X-ray resistance in multidrug-resistant Gram-negative nosocomial pathogens: An in vitro assessment of bacterial survival across radiation dose thresholds

Background: X-rays used for diagnostic and therapeutic purposes have various effects on nosocomial pathogens. Thanks to advanced repair mechanisms, bacteria, among the earliest life forms on Earth, can survive exposure to ionizing radiation. It is important to determine the radiation threshold for nosocomial pathogens with drug resistance. In this study, we investigated the survival responses of Gram-negative bacteria, which exhibit antimicrobial resistance in the clinical setting, to different doses of ionizing radiation. Materials and Methods: Bacterial isolates obtained from pure culture and adjusted to 0.5 McFarland turbidity were exposed to radiation doses of 0 (Control), 12.5, 25, 50, and 100 Gy in an X-ray machine used in clinical treatment. The results obtained were evaluated by comparing the number of microorganisms that remained alive after exposure to X-ray radiation with the control group. Results: No significant reduction in bacterial growth was observed following exposure to 12.5 Gy and 25 Gy. At 50 Gy, 3 isolates exhibited reduced viability. Exposure to a dose of 100 Gy induced a substantial reduction in Colony-Forming Unit (CFU) counts in 14 isolates and caused complete lethality in P. mendocina. These effects followed a dose-dependent trend. Conclusions: MDR Gram-negative pathogens are resilient against radiation doses typically applied in clinical practice. Bactericidal effects were only observed at doses ≥50 Gy, levels far exceeding what is biologically tolerable for human tissues. These findings underscore the need for precise dose classification when discussing bacterial radiation responses and emphasize that such high doses are suitable only for external sterilization, not patient-based applications.