Biofilm formation in medical device-related infection

Advances in Antibacterial Polymer Coatings Synthesized via Chemical Vapor Deposition

Biofouling is a major issue across various industries ranging from healthcare to the production of food and water and transportation. Biofouling is often induced or mediated by environmental microbes, such as bacteria. Therefore, developing antibacterial coatings has been an essential focus of recent research on functional polymer thin films. To achieve high film quality, vapor-phase techniques represent promising alternatives to traditional solution-based methods, especially for the design and synthesis of antibacterial polymer coatings, as they enable highly uniform, chemically precise, and substrate-independent coatings. This Perspective examines the potential of vapor-phase polymerization techniques to create novel antibacterial polymer coatings. Current advancements in the design of antifouling, bactericidal, antibiofilm, and multifunctional coatings via vapor-phase techniques are organized based on their action mechanisms and design principles. The opportunities and challenges associated with implementing vapor-phase polymerization for developing antibacterial coatings are highlighted.

Medical Device-Associated Infections Caused by Biofilm-Forming Microbial Pathogens and Controlling Strategies

Hospital-acquired infections, also known as nosocomial infections, include bloodstream infections, surgical site infections, skin and soft tissue infections, respiratory tract infections, and urinary tract infections. According to reports, Gram-positive and Gram-negative pathogenic bacteria account for up to 70% of nosocomial infections in intensive care unit (ICU) patients. Biofilm production is a main virulence mechanism and a distinguishing feature of bacterial pathogens. Most bacterial pathogens develop biofilms at the solid-liquid and air-liquid interfaces. An essential requirement for biofilm production is the presence of a conditioning film. A conditioning film provides the first surface on which bacteria can adhere and fosters the growth of biofilms by creating a favorable environment. The conditioning film improves microbial adherence by delivering chemical signals or generating microenvironments. Microorganisms use this coating as a nutrient source. The film gathers both inorganic and organic substances from its surroundings, or these substances are generated by microbes in the film. These nutrients boost the initial growth of the adhering bacteria and facilitate biofilm formation by acting as a food source. Coatings with combined antibacterial efficacy and antifouling properties provide further benefits by preventing dead cells and debris from adhering to the surfaces. In the present review, we address numerous pathogenic microbes that form biofilms on the surfaces of biomedical devices. In addition, we explore several efficient smart antiadhesive coatings on the surfaces of biomedical device-relevant materials that manage nosocomial infections caused by biofilm-forming microbial pathogens.

Biomimetic polymers with phosphorylcholine groups as biomaterials for medical devices

Biomimetic molecular designs can yield superior biomaterials. Polymers with a phosphorylcholine group, a polar group of phospholipid molecules, are particularly interesting. A methacrylate monomer, 2-methacryloyloxyethyl phosphorylcholine (MPC), was developed using efficient synthetic reactions and purification techniques. This process has been applied in industrial production to supply MPC globally. Polymers with various structures can be readily synthesized using MPC and their properties have been studied. The MPC polymer surface has a highly hydrated structure in biological conditions, leading to the prevention of adsorption of proteins and lipid molecules, adhesion of cells, and inhibition of bacterial adhesion and biofilm formation. Additionally, it provides an extremely lubricious surface. MPC polymers are used in various applications and can be stably immobilized on material surfaces such as metals and ceramics and polymers such as elastomers. They are also stable under sterilization and in vivo conditions. This makes them ideal for application in the surface treatment of various medical devices, including artificial organs, implanted in humans.

Staphylococcus epidermidis isolates from atopic or healthy skin have opposite effect on skin cells: potential implication of the AHR pathway modulation

Introduction

Staphylococcus epidermidis is a commensal bacterium ubiquitously present on human skin. This species is considered as a key member of the healthy skin microbiota, involved in the defense against pathogens, modulating the immune system, and involved in wound repair. Simultaneously, S. epidermidis is the second cause of nosocomial infections and an overgrowth of S. epidermidis has been described in skin disorders such as atopic dermatitis. Diverse isolates of S. epidermidis co-exist on the skin. Elucidating the genetic and phenotypic specificities of these species in skin health and disease is key to better understand their role in various skin conditions. Additionally, the exact mechanisms by which commensals interact with host cells is partially understood. We hypothesized that S. epidermidis isolates identified from different skin origins could play distinct roles on skin differentiation and that these effects could be mediated by the aryl hydrocarbon receptor (AhR) pathway.

Methods

For this purpose, a library of 12 strains originated from healthy skin (non-hyperseborrheic (NH) and hyperseborrheic (H) skin types) and disease skin (atopic (AD) skin type) was characterized at the genomic and phenotypic levels.

Results and discussion

Here we showed that strains from atopic lesional skin alter the epidermis structure of a 3D reconstructed skin model whereas strains from NH healthy skin do not. All strains from NH healthy skin induced AhR/OVOL1 path and produced high quantities of indole metabolites in co-culture with NHEK; especially indole-3-aldehyde (IAld) and indole-3-lactic acid (ILA); while AD strains did not induce AhR/OVOL1 path but its inhibitor STAT6 and produced the lowest levels of indoles as compared to the other strains. As a consequence, strains from AD skin altered the differentiation markers FLG and DSG1. The results presented here, on a library of 12 strains, showed that S. epidermidis originated from NH healthy skin and atopic skin have opposite effects on the epidermal cohesion and structure and that these differences could be linked to their capacity to produce metabolites, which in turn could activate AHR pathway. Our results on a specific library of strains provide new insights into how S. epidermidis may interact with the skin to promote health or disease.

Investigating the Impacts of UVC Radiation on Natural and Cultured Biofilms: An assessment of Cell Viability

Biofilms are conglomerates of cells, water, and extracellular polymeric substances which can lead to various functional and financial setbacks. As a result, there has been a drive towards more environmentally friendly antifouling methods, such as the use of ultraviolet C (UVC) radiation. When applying UVC radiation, it is important to understand how frequency, and thus dose, can influence an established biofilm. This study compares the impacts of varying doses of UVC radiation on both a monocultured biofilm consisting of Navicula incerta and field-developed biofilms. Both biofilms were exposed to doses of UVC radiation ranging from 1626.2 mJ/cm2 to 9757.2 mJ/cm2 and then treated with a live/dead assay. When exposed to UVC radiation, the N. incerta biofilms demonstrated a significant reduction in cell viability compared to the non-exposed samples, but all doses had similar viability results. The field biofilms were highly diverse, containing not only benthic diatoms but also planktonic species which may have led to inconsistencies. Although they are different from each other, these results provide beneficial data. Cultured biofilms provide insight into how diatom cells react to varying doses of UVC radiation, whereas the real-world heterogeneity of field biofilms is useful for determining the dosage needed to effectively prevent a biofilm. Both concepts are important when developing UVC radiation management plans that target established biofilms.

Biofilm growth monitoring using guided wave ultralong-range Surface Plasmon Resonance: A proof of concept

Unwelcomed biofilms are problematic in food industries, surgical devices, marine applications, and wastewater treatment plants, essentially everywhere where there is moisture. Very recently, label-free advanced sensors such as localized and extended surface plasmon resonance (SPR) have been explored as tools for monitoring biofilm formation. However, conventional noble metal SPR substrates suffer from low penetration depth (100-300 nm) into the dielectric medium above the surface, preventing the reliable detection of large entities of single or multi-layered cell assemblies like biofilms which can grow up to a few micrometers or more. In this study, we propose using a plasmonic insulator-metal-insulator (IMI) structure (SiO₂-Ag-SiO₂) with a higher penetration depth based on a diverging beam single wavelength format of Kretschmann configuration in a portable SPR device. An SPR line detection algorithm for locating the reflectance minimum of the device helps to view changes in refractive index and accumulation of the biofilm in real-time down to 10^-7 RIU precision. The optimized IMI structure exhibits strong penetration dependence on wavelength and incidence angle. Within the plasmonic resonance, different angles penetrate different depths, showing a maximum near the critical angle. At the wavelength of 635 nm, a high penetration depth of more than 4 μm was obtained. Compared to a thin gold film substrate, for which the penetration depth is only ∼200 nm, the IMI substrate provides more reliable results. The average thickness of the biofilm after 24 h of growth was found to be between 6 and 7 μm with ∼63% live cell volume, as estimated from confocal microscopic images using an image processing tool. To explain this saturation thickness, a graded index biofilm structure is proposed in which the refractive index decreases with the distance from the interface. Furthermore, when plasma-assisted degeneration of biofilms was studied in a semi-real-time format, there was almost no effect on the IMI substrate compared to the gold substrate. The growth rate over the SiO₂ surface was higher than on gold, possibly due to differences between surface charge effects. On the gold, the excited plasmon generates an oscillating cloud of electrons, while for the SiO₂ case, this does not happen. This methodology can be utilized to detect and characterize biofilms with better signal reliability with respect to concentration and size dependence.

