Antibiotic susceptibility variations of Methicillin-resistant Staphylococcus aureus after gamma irradiation.

Background: Radiation might affect many different aspects of micro-organisms. Considering their learning ability and adaptive behaviors in special environmental conditions such as irradiation, we expected that their sensitivities to different antibiotics would change after being exposed to gamma radiation. Knowing that ionizing radiation creates radical ions, and noting that many parts of micro-organisms contain hydrogen and oxygen, such variations of antibiotic susceptibilities were rational to envisage. This experimental work paper is devoted to report Methicillin-resistant Staphylococcus aureus's antibiotic susceptibility variations in six different antibiotics after irradiation.Methods: One strain of Methicillin-resistant Staphylococcus aureus was cultured on Mueller-Hinton agar (MHA) then kept in an incubator at 37°C. Irradiation achieved twice using a cobalt gamma cell, and antibiotic susceptibility tests completed following the Clinical & Laboratory Standards Institute (CLSI) disk diffusion method.Results: Diameters of the inhibition zones were measured, tabled, and compared before and after irradiation that shows susceptibility changes for different antibiotics. For instance, inhibition zones' diameters for Oxacillin (OX) were 14 and 40 mm before and after irradiation, respectively, that means the bacteria became more susceptible to Oxacillin after irradiation.Conclusion: It is shown that bacteria's resistance against antibiotics changes after being irradiated, by knowing the mechanism of actions for each antibiotic, and knowing how radiation changed bacteria's susceptibilities, we concluded how radiation might have affected the bacterium's cell.