Effects of tetracycline on entomopathogenic nematodes and their bacterial symbionts

Among the new contaminants relevant for environment, one of the most significant roles is played by pharmaceuticals like antibiotic products for either human or veterinary use. Their presence could cause serious damage to bacteria and microfauna, like nematodes. Within the widely investigated nematodes, very little is known about the interaction between antibiotics and entomopathogenic nematodes (EPN). EPNs have been used for biological control of crops, due to their ability to penetrate arthropod pests and kill their hosts thanks to a complex symbiotic mechanism with specific gram-negative bacteria. Tetracycline is an antibiotic used in human and veterinary medicine, both for therapeutic purposes and for the growth of livestock. Since its action against gram-negative bacteria is documented, we verified in this study the survival, growth and pathogenicity of two species of EPNs, Steinernema vulcanicum and S. feltiae. All tests were performed with tetracycline in 1% ethanol solution and up to 300 mg/L. Apparently, this incubation did not harm the vitality of EPNs. Both S. vulcanicum as S. feltiae recovered their vitality and entomopathogenic ability after 48 h. Moreover, the latter EPN species did not grow nor reproduce in the hemolymph of the Greater Wax Moth, Galleria mellonella, and their endosymbionts did not grow on MacConkey Agar. Our results suggest that the first EPN species has always retained all its abilities and that endosymbionts have acquired resistance to tetracycline, while experiments with the second EPN species provided some contrasting results in time that will require further investigations.