Modulation of the antibiotic susceptibility profiles of some microbial strains isolated from wastewater under the influence of the electromagnetic field

The wastewater treatment plants are considered to be hotspots for antibiotic resistance
selection, transfer and dissemination. Wastewater offers favorable conditions for the
development of antibiotic resistant bacteria because it contains high amounts of organic
matter, favoring the rapid multiplication of microbial cells and the development of biofilms in
which microbial cells are in close proximity, the presence of pollutants (pesticides, heavy
metals, antibiotics) acting as selective pressure agents for resistance.
The aim of this paper is to investigate how the antibiotics susceptibility profiles of some
microbial strains isolated from wastewater are influenced by electromagnetic fields.
A number of 10 bacterial strains isolated from wastewater (E. coli, Salmonella sp.,
Enterobacter sp., Enterococcus sp., Citrobacter sp., Klebsiella sp.) were exposed to an
electromagnetic field (50Hz electric field at different voltages) for 24 hours, at 37°C. Thereafter,
the antibiotic susceptibility testing was performed for both treated and control strains, by disk
diffusion method, according to CLSI 2016.
The obtained results proved that the electromagnetic field induced in some cases a decrease
of the growth inhibition diameters such as penicillins, cephalosporins, aminoglycosides and
vancomycin, while in other cases an increase of bacterial strains susceptibility to the tested
antibiotics.
These preliminary results demonstrate that the electromagnetic filed in addition with other
selective factors which are present in the wastewaters could modulate the environmental
reservoir of antibiotic resistance and influence the frequency of the selection of resistant
bacteria and the magnitude of the potential risk of dissemination into the environment and of
contamination of animals and humans.