Quartz crystal microbalance-based aptasensor integrated with magnetic pre-concentration system for detection of Listeria monocytogenes in food samples.

A fast and accurate identification of Listeria monocytogenes. A new quartz crystal microbalance (QCM) aptasensor was designed for the specific and rapid detection of L. monocytogenes. Before detection of the target bacterium from samples in the QCM aptasensor, a magnetic pre-enrichment system was used to eliminate any contaminant in the samples. The prepared magnetic system was characterized using ATR-FTIR, SEM, VSM, BET, and analytical methods. The saturation magnetization values of the Fe3O4, Fe3O4@PDA, and Fe3O4@PDA@DAPEG particles were 57.2, 40.8, and 36.4 emu/g, respectively. The same aptamer was also immobilized on the QCM crystal integrated into QCM flow cell and utilized to quantitatively detect L. monocytogenes cells from the samples. It was found that a specific aptamer-magnetic pre-concentration system efficiently captured L. monocytogenes cells in a short time (approximately 10 min). The Fe3O4@PDA@DA-PEG-Apt particles provided selective isolation of L. monocytogenes from the bacteria-spiked media up to 91.8%. The immobilized aptamer content of the magnetic particles was 5834 µg/g using 500 ng Apt/mL. The QCM aptasensor showed a very high range of analytical performance to the target bacterium from 1.0 × 102 and 1.0 × 107 CFU/mL. The limit of detection (LOD) and limit of quantitation (LOQ) were 148 and 448 CFU/mL, respectively, from the feeding of the QCM aptasensor flow cell with the eluent of the magnetic pre-concentration system. The reproducibility of the aptasensor was more than 95%. The aptasensor was very specific to L. monocytogenes compared to the other Listeria species (i.e., L. ivanovii, L. innocua, and L. seeligeri) or other tested bacteria such as Staphylococcus aureus, Escherichia coli, and Bacillus subtilis. The QCM aptasensor was regenerated with NaOH solution, and the system was reused many times.

Evaluation of phytotherapeutic activities and phytochemical content of Phormidium autumnale Gomont from natural freshwater sources.

The information available on microalgae-sourced compounds, especially antibiotics and other bioactive compounds, and their potential commercial applications is still insufficient. In this study, antibacterial activity, metabolites, and molecular characterization of Phormidium autumnale, which was isolated from samples collected from different natural freshwater sources in Ankara, Turkey, were investigated. Sequencing results of 16s rDNA confirmed the molecular identification of P. autumnale by 99%. It was determined that the peak values of some phenolic compounds and cyclic peptides were consistent with the 1653-1389 cm-1 band regions in the FTIR spectra of the species. The antibacterial activities of P. autumnale cyanobacteria (CBA) extracts that were obtained by using different solvents were tested on Escherichia coli, Staphylococcus epidermidis, methicillin-resistant (MR) Staphylococcus aureus, Streptococcus agalactiae, and Enterococcus faecalis by using a disc diffusion method. Also, the minimum inhibition concentration (MIC) and antimicrobial indexes of all extracts were determined. It was found that P. autumnale methanol extracts showed antibacterial activity on all test bacteria, whereas acetone extracts showed effects only on E. coli. For the inhibition of MR S. aureus, the control methanol extract was found to give very similar results to those exhibited by the control antibiotics, and the antimicrobial index results were determined to be 58.7-67.5%. According to the results of the analysis of methanol extract, gentisic acid, vanillic acid, 4-hydroxybenzoic acid, p-coumaric acid, and catechin (especially phenolic compounds) were determined to be the active compounds. It can be concluded that P. autumnale is an alternative to current commercial applications as an antibacterial agent in phytotherapy.

Spatial and temporal variations in composition of algae assemblages with environmental variables in an urban stream (Ankara, Turkey).

Phytoplankton and epipelon assemblages form the main constituents, and they are producers in aquatic ecosystems, such as streams and rivers. This study was carried out between May 2008 and April 2009 to determine the impacts of polluted water on species variations, compositions, and community metrics in phytoplankton and epipelon at six stations on Ankara Stream. A total of 231 taxa were recorded during the study period, with 131 Bacillariophyta, 3 Charophyta, 41 Chlorophyta, 30 Cyanobacteria, 25 Euglenophyta, and 1 Ochrophyta. Heterogeneity of the stream stations was determined by the use of hierarchical cluster analysis (HCA). Community metrics were compared by using non-parametric tests, while canonical correspondence analysis (CCA) was used for the relationships between environmental variables and species. Variations in water quality and species composition along the stream flow revealed a significant spatial heterogeneity (p < 0.05). However, the upper stations of the stream were represented by unpolluted water quality with low nutrients and conductivity, and the mid- and downstream stations were characterized by high concentrations of ammonia (up to 60 mg L-1) and o-phosphate (up to 25 mg/L), with low concentrations of dissolved oxygen (< 1 mg L-1). The results, clearly supported by indicator taxa, showed that various domestic and industrial discharges affected the increase in pollution and the spatial heterogeneity. The findings obtained in this study will contribute to future improvements in Ankara Stream watershed studies.