains. Regardless of the strain, the motility was reduced in Δagr mutants. And there was an increase in the long chain fatty acid in phospholipid fatty acid composition of Δagr mutants. Other properties such as biofilm formation, pigmentation, motility, and membrane properties were different in both Δagr mutants. The Agr regulator may have a common role like the control of motility and straindependent roles such as antibiotic resistance, biofilm formation, change of membrane, and pigment production. It does not seem easy to control all MRSA by targeting the Agr regulator only as it showed strain-dependent behaviors.

Growth of Staphylococcus epidermidis on the Surface of Teatcups from Milking Parlours

The growth of two Staphylococcus epidermidis isolates (one biofilm-forming and one not) on teatcups for cattle (made of rubber) or sheep (made of silicone) were assessed in nine multiplicates for 24 h post-smearing on the teatcup surface. Staphylococci were smeared on an area of 0.0003142 m² on the material and their growth and expansion further on were monitored for 24 h. There were no differences in the frequency of recoveries between the two isolates (p > 0.82 for all comparisons). There were more recoveries from sheep teatcups than from cattle teatcups: 1280/1728 (74.1%) versus 942/1728 (54.5%), for both isolates (p < 0.0001). Significance was observed only 6 h to 15 h after smearing (p < 0.0001 for all comparisons). The median speed of linear dissemination of the isolates was 0.00000021 m s⁻¹ on cattle teatcups and 0.00000033 m s⁻¹ on sheep teatcups (p < 0.0001). The increased growth and faster expansion of staphylococci on silicone teatcups raise important points from a clinical viewpoint. The model could be used in the testing of staphylococcal growth in the material of milking parlours in various conditions.

Transient surface hydration impacts biogeography and intercellular interactions of non-motile bacteria

There are many hydrated surface niches that are neither static nor continuously flowing that are colonized by microbes such as bacteria. Such periodic hydrodynamic regimes are distinct from aquatic systems where microbial dissemination is reasonably predicted by assuming continuous flow or static systems where motile microbes largely control their own fate. Here we show how non-motile bacteria exhibit rapid, dispersive bursts of movement over surfaces using transient confluent hydration from the environment, which we term "surface hydrodispersion" where cells traverse thousands of cell lengths within minutes. The fraction of the population disseminated by surface hydrodispersion is small-on order of 1 cell per million. Thus, surface hydrodispersion can promote isolated distribution of single cells, which is unlike other characterized active and passive surface motilities. We describe this translocation using a continuous time random walk modeling approach and find in computational simulations that transient fluid accumulation, dilution, and gravitational pull are the contributing factors. Surface hydrodispersion, consistent with advection, is unlike simple colony expansion as it dramatically alters spatial relationships, shown here with Staphylococcus aureus, which becomes increasingly virulent when isolated from Corynebacterium striatum Surface hydrodispersion of non-motile bacteria exploiting transient fluid availability and gravity is a mechanism that can result in sporadic and sudden shifts in microbial community behavior. To better understand how this movement can impact biogeography on the millimeter scale, this work describes a system for study of primary factors behind this movement as well as a stochastic model describing this dispersal.Importance: Understanding the dynamics within microbiome communities is a challenge. Knowledge of phylogeny and spatial arrangement has led to increased understanding of numerous polymicrobial communities yet, these snapshots do not convey the dynamics of populations over time. The actual biogeography of any microbiome controls the potential interactions, governing any possible antagonistic or synergistic behavior. Accordingly, a shift in biogeography can enable new behavior. Little is known about the movement mechanisms of "non-motile" microbes. Here we characterize a universal means of movement we term hydrodispersion where non-motile bacteria are transported thousands of cell lengths in minutes. We show that only a small fraction of the population is translocated by hydrodispersion and describe this movement further using a random-walk mathematical model approach in silico We demonstrate the importance of hydrodispersion by showing that Staphylococcus aureus can separate from a coculture inoculation with Corynebacterium striatum thus permitting transition to a more virulent state.

