## 4 Discussion  
The sterilization of microbiological culture media using a conventional microwave could become a simple and affordable method for most laboratories. However, when establishing a new protocol for the sterilization of culture media, several parameters must be considered, particularly exposure times and safety issues, as microwaves are not specifically designed for this purpose. Most of the studies carried out to study the sterilization capacity of microwave ovens have been performed on food samples, for which the maintenance of sterility is not necessary [26; 27], or on surgical materials [28]. Previous studies have described the effects on micro-organisms (either live or in their sporulated form) when they are sterilized in a microwave oven, being thermal and non-thermal [7; 11; 12]. Only the study performed by [PERSON] et al. assessed the utility of a microwave for the preparation of SDA, adding a UV treatment during the gelling process [7]. In our study, for the first time, an innovative and simple system for the preparation of culture media was developed, based on the use of a water bath made from polycarbonate covering the rehydrated media, in order to ensure the homogeneous distribution of the temperature and to act as safety containment to avoid any possible event related to high temperatures and possible container breakage. To evaluate the new sterilization system, we assessed the microbiological properties of media prepared in a microwave (for different exposure times) in comparison with those of autoclaved media. We started by first establishing the minimum power and time required for the complete sterilization of the culture medium (TSA), while measuring the temperature of the culture medium as it was exposed to the microwave oven. Figure 9: The pH values obtained after the preparation of the media (TSA, SDA, and VRBG) using conventional methods (autoclaving/boiling) or using microwave exposure for different durations. We established that an exposure duration of 7 min at a power of 1000 W was sufficient to sterilize the culture medium. Based on the improvement observed in the growth of an important number of species in media exposed to a microwave, in comparison to the same autoclaved media, we can suggest that these conditions are softer than the autoclaving conditions and, thus, less degradation of nutrients and less generation of toxic compounds, such as reactive oxygen species (ROS), would occur under this microwave treatment. Due to contamination risk and the bottle design, temperature measurement was only possible on the glass bottle, being an indirect measure of the temperature reached in the culture medium. Glass was the selected material for the bottle as it maintains the temperature of the culture medium during the sterilization and resists pressure increases. Regarding the temperature measurement, a sustained exponential increase was observed over time. At the minimum sterilization time (7 min), the temperature of the glass bottle was around 90 \({}^{\circ}\)C, thus indicating a higher temperature of the culture media at this time. When comparing the temperature curves of the autoclave and microwave oven, a higher temperature was reached in both at 15-16 min [29]. However, the whole sterilization process was drastically reduced in the microwave method as, after 7 min, sterilization was achieved and the process of gas elimination was quicker, whereas the whole process in the autoclave, including the temperature increase, sterilization (commonly 21 min), and pressure decrease, may take up to 1.5 h [29]. Moreover, in the autoclave, higher pressures are likely to be reached than in the microwave system, due to the larger size of the autoclave and the autoclaving conditions. This is the most notable difference between the two devices, making sterilization in a microwave oven a faster and safer process, without the inconvenience of needing to wait for the pressure to decrease.