Abstract
This study examined the microbicidal activity of ultraviolet (UV)-C185–256-nm irradiance (robot 1) and ozone generated at UV-C185-nm by low-pressure mercury vapor lamps (robot 2) adapted to mobile robotic devices for surface decontamination, which was achieved in less than 1 h. Depending on their wall structure and outer envelopes, many microorganisms display different levels of resistance to decontaminating agents. Thus, the need for novel disinfection approaches is further exacerbated by the increased prevalence of multidrug-resistant bacteria, as well as the potential of novel microorganisms, with the ability to cause disease outbreaks. To set up a rapid and effective approach for microorganisms propagation prevention, we focused on the effects of UV-C and ozone on a distinct microorganism survival ratio. A set of microorganisms, including Escherichia coli, Micrococcus luteus, Saccharomyces cerevisiae, Trichoderma harzianum, and Bacillus subtilis, were used to evaluate the disinfection power of UV-C and UV-C plus ozone generating robots. UV-C disinfection can be suited to ad hoc tasks, is easy to operate, requires low maintenance, does not have the need for the storage of dangerous chemicals, and does not produce by-products that may affect human health and the environment. The robotic cumulative irradiation technology developed (fluence accumulated values of 2.28 and 3.62 mJ cm−2, for robot 1 and 2, respectively), together with the production of ozone (with a maximum peak of 0.43 ppm) capable of reaching UV-C shaded surfaces, and analyzed in the current study, despite being designed for the need to reduce the risk of epidemic outbreaks in real-life scenarios, represents a versatile tool that could be employed for air and surface disinfection within many circumstances that are faced daily.
Highlights
Microbiological disinfection hierarchy is a concept based on the general descending order of susceptibility of classes of microorganisms to antimicrobial chemicals
Our objective was to obtain high-level disinfection (HLD) through the complete elimination of all viable microorganisms, except for some fungal conidia and bacterial endospores, when they were present in a significant amount, on the four inanimate surfaces considered after 1 h of dynamic exposure to UV-C and UV-C plus ozone generated by robots 1 and 2, respectively
The UV-C fluence values shown in Table 1 were obtained in the 135 m3 room in which the robots were working for 1 h, with indications of different distances between the luminaire and sensor
Summary
Microbiological disinfection hierarchy is a concept based on the general descending order of susceptibility of classes of microorganisms to antimicrobial chemicals. Disinfection kills most, but not necessarily all, microorganisms, and depending on the efficacy of the methods and the resistance of the microorganisms, two types of disinfection hierarchy are usually established, namely: (i) the one that evaluates disinfection systems and their efficacy, starting from cleaning and disinfectant cleaning (hygienization) to sanitization and disinfection, until reaching sterilization, which kills all microorganisms, and (ii) the one that is distinguished by the placement across levels different microorganisms depending on their different structures, compositions, and physiologies which determines the order of resistance to antiseptics and disinfectants [1]. Most microbial-based hierarchical distributions are built according to the variety of susceptibilities of human pathogens to chemical disinfectants. Approaches with surrogate microorganisms are based on the axiom that the experimental disinfection or sterilization action on a hardier microorganism to physical treatments and chemical agents, including heat, drying, radiation, and chemicals, will necessarily be more effective against less resistant ones
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