An ex vivo model of medical device-mediated bacterial skin translocation

The skin is a barrier and part of the immune system that protects us from harmful bacteria. Because indwelling medical devices break this barrier, they greatly increase the risk of infection by microbial pathogens. To study how these infections can be prevented through improved clinical practices and medical device technology, it is important to have preclinical models that replicate the early stages of microbial contamination, ingress, and colonization leading up to infection. At present, there are no preclinical ex vivo models specifically developed to simulate conditions for indwelling medical devices. Translocation of pathogens from outside the body across broken skin to normally sterile internal compartments is a rate-limiting step in infectious pathogenesis. In this work, we report a sensitive and reproducible ex vivo porcine skin-catheter model to test how long antimicrobial interventions can delay translocation. Skin preparation was first optimized to minimize tissue damage. The presence of skin dramatically decreased bacterial migration time across the polyurethane catheter interface from > 96 h to 12 h. Using visual colony detection, fluorescence, a luminescent in vitro imaging system, and confocal microscopy, the model was used to quantify time-dependent differences in translocation for eluting and non-eluting antimicrobial catheters. The results show the importance of including tissue in preclinical biofilm models and help to explain current gaps between in vitro testing and clinical outcomes for antimicrobial devices.

Friends or enemies? The complicated relationship between Pseudomonas aeruginosa and Staphylococcus aureus

Pseudomonas aeruginosa (Pa) and Staphylococcus aureus (Sa) are opportunistic pathogens that are most commonly co-isolated from chronic wounds and the sputum of cystic fibrosis patients. Over the last few years, there have been plenty of contrasting results from studies involving P. aeruginosa and S. aureus co-cultures. The general concept that P. aeruginosa outcompetes S. aureus has been challenged and there is more evidence now that they can co-exist. Nevertheless, it still remains difficult to mimic polymicrobial infections in vitro and in vivo. In this review, we discuss recent advances in regard to Pa-Sa molecular interactions, their physical responses, and in vitro and in vivo models. We believe it is important to optimize growth conditions in the laboratory, determine appropriate bacterial starting ratios, and consider environmental factors to study the co-existence of these two pathogens. Ideally, optimized growth media should reflect host-mimicking conditions with or without host cells that allow both bacteria to co-exist. To further identify mechanisms that could help to treat these complex infections, we propose to use relevant polymicrobial animal models. Ultimately, we briefly discuss how polymicrobial infections can increase antibiotic tolerance.

UvrY is required for the full virulence of Aeromonas dhakensis

Aeromonas dhakensis is an emerging human pathogen which causes fast and severe infections worldwide. Under the gradual pressure of lacking useful antibiotics, finding a new strategy against A. dhakensis infection is urgent. To understand its pathogenesis, we created an A. dhakensis AAK1 mini-Tn10 transposon library to study the mechanism of A. dhakensis infection. By using a Caenorhabditis elegans model, we established a screening platform for the purpose of identifying attenuated mutants. The uvrY mutant, which conferred the most attenuated toxicity toward C. elegans, was identified. The uvrY mutant was also less virulent in C2C12 fibroblast and mice models, in line with in vitro results. To further elucidate the mechanism of UvrY in controlling the toxicity in A. dhakensis, we conducted a transcriptomic analysis. The RNAseq results showed that the expression of a unique hemolysin ahh1 and other virulence factors were regulated by UvrY. Complementation of Ahh1, one of the most important virulence factors, rescued the pore-formation phenotype of uvrY mutant in C. elegans; however, complementation of ahh1 endogenous promoter-driven ahh1 could not produce Ahh1 and rescue the virulence in the uvrY mutant. These findings suggest that UvrY is required for the expression of Ahh1 in A. dhakensis. Taken together, our results suggested that UvrY controls several different virulence factors and is required for the full virulence of A. dhakensis. The two-component regulator UvrY therefore a potential therapeutic target which is worthy of further study.

Rhizobial Chemotaxis and Motility Systems at Work in the Soil

Bacteria navigate their way often as individual cells through their chemical and biological environment in aqueous medium or across solid surfaces. They swim when starved or in response to physical and chemical stimuli. Flagella-driven chemotaxis in bacteria has emerged as a paradigm for both signal transduction and cellular decision-making. By altering motility, bacteria swim toward nutrient-rich environments, movement modulated by their chemotaxis systems with the addition of pili for surface movement. The numbers and types of chemoreceptors reflect the bacterial niche and lifestyle, with those adapted to complex environments having diverse metabolic capabilities, encoding far more chemoreceptors in their genomes. The Alpha-proteobacteria typify the latter case, with soil bacteria such as rhizobia, endosymbionts of legume plants, where motility and chemotaxis are essential for competitive symbiosis initiation, among other processes. This review describes the current knowledge of motility and chemotaxis in six model soil bacteria: Sinorhizobium meliloti, Agrobacterium fabacearum, Rhizobium leguminosarum, Azorhizobium caulinodans, Azospirillum brasilense, and Bradyrhizobium diazoefficiens. Although motility and chemotaxis systems have a conserved core, rhizobia possess several modifications that optimize their movements in soil and root surface environments. The soil provides a unique challenge for microbial mobility, since water pathways through particles are not always continuous, especially in drier conditions. The effectiveness of symbiont inoculants in a field context relies on their mobility and dispersal through the soil, often assisted by water percolation or macroorganism movement or networks. Thus, this review summarizes the factors that make it essential to consider and test rhizobial motility and chemotaxis for any potential inoculant.

