(306d) Chitosan-Coated Selenium Nanoparticles and Their Affects on Bacterial Growth Kinetics

Authors: 
De La Torre, N., Northeastern University
Stolzoff, M., Northeastern University
Webster, T. J., Northeastern University
Introduction:

The prevalence of antibiotic-resistant bacteria has continued to grow in recent years, resulting from increased use (and misuse) of antibiotics in daily life. It is imperative, then, to develop novel bactericidal treatments and therapies to combat these pathogens. Unfortunately, the discovery of new antibiotics, in the traditional sense, has become increasingly difficult in recent years. Selenium is an essential trace material found in the body associated with antioxidant and metabolic mechanisms that play a role in preventing cell damage. Selenium nanoparticles (SeNP) have been previously found to be antibacterial without any apparent toxicity to healthy mammalian cells. Here, we have developed SeNP synthesized with a chitosan coating to improve colloidal stabilization and to introduce new surface chemistries for further targeting and delivery options. The chitosan-coated SeNP (Ch-SeNP) were able to conserve the size distribution and the antibacterial efficacy seen with previous iterations of SeNP. To compare these results, we employed the Gompertz kinetic growth models to analyze the changes in lag time (time in which it takes the bacteria to enter their exponential growth phase) and maximum growth rate, with respect to different concentrations of SeNP and Ch-SeNP. The results showed an increase in the lag time and a decrease in the growth of S. aureus bacteria with Ch-SeNP.

Materials and Methods:

Ch-SeNP were produced using a colloidal suspension method. Briefly, chitosan in a 1% acetic acid solution was added dropwise into a stirred sodium selenite solution. Ascorbic acid was then added dropwise to the solution and stirred until equilibrium was reached. The nanoparticles were centrifuged for 10 minutes to remove excess reactants, and subsequently resuspended into DI water. DLS and TEM were used to characterize the Ch-SeNP to determine the size and surface charge. The growth kinetics were measured by incubating S. aureuswith various Ch-SeNP concentrations in 3% TSB. The optical density (at 592 nm) was measured regularly for 24 hours throughout the growth assay. Gompertz and Richards growth models were applied to develop the growth kinetics to understand the role of the selenium nanoparticles on the bacteriaâ??s proliferation. All experiments were replicated three times and statistical significance analyzed via ANOVA. The data obtained was compared with controls using a two-tailed, unpaired Studentâ??s t-test, with p<0.05 considered to be statistically significant.

Results and Discussion:

The Ch-SeNP inhibited S. aureusgrowth over time. Most notably, the lag time of the growth curves increased while the growth rate decreased with increasing concentrations of Ch-SeNP treatments. Even for Ch-SeNP concentrations as low as 0.0023 mg/ml, both the lag time and growth rate changed significantly compared to untreated controls.

Conclusion:

Selenium nanoparticles coated with chitosan have easily reproducible batch-to-batch characteristics and are able to effectively inhibit the growth of S. aureus. Using the Gompertz growth model, the present study accurately calculated the growth kinetics of S. aureus with the chitosan coated selenium nanoparticles. Future studies can use the Gompertz and Richards model to accurately standardize the effectiveness of nanoparticles on the growth of S. aureus. Moreover, further studies regarding the mechanism of antibacterial action of selenium nanoparticles coated with chitosan are needed.

Acknowledgements:

The authors thank Northeastern University and the Department of Chemical Engineering for funding this research.