First Identification of β-Lactamases in Antibiotic-Resistant Escherichia coli , Citrobacter freundii , and Aeromonas spp. Isolated in Stream Macroinvertebrates in a Central Italian Region.

Antibiotic-resistant bacteria (ARB) are widespread in nature and represent a serious public and environmental problem. In the present study, we report for the first time the presence of bacterial β-lactamases in two macroinvertebrate species with different feeding traits. The class A β-lactamases, SHV-1 and TEM-1, were found in Citrobacter freundii isolated from Gammarus elvirae and Escherichia coli from water samples, respectively. The metallo-β-lactamase CphA was found in Aeromonas veronii and Aeromonas hydrophila strains isolated from the predator Dina lineata . The presence of a large plasmid was ascertained only in E. coli strains isolated from water. In all strains studied, an integrase I typical of class I integrin was found. In contaminated freshwater habitats, ARB and antibiotic resistance genes could be disseminated through trophic links with important ecological implications. Transmission through the food chain may contribute to spreading and transferring antibiotic resistance not only in freshwater ecosystems but also outside the aquatic habitat.