Antibacterial and antibiofilm efficacy of colistin & meropenem conjugated silver nanoparticles against Escherichia coli and Klebsiella pneumoniae.

The progressive increase in infections caused by multidrug-resistant (MDR) Gram-negative bacteria and the emergence of resistance to last-resort antimicrobial drugs in recent years necessitate the development of new therapeutic strategies. This study was conducted to obtain nanostructured antimicrobials by conjugating colistin (COL) and meropenem (MEM) antibiotics with biosynthesized silver nanoparticles (bio-AgNPs) via the green synthesis method using Rosa damascena extract, and to investigate the antibacterial and antibiofilm activity of these nanostructures against Escherichia coli and Klebsiella pneumoniae strains. Ultraviolet-visible spectrophotometry, high-resolution-transmission electron microscopy, atomic force microscopy, X-ray diffraction, and Fourier transform-infrared spectroscopy analyses were performed to determine the physical and chemical properties of synthesized bio-AgNPs, COL@bio-AgNPs, MEM@bio-AgNPs, and COL&MEM@bio-AgNPs. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration of nanoparticles were determined on standard and MDR clinical strains. The antibiofilm efficacy and cytotoxic effect of nanoparticles were evaluated by the crystal violet dye method and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide dye method, respectively. The characterization analyses demonstrated that the synthesized nanoparticles had crystal structure and spherical morphology (5.6-30.2 nm in size). Antibiotic conjugated nanoparticles exhibited better antimicrobial activity and lower MIC values (0.125-4 µg/mL) on the tested strains compared to free antibiotics, and MIC values were decreased up to 1024-fold (p < 0.05). Antibiotic conjugated nanoparticles were found to be more effective in biofilm eradication than free antibiotics and bio-AgNPs and had a less inhibitory effect on peripheral blood mononuclear cell viability. The findings revealed that antibiotic-conjugated nanoparticles have the potential to be used as an effective antimicrobial drug against MDR E. coli and K. pneumoniae strains.

Mechanical reduction in intracanal Enterococcus faecalis when using three different single-file systems: an ex vivo comparative study.

AIM: To evaluate the bacterial reduction achieved by WaveOne Gold (Dentsply Sirona Endodontics, Ballaigues, Switzerland), Hyflex EDM (Coltene-Whaledent, Altstätten, Switzerland), and XP-endo Shaper (FKG Dentaire SA, La Chaux-de-Fonds, Switzerland) in canals infected with Enterococcus faecalis. The null hypothesis (H0 ) was that there would be no difference amongst the NiTi systems in reducing the root canal bacterial load. METHODOLOGY: Seventy-four mandibular premolar teeth with straight and round root canals were selected. Sixty-two root canals were contaminated with E. faecalis for 4 weeks and subjected to mechanical preparation with one of three single-file NiTi rotary systems (WaveOne Gold, Hyflex EDM, and XP Endo Shaper). Twelve non-contaminated root canals were used as negative controls. Bacterial samples were collected with sterile paper points (Dentsply Sirona Endodontics) before and after rotary instrumentation to quantify the bacterial load. Five roots from each instrumentation group were evaluated topographically from the coronal, middle and apical thirds by SEM. The bacterial reduction was calculated and analysed statistically by the Kruskal-Wallis and Dunn post hoc tests, all at 5% significance. RESULTS: The samples taken before instrumentation showed approximately 9.64 log CFU bacterial load. Instrumentation with the Hyflex EDM and XP-endo Shaper resulted in significantly greater bacterial reduction than those with WaveOne Gold (P = 0.00). All specimens had bacterial growth. SEM images supported the CFU/mL data. Thick and dense debris was observed in WaveOne Gold samples. Instrumentation resulted in the disruption of the biofilm-like structure, and both areas of clean and open dentinal tubules and areas with thick debris were observed in Hyflex EDM and XP-endo Shaper samples. CONCLUSIONS: Instrumentation in straight and round canals of premolar teeth with the Hyflex EDM and XP-endo Shaper resulted in significantly greater bacterial reduction than WaveOne Gold. No instrumentation system rendered root canals completely free from bacteria.