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Antimicrobial activity of amine-functionalised mesoporous
silica microparticles
Niamh Mohan - niamh.mohan@mydit.ie
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Progress Poster Final Version - Niamh Mohan

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Progress Poster Final Version - Niamh Mohan

  1. 1. Antimicrobial activity of amine-functionalised mesoporous silica microparticles Niamh Mohan - niamh.mohan@mydit.ie Supervisors – Jesus Frias & Jose M Barat Co Supervisor – Maria Ruiz-Rico Dublin Inst. of Technology, Faculty of Food Science and Environmental Health, Cathal Brugha street, Dublin. Universidad Politecnica de Valencia, Faculty of Biochemical and Microbiological Engineering, Valencia, Spain. Introduction & Aim of Research The overuse of antibiotics and antimicrobial agents has resulted in the emergence of multi drug resistant bacteria (Hajipour et al., 2012). Nanotechnology has helped develop different strategies than those used in conventional therapies to tackle these resilient microbes. The concept of using nanotechnology to synthesise antibacterial agents is relatively new. Ongoing research is being conducted on various types of nano- and microparticles such as metal particles, magnetic particles and loaded/functionalised particles each with different mechanisms of action. Mesoporous silica particles loaded and/or functionalised with organic molecules have demonstrated interesting applications as suitable systems for controlled release (Slowing et al., 2008). Another possibility involves using these types of particles as antimicrobial supports as a result of the bioactive compound loaded or attached in the matrix. This project aims to determine the antimicrobial activity of amine-functionalised mesoporous silica microparticles against Listeria monocytogenes. Finally, the activity of the functionalised microstructures will then be tested against L. monocytogenes in contaminated liquid foods to investigate the effect of the particles in a complex food system. Discussion The zeta potential values revealed that the correct functionalisation of the mesoporous silica microparticles with amine was achieved. Figure 2 highlights that the particles were positively charged due to the amine on their surface. The degree of functionalisation of the solid was determined by thermogravimetric analyses and the amount of amine anchored to the particles was 35.97±2.59 mg/g SiO2. In contrast, the particles suspended in nutrient broth lost their positive charge due to interactions with components of the dissolvent. The results of the particles in Ringer buffer imply that the functionalised particles are effective as antimicrobial agents with a minimum bacterial concentration between 10 and 50 µg/mL in Ringer buffer. If the results of amine-functionalised particles and free amine are compared, it can be observed that free amine has no antimicrobial properties or shows an lower effect than the attached amine (Fig 3). The study on the influence of different pH and nutrient broths show that the activity of the particles decreased when in the presence of the organic molecules in the media. In the same way, the activity of the particles in the food system were affected by the presence of organic molecules such as proteins, sugars, etc. (Fig. 4 and 5). In conclusion, amine-functionalised mesoporous silica particles have antimicrobial activity against L. monocytogenes in model solutions. The antimicrobial efficiency of these particles in food systems appears to be affected by the matrix and hence, the activity is decreased. Further studies should be carried out to understand the lose of efficiency of the particles as well as trying other types of functionalisation. Methodology Microparticle synthesis & functionalisation Materials characterization Transmission electron microscopy (TEM) Zeta potential and amine quantification Food System Assays Fruit Juice Milk Microbiological Assays Minimum bactericidal concentration (MBC) Influemce of pH and media on antimicrobial activity Results Figure 1. TEM image of MCM-41 microparticulate structure. 0 1 2 3 4 5 6 pH 3.5 pH 5 pH 7.5 pH 9 pH 10.5 logCFU/mL Ringer buffer 0 1 2 3 4 5 6 7 PBS BPW TSB BHB NB logCFU/mL Ringer buffer Figure 4. Influence of pH and media on antimicrobial activity of amine-functionalised microparticles (750 µg/mL) against L. monocytogenes. Control in dark blue and particles in purple. Figure 2. Zeta potential values of amine- functionalised MSPs dispersed in different buffer and culture broth. -40 -20 0 20 40 60 80 Ringer pH 3.5 Ringer pH 5 Ringer pH 7.5 Ringer pH 9 Ringer pH 10.5 PBS BPW TSB BHB NB Zetapotential(mV) Figure 3. Reduction of microbial growth of L. monocytogenes with amine-functionalised microparticles and free amine at 2 h of treatment. 0 20 40 60 80 100 120 5 10 50 100 150 200 Survival(%) Amine-functionalised MCM-41 (µg/mL) 0 10 20 30 40 50 60 70 80 90 100 1000 1250 1500 1750 2000 Survival(%) N3 concentration (µg/mL) Figure 5. Effect of amine-functionalised microparticles against L. monocytogenes inoculated in orange juice. 2 hours incubation in dark blue and 24 hours in purple. 0 20 40 60 80 100 120 100 500 1000 1500 2000 2500 3000 3500 Survival(%) Amine-functionalised particles (µg/mL) References Hajipour, M. J., Fromm, K. M., Ashkarran, A. A., Jimenez de Aberasturi, D., de Larramendi, I. R., Rojo, T., Mahmoudi, M. (2012). Antibacterial properties of nanoparticles. Trends in Biotechnology, 30(10), 499–511. Slowing, I. I., Vivero-Escoto, J. L., Wu, C.-W., & Lin, V. S.-Y. (2008). Mesoporous silica nanoparticles as controlled release drug delivery and gene transfection carriers. Advanced Drug Delivery Reviews, 60(11), 1278–88.