The growth rates were determined for following groups: 1.) control group, 2.) expoure group, 3.) kanamycin, 4.) kanamycin + exposure, and 5.) amikacin + exposure.
The antibiotic susceptibility was determined by the minimal inhibitory concentration (the dilution value at which no visible growth occurred in the bacteria) of the two bacteria strains in presence and absence of an extremely low-frequency magnetic field. Following antibiotics were tested: kanamycin, amikacin, ampicillin, ceftazidime, levofloxacin, cefazolin, ceftriaxone, and moxalactam.
Exposure duration: continuous for up to 24 h
|Setup||pair of Helmholtz coils with a mean radius of 13 ± 0.5 cm; each coil consisted of 800 turns of 2 mm² wire; coils spaced vertically 13.5 ± 0.5 cm apart; field uniformity better than 1% in the exposure area; four Falcon multiwell plates with 96 wells or twelve 20 ml glas tubes exposed simultaneously; exposure system placed inside an incubator with constant temperature of 37 ± 0.3 °C|
|Sham exposure||A sham exposure was conducted.|
|magnetic flux density||2 mT||-||measured||-||-|
No remarkable differences were found in the antibiotic susceptibility and on the growth rates of both bacteria comparing the exposed group (group 2) with the control group (group 1).
However, exposure to an extremely low-frequency magnetic field showed a significant effect on the growth rate of both strains when incubated in the presence of subinhibitory concentrations of kanamycin (1 µg/ml, group 4) and amikacin (O.5 µg/ml, group 5). In particular, at 4, 6, and 8 h exposure the number of cells was significantly decreased in exposed bacteria compared with the control (group 3). Additionally, at 24 h exposure, the percentage of cells increased in treated groups with respect to the control group suggesting a progressive adaptive response.