Abstract <p>The luminescence of gram-positive (<i>Staphylococcus aureus</i>) and gram-negative (<i>Leminorella richardii</i>) bacteria was studied in the excitation wavelength range of 265–295 nm before and after interaction with OH^• radicals. For the gram-negative bacteria, luminescence was recorded at a wavelength of 330 nm. For the gram-positive bacteria, in addition to the peak at 330 nm, a peak at a wavelength of 303 nm was visible. The fluorescence spectra of bacteria in the excitation wavelength range of 265–295 nm made it possible to distinguish between gram-positive and gram-negative bacteria. After reaction with OH^• radicals at a dose greater than 240 J/(10 mL), a peak of tyrosine at 303 nm was observed in the luminescence of both bacteria.</p>