Effect of Magnesium Isotopes on Antibiotic Sensitivity of E. coli

The effect of Mg-25, a magnetic magnesium isotope, on the sensitivity of Escherichia coli K12 TG1 to quinolone/fluoroquinolone (nalidixic acid and ciprofloxacin) and aminoglycoside antibiotics (amikacin and tobramycin) was found. In the case of fluoroquinolones, determination of antibiotic sensitivity by the disc diffusion method revealed the 7-14% larger growth inhibition zones on the medium with the magnetic magnesium isotope than for the same antibiotics in the variants with Mg-24, Mg-26, or the natural Mg isotope. The effect of the magnetic magnesium isotope Mg-25 on the increase in resistance to the quinolones/fluoroquinolones group of antibiotics was observed independently of the determining method: the growth rate of E. coli culture incubated in the medium with Mg-25 and ciprofloxacin decreased by 80% compared to the control without antibiotics, while in the variants with Mg-24, Mg-26, and natural Mg the decrease did not exceed 50%. An increase in antibiotic resistance (opposite magnetic isotopic effect) was shown for amikacin, tobramycin, and clindamycin. In the variants with amikacin and clindamycin, the growth inhibition zones of bacteria enriched with Mg-25 were 16-17 and 17-24% smaller, respectively. An increase in resistance to tobramycin (aminoglycosides) was observed for submerged E. coli cultures growing in the medium with Mg-25: at the antibiotic concentration two times lower than the MIC, the growth rate of E. coli was 86% of the control, while in the variants with nonmagnetic isotopes or natural magnesium it decreased by 40-50%. The mechanisms of magnetic isotopic effects of Mg-25 are discussed: its effect on the enzymatic activity of Mg-dependent enzymes involved in protection of the cells from the action of antibiotics.