Biofilm ecology: On-line methods bring new insights into mic and microbial biofouling

Exploring the Antibiofilm Effect of Sertraline in Synergy with Cinnamomum verum Essential Oil to Counteract Candida Species

The emergence and spread of drug-resistant pathogens, resulting in antimicrobial resistance, continue to compromise our capability to handle commonly occurring infectious diseases. The rapid global spread of multi-drug-resistant pathogens, particularly systemic fungal infections, presents a significant concern, as existing antimicrobial drugs are becoming ineffective against them. In recent decades, there has been a notable increase in systemic fungal infections, primarily caused by Candida species, which are progressively developing resistance to azoles. Moreover, Candida species biofilms are among the most common in clinical settings. In particular, they adhere to biomedical devices, growing as a resilient biofilm capable of withstanding extraordinarily high antifungal concentrations. In recent years, many research programs have concentrated on the development of novel compounds with possible antimicrobial effects to address this issue, and new sources, such as plant-derived antimicrobial compounds, have been thoroughly investigated. Essential oils (EOs), among their numerous pharmacological properties, exhibit antifungal, antibacterial, and antiviral activities and have been examined at a global scale as the possible origin of novel antimicrobial compounds. A recent work carried out by our research group concerned the synergistic antibacterial activities of commercially available and chemically characterized Cinnamomum verum L. essential oil (C. verum EO) in association with sertraline, a selective serotonin reuptake inhibitor whose repositioning as a non-antibiotic drug has been explored over the years with encouraging results. The aim of this work was to explore the synergistic effects of C. verum EO with sertraline on both planktonic and sessile Candida species cells. Susceptibility testing and testing of the synergism of sertraline and C. verum EO against planktonic and sessile cells were performed using a broth microdilution assay and checkerboard methods. A synergistic effect was evident in both the planktonic cells and mature biofilms, with significant reductions in fungal viability. Indeed, the fractional inhibitory concentration index (FICI) was lower than 0.5 for all the associations, thus indicating significant synergism of the associations with the Candida strains examined. Moreover, the concentrations of sertraline able to inhibit Candida spp. strain growth and biofilm formation significantly decreased when it was used in combination with C. verum EO for all the strains considered, with a reduction percentage in the amount of each associated component ranging from 87.5% to 97%.

Antifungal Biofilm Inhibitory Effects of Combinations of Diclofenac and Essential Oils

Systemic fungal infections have risen in recent decades and most of them are caused by Candida species, which are becoming increasingly resistant to conventional antifungal drugs. Biofilm production has been considered the most common growth form of Candida cells and is associated with a high level of antifungal resistance. At present, international research reports on the antifungal activity of non-traditional antimicrobial drugs and their potential use against life-threatening resistant fungal infections. Indeed, drug repurposing has led to the consideration of well-known compounds as a last-line therapy. The goal of this work is to evaluate the potential synergistic antifungal biofilm activity of new combinations between diclofenac sodium salt (DSS), a widely used non-steroidal anti-inflammatory drug (NSAID), with the essential oils (EOs) of Mentha piperita, Pelargonium graveolens, and Melaleuca alternifolia, whose antifungal activity has been well documented over the years. The in vitro antifungal activity of DSS and EOs was determined on different Candida strains. Susceptibility testing and the synergism of DSS and EOs versus biofilm cells was performed by using the broth microdilution assay and checkerboard methods. Minimum inhibitory concentrations (sMIC50) of DSS alone ranged from 1.25 to 2.05 mg/mL for all the strains considered. These values significantly decreased when the drug was used in combination with the EOs. The fractional inhibitory concentration index (FICI) was lower than 0.5 for almost all the associations, thus indicating a significant synergism, particularly for the DSS-Pelargonium graveolens combination towards the Candida strains examined. These preliminary results show that the combination of the EOs with DSS improves the antifungal activity on all the tested Candida strains, significantly lowering the concentrations of the components used and thus allowing any toxic effects to be overcome.