Bacterial Crosstalk via Antimicrobial Peptides on the Human Skin: Therapeutics from a Sustainable Perspective

The skin's epidermis is an essential barrier as the first guard against invading pathogens, and physical protector from external injury. The skin microbiome, which consists of numerous bacteria, fungi, viruses, and archaea on the epidermis, play a key role in skin homeostasis. Antibiotics are a fast-acting and effective treatment method, however, antibiotic use is a nuisance that can disrupt skin homeostasis by eradicating beneficial bacteria along with the intended pathogens and cause antibiotic-resistant bacteria spread. Increased numbers of antimicrobial peptides (AMPs) derived from humans and bacteria have been reported, and their roles have been well defined. Recently, modulation of the skin microbiome with AMPs rather than artificially synthesized antibiotics has attracted the attention of researchers as many antibiotic-resistant strains make treatment mediation difficult in the context of ecological problems. Herein, we discuss the overall insights into the skin microbiome, including its regulation by different AMPs, as well as their composition and role in health and disease.

Design and synthesis of hybrid compounds as novel drugs and medicines

The development of highly effective conjugate chemistry approaches is a way to improve the quality of drugs and of medicines. The aim of this paper is to highlight and review such hybrid compounds and the strategies underpinning their design. A variety of unique hybrid compounds provide an excellent toolkit for novel biological activity, e.g. anticancer and non-viral gene therapy (NVGT), and as templates for killing bacteria and preventing antibiotic drug resistance. First we discuss the anticancer potential of hybrid compounds, containing daunorubicin, benzyl- or tetrahydroisoquinoline-coumarin, and cytotoxic NSAID-pyrrolizidine/indolizine hybrids, then NVGT cationic lipid-based delivery agents, where steroids or long chain fatty acids as the lipid moiety are bound to polyamines as the cationic moiety. These polyamines can be linear as in spermidine or spermine, or on a polycyclic sugar template, aminoglycosides kanamycin and neomycin B, the latter substituted with six amino groups. They are highly efficient for the delivery of both fluorescent DNA and siRNA. Molecular precedents can be found for the design of hybrid compounds in the natural world, e.g., squalamine, the first representative of a previously unknown class of natural antibiotics of animal origin. These polyamine-bile acid (e.g. cholic acid type) conjugates display many exciting biological activities with the bile acids acting as a lipidic region and spermidine as the polycationic region. Analogues of squalamine can act as vectors in NVGT. Their natural role is as antibiotics. Novel antibacterial materials are urgently needed as recalcitrant bacterial infection is a worldwide problem for human health. Ribosome inhibitors founded upon dimers of tobramycin or neomycin, bound as ethers by a 1,6-hexyl linker or a more complex diether-disulfide linker, improved upon the antibiotic activity of aminoglycoside monomers by 20- to 1200-fold. Other hybrids, linked by click chemistry, conjugated ciprofloxacin to neomycin, trimethoprim, or tedizolid, which is now in clinical trials.

The expression of glycosyltransferases sdgA and sdgB in Staphylococcus epidermidis depends on the conditions of biofilm formation

The Staphylococcus aureus SdrG protein is glycosylated by SdgA and SdgB for protection against its degradation by the neutrophil cathepsin G. So far, there is no information about the role of Staphylococcus epidermidis SdgA or SdgB in biofilm-forming; therefore, the focus of this work was to determine the distribution and expression of the sdrG, sdgA and sdgB genes in S. epidermidis under in vitro and in vivo biofilm conditions. The frequencies of the sdrG, sdgA and sdgB genes were evaluated by PCR in a collection of 75 isolates. Isolates were grown in dynamic (non-biofilm-forming) or static (biofilm-forming) conditions. The expression of sdrG, sdgA and sdgB was determined by RT-qPCR in cells grown under dynamic conditions (CGDC), as well as in planktonic and sessile cells from a biofilm and cells adhered to a catheter implanted in Balb/c mice. The sdrG and sdgB genes were detected in 100% of isolates, while the sdgA gene was detected in 71% of the sample (p < 0.001). CGDC did not express sdrG, sdgA and sdgB mRNAs. Planktonic and sessile cells expressed sdrG and sdgB, and the same was observed in cells adhered to the catheter. In particular, one isolate, capable of inducing a biofilm under treatment with cathepsin G, expressed sdrG and sdgB in planktonic and sessile cells and cells adhering to the catheter. This suggests that bacteria require biofilm conditions as an important factor for the transcription of the sdgA, sdgB and sdrG genes.

The Fusaric Acid Derivative qy17 Inhibits Staphylococcus haemolyticus by Disrupting Biofilm Formation and the Stress Response via Altered Gene Expression

Staphylococcus haemolyticus (S. haemolyticus) is the second most commonly isolated coagulase-negative staphylococcus (CoNS) in patients with hospital-acquired infections. It can produce phenol-soluble modulin (PSM) toxins and form biofilms. Compared with the wealth of information on Staphylococcus aureus and Staphylococcus epidermidis, very little is known about S. haemolyticus. There is an urgent need to find an effective preparation to combat the harm caused by S. haemolyticus infection. Chinese herbs have been utilized to cure inflammation and infectious diseases and have a long history of anticancer function in China. Here, we modified fusaric acid characterized from the metabolites of Gibberella intermedia, an endophyte previously isolated from Polygonum capitatum. This study shows that fusaric acid analogs (qy17 and qy20) have strong antibacterial activity against S. haemolyticus. In addition, crystal violet analyses and scanning electron microscopy observations demonstrated that qy17 inhibited biofilm formation and disrupted mature biofilms of S. haemolyticus in a dose-dependent manner. Additionally, it reduced the number of live bacteria inside the biofilm. Furthermore, the antibiofilm function of qy17 was achieved by downregulating transcription factors (sigB), transpeptidase genes (srtA), and bacterial surface proteins (ebp, fbp) and upregulating biofilm-related genes and the density-sensing system (agrB). To further elucidate the bacteriostatic mechanism, transcriptomic analysis was carried out. The following antibacterial mechanisms were uncovered: (i) the inhibition of heat shock (clpB, groES, groL, grpE, dnaK, dnaJ)-, oxidative stress (aphC)- and biotin response (bioB)-related gene expression, which resulted in S. haemolyticus being unable to compensate for various stress conditions, thereby affecting bacterial growth; and (ii) a reduction in the expression of PSM-beta (PSMβ1, PSMβ2, PSMβ3) toxin- and Clp protease (clpP, clpX)-related genes. These findings could have major implications for the treatment of diseases caused by S. haemolyticus infections. Our research reveals for the first time that fusaric acid derivatives inhibit the expression of biofilm formation-related effector and virulence genes of S. haemolyticus. These findings provide new potential drug candidates for hospital-acquired infections caused by S. haemolyticus.

Antimicrobial photodynamic therapy (aPDT) for biofilm treatments. Possible synergy between aPDT and pulsed electric fields

Currently, microbial biofilms have been the cause of a wide variety of infections in the human body, reaching 80% of all bacterial and fungal infections. The biofilms present specific properties that increase the resistance to antimicrobial treatments. Thus, the development of new approaches is urgent, and antimicrobial photodynamic therapy (aPDT) has been shown as a promising candidate. aPDT involves a synergic association of a photosensitizer (PS), molecular oxygen and visible light, producing highly reactive oxygen species (ROS) that cause the oxidation of several cellular components. This therapy attacks many components of the biofilm, including proteins, lipids, and nucleic acids present within the biofilm matrix; causing inhibition even in the cells that are inside the extracellular polymeric substance (EPS). Recent advances in designing new PSs to increase the production of ROS and the combination of aPDT with other therapies, especially pulsed electric fields (PEF), have contributed to enhanced biofilm inhibition. The PEF has proven to have antimicrobial effect once it is known that extensive chemical reactions occur when electric fields are applied. This type of treatment kills microorganisms not only due to membrane rupture but also due to the formation of reactive compounds including free oxygen, hydrogen, hydroxyl and hydroperoxyl radicals. So, this review aims to show the progress of aPDT and PEF against the biofilms, suggesting that the association of both methods can potentiate their effects and overcome biofilm infections.

