The characteristics of Pseudomonas fluorescens biofilms formed under three different linear flow velocities (u=0.1, 0.4, and 0.8 m/s; Reynolds numbers of 1,000, 4,000, and 8,000, respectively) were studied providing an extension to the studies of earlier researchers. A flow cell reactor system was used to form biofilms, and they were characterized in terms of thickness, morphological structure, mass, cell density, outer membrane protein expression, and matrix and total protein and polysaccharide content. The external mass transfer coefficients were also assessed. The biofilms developed at u=0.4 and 0.8 m/s had similar characteristics but were significantly different from those developed at 0.1 m/s. High flow velocities formed thinner biofilms with higher cell densities and contents of matrix/extracellular proteins and polysaccharides. The increase of flow velocity from 0.4 to 0.8 m/s caused a higher production of matrix proteins and polysaccharides. The external mass transfer coefficients sugg...

Background: Dental caries remains the most prevalent and costly oral infectious disease worldwide, encouraging the search for new and more effective antimicrobials. Therefore, the aim of this work was to study the antimicrobial action of selected phytochemicals (eugenol, citronellol, sabinene hydrate, trans-cinnamaldehyde, terpineol and cinnamic acid) againstStreptococcus mutansin planktonic and biofilm states as well as the cytotoxicity of these compounds.Methods: The antibacterial activity of the selected compounds was evaluated by the determination of the minimal bactericidal concentration. The resazurin assay was used to assess the metabolic activity of sessileS. mutans. The cytotoxicity was determined using a fibroblast cell line.Results: Among the tested phytochemicals, citronellol, cinnamic acid and trans-cinnamaldehyde were the most effective against both planktonic and sessileS. mutans, an effect apparently related to their hydrophobic character. Additionally, these three compounds did not compromise fibroblasts cell viability.Discussion: Citronellol, cinnamic acid and trans-cinnamaldehyde demonstrated significant antimicrobial activity and low cytotoxicity proposing their potential as a novel group of therapeutic compounds to control oral infectious diseases. Moreover, their effects are particularly relevant when benchmarked against eugenol, a phytochemical commonly used for prosthodontic applications in dentistry.

The indiscriminate use of biocides for general disinfection has contributed to the increased incidence of antimicrobial tolerant microorganisms. This study aims to assess the potential of seven phytochemicals (tyrosol, caffeic acid, ferulic acid, cinnamaldehyde, coumaric acid, cinnamic acid and eugenol) in the control of planktonic and sessile cells of Staphylococcus aureus and Escherichia coli. Cinnamaldehyde and eugenol showed antimicrobial properties, minimum inhibitory concentrations of 3–5 and 5–12 mM and minimum bactericidal concentrations of 10–12 and 10–14 mM against S. aureus and E. coli, respectively. Cinnamic acid was able to completely control adhered bacteria with effects comparable to peracetic acid and sodium hypochlorite and it was more effective than hydrogen peroxide (all at 10 mM). This phytochemical caused significant changes in bacterial membrane hydrophilicity. The observed effectiveness of phytochemicals makes them interesting alternatives and/or complementary products to commonly used biocidal products. Cinnamic acid is of particular interest for the control of sessile cells.

New biocidal solutions are needed to combat effectively the evolution of microbes developing antibiotic resistance while having a low or no environmental toxicity impact. This work aims to assess the efficacy of commonly used biocides and natural-based compounds on the disinfection of silicone and stainless steel (SS) surfaces seeded with different Staphylococcus aureus strains. Minimum inhibitory concentration was determined for synthetic (benzalkonium chloride-BAC, glutaraldehyde-GTA, ortho-phthalaldehyde-OPA and peracetic acid-PAA) and natural-based (cuminaldehyde-CUM), eugenol-EUG and indole-3-carbinol-I3C) biocides by the microdilution method. The efficacy of selected biocides at MIC, 10×MIC and 5500 mg/L (representative in-use concentration) on the disinfection of sessile S. aureus on silicone and SS was assessed by viable counting. Silicone surfaces were harder to disinfect than SS. GTA, OPA and PAA yielded complete CFU reduction of sessile cells for all test concentrations as well as BAC at 10×MIC and 5500 mg/L. CUM was the least efficient compound. EUG was efficient for SS disinfection, regardless of strains and concentrations tested. I3C at 10×MIC and 5500 mg/L was able to cause total CFU reduction of silicone and SS deposited bacteria. Although not so efficient as synthetic compounds, the natural-based biocides are promising to be used in disinfectant formulations, particularly I3C and EUG.

Plants have been long scrutinized in the quest for new antibiotics, but no strong antibiotic molecule was ever found. Evidence exists that most phytochemicals have a regulatory or adjuvant effect on other antibacterial compounds, thus promoting a greater therapeutic effect. The current study assessed twenty-eight plants from different families for their antibacterial activity and as adjuvants in antibiotic therapy against Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA). Eucalyptus globulus, Castanea sativa, Agrimonia eupatoria and Fraxinus excelsior methanolic extracts showed antibacterial activity with minimal inhibitory concentrations (MICs) of 0.125–0.5, 0.5–1.0, 1.0–2.0, and 2.0–4.0 g L⁻¹, respectively. Non-antibacterial plants were assessed in combination with ampicillin, oxacillin, ciprofloxacin, erythromycin and tetracycline by a modified disc diffusion test. Methanolic extracts of Acacia dealbata, Prunus spp. plants, Centaurea nigra, Eupatorium cannabium and Buxus sempervirens showed a potentiating effect mostly of ciprofloxacin, erythromycin and tetracycline. B. sempervirens was selected for its potentiating activity and applied against S. aureus biofilms. B. sempervirens (1 g L⁻¹) was able to cause an 88% reduction of S. aureus within 1 h exposure. Further phytochemical investigation of B. sempervirens allowed to identify betulinic acid as a major component, together with other triterpenoids. Betulinic acid and other common terpernoids – lupeol, betulin, hederagenin, ursolic acid and oleanolic acid, were tested for antibacterial and antibiotic-potentiating activities. Among the tested compounds, oleanolic acid and ursolic acid – were highlighted, showing MIC of 62.5 and 15.6 mg L⁻¹, respectively, against S. aureus. Additionally, oleanolic acid showed synergism when combined with tetracycline and erythromycin and caused biofilm reductions of 70, 81 and 85% when applied at 1/2 MIC, MIC and 2 × MIC, respectively.