Background/Objectives: The emergence of antimicrobial resistance has urged researchers to explore new antimicrobial agents, such as essential oils (EOs). The aim of this study was to examine chemical composition and antimicrobial activity of the EOs from the needles and green cones of four Pinus species (Pinus mugo Turra., P. nigra J.F., P. syilvestris L., and P. halepensis Miller) from Bosnia and Herzegovina. Methods: Chemical profiles of EOs were assessed by gas chromatography, while microdilution method was used to test their antimicrobial activity. A synergistic action of EOs and gentamicin was investigated by the checkerboard assay. Results: The chemical composition of the tested EOs showed a high percentage of α-pinene, (E)-caryophyllene, limonene, germacrene D, myrcene, and δ-3-carene. EO from green cones of P. sylvestris showed high efficiency against S. aureus and E. faecalis. The MIC of P. nigra cones’ EO was 100 μg/mL against E. coli. The EO of P. halepensis green cones demonstrated the strongest activity against E. faecalis. EOs of P. halepensis needles and green cones exhibited the highest activity against C. albicans. Further, synergistic interaction was detected in combination of the selected EOs/gentamicin toward S. aureus and K. pneumoniae. Conclusions: Among the tested EOs, oils of P. sylvestris cones and P. halepensis cones and needles showed the greatest antimicrobial activity. The same EOs and EO from P. nigra cones displayed synergistic potential in combination with gentamicin, supporting their utilization as antimicrobial agents alone or in combination with antibiotics, which is in line with their ethnopharmacological usage and circular bioeconomy principles.

Aims: To investigate the synergistic activity of colistin and selenium nanoparticles (SeNPs) against pandrug-resistant (PDR) Ac. baumannii. Methods and Results: Chequerboard and time-kill assays were employed to explore the potential synergistic interactions between colistin and SeNPs against Ac. baumannii isolates (8), previously determined as colistin-resistant (MIC range 16–256 μg ml−1). Also, whole-genome sequencing (WGS) and gene expression analyses were used to elucidate the mechanisms of colistin resistance. Exceptionally strong synergistic activity (FICI range 0.004–0.035) of colistin and SeNPs against colistin-resistant isolates was revealed. Colistin (0.5 or 1 μg ml−1) used in combination with SeNPs (0.5 μg ml−1) was able to reduce initial inoculum during the first 4 h of incubation, in contrast to colistin (0.5, 1 or 2 μg ml−1) alone. Conclusions: These findings propose colistin/SeNPs combination as a new option to fight PDR Ac. baumannii, the therapeutic possibilities of which should be proved in future in vivo studies. Significance and Impact of Study: Here we present the first evidence of synergy between colistin and selenium compounds against bacteria in general. Also, WGS and gene expression analyses provide some new insights into Ac. baumannii colistin resistance mechanisms.

Biofilm production facilitates microbial colonization of wounds and catheters. Acinetobacter baumannii produces high levels of biofilm and causes difficult-to-treat nosocomial infections. Candida albicans is another strong biofilm producer which may facilitate A. baumannii adhesion by providing hyphae-mediated OmpA-binding sites. Here we tested the potential of 2'-hydroxychalcones to inhibit dual-species biofilm production of A. baumannii and Candida spp., and further predicted the mechanism of structure-related difference in activity. The results suggest that 2'-hydroxychalcones exhibit potent activity against Candida spp./A. baumannii dual-species biofilm production. Particularly active was trifluoromethyl-substituted derivative (p-CF₃), which decreased C. albicans/A. baumannii biomass produced on vein-indwelling parts of the central venous catheterization set by up to 99%. Further, higher OmpA-binding affinity was also calculated for p-CF₃, which together with demonstrated significant ompA-downregulating activity, suggests that superior antibiofilm activity of this chalcone against the tested dual-species community of A. baumannii is mediated through the OmpA.

Multidrug-resistant bacterial strains represent an emerging global health threat and a great obstacle for bone tissue engineering. One of the major components of the extracellular matrix of the bone is a collagen protein, while selenium is an element that has antimicrobial potential, and is also important for bone metabolism and bone health. Here we represent the incorporation of selenium nanoparticles (SeNPs) synthesized by the green chemical reduction method into collagen gels to produce a composite material, collagen/SeNPs, with antimicrobial properties. The samples were comprehensively characterized by zeta potential measurements, dynamic light scattering inductively coupled plasma-mass spectrometry (ICP-MS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), optical microscopy, field-emission scanning electron microscopy (FE-SEM), and differential scanning calorimetry The cytotoxicity of the SeNPS, as well as collagen/SeNPs, was tested on the MRC-5 cells. It was revealed that collagen/SeNPS expressed a lower cytotoxic effect. Collagen/SeNPs showed significant antibacterial activity against all tested Gram-positive strains, the major causative agents of orthopedic infections as well as Candida albicans. Furthermore, three-dimensional β-tricalcium phosphate (3D-TCP) scaffolds were fabricated by a well-established 3D printing (lithography) method, and afterward preliminary coated by newly-synthesized SeNPs or collagen/SeNPs. In addition, uncoated 3D-TCP scaffolds as well as coated by collagen/SeNPs were subjected to biofilm formation. The production of Staphylococcus aureus biofilm on coated scaffolds by collagen/SeNPs was significantly reduced compared to the uncoated ones.

Background/Aim. Plant essential oils (EOs) can have a significant antibacterial effect especially through additive or synergistic action as antibiotic adjuvants. We investigated the composition and activity of EOs of two species of genus Salvia (S) from Greece with the aim to determine their antimicrobial activity as well as the activity in combination with selected antibiotics. Methods. The aerial parts of wild-growing S. fruticosa and S. ringens were subjected to a steam distillation and the obtained EOs were analyzed by gas chromatography and gas chromatography/mass spectrometry. The broth-microdilution method was used in order to determine the minimum inhibitory concentrations (MICs) of EOs on seven strains of bacteria and one yeast. Antimicrobial activity of the combination of EO and antibiotics was investigated by checkerboard method and estimated by calculating fractional inhibitory concentration (FIC) of each component and fractional inhibitory concentration index (FICI). Results. Dominant component of S. fruticosa EO was transthujone (54.2%) and for S. ringens EO i t w as ?-pinene (28.1%). The MICs of EOs of both species were in the range from 200 ?g/mL to > 500 ?g/mL. The strongest antimicrobial effect was achieved against Bacillus subtilis and Candida albicans. According to FICI values, EO of S. fruticosa had additive effect with ciprofloxacin against most of bacterial strains but not with amikacin. Conclusion. The essential oils of S. ringens and S. fruticosa showed modest antimicrobial activity. However, the essential oil of S. fruticosa showed a promising additive effect in combination with ciprofloxacin.