Interspecies transmission of antimicrobial-resistant bacteria between wild birds and mammals in urban environment.

The transmission of antibiotic-resistant bacteria among wild animal species may hold significant epidemiological implications. However, this issue is seldom explored due to the perceived complexity of these systems, which discourages experimental investigation. To address this knowledge gap, we chose a configuration of birds and mammals coexisting in an urban green area as a research model: the rook Corvus frugilegus and the striped field mouse Apodemus agrarius. The indirect transmission of antimicrobial-resistant bacteria between these species is possible because rodents inhabiting rook colonies frequently come into contact with the birds' faeces and pellets. The study was conducted in two cities in eastern Poland (Central Europe) - Lublin and Chełm. Among 71 Escherichia (E.) coli isolates studied, 19.7% showed resistance to from one to six of the antibiotics tested, with much higher prevalence of antibiotic-resistant bacteria in the birds (32%) than in the rodents (7%). Whole genome sequencing was performed on 10 selected E. coli isolates representing similar resistance phenotypes. The following antimicrobial resistance genes were detected: bla, tet(A), tet(B), aph(6)-Id, aph(3'')-Ib, aadA1, aadA2, catA1, floR, cmlA, sul2, sul3, dfrA14, and dfrA2. Birds from the same city and also from both neighbouring cities shared E. coli bacteria with the same sequence types, whereas isolates detected in birds were not found to have been transferred to the mammalian population, despite close contact. This demonstrates that even intensive exposure to sources of these pathogens does not necessarily lead to effective transmission of antibiotic-resistant E. coli strains between birds and mammals. Further efforts should be dedicated to investigating actual transmission of antimicrobial-resistant bacteria in various ecological systems, including those that are crucial for public health, such as urban environments. This will facilitate the development of more accurate models for epidemiological threats and the formulation of well-balanced decisions regarding the coexistence of humans and urban wildlife.