A Two-Step Silane Coating Incorporated with Quaternary Ammonium Silane for Mitigation of Microbial Corrosion of Mild Steel

Quaternary ammonium compounds have been used as antibacterial materials. However, as they are hydrophilic and produce a positively charged surface, it is challenging to develop a durable antimicrobial coating of such compounds. The objective of this study is to investigate a two-step silane coating incorporated with quaternary ammonium silane for mitigation of microbiologically influenced corrosion (MIC) of mild steel in biotic solution (a marine environment with bacteria). The corrosion resistance was characterized by electrochemical impedance spectroscopy and potentiodynamic polarization tests. The intact silane coating and that pre-exposed to the biotic solution were characterized by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The most probable method (MPN) was used to quantify the active microorganisms attached to the uncoated and silane-coated surfaces. Electrochemical results reveal that the coating thus developed improved the corrosion resistance of steel in the biotic solution. The MPN, FTIR, and scanning electron microscopy suggest a significant decrease in the number of active cells that get attached to the coated surface.

Investigation of microbial biofilm structure by laser scanning microscopy

Microbial bioaggregates and biofilms are hydrated three-dimensional structures of cells and extracellular polymeric substances (EPS). Microbial communities associated with interfaces and the samples thereof may come from natural, technical, and medical habitats. For imaging such complex microbial communities confocal laser scanning microscopy (CLSM) is the method of choice. CLSM allows flexible mounting and noninvasive three-dimensional sectioning of hydrated, living, as well as fixed samples. For this purpose a broad range of objective lenses is available having different working distance and resolution. By means of CLSM the signals detected may originate from reflection, autofluorescence, reporter genes/fluorescence proteins, fluorochromes binding to specific targets, or other probes conjugated with fluorochromes. Recorded datasets can be used not only for visualization but also for semiquantitative analysis. As a result CLSM represents a very useful tool for imaging of microbiological samples in combination with other analytical techniques.

Presence and effects of marine microbial biofilms on biocide-based antifouling paints

Marine microorganisms are capable of successfully colonizing toxic surfaces through the formation of biofilm structures. In this article, most of the literature reporting the presence of marine biofilms on chemically-active antifouling paints is briefly reviewed. Of special concern is the influence of the dense extracellular polymeric substances (EPS) matrix on the release rate of the compounds involved in antifouling paint performance (i.e. active compounds and controlled-release binder molecules). A deeper understanding of these phenomena is of interest for both environmental legislators and paint formulators.

Influence of surface characteristics and microstructure on adhesion of bacterial cells onto a type 304 stainless steel

A study was carried out to understand the influence of the surface characteristics/microstructure of a type 304 stainless steel on bacterial adhesion by exposing solution-annealed, sensitized and air-oxidized stainless steel specimens in a culture of Pseudomonas sp. in dilute nutrient broth. Epifluorescence microscopy of the exposed surfaces revealed that the pattern of adhesion as well as number density of bacterial cells was different depending on the metallurgical condition of the substratum. Among the specimens with different microstructures, the sensitized specimens had the highest bacterial density, followed by the solution annealed and the oxidized specimens. The same trend was shown by the total viable counts on the various surfaces, estimated by a plate count technique. The study assumes significance in the context of the widely reported observation of preferential attack of the welded region during microbiologically influenced corrosion of fabricated components.

Quantifying biofilm structure using image analysis

We have developed and implemented methods of extracting morphological features from images of biofilms in order to quantify the characteristics of the inherent heterogeneity. This is a first step towards quantifying the relationship between biofilm heterogeneity and the underlying processes, such as mass-transport dynamics, substrate concentrations, and species variations. We have examined two categories of features, areal, which quantify the relative magnitude of the heterogeneity and textural, which quantify the microscale structure of the heterogeneous elements. The feature set is not exhaustive and has been restricted to two-dimensional images to this point. Included in this paper are the methods used to extract the structural information and the algorithms used to quantify the data. The features discussed are porosity, fractal dimension, diffusional length, angular second moment, inverse difference moment and textural entropy. We have found that some features are better predictors of biofilm behavior than others and we discuss possible future directions for research in this area.