A bacteriocin-based treatment option for Staphylococcus haemolyticus biofilms

Bacteriocins are ribosomally-synthesized antimicrobial peptides, showing great potential as novel treatment options for multidrug-resistant pathogens. In this study, we designed a novel hybrid bacteriocin, Hybrid 1 (H1), by combing the N-terminal part and the C-terminal part of the related bacteriocins enterocin K1 (K1) and enterocin EJ97 (EJ97), respectively. Like the parental bacteriocins, H1 used the membrane-bound protease RseP as receptor, however, it differed from the others in the inhibition spectrum. Most notably, H1 showed a superior antimicrobial effect towards Staphylococcus haemolyticus—an important nosocomial pathogen. To avoid strain-dependency, we further evaluated H1 against 27 clinical and commensal S. haemolyticus strains, with H1 indeed showing high activity towards all strains. To curtail the rise of resistant mutants and further explore the potential of H1 as a therapeutic agent, we designed a bacteriocin-based formulation where H1 was used in combination with the broad-spectrum bacteriocins micrococcin P1 and garvicin KS. Unlike the individual bacteriocins, the three-component combination was highly effective against planktonic cells and completely eradicated biofilm-associated S. haemolyticus cells in vitro. Most importantly, the formulation efficiently prevented development of resistant mutants as well. These findings indicate the potential of a bacteriocins-based formulation as a treatment option for S. haemolyticus.

Effect of Precursor Deficiency Induced Ca/P Ratio on Antibacterial and Osteoblast Adhesion Properties of Ag-Incorporated Hydroxyapatite: Reducing Ag Toxicity

Ag-containing hydroxyapatite (HA) can reduce risks associated with bacterial infections which may eventually require additional surgical operations to retrieve a failed implant. The biological properties of HA in such applications are strongly affected by its composition in terms of dopants as well as Ca/P stoichiometry, which can be easily controlled by altering processing parameters, such as precursor concentrations. The objective of this in vitro study was to understand the effect of variations in HA precursor solutions on antibacterial properties against Escherichia coli (E. coli) and for promoting osteoblast (bone-forming cell) adhesion on Ag incorporated HA (AgHA) which has not yet been investigated. For this, two groups of AgHAs were synthesized via a precipitation method by adjusting precursor reactants with a stoichiometric value of 1.67, being either (Ca + Ag)/P (Ca-deficient) or Ca/(P + Ag) (P-deficient), and were characterized by XRD, FTIR, and SEM-EDS. Results showed that Ag⁺ incorporated into the Ca²⁺ sites was associated with a corresponding OH⁻ vacancy. Additional incorporation of CO₃²⁻ into PO₄³⁻ sites occurred specifically for the P-deficient AgHAs. While antibacterial properties increased, osteoblast adhesion decreased with increasing Ag content for the Ca-deficient AgHAs, as anticipated. In contrast, significant antibacterial properties with good osteoblast behavior were observed on the P-deficient AgHAs even with a lower Ag content, owing to carbonated HA. Thus, this showed that by synthesizing AgHA using P-deficient precursors with carbonate substitution, one can keep the antibacterial properties of Ag in HA while reducing its toxic effect on osteoblasts.

Artificial Sweeteners Negatively Regulate Pathogenic Characteristics of Two Model Gut Bacteria, E. coli and E. faecalis

Artificial sweeteners (AS) are synthetic sugar substitutes that are commonly consumed in the diet. Recent studies have indicated considerable health risks which links the consumption of AS with metabolic derangements and gut microbiota perturbations. Despite these studies, there is still limited data on how AS impacts the commensal microbiota to cause pathogenicity. The present study sought to investigate the role of commonly consumed AS on gut bacterial pathogenicity and gut epithelium-microbiota interactions, using models of microbiota (Escherichia coli NCTC10418 and Enterococcus faecalis ATCC19433) and the intestinal epithelium (Caco-2 cells). Model gut bacteria were exposed to different concentrations of the AS saccharin, sucralose, and aspartame, and their pathogenicity and changes in interactions with Caco-2 cells were measured using in vitro studies. Findings show that sweeteners differentially increase the ability of bacteria to form a biofilm. Co-culture with human intestinal epithelial cells shows an increase in the ability of model gut bacteria to adhere to, invade and kill the host epithelium. The pan-sweet taste inhibitor, zinc sulphate, effectively blocked these negative impacts. Since AS consumption in the diet continues to increase, understanding how this food additive affects gut microbiota and how these damaging effects can be ameliorated is vital.

Biofilm-Formation Ability and the Presence of Adhesion Genes in Coagulase-Negative Staphylococci Isolates from Chicken Broilers

Simple Summary

Bacteria of the genus Staphylococcus are universally present on the mucous membranes and skin of warm-blooded animals. They are divided into two groups on the basis of their ability to clot blood plasma: the coagulase-positive (CoPS) and coagulase-negative staphylococci (CoNS). Some species can cause opportunistic infections in poultry. Identification and characterization of strains of the genus Staphylococcus isolated from farm animals are crucial in epidemiological research and for developing effective methods to treat infections and food poisoning induced by these bacteria. The main virulence factor of coagulase-negative staphylococci is considered to be their ability to form complex biofilm structures on the surfaces of damaged tissues. Biofilms increase the invasive properties of CoNS and their ability to cause infection. The purpose of this study was to determine the biofilm-forming potential of coagulase-negative Staphylococcus strains isolated from poultry. The frequency of selected genes potentially playing a role in the biofilm formation process was also determined. The results of the study indicate that the majority (79.3%) of CoNS isolated from broiler chickens in this study were capable of producing a biofilm.

Abstract

The aim of the study was to analyze the biofilm-production capacity of 87 coagulase-negative Staphylococcus strains (CoNS) isolated from broiler chickens and to determine the occurrence of biofilm-associated genes. The biofilm production capacity of staphylococci was assessed using the microtiter plate method (MTP), and the frequency of genes was determined by PCR. The ability to form a biofilm in vitro was shown in 79.3% of examined strains. Strong biofilm capacity was demonstrated in 26.4% of strains, moderate capacity in 25.3%, weak capacity in 27.6%, and a complete lack of biofilm production capacity in 20.7% of strains. The icaAB gene responsible for the production of extracellular polysaccharide adhesins was detected in 6.9% of strains. The other four genes, i.e., bap (encoding biofilm-associated protein), atlE (encoding cell surface protein exhibiting vitronectin-binding activity), fbe (encoding fibrinogen-binding protein), and eno (encoding laminin-binding protein) were detected in 5.7%, 19.5%, 8%, and 70.1% of strains, respectively. Demonstration of genes that play a role in bacterial biofilm formation may serve as a genetic basis to distinguish between symbiotic and potentially invasive coagulase-negative staphylococcal strains.

Preparation of silver-decorated Soluplus® nanoparticles and antibacterial activity towards S. epidermidis biofilms as characterized by STEM-CL spectroscopy

Biofilm infections present a serious problem because antibacterial drugs are not effective against mature biofilms or biofilms formed by drug-resistant bacteria. To address this issue, we developed a drug delivery system based on metal-decorated polymeric particles. Polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft copolymer (Soluplus®) is an amphiphilic polymer used in biomedical formulations, while silver nanoparticles are widely acknowledged to have high antibacterial activity. We prepared silver-decorated Soluplus® micelle nanoparticles with high antibacterial activity using the emulsion solvent diffusion method. Decoration of Soluplus® micelles with silver nanoparticles was found to increase their antibacterial activity. Scanning transmission electron microscopy-cathodoluminescence (STEM-CL) spectroscopy allows imaging of the spatial distribution of labeled targets and the chemical identification of materials. However, STEM-CL spectroscopy of fragile polymer materials is challenging. We optimized the STEM-CL spectroscopy technique to determine the distribution of silver nanoparticles in Soluplus® micelles. Additionally, the surface plasmon properties of the silver nanoparticles were successfully characterized without deactivation. The developed silver-decorated Soluplus® nanoparticles were effective against biofilm infections and have the potential to be applied for other biofilm-related diseases. Additionally, the optimized STEM-CL spectroscopy technique is expected to contribute to the analysis and imaging of fragile polymer materials, as well as other soft materials such as cells and tissues.

