Abstract
Using microwave oven nowadays has become necessary due to the need for speed in our daily activities. It is widely used in hating, thawing, and even cooking of food. It has been also used in sterilization and decontamination of food from microorganisms. This study aimed to evaluate thermal and non-thermal effect of a regular house holding microwave oven on Staphylococcus aureus and Escherichia coli. Bacterial suspension is exposed to microwave radiations in different strength and durations and compared to unexposed cultures. During microwave treatment, non-thermal effect is evaluated by putting the suspension crushed ice. The results indicate that the viability of both gram positive and negative was highly reduced with thermal effect of microwave radiations, leading to complete inactivation at three minutes. Non-thermal microwave radiations were also able to cause change in the microbial viability of both tested organisms on at least two-exposure occasion. The evaluation of antibiotic susceptibility before and after microwave radiations treatment indicate that antibiotic resistance was highly increased to tested antibiotics specially after three-minute exposure, except for Staphylococcus aureus to Amoxicillin, which became more sensitive. Microwave radiations reported to have a strong activity in eliminating the number of microbes but, it may have an important role in development of antibiotic resistance that should not be ignored.
Highlights
Microwave is defined as electromagnetic non-ionizing waves ranging from 0.3 to 300 gigahertz (GHz) frequencies (Cohen & Wald, 2016)
The results indicate that the viability of both gram positive and negative was highly reduced with thermal effect of microwave radiations, leading to complete inactivation at three minutes
This study indicated that microwave radiations (MR) reported to have better effect in thermal phase, compared to nonthermal phase as presented in table 1 which presents that E. coli was more sensitive to MR than S. aureus
Summary
Microwave is defined as electromagnetic non-ionizing waves ranging from 0.3 to 300 gigahertz (GHz) frequencies (Cohen & Wald, 2016). The thermal and/or non-thermal effect of microwave irradiation could cause the abnormal permeability of bacterial cell membrane and the degeneration of protein, resulting in bacterial metabolic abnormalities and irreversible damage of bacteria Depending on the strength and frequency of radiation, MR may affect the viability of microorganisms. When irradiating living organisms, microwaves produce two types of effect, thermal and non-thermal. Thermal effects are the consequences of absorption of MR by cell molecules. It was suggested that killing microorganism is achieved by thermal effect of microwave exposure (Kang & Kato, 2014; Wilbur & Al Tawengi, 2016). Alharbi et al, (2016) study on different biological models reported that the effect of MR depends on the type, frequency, duration, and organism model
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