## 1 Introduction  
In the present era of rapid methods (including molecular and serological ones), the method involving culture and isolation is still recommended by the current regulations for the microbiological analysis of food, medical products, and so on, in order to assess key characteristics of the micro-organisms, such as their antibiotic microbial sensitivities [1, 2, 3]. One key element is the sterilization of culture media and related materials to ensure the isolation of micro-organisms. However, autoclaving, as a sterilization method, is associated with certain drawbacks, such as high energy and equipment costs, long cycles, and the occupancy of considerable laboratory space, making it potentially unaffordable for laboratories around the world. Moreover, it is known that common autoclaving conditions can degrade key nutrients (such as peptones, agar, yeast extracts, and so on) and generate toxic compounds to which micro-organisms are sensitive [4]. The generation of reactive oxygen species (ROS) or products of Maillard reactions (such as melanoidins) has been reported as compromising the culturability of certain sensitive species [1; 5; 6; 7; 8].  
A reduction in the autoclaving conditions, or the separation of agar from the rest of the components during autoclaving [6], have been demonstrated to increase the productivity of different media, particularly for key sensitive species.  
There is also interest in the use of alternatives to the autoclave for sterilizing culture media, which could maintain the properties of the medium and even increase microbial growth and selectivity [6; 8]. Alternative sterilization methods could include filtration, ionizing radiation, or microwave sterilization. However, filtration is not a viable option for large amounts of media and cannot eliminate viruses, while ionizing radiation (e.g., gamma radiation) is not a feasible and economical option for most laboratories [9; 10], and is typically reserved for key culture media or ingredients.  
Microwave technology has been gaining increasing interest as a potential alternative method for the sterilization of culture media, as it can produce high-quality media, while saving significant time and energy, and is considerably more affordable than autoclaves [11; 12; 13].  
It is known that microwave irradiation can destroy micro-organisms though thermal and non-thermal effects [14; 15; 16; 17; 18]. However, in the current routine by microbiological laboratories, its use is limited to melting certain solid media or to regenerate media intended for anaerobic growth, such as sulfite polymyxin sulfadiazine (SPS). To date, however, few studies have explored the utility of microwaves to prepare culture media from dehydrated ingredients in comparison with autoclaves. In a previous study, the use of microwaves was demonstrated to be an efficient alternative for the preparation of Sabouraud dextrose agar (SDA) [7]. However, the additional devices required to ensure safety (for gas elimination) and to maintain the tightness of the media container during the microwave process are issues that have not yet properly been assessed. In normal conditions, common bottles do not resist the generated pressure and, due to the loosening of normal caps, leaks of the medium from the container are common.  
In the present study, the use of a microwave was compared to autoclave sterilization for the production of common microbiological culture media, including tryptone soy agar (TSA), tryptone soy broth (TSB), Sabouraud 4% dextrose agar (SDA), Sabouraud dextrose broth, and violet red bile glucose agar (VRBG), through the implementation of an innovative device based on the use of a water bath made out of polycarbonate, and an easily perforated rubber cap, allowing medium depressurization. A commonly used power level (1000 W) and different exposure times (min) were assessed.