African Plant-Based Natural Products with Antivirulence Activities to the Rescue of Antibiotics

The worldwide emergence of antibiotic-resistant bacteria and the thread of widespread superbug infections have led researchers to constantly look for novel effective antimicrobial agents. Within the past two decades, there has been an increase in studies attempting to discover molecules with innovative properties against pathogenic bacteria, notably by disrupting mechanisms of bacterial virulence and/or biofilm formation which are both regulated by the cell-to-cell communication mechanism called ‘quorum sensing’ (QS). Certainly, targeting the virulence of bacteria and their capacity to form biofilms, without affecting their viability, may contribute to reduce their pathogenicity, allowing sufficient time for an immune response to infection and a reduction in the use of antibiotics. African plants, through their huge biodiversity, present a considerable reservoir of secondary metabolites with a very broad spectrum of biological activities, a potential source of natural products targeting such non-microbicidal mechanisms. The present paper aims to provide an overview on two main aspects: (i) succinct presentation of bacterial virulence and biofilm formation as well as their entanglement through QS mechanisms and (ii) detailed reports on African plant extracts and isolated compounds with antivirulence properties against particular pathogenic bacteria.

Gas gangrene-associated gliding motility is regulated by the Clostridium perfringens CpAL/VirSR system

Clostridium perfringens strains cause a wide variety of human and animal disease, including gas gangrene or myonecrosis. Production of toxins required for myonecrosis, PFO and CPA, is regulated by the C. perfringens Agr-like (CpAL) system via the VirSR two-component system. Myonecrosis begins at the site of infection from where bacteria migrate deep into the host tissue likely using a previously described gliding motility phenotype. We therefore assessed whether gliding motility was under the control of the CpAL/VirSR regulon. The migration rate of myonecrosis-causing C. perfringens strain 13 (S13) was investigated during a 96 h period, including an adaptation phase with bacterial migration (∼1.4 mm/day) followed by a gliding phase allowing bacteria faster migration (∼8.6 mm/day). Gliding required both an intact CpAL system, and signaling through VirSR. Mutants lacking ΔagrB, or ΔvirR, were impaired for onward gliding while a complemented strain S13ΔagrB/pTS1303 had the gliding phenotype restored. Gene expression studies revealed upregulated transcription of pili genes (pilA1, pilA2 and pilT) whose encoded proteins were previously found to be required for gliding motility and CpAL/VirSR-regulated pfoA and cpa toxin genes. Compared to S13, transcription of cpa and pfoA significantly decreased in S13ΔagrB, or S13ΔvirR, strains but not that of pili genes. Further experiments demonstrated that mutants S13ΔpfoA and S13Δcpa migrated at the same rate as S13 wt. We demonstrated that CpAL/VirSR regulates C. perfringens gliding motility and that gliding bacteria have an increased transcription of toxin genes involved in myonecrosis.

A Trace Amount of Surfactants Enables Diffusiophoretic Swimming of Bacteria

From birth to health, surfactants play an essential role in our lives. Due to the importance, their environmental impacts are well understood. One of the aspects that has been extensively studied is their impact on bacteria, particularly on their motility. Here, we uncover an alternate chemotactic strategy triggered by surfactants-diffusiophoresis. We show that even a trace amount of ionic surfactants, down to a single ppm level, can promote the bacterial diffusiophoresis by boosting the surface charge of the cells. Because diffusiophoresis is driven by the surface-solute interactions, surfactant-enhanced diffusiophoresis is observed regardless of the types of bacteria. Whether Gram-positive or -negative, flagellated or nonflagellated, the surfactants enable fast migration of freely suspended bacteria, suggesting a ubiquitous locomotion mechanism that has been largely overlooked. We also demonstrate the implication of surfactant-enhanced bacterial diffusiophoresis on the rapid formation of biofilms in flow networks, suggesting environmental and biomedical implications.

