The application of selenium nanoparticles for enhancing the efficacy of photodynamic inactivation of planktonic communities and the biofilm of Streptococcus mutans.

OBJECTIVE: Streptococcus mutans is one of the principal causative agents of dental caries (tooth decay) found in the oral cavity. Therefore, this study investigates whether selenium nanoparticles (SeNPs) enhance the efficacy of photodynamic therapy (PDT) against both planktonic communities and the one-day-old biofilm of S. mutans. In this study, the planktonic and 24-h biofilm of S. mutans have been prepared in 96-cell microplates. These forms were treated by methylene blue (MB) and SeNPs and then were exposed to light-emitting diode (LED) lighting. Finally, the results have been reported as CFU/ml. RESULTS: The outcomes demonstrated that MB-induced PDT and SeNPs significantly reduced the number of planktonic bacteria (P-value < 0.001). The comparison between the treated and untreated groups showed that combining therapy with SeNPs and PDT remarkably decreased colony-forming units of one-day-old S. mutans biofilm (P-value < 0.05). The findings revealed that PDT modified by SeNPs had a high potential to destroy S. mutans biofilm. This combination therapy showed promising results to overcome oral infection in dental science.

Prevalence and molecular mechanisms of colistin resistance in Acinetobacter baumannii clinical isolates in Tehran, Iran.

Colistin is one of the last remaining active antibiotics against multidrug resistant Gram-negative bacteria. However, several recent studies reported colistin-resistant (ColR) Acinetobacter baumannii from different countries. In the current study, we investigated molecular mechanisms involved in colistin resistance in A. baumannii isolates from different clinical samples.A total of 110 clinical A. baumannii isolates were collected from two hospitals in Tehran. Minimum inhibitory concentrations (MICs) were determined by broth microdilution according to the Clinical and Laboratory Standards Institute. For the ColR isolates, mutation was detected in pmrA, pmrB, lpxA, lpxC, and lpxD genes using the polymerase chain reaction (PCR) and sequencing. Moreover, the relative expression of the pmrC gene was calculated using quantitative reverse transcription PCR. Three colistin resistant isolates were identified with MIC between 8 and 16 µg/mL and were resistant to all the tested antimicrobial agents. All the three isolates had a mutation in the pmrB, pmrA, lpxA, lpxD, and lpxC genes. Moreover, the overexpression of pmrC gene was observed in all isolates. Our results showed that the upregulation of the PmrAB two component system was the primary mechanism linked to colistin resistance among the studied colistin resistant A. baumannii isolates.

Antimicrobial effects of selenium nanoparticles in combination with photodynamic therapy against Enterococcus faecalis biofilm.

BACKGROUND: Selenium Nanoparticles (SeNPs) were reported as an agent that may enhance the effectiveness of Photodynamic Antimicrobial Chemotherapy (PACT). This in vitro study evaluates the effect of SeNPs on the efficacy of Methylene Blue (MB)-induced PACT against the biofilm formated in 96-well plates and the dentine tubule biofilm of Enterococcus faecalis. METHODS: Chitosan coated SeNPs were synthesized using chemical reduction method and were characterized by Transmission Electron Microscope (TEM) and Dynamic Light Scattering (DLS). Twenty-four-hour biofilms of E. faecalis were developed on 96-well plates and treated with SeNPs, MB, and Light-Emitting Diode (LED). Also, three-week biofilms of E. faecalis were formed on 67 specimens of dentinal tubules, and the antibacterial effects of MB+SeNPs on these biofilms were studied. RESULTS: The average hydrodynamic diameter of SeNPs was 80/3 nm according to DLS measurement. The combined use of MB and SeNPs significantly reduced Colony-Forming Units (CFUs) of one-day-old E. faecalis biofilms in comparison with the control group (P value < 0.05). Besides, combination therapy had the most antibacterial effect on root canal E. faecalis biofilms at both 200 and 400 µm depths of dentine tubules (P value < 0.001). Of note, about 50% of human fibroblast cells survived at a concentration of 128 µg/ml of SeNPs, compared to the control group. CONCLUSION: The results demonstrated that the photodynamic therapy modified by SeNPs could be an effective disinfection alternative to the destruction of E. faecalis biofilms and root canal treatment.