Occurrence of blaTEM and blaCTXM Genes and Biofilm-Forming Ability among Clinical Isolates of Pseudomonas aeruginosa and Acinetobacter baumannii in Yaoundé, Cameroon

Background: Pseudomonas aeruginosa (PSA) and Acinetobacter baumannii (ACB) are non-fermentative bacteria mostly associated with nosocomial infections in humans. Objective: This study aimed to determine the antimicrobial resistance profiles and virulence gene of PSA and ACB previously isolated from humans in selected health facilities in Yaoundé, Cameroon. Methods: A total of 77 and 27 presumptive PSA and ACB isolates, respectively, were collected from the Yaoundé teaching hospital. These isolates were previously isolated from various samples including pus, blood and broncho-alveolar lavage. The identities of the isolates were determined through polymerase chain reaction (PCR) amplification of PSA and ACB specific sequences. Antimicrobial susceptibility testing (AST) was performed using the Kirby–Bauer disc diffusion method. Phenotypical expression of AmpC β-lactamases (AmpC), extended spectrum β-lactamases (ESBLs) and metallo β-Lactamases (MBLs) were determined using the combined disc method. Bacterial genomes were screened for the presence of β-lactamases bla_TEM and bla_CTXM genes using specific PCR. The pathogenicity of PSA and ACB was assessed through amplification of the lasB, exoA, pslA and exoS as well as OmpA and csuE virulence genes, respectively. Results: Of the 77 presumptive PSA isolates, a large proportion (75 to 97.4%) were positively identified. All (100%) of the presumptive 27 ACB harbored the ACB-specific ITS gene fragment by PCR. Twenty five percent of the PSA isolates produced ESBLs phenotypically while more than 90% of these isolates were positive for the lasB, exoA, pslA and exoS genes. A large proportion (88%) of the ACB isolates harboured the OmpA and csuE genes. bla_TEM and bla_CTXM were detected in 17 and 4% of PSA, respectively, while a much higher proportion (70 and 29%) of the ACB isolates possessed these resistance determinants respectively. Conclusion: Our findings reveal the occurrence of both virulence and drug-resistant determinants in clinical PSA and ACB isolates from patients in health care settings in Yaoundé, Cameroon, thus suggesting their role in the pathological conditions in patients.

Encapsulation of Essential Oils via Nanoprecipitation Process: Overview, Progress, Challenges and Prospects

Essential oils are of paramount importance in pharmaceutical, cosmetic, agricultural, and food areas thanks to their crucial properties. However, stability and bioactivity determine the effectiveness of essential oils. Polymeric nanoencapsulation is a well-established approach for the preservation of essential oils. It offers a plethora of benefits, including improved water solubility, effective protection against degradation, prevention of volatile components evaporation and controlled and targeted release. Among the several techniques used for the design of polymeric nanoparticles, nanoprecipitation has attracted great attention. This review focuses on the most outstanding contributions of nanotechnology in essential oils encapsulation via nanoprecipitation method. We emphasize the chemical composition of essential oils, the principle of polymeric nanoparticle preparation, the physicochemical properties of essential oils loaded nanoparticles and their current applications.

Biofilm production by coagulase-negative Staphylococcus: a review

ABSTRACT: This review aimed to describe the biofilm formation ability of coagulase-negative Staphylococcus, addressing its impact to the food industry. Coagulase-negative Staphylococcus have the ability to produce enterotoxins in food, making it an important line of study, as it constitutes a risk to public health. The biofilm formation by these microorganisms requires physicochemical processes, such as hydrophobic forces, which are essential for the first phase of fixing the biofilm on the surface. In industrial facilities, stainless steel equipment is the most associated with the formation of biofilms, due to the presence grooves and cracks. Many species of coagulase-negative Staphylococcus produce biofilm, but the most studied is S. epidermidis, as it is the most frequently isolated from food. Coagulase-negative Staphylococcus form biofilm on different surfaces in the food industry, and can become a source of permanent contamination, that can be present in the final product, intended for human consumption. Among other alternatives to combat the formation of biofilm in industrial food facilities, there is the implementation of Good Manufacturing Practices, which is effective in preventing bacterial adhesion, and therefore, the formation of biofilm. However, further studies are needed in order to quantify the occurrence of coagulase-negative Staphylococcus biofilms in the food industry.

Silver-Doped Hydroxyapatite Thin Layers Obtained by Sol-Gel Spin Coating Procedure

The main objective of this paper is to develop silver-doped hydroxyapatite suspensions (HApAg) with different concentrations of silver (?Ag = 0.05 and ?Ag = 0.2) in order to obtain uniform and homogenous layers by spin-coating procedure. The colloidal properties of HApAg suspensions are evaluated by dynamic light scattering (DLS) analysis, ζ-potential (ZP), and ultrasound measurements. The ultrasound studies show that the HApAg20 sample revealed better stability than the HApAg5 sample. The structural and morphological analysis on suspensions and thin layers is also conducted. It is observed that the particles of the two samples have a similar shape and are uniform. The layers obtained present a homogeneous appearance of the surface without evidence of cracks or interruption of the coatings. The in vitro antifungal studies conducted on the two thin layers at two different time intervals (24 and 48 h) show that both HApAg5 (?Ag = 0.05) and HApAg20 (?Ag = 0.05) nanoparticles suspensions and composite layers inhibit the development of colony forming units (CFU) even after 24 h of incubation comparative to the control, represented by the Candida albicans (C. albicans) culture in a proper medium. The fungicidal effect was evident after 48 h of incubation in the case of both HApAg20 nanoparticles suspensions and composite layers.

Differences in distribution of MLS antibiotics resistance genes in clinical isolates of staphylococci belonging to species: S. epidermidis, S. hominis, S. haemolyticus, S. simulans and S. warneri

Background

Macrolides and lincosamides are two leading types of antibiotics commonly used in therapies. The study examines the differences in resistance to these antibiotics and their molecular bases in S. epidermidis as well as in rarely isolated species of coagulase-negative staphylococci such as S. hominis, S. haemolyticus, S. warneri and S. simulans. The isolates were tested for the presence of the erm(A), erm(B), erm(C), lnu(A), msr(A), msr(B), mph(C), ere(A) and ere(B) genes. Phenotypic resistance to methicillin and mecA presence were also determined.

Results

The MLS_B resistance mechanism was phenotypically found in isolates of species included in the study. The most prevalent MLS_B resistance mechanism was observed in S. hominis, S. haemolyticus and S. epidermidis isolates mainly of the MLS_B resistance constitutive type. Macrolide, lincosamide and streptogramin B resistance genes were rarely detected in isolates individually. The erm(B), ere(A) and ere(B) genes were not found in any of the strains. The erm(A) gene was determined only in four strains of S. epidermidis and S. hominis while lnu(A) was seen in eight strains (mainly in S. hominis). The erm(C) gene was present in most of S. epidermidis strains and predominant in S. hominis and S. simulans isolates. The examined species clearly differed between one another in the repertoire of accumulated genes.

Conclusions

The presence of genes encoding the MLS_B resistance among CoNS strains demonstrates these genes’ widespread prevalence and accumulation in opportunistic pathogens that might become gene reservoir for bacteria with superior pathogenic potential.