Capillary bacterial migration on non-nutritive solid surfaces

Here we describe an additional type of bacterial migration in which bacterial cells migrate vertically across a non-nutritive solid surface carried by capillary forces. Unlike standard motility experiments, these were run on a glass slide inserted into a Falcon tube, partly immersed in a nutrient medium and partly exposed to air. Observations revealed that capillary forces initiated upward cell migration when biofilm was formed at the border between liquid and air. The movement was facilitated by the production of extracellular polymeric substances (EPS). This motility differs from earlier described swarming, twitching, gliding, sliding, or surfing, although these types of movements are not excluded. We therefore propose to call it “capillary movement of biofilm”. This phenomenon may be an ecologically important mode of bacterial motility on solid surfaces.

The cyclic lipopeptides suppress the motility of Vibrio alginolyticus via targeting the Na+ -driven flagellar motor component MotX

In our previous study, we found that pumilacidin-like cyclic lipopeptides (CLPs) derived from marine bacterium Bacillus sp. strain 176 significantly suppressed the mobile capability and virulence of Vibrio alginolyticus. Here, to further disclose the mechanism of CLPs inhibiting the motility of V. alginolyticus, we first applied transcriptomic analysis to V. alginolyticus treated with or without CLPs. The transcriptomic results showed that the expression of several important components of the Na⁺ -driven flagellar motor closely related to bacterial motility were markedly suppressed, suggesting that the structure and function of Na⁺ -driven flagellar motor might be disabled by CLPs. The transcriptomic data were further analysed by the protein-protein interaction network, and the results supported that MotX, one of the essential components of Na⁺ -driven flagellar motor was most likely the action target of CLPs. In combination of gene knockout, electrophoretic mobility shift assay and immunoblotting techniques, CLPs were demonstrated to affect the rotation of flagella of Vibrio alginolyticus via direct interacting with the Na⁺ -driven flagellar motor component MotX, which eventually inhibited the bacterial motility. Interestingly, homologues of MotX were found broadly distributed and highly conserved in different pathogenic species, which extends the application range of CLPs as an antibacterial drug targeting bacterial motility in many pathogens.

Agaric acid reduces Salmonella biofilm formation by inhibiting flagellar motility

Salmonella biofilms are a common cause of contaminations in the food or feed industry. In a screening for novel compounds to combat biofilm-associated foodborne outbreaks, we identified agaric acid as a Salmonella Typhimurium biofilm inhibitor that does not affect planktonic growth. Importantly, the remaining biofilm cells after preventive treatment with agaric acid were significantly more sensitive to the common disinfectant hydrogen peroxide. Screening of a GFP-promoter fusion library of biofilm related genes revealed that agaric acid downregulates the transcription of genes responsible for flagellar motility. Concurrently, swimming motility was completely abrogated in the presence of agaric acid, indicating that biofilm inhibition occurs via interference with the motility phenotype. Moreover, agaric acid also reduced biofilm formation of Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli. Agaric acid thus shows potential as an anti-virulence compound that inhibits both motility and biofilm formation.

Involvement of Heme in Colony Spreading of Staphylococcus aureus

Staphylococcus aureus spreads rapidly on the surface of soft agar medium. The spreading depends on the synthesis of biosurfactants, i.e., phenol soluble modulins (PSMs), which facilitate colony spreading of S. aureus. Our earlier study demonstrated that water accumulates in a colony is important to modulate colony spreading of S. aureus. The current study screened a transposon-based mutant library of S. aureus HG001 and obtained four non-spreading mutants with mutations in hemY and ctaA, which are involved in heme synthesis. The spreading ability of these mutants was restored when the mutants are transformed with a plasmid encoding hemY or ctaA, respectively. HemY mutants, which do not synthesize heme B, were able to spread on agar medium supplemented with hemin, a heme B derivative. By contrast, hemin supplementation did not rescue the spreading of the ctaA mutant, which lacks heme B and heme A, indicating that heme A is also critical for colony spreading. Moreover, mutations in hemY and ctaA had little effect on PSMs production but affect ATP production and water accumulation in the colony. In conclusion, this study sheds light on the role of heme synthesis and energy production in the regulation of S. aureus colony spreading, which is important for understanding the movement mechanisms of bacteria lacking a motor apparatus.