Effect of magnetic hyperthermia on the structure of biofilm and cellular viability of a food spoilage bacterium

Abstract

This work evaluated the effect of magnetic hyperthermia (MH) on planktonic cells and biofilms of a major food spoilage bacterium Pseudomonas fluorescens and its performance compared to a conventional direct heating (DH) technique. The results showed that MH had a greater and faster bactericidal effect, promoting a significant reduction in cell viability (≥3 Log CFU) in planktonic and biofilm cells, and leading to a complete eradication of planktonic cells at 55 °C (after only ~8 min). Accordingly, when comparing the same final temperatures, MH was more harmful to the integrity of cell membranes than DH, as observed in confocal laser scanning microscope images. Additionally, scanning electron microscope images revealed that exposure to MH had promoted modifications of the bacterial cell surface as well as of the structure of the biofilm. These results present the possibility of using MH out of the biomedical field as a potential disinfection method in food-related environments.

Keywords:

• magnetite nanoparticles
• magnetic hyperthermia
• biofilm
• planktonic bacteria
• Pseudomonas fluorescens

Acknowledgements

This work was partly supported by the European Regional Development Fund (ERDF) under the Northern Regional Operational Programme ON.2–O Novo Norte- for the acquisition of the main equipment used in this research. DR also acknowledges the financial support of the Portuguese Foundation for Science and Technology (FCT) through [grant SFRH/BPD/72632/2010]. The authors are very grateful to Dr Edith Ariza and Dr Cláudia Mota for their technical assistance in the SEM studies.