UV-Responsive Multilayers with Multiple Functions for Biofilm Destruction and Tissue Regeneration

The increasing demands of surgical implantation highlight the significance of anti-infection of medical devices, especially antibiofilm contamination on the surface of implants. The biofilms developed by colonized microbes will largely hinder the adhesion of host cells, leading to failure in long-term applications. In this work, UV-responsive multilayers were fabricated by stepwise assembly of poly(pyrenemethyl acrylate- co-acrylic acid) (P(PA- co-AA)) micelles and chitosan on different types of substrates. Under UV irradiation, the cleavage of pyrene ester bonds in the P(PA- co-AA) molecules resulted in the increase of roughness and hydrophilicity of the multilayers. During this process, reactive oxygen species were generated in situ within 10 s, which destroyed the biofilms of Staphylococcus aureus, leading to the degradation of the bacterial matrix. The antibacterial rate was above 99.999%. The UV-irradiated multilayers allowed the attachment and proliferation of fibroblasts, endothelial cells, and smooth muscle cells, benefiting tissue integration of the implants. When poly(dimethylsiloxane) slices with the multilayers were implanted in vivo and irradiated by UV, the density of bacteria and the inflammatory level (judging from the number of neutrophils) decreased significantly. Moreover, formation of neo blood vessels surrounding the implants was observed after implantation for 7 days. These results reveal that the photoresponsive multilayers endow the implants with multifunctions of simultaneous antibiofilm and tissue integration, shedding light for applications in surface modification of implants in particular for long-term use.

Salinomycin and its derivatives - A new class of multiple-targeted "magic bullets"

The history of drug development clearly shows the scale of painstaking effort leading to a finished product - a highly biologically active agent that would be at the same time no or little toxic to human organism. Moreover, the aim of modern drug discovery can move from "one-molecule one-target" concept to more promising "one-molecule multiple-targets" one, particularly in the context of effective fight against cancer and other complex diseases. Gratifyingly, natural compounds are excellent source of potential drug leads. One of such promising naturally-occurring drug candidates is a polyether ionophore - salinomycin (SAL). This compound should be identified as multi-target agent for two reasons. Firstly, SAL combines a broad spectrum of bioactivity, including antibacterial, antifungal, antiviral, antiparasitic and anticancer activity, with high selectivity of action, proving its significant therapeutic potential. Secondly, the multimodal mechanism of action of SAL has been shown to be related to its interactions with multiple molecular targets and signalling pathways that are synergistic for achieving a therapeutic anticancer effect. On the other hand, according to the Paul Ehrlich's "magic bullet" concept, invariably inspiring the scientists working on design of novel target-selective molecules, a very interesting direction of research is rational chemical modification of SAL. Importantly, many of SAL derivatives have been found to be more promising as chemotherapeutics than the native structure. This concise review article is focused both on the possible role of SAL and its selected analogues in future antimicrobial and/or cancer therapy, and on the potential use of SAL as a new class of multiple-targeted "magic bullet" because of its multimodal mechanism of action.

[The inhibition of accessory gene regulator C specific binding peptides on biofilm formation of Staphylococcus epidermidis on the surface of polyvinyl chloride in vitro]

Objective

To investigate the effect of accessory gene regulator C (agr C) specific binding peptides (named N1) on the biofilm formation of Staphylococcus epidermidis on the surface of polyvinyl chloride (PVC) materials in vitro.

Methods

Firstly, the two strains (ATCC35984, ATCC12228) were cultured with N1 at concentrations of 100, 200, 400, 800, and 1 600 μg/mL, respectively. The control group was cultured with agrC specific binding unrelated peptides (named N0) at the same concentrations and the absorbance ( A) value was measured after 24 hours to determine the optimal bacteriostatic concentration of N1. The two strains were cultured with N1 and N0 of the optimal concentration, respectively. The A values were measured at 6, 12, 18, 24, 30, and 48 hours to observe the effect of N1 on the biofilm formation ability of Staphylococcus epidermidis. On this basis, the surface structure of the biofilm on the surface of PVC material was observed by scanning electron microscopy after 6, 12, 18, 24, and 30 hours of incubation with PVC material sheet. The thickness of the biofilm was observed by laser confocal microscopy after 6, 12, 18, and 24 hours of incubation with ATCC35984 strain.

Results

The optimal bacteriostatic concentration of N1 was 800 μg/mL. ATCC 12228 strain did not form obvious biofilm after being cultured with N1 and N0. When ATCC35984 strain was cultured with N1 and N0 for 12 hours, the difference in biofilm formation ability between groups N1 and N0 was statistically significant ( P<0.05), but there was no significant difference at 6, 18, 24, 30, and 48 hours ( P>0.05). Scanning electron microscopy examination showed that mature biofilm structure was observed in ATCC35984 strain and was not observed in ATCC12228 strain. Laser confocal microscopy observation showed that the number of bacteria in the group N1 was significantly lower than that in the group N0 at 12 hours, and the most of bacteria were dead bacteria. There was no significant difference in the number of bacteria at 6, 18, and 24 hours, and the most of them were live bacteria. The biofilm thickness of group N1 was significantly lower than that of group N0 at 12 and 18 hours ( P<0.05).

Conclusion

The intensity of N1 inhibiting the formation of Staphylococcus epidermidis biofilm is dose-dependent. During the aggregation period, N1 can inhibit the biofilm formation by hindering the bacterial growth and aggregation. The inhibition effect on mature biofilm is not obvious.

Bacterial Biofilms on Extracorporeal Membrane Oxygenation Catheters

Despite the advantages of extracorporeal membrane oxygenation (ECMO), secondary catheter infection remains a major concern during ECMO support. In this study, to clarify the mechanism of ECMO catheter-related infection, we evaluated the impact of infection on biofilm formation on the surfaces of ECMO catheters, and we investigated clinical factors associated with biofilm formation. Catheters used for ECMO were prospectively collected aseptically from the femoral vein, internal jugular vein, and femoral artery of 81 patients with acute cardiorespiratory failure between January 2015 and October 2016. Prepared catheter sections were investigated by fluorescence microscopy, confocal scanning laser microscopy, transmission electron microscopy, and using semiquantitative culture methods. Of the 81 patients, 51 were assigned to the infection group and 30 to a control group. Biofilms were identified in 43.1% patients in the infection group, and in 20% controls (p = 0.034). Extracorporeal membrane oxygenation flow, systemic infection, and carbapenem-resistant Acinetobacter baumannii (CRAB) infection were associated with biofilm formation in a univariate analysis (odds ratio [OR]: 1.00, 95% confidence interval [CI]: 1.00-1.00, p = 0.007; OR: 3.03, 95% CI: 1.06-8.69, p = 0.039; OR: 9.60, 95% CI: 2.94-31.30, p < 0.001, respectively). However, of these factors, only CRAB infection was found to independently predict the presence of a biofilm by a multivariate logistic regression analysis (OR: 9.60, 95% CI: 2.94-31.30; p < 0.001). Biofilms were more prevalent in patients with an infection than in uninfected controls. Carbapenem-resistant A. baumannii infection was identified as an independent risk factor for biofilm formation on ECMO catheters.

Recommendations for design and conduct of preclinical in vivo studies of orthopedic device-related infection

Orthopedic device-related infection (ODRI), including both fracture-related infection (FRI) and periprosthetic joint infection (PJI), remain among the most challenging complications in orthopedic and musculoskeletal trauma surgery. ODRI has been convincingly shown to delay healing, worsen functional outcome and incur significant socio-economic costs. To address this clinical problem, ever more sophisticated technologies targeting the prevention and/or treatment of ODRI are being developed and tested in vitro and in vivo. Among the most commonly described innovations are antimicrobial-coated orthopedic devices, antimicrobial-loaded bone cements and void fillers, and dual osteo-inductive/antimicrobial biomaterials. Unfortunately, translation of these technologies to the clinic has been limited, at least partially due to the challenging and still evolving regulatory environment for antimicrobial drug-device combination products, and a lack of clarity in the burden of proof required in preclinical studies. Preclinical in vivo testing (i.e. animal studies) represents a critical phase of the multidisciplinary effort to design, produce and reliably test both safety and efficacy of any new antimicrobial device. Nonetheless, current in vivo testing protocols, procedures, models, and assessments are highly disparate, irregularly conducted and reported, and without standardization and validation. The purpose of the present opinion piece is to discuss best practices in preclinical in vivo testing of antimicrobial interventions targeting ODRI. By sharing these experience-driven views, we aim to aid others in conducting such studies both for fundamental biomedical research, but also for regulatory and clinical evaluation. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:271-287, 2019.

Label-Free SERS Discrimination and In Situ Analysis of Life Cycle in Escherichia coli and Staphylococcus epidermidis

Surface enhanced Raman spectroscopy (SERS) has been proven suitable for identifying and characterizing different bacterial species, and to fully understand the chemically driven metabolic variations that occur during their evolution. In this study, SERS was exploited to identify the cellular composition of Gram-positive and Gram-negative bacteria by using mesoporous silicon-based substrates decorated with silver nanoparticles. The main differences between the investigated bacterial strains reside in the structure of the cell walls and plasmatic membranes, as well as their biofilm matrix, as clearly noticed in the corresponding SERS spectrum. A complete characterization of the spectra was provided in order to understand the contribution of each vibrational signal collected from the bacterial culture at different times, allowing the analysis of the bacterial populations after 12, 24, and 48 h. The results show clear features in terms of vibrational bands in line with the bacterial growth curve, including an increasing intensity of the signals during the first 24 h and their subsequent decrease in the late stationary phase after 48 h of culture. The evolution of the bacterial culture was also confirmed by fluorescence microscope images.

Disease-associated genotypes of the commensal skin bacterium Staphylococcus epidermidis

Some of the most common infectious diseases are caused by bacteria that naturally colonise humans asymptomatically. Combating these opportunistic pathogens requires an understanding of the traits that differentiate infecting strains from harmless relatives. Staphylococcus epidermidis is carried asymptomatically on the skin and mucous membranes of virtually all humans but is a major cause of nosocomial infection associated with invasive procedures. Here we address the underlying evolutionary mechanisms of opportunistic pathogenicity by combining pangenome-wide association studies and laboratory microbiology to compare S. epidermidis from bloodstream and wound infections and asymptomatic carriage. We identify 61 genes containing infection-associated genetic elements (k-mers) that correlate with in vitro variation in known pathogenicity traits (biofilm formation, cell toxicity, interleukin-8 production, methicillin resistance). Horizontal gene transfer spreads these elements, allowing divergent clones to cause infection. Finally, Random Forest model prediction of disease status (carriage vs. infection) identifies pathogenicity elements in 415 S. epidermidis isolates with 80% accuracy, demonstrating the potential for identifying risk genotypes pre-operatively.

Biofilm Formation by ica-Negative Ocular Isolates of Staphylococcus haemolyticus

Staphylococcus haemolyticus is the second most frequently isolated CoNS from ocular infections and human blood cultures. In this study, we examined 18 ocular S. haemolyticus isolates for their capacity to form biofilm and conducted detachment assay to determine the composition of the biofilm matrix and involvement of various elements in cell lysis. PCR identified the presence of biofilm-associated genes, and ica operon and CLSM visualized the components of the biofilm matrix. We found that PIA-independent biofilm formation is the characteristic feature of S. haemolyticus isolates, irrespective of the sources of isolation, and protein or DNA or both are the major components of the biofilm matrix. Cell lysis enabling DNA release was an essential step for biofilm attachment during the initial stages of biofilm development. The srtA transcript expression study indicates its role in the early stages of biofilm development. We found the presence of antibiotic resistance genes in the eDNA and gDNA thus suggesting the possible role of biofilm in horizontal gene transfer of antibiotic resistance determinants. The overall study indicates that S. haemolyticus formed the biofilm comprising of protein or DNA or both and srtA play a role in the initial development of biofilm.

Nicotine Enhances Staphylococcus epidermidis Biofilm Formation by Altering the Bacterial Autolysis, Extracellular DNA Releasing, and Polysaccharide Intercellular Adhesin Production

Staphylococcus epidermidis is a common bacterial colonizer of human skin and mucous membranes, yet it has emerged as an important nosocomial pathogen largely due to its ability to form biofilms. Tobacco smoke has been demonstrated as a contributor to various infection diseases by improving the biofilm formation of multiple bacterial species; however, the association between tobacco smoke and S. epidermidis biofilm is still unclear. In this study, we tested the effect of nicotine, one of the most active components of tobacco, on S. epidermidis biofilm formation, and we studied the underlying mechanisms. Our results showed that nicotine promoted the biofilm formation of S. epidermidis 1457 strain (SE1457) and enhanced its initial attachment to a polyethylene surface as well as polysaccharide intercellular adhesin (PIA) production. In addition, an increased extracellular DNA release and a higher autolysis rate of SE1457 was detected after nicotine treatment, which was consistent with the increased ratio of dead cells in nicotine-treated SE1457 biofilm observed with confocal laser-scanning microscopy. Furthermore, the effect of nicotine on several autolysis-related and biofilm-related gene knockout mutants of SE1457 was tested. It showed that in ΔsaeRS, ΔlytSR, and ΔsceD, nicotine induced increase in biofilm formation was similar to that in SE1457; but in ΔarlRS, ΔatlE, and ΔicaC, the effect was obviously impaired. Consistently, the increase of the bacterial autolysis rate in ΔarlRS and ΔatlE induced by nicotine was not as significant as that in SE1457. Meanwhile, the growth inhibition of nicotine on SE1457 was observed, and it was much less on ΔarlRS and restored by the arlRS complementation. The arlRS transcription in SE1457 was inhibited by nicotine during cultivation as indicated by a promoter reporter assay using green fluoresent protein. Taken together, our study indicates that nicotine improves S. epidermidis biofilm formation by promoting its initial attachment and intercellular accumulation; the arlRS, atlE, and ica genes mediating bacterial autolysis and PIA production play an important role in this process.

Direct covalent attachment of silver nanoparticles on radical-rich plasma polymer films for antibacterial applications

Prevention and treatment of biomaterial-associated infections (BAI) are imperative requirements for the effective and long-lasting function of orthopedic implants. Surface-functionalization of these materials with antibacterial agents, such as antibiotics, nanoparticles and peptides, is a promising approach to combat BAI. The well-known silver nanoparticles (AgNPs) in particular, although benefiting from strong and broad-range antibacterial efficiency, have been frequently associated with mammalian cell toxicity when physically adsorbed on biomaterials. The majority of irreversible immobilization techniques employed to fabricate AgNP-functionalized surfaces are based on wet-chemistry methods. However, these methods are typically substrate-dependent, complex, and time-consuming. Here we present a simple and dry strategy for the development of polymeric coatings used as platforms for the direct, linker-free covalent attachment of AgNPs onto solid surfaces using ion-assisted plasma polymerization. The resulting coating not only exhibits long-term antibiofilm efficiency against adherent Staphylococcus aureus (S. aureus), but also enhances osteoblast adhesion and proliferation. High resolution X-ray photoelectron spectroscopy (XPS), before and after sodium dodecyl sulfate (SDS) washing, confirms covalent bonding. The development of such silver-functionalized surfaces through a simple, plasma-based process holds great promise for the fabrication of implantable devices with improved tissue-implant integration and reduced biomaterial associated infections.

Low-Virulence Organisms and Periprosthetic Joint Infection-Biofilm Considerations of These Organisms

PURPOSE OF REVIEW

The purpose of this manuscript is to provide a critical review of peer-reviewed literature over the last 5 years related to low virulent organisms associated with periprosthetic joint infection (PJI). We evaluated the most common organisms, the diagnostic challenges, and the novel tools available in the perioperative workup of PJI as well as the current understanding of how biofilm potentiates the indolent clinical presentation and explore a possible shift in the surgical management of these patients.

RECENT FINDINGS

Biofilm actively prevents macrophage phagocytosis by suppressing proinflammatory activity through the recruitment of myeloid-derived suppressor cells. Given the appropriate host and organism conditions, increased utilization of one-stage exchange arthroplasty in the surgical treatment of these low virulent infections may be on the rise. Biomarkers and molecular techniques offer encouraging results to diagnose low virulent organisms and future research focused on the disruption of biofilm may ultimately give rise to improved treatment strategies.

Monitoring metabolic reactions in Staphylococcus epidermidis exposed to silicon nitride using in situ time-lapse Raman spectroscopy

Staphylococcus epidermidis (S. epidermidis) is one of the leading nosocomial pathogens, particularly associated with periprosthetic infections of biomedical implants. Silicon nitride (Si3N4), a nonoxide biomaterial widely used in spinal implants, has shown bacteriostatic effects against both gram-positive and gram-negative bacteria; however, the physicochemical interactions between Si3N4 and bacteria yet remain conspicuously unexplored. In situ time-lapse Raman spectroscopic experiments were conducted by exposing S. epidermidis for 12, 24, and 48 h to Si3N4 substrates to understand the evolution of bacterial metabolism and to elucidate the ceramics antimicrobial behavior. The Raman probe captured an initial metabolic response of the bacteria to the adverse chemistry of the Si3N4 surface, which included peroxidation of membrane phospholipids and protein structural modifications to adjust for survivorship. However, beyond 24 h of exposure, the Raman signals representing DNA, lipids, proteins, and carbohydrates showed clear fingerprints of bacterial lysis. Bands related to biofilm formation completely disappeared or underwent drastically reduced intensity. Bacterial lysis was confirmed by conventional fluorescence microscopy methods. Spectroscopic experiments suggested that a pH change at the Si3N4's surface induced variations in the membrane structure and D-alanylation of teichoic acids in its peptidoglycan layer. Concurrent stimulation of peptidoglycan hydrolase (i.e., an enzyme involved with autolysis) ultimately led to membrane degradation and cellular death. An additional finding was that modulating the Si3N4 surface by increasing the population of amine groups improved the efficiency of the substrate against S. epidermidis, thus suggesting that optimization of the near-surface (alkaline) conditions may be a viable approach to bacterial reduction.

Inner Leaf Gel of Aloe striata Induces Adhesion-Reducing Morphological Hyphal Aberrations

Fungi, particularly molds that are cosmopolitan in soils, are frequent etiologic agents of opportunistic mycoses. Members of the Fusarium solani and Fusarium oxysporum species complexes are the most commonly implicated etiologic agents of opportunistic fusarial infections in mammals, while Paecilomyces variotii is one of the most frequently encountered Paecilomyces species in human infections. Prevention and treatment of these mycoses are problematic because available antimycotics are limited and often have toxic side effects. Popular folk medicines, such as the inner leaf gel from Aloe spp., offer potential sources for novel antimycotic compounds. To screen for antifungal properties of Aloe striata, we treated conidia of three strains each of F. solani, F. oxysporum, and P. variotii with homogenized and filtered inner leaf gel. Exposure to gel homogenates caused minimal inhibition of conidial germination in tested strains. However, it significantly increased the frequency of hyphal aberrations characterized by increased hyphal diameters that resulted in intervals of non-parallel cell walls. Non-parallel cell walls ostensibly reduce total hyphal surface area available for adhesion. We found a significant decrease in the ability of aberrated P. variotii hyphae to remain adhered to microscope slides after repeated washing with reverse osmosis water. Our results suggest that treatment with A. striata contributes to a decrease in the adhesion frequency of tested P. variotii strains.

Photodynamic Action of Tri-meso (N-methylpyridyl), meso (N-tetradecyl-pyridyl) Porphine on Staphylococcus Epidermidis Biofilms Grown on Ti6Al4V Alloy

Staphylococcus epidermidis is a leading cause of nosocomial infections, and its virulence is attributable to formation of biofilm, especially on implanted devices. Photodynamic treatment (PDT) has been actively investigated for the eradication of bacterial biofilm growing on dental plaques and oral implants. In this study, we used Tri-meso (N-methyl-pyridyl), meso (N-tetradecyl-pyridyl) porphine (C14) for inactivation of two structurally distinct S. epidermidis biofilms grown on Ti6Al4V alloy and compared its photosensitizing efficiency with that of the parent molecule, tetra-substituted N-methylpyridyl-porphine (C1). A more significant reduction in bacterial survival was observed when both bacterial biofilms were exposed to a lower dose of C14, and simultaneously to visible light in comparison with C1. The different responses of both staphylococcal biofilms to C1- or C14-treatment appeared to depend on photosensitizer endocellular concentration. C14 bound to both biofilms to a greater extent than C1. Moreover, C14 penetrates deeper into the bacterial membranes, as determined by fluorescence quenching experiments with methylviologen, allowing for better bacterial killing photoefficiency. Confocal laser scanning microscope (CLSM) analysis indicated damage to bacterial cell membranes in both photodynamically treated biofilms, while disruption of PDT-treated biofilm was confirmed by scanning electron microscopy (SEM). In summary, C14 may be a potential photosensitizer for the inactivation of staphylococcal biofilms for many device-related infections which are accessible to visible light.

Rapid Identification of Staphylococci from Prosthetic Joint Infections Using MALDI-TOF Mass-Spectrometry

Hospital-acquired infections associated with implanted medical devices are most commonly caused by staphylococci. Current methods of species identification are slow, costly, and sometimes unreliable. We evaluated the ability of a Bruker Daltonics Microflex MALDI-TOF/MS in conjunction with MALDI Biotyper software to identify 158 characterized staphylococcal isolates from prosthetic joint infections, including 36 Staphylococcus aureus, 100 Staphylococcus epidermidis, 10 Staphylococcus capitis, 8 Staphylococcus lugdunensis, 2 Staphylococcus warneri, and 2 Staphylococcus haemolyticus isolates using the extraction method recommended by Bruker Daltonics. The suggested species identification by the MALDI Biotyper software was correct for all isolates, indicating reliable differentiation between S. aureus and coagulase-negative staphylococci. Applying the recommended criteria of the MALDI Biotyper software all 158 isolates gave scores ≥2.0, implying secure genus and probable species identification for all isolates. 34/36 S. aureus, 36/100 S. epidermidis, 5/10 S. capitis, 6/8 S. lugdunensis, 2/2 S. haemolyticus, 0/2 S. warneri displayed scores ≥2.3 implying highly probable species identification. For S. epidermidis 25/100 additional isolates had a score close to 2.3. It appears that additional clinically relevant staphylococcal isolates in the data base might aid in identification at scores implying highly probable species identification. The ability of the MALDI Biotyper software to recognize clonally-related strains within a species group (i.e. sub-typing) was investigated, and showed great potential. In conclusion, the MALDI-TOF/MS MALDI Biotyper system provides a promising rapid and reliable method of identifying clinical isolates from prosthetic joint infections to the species level, and has potential for sub-typing.

Antimicrobial and Antifouling Strategies for Polymeric Medical Devices

Hospital-acquired infections arising from implanted polymeric medical devices continue to pose a significant challenge for medical professionals and patients. Often times, these infections arise from biofilm accumulation on the device, which is difficult to eradicate and usually requires antibiotic treatment and device removal. In response, significant efforts have been made to design functional polymeric devices or coatings that possess antimicrobial or antifouling properties that limit biofilm formation and subsequent infection by inhibiting or eliminating bacteria near the device surface or by limiting the initial attachment of proteins and bacteria. In this Viewpoint, we highlight the magnitude of device-associated infections, the role of biofilm formation in human pathogenesis, and recent advances in antimicrobial and antifouling polymers, as well as current strategies employed in commercial devices for preventing infection.

Disruption of Staphylococcus Epidermidis Biofilms by Medicinal Maggot Lucilia Sericata Excretions/Secretions

Chronic infections are commonly associated with biofilms formed by bacteria such as Staphylococcus epidermidis. With the increase in antibiotic resistant bacteria, maggot debridement therapy has been reintroduced for the treatment of chronic wounds. Studies have shown that the excretion/secretions (ES) of Lucilia sericata larvae (maggots) contain many bioactive compounds which may contribute to the efficacy of maggot therapy. The present study evaluates the effect of L. sericata ES on the formation and disruption of S. epidermidis 7457 and 5179-R1 biofilms. These strains employ either polysaccharide intercellular adhesin (PIA) or accumulation associated protein (Aap) for intercellular adhesion.

A semiquantitative biofilm assay was used to measure the formation/disruption of S. epidermidis 7457 and 5179-R1 biofilms by ES. ES activity was characterized according to concentration, incubation time and temperature, thermal stability, and size. Immunofluorescence microscopy was used to ascertain the effect of ES on PIA and Aap.

In the presence of ES, S. epidermidis 7457 and 5179-R1 nascent bio film formation was inhibited, and pre-formed biofilms disrupted. ES activity was temperature and time dependent, inactivated by heat treatment, and disruption depended on the mechanism of intercellular adhesion. The molecule(s) responsible was >10 kDa in size and appeared to have protease or glucosaminidase activity.

ES interferes with S. epidermidis biofilm formation, specifically degrading factors employed in biofilm accumulation, which would increase bacterial susceptibility to antibiotics and the host's immune system. In purified form, ES-factors may have general applicability for the treatment or prevention of chronic biofilm infections caused by staphylococci.

Biotechnological War against Biofilms. Could Phages Mean the End of Device-Related Infections?

Microorganisms universally attach to surfaces, resulting in biofilm formation. These biofilms entail a serious problem in daily clinical practice because of the great prevalence of implantable device-related infections. Differences in antibiotic activity against planktonic and sessile bacteria may relate to clinical failures in the treatment of biofilm-related infections (BRI). Bacteriophages have several characteristics that make them potentially attractive therapeutic agents in some selected clinical settings, like for example BRI. They are highly specific and very effective in lysing targeted bacteria, moreover, they appear to be safe for humans. Many studies have shown the potential of phages for the treatment of infectious diseases in plants and animals, including infections with highly drug-resistant bacteria. The therapeutic use of bacteriophages, possibly in combination with antibiotics, may be a valuable approach in BRI. However, many important questions still remain that must be addressed before phages can be endorsed for therapeutic use in humans.

The Alpha-Like Surface Proteins: An Example of an Expanding Family of Adhesins

The Alpha-like protein (Alp) family, repeat-containing surface proteins once thought to be important adhesion factors confined to pathogenic streptococci and enterococci, is broader than previously known. Analysis of the annotated microbial genomes has identified new potential members of the Alp family not only in other Gram- positive opportunistic pathogens but also in commensal microflora of the human gut and the skin. This finding has highlighted the importance of genome sequencing projects for unraveling in greater detail lateral gene transfer events involving virulence factors between pathogens and commensals. These should receive constant attention not only as part of infectious disease prevention programs, but also in the food and biotechnology industries. (Int J Artif Organs 2008; 31: 834–40)

Regulation of Biofilm Formation by σB is a Common Mechanism in Staphylococcus Epidermidis and is not Mediated by Transcriptional Regulation of sarA

Biofilm formation is a major pathogenetic factor of Staphylococcus epidermidis. In S. epidermidis the alternative sigma factor σB was identified to regulate biofilm formation in S. epidermidis 1457. In S. aureus σB dependent regulation plays a minor role, whereas sarA (Staphylococcus accessory regulator) is an essential regulator. Therefore, we investigated the impact of σB on sarA transcription and biofilm formation in three independent S. epidermidis isolates. Mutants with dysfunctional σB displayed a strongly reduced biofilm formation, whereas in mutants with constitutive σB activity bio film formation was increased. Transcriptional analysis revealed that IcaA transcription was down-regulated in all σB negative mutants while icaR transcription was up-regulated. However, transcriptional differences varied between individual strains, indicating that additional σB-dependent regulators are involved in biofilm expression. Interestingly, despite the presence of a σB promoter beside two σA promoters no differences, or only minor ones, were observed in sarA transcription, indicating that σB-dependent sarA transcript has no influence on the phenotypic changes. The data observed in independent clinical S. epidermidis isolates suggests that, in contrast to S. aureus, regulation of biofilm formation by σB is a general feature in S. epidermidis. Additionally, we were able to demonstrate that the sarA- dependent regulation is not involved in this regulatory pathway.

Staphylococcus Biofilm Components as Targets for Vaccines and Drugs

Staphylococci have become the most common cause of nosocomial infections, especially in patients with predisposing factors such as indwelling or implanted foreign polymer bodies. The pathogenesis of foreign-body associated infections with S. aureus and S. epidermidis is mainly related to the ability of these bacteria to form thick, adherent multilayered biofilms. In a biofilm, staphylococci are protected against antibiotic treatment and attack from the immune system, thus making eradication of the infections problematic. This necessitates the discovery of novel prophylactic and therapeutic strategies to treat these infections. In this review, we provide an overview of staphylococcal biofilm components and discuss new possible approaches to controlling these persistent biofilm-dwelling bacteria.

Panton-Valentine Leukocidin Gene Detected in a Staphylococcus Aureus Strain Isolated from a Knee Arthroprosthesis Infection

This report focuses on the molecular characterization of a Staphylococcus aureus strain isolated from a knee arthroprosthesis infection and recognized retrospectively as a carrier of the Panton-Valentine leukocidin gene. The stored microbiological isolate, which belonged to the strain collection of the Research Unit on Implant Infections of the Rizzoli Orthopaedic Institute, was retrieved for molecular analysis. Genotyping was carried out, revealing an interesting profile. In addition to the positivity for the Panton-Valentine toxin gene, the results indicated that the isolate belonged to the agr III group and was endowed with bbp and cna genes, both encoding for staphylococcal adhesins that bind bone proteins. The strain had the mecA gene for methicillin resistance, even though it was unable to resist any of the β-lactam or other antibiotics. Its gene configuration matched that of other community-acquired methicillin-resistant and methicillin-susceptible Staphylococcus aureus (CA-MRSA and CA-MSSA) strains which have recently been reported worldwide. As far as we know, this is the first report on a PVL-positive S. aureus strain associated with an orthopedic implant (knee arthroprosthesis) infection.

Effects of Tigecycline, Linezolid and Vancomycin on Biofilms of Viridans Streptococci Isolates from Patients with Endocarditis

Background

Endocarditis, and prosthetic valve endocarditis in particular, is a serious disease with high morbidity and mortality. We investigate the effects of tigecycline, linezolid and vancomycin on biofilms of viridans group streptococci (VGS) isolated from patients with definite native or prosthetic valve endocarditis.

Methods and Results

Ten of 20 VGS blood stream isolates from patients with endocarditis formed biofilms in the microtiter plate biofilm model. The minimal inhibitory concentrations (MIC) for tigecycline, linezolid and vancomycin were determined using the microdilution broth method. Biofilms were grown for 24 hours and were incubated with tigecycline, linezolid and vancomycin at increasing concentrations from 1-128x MIC of the isolate being tested. Biofilm thickness was quantified by measuring the optical density (OD) after dyeing it with crystal violet. The incubation of the biofilms with tigecycline, linezolid or vancomycin resulted in a significant reduction of OD compared to the control biofilm without antibiotic (p<0.05). The optical density ratio (Odr) decreased significantly at 2x MIC for tigecycline, and at 8x MIC for linezolid and vancomycin (p<0.05). Although biofilms persisted even at the highest antibiotic concentrations of 128x MIC, bacterial growth was eradicated starting at concentrations of 16x MIC for vancomycin and of 32x MIC for linezolid, but not for tigecycline, up to a concentration of 128x MIC.

Conclusions

In the present study on viridans streptococci isolated from patients with endocarditis, tigecycline and linezolid reduced the density of the biofilms as effectively as vancomycin. However, linezolid and vancomycin were bactericidal at higher concentrations. Linezolid and vancomycin at very high doses may be useful in the treatment of biofilm-associated diseases caused by VGS infections.

Biofilm Formation is not Necessary for Development of Quinolone-Resistant “Persister” cells in an Attached Staphylococcus Epidermidis Population

Staphylococcus epidermidis is a common pathogen in device-associated infections which is able to attach onto polymeric surfaces and develop multilayered biofilms. Attached S. epidermidis displays reduced susceptibility to antimicrobial agents. In this study we investigated the influence of ciprofloxacin and the group IV quinolones gatifloxacin, gemifloxacin, and moxifloxacin with the minimal attachment killing (MAK) assay. MAK concentrations were determined for three biofilm-positive wild-type strains and their isogenic biofilm-negative mutants Depending on strain and investigated quinolone, it was possible to distinguish between a heterogeneous MAK (MAKhetero), and a homogeneous resistance (MAKhomo) which corresponds to the model of a few persisting cells under antibiotic treatment. A lower MAKhomo was detected for the biofilm-negative mutants as well as for the corresponding wild-types for some of the tested quinolones, which seems to be a result of higher bacterial inocula, whereas the MAKhetero concentrations were comparable for mutants and wild-types for nearly all of the tested antibiotics and strains. These data indicate that biofilm formation is not necessary for persistence of attached S. epidermidis cells under treatment with quinolones and could explain therapeutic failure in foreign body-associated infections due to biofilm-negative S. epidermidis isolates. The individual resistance phenotypes of investigated strains indicate that the determination of MAK concentrations might help to predict the therapy outcome of foreign body-associated infections with both biofilm-positive and biofilm-negative S. epidermidis. Thus, the relatively high activity displayed by group IV quinolones against individual attached staphylococcal isolates indicates a possible treatment option with the respective quinolones for foreign body-associated infections due to these isolates. (Int J Artif Organs 2008; 31